Patent Publication Number: US-2006002935-A1

Title: Tumor Necrosis Factor Receptor 1 antagonists and methods of use therefor

Description:
RELATED APPLICATIONS  
      This application is a continuation-in-part of:  
      1) International Application No. PCT/GB2004/004253, which designated the United States and was filed on Oct. 8, 2004; and  
      2) International Application No. PCT/GB2003/005646, which designated the United States, was filed on Dec. 24, 2003, and claims priority to United Kingdom Application No. GB 0230202.4, filed Dec. 27, 2002 and United Kingdom Application No. GB 0327706.8 filed Nov. 28, 2003, which is  
      a continuation-in-part of International Application No. PCT/GB2003/002804, which designated the United States, was filed on Jun. 30, 2003, and claims priority to United Kingdom Application No. GB 0230202.4, filed Dec. 27, 2002, which is  
      a continuation-in-part of International Application No. PCT/GB02/03014, which designated the United States and was filed on Jun. 28, 2002.  
      The entire teachings of the above applications are incorporated herein by reference.  
    
    
     BACKGROUND OF THE INVENTION  
      The antigen binding domain of an antibody comprises two separate regions: a heavy chain variable domain (V H ) and a light chain variable domain (V L : which can be either V κ  or V 80 ). The antigen binding site itself is formed by six polypeptide loops: three from V H  domain (H1, H2 and H3) and three from V L  domain (L1, L2 and L3). A diverse primary repertoire of V genes that encode the V H  and V L  domains is produced by the combinatorial rearrangement of gene segments. The V H  gene is produced by the recombination of three gene segments, V H , D and J H . In humans, there are approximately 51 functional V H  segments (Cook and Tomlinson (1995)  Immunol Today,  16: 237), 25 functional D segments (Corbett et al. (1997)  J. Mol. Biol.,  268: 69) and 6 functional J H  segments (Ravetch et al. (1981)  Cell,  27: 583), depending on the haplotype. The V H  segment encodes the region of the polypeptide chain which forms the first and second antigen binding loops of the V H  domain (H1 and H2), whilst the V H , D and J H  segments combine to form the third antigen binding loop of the V H  domain (H3). The V L  gene is produced by the recombination of only two gene segments, V L  and J L . In humans, there are approximately 40 functional V κ  segments (Schäble and Zachau (1993)  Biol. Chem. Hoppe - Seyler,  374: 1001), 31 functional V κ segments (Williams et al. (1996)  J. Mol. Biol.,  264: 220; Kawasaki et al. (1997)  Genome Res.,  7: 250), 5 functional J κ  segments (Hieter et al. (1982)  J. Biol. Chem.,  257: 1516) and 4 functional J λ  segments (Vasicek and Leder (1990)  J. Exp. Med.,  172: 609), depending on the haplotype. The V L  segment encodes the region of the polypeptide chain which forms the first and second antigen binding loops of the V L  domain (L1 and L2), whilst the V L  and J L  segments combine to form the third antigen binding loop of the V L  domain (L3). Antibodies selected from this primary repertoire are believed to be sufficiently diverse to bind almost all antigens with at least moderate affinity. High affinity antibodies are produced by “affinity maturation” of the rearranged genes, in which point mutations are generated and selected by the immune system on the basis of improved binding.  
      Analysis of the structures and sequences of antibodies has shown that five of the six antigen binding loops (H1, H2, L1, L2, L3) possess a limited number of main-chain conformations or canonical structures (Chothia and Lesk (1987)  J. Mol. Biol.,  196: 901; Chothia et al. (1989)  Nature,  342: 877). The main-chain conformations are determined by (i) the length of the antigen binding loop, and (ii) particular residues, or types of residue, at certain key position in the antigen binding loop and the antibody framework. Analysis of the loop lengths and key residues has enabled us to the predict the main-chain conformations of H1, H2, L1, L2 and L3 encoded by the majority of human antibody sequences (Chothia et al. (1992)  J. Mol. Biol.,  227: 799; Tomlinson et al. (1995)  EMBO J.,  14: 4628; Williams et al. (1996)  J. Mol. Biol.,  264: 220). Although the H3 region is much more diverse in terms of sequence, length and structure (due to the use of D segments), it also forms a limited number of main-chain conformations for short loop lengths which depend on the length and the presence of particular residues, or types of residue, at key positions in the loop and the antibody framework (Martin et al. (1996)  J. Mol. Biol.,  263: 800; Shirai et al. (1996)  FEBS Letters,  399: 1.  
      Bispecific antibodies comprising complementary pairs of V H  and V L  regions are known in the art. These bispecific antibodies must comprise two pairs of V H  and V L s, each V H /V L  pair binding to a single antigen or epitope. Methods described involve hybrid hybridomas (Milstein &amp; Cuello AC, Nature 305:537-40), minibodies (Hu et al., (1996) Cancer Res 56:3055-3061;), diabodies (Holliger et al., (1993) Proc. Natl. Acad. Sci. USA 90, 6444-6448; WO 94/13804), chelating recombinant antibodies (CRAbs; (Neri et al., (1995) J. Mol. Biol. 246, 367-373), biscFv (e.g. Atwell et al., (1996) Mol. Immunol. 33, 1301-1312), “knobs in holes” stabilised antibodies (Carter et al., (1997) Protein Sci. 6, 781-788). In each case each antibody species comprises two antigen-binding sites, each fashioned by a complementary pair of V H  and V L  domains. Each antibody is thereby able to bind to two different antigens or epitopes at the same time, with the binding to EACH antigen or epitope mediated by a V H  and its complementary V L  domain. Each of these techniques presents its particular disadvantages; for instance in the case of hybrid hybridomas, inactive V H /V L  pairs can greatly reduce the fraction of bispecific IgG. Furthermore, most bispecific approaches rely on the association of the different V H /V L  pairs or the association of V H  and V L  chains to recreate the two different V H /V L  binding sites. It is therefore impossible to control the ratio of binding sites to each antigen or epitope in the assembled molecule and thus many of the assembled molecules will bind to one antigen or epitope but not the other. In some cases it has been possible to engineer the heavy or light chains at the sub-unit interfaces (Carter et al., 1997) in order to improve the number of molecules which have binding sites to both antigens or epitopes but this never results in all molecules having binding to both antigens or epitopes.  
      There is some evidence that two different antibody binding specificities might be incorporated into the same binding site, but these generally represent two or more specificities that correspond to structurally related antigens or epitopes or to antibodies that are broadly cross-reactive. For example, cross-reactive antibodies have been described, usually where the two antigens are related in sequence and structure, such as hen egg white lysozyme and turkey lysozyme (McCafferty et al., WO 92/01047) or to free hapten and to hapten conjugated to carrier (Griffiths A D et al.  EMBO J  1994 13:14 3245-60). In a further example, WO 02/02773 (Abbott Laboratories) describes antibody molecules with “dual specificity”. The antibody molecules referred to are antibodies raised or selected against multiple antigens, such that their specificity spans more than a single antigen. Each complementary V H /V L  pair in the antibodies of WO 02/02773 specifies a single binding specificity for two or more structurally related antigens; the V H  and V L  domains in such complementary pairs do not each possess a separate specificity. The antibodies thus have a broad single specificity which encompasses two antigens, which are structurally related. Furthermore natural autoantibodies have been described that are polyreactive (Casali &amp; Notkins, Ann. Rev. Immunol. 7, 515-531), reacting with at least two (usually more) different antigens or epitopes that are not structurally related. It has also been shown that selections of random peptide repertoires using phage display technology on a monoclonal antibody will identify a range of peptide sequences that fit the antigen binding site. Some of the sequences are highly related, fitting a consensus sequence, whereas others are very different and have been termed mimotopes (Lane &amp; Stephen, Current Opinion in Immunology, 1993, 5, 268-271). It is therefore clear that a natural four-chain antibody, comprising associated and complementary V H  and V L  domains, has the potential to bind to many different antigens from a large universe of known antigens. It is less clear how to create a binding site to two given antigens in the same antibody, particularly those which are not necessarily structurally related.  
      Protein engineering methods have been suggested that may have a bearing on this. For example it has also been proposed that a catalytic antibody could be created with a binding activity to a metal ion through one variable domain, and to a hapten (substrate) through contacts with the metal ion and a complementary variable domain (Barbas et al., 1993 Proc. Natl. Acad. Sci USA 90, 6385-6389). However in this case, the binding and catalysis of the substrate (first antigen) is proposed to require the binding of the metal ion (second antigen). Thus the binding to the V H /V L  pairing relates to a single but multi-component antigen.  
      Methods have been described for the creation of bispecific antibodies from camel antibody heavy chain single domains in which binding contacts for one antigen are created in one variable domain, and for a second antigen in a second variable domain. However the variable domains were not complementary. Thus a first heavy chain variable domain is selected against a first antigen, and a second heavy chain variable domain against a second antigen, and then both domains are linked together on the same chain to give a bispecific antibody fragment (Conrath et al., J. Biol. Chem. 270, 27589-6-27594). However the camel heavy chain single domains are unusual in that they are derived from natural camel antibodies which have no light chains, and indeed the heavy chain single domains are unable to associate with camel light chains to form complementary V H  and V L  pairs.  
      Single heavy chain variable domains have also been described, derived from natural antibodies which are normally associated with light chains (from monoclonal antibodies or from repertoires of domains; see EP-A-0368684). These heavy chain variable domains have been shown to interact specifically with one or more related antigens but have not been combined with other heavy or light chain variable domains to create a ligand with a specificity for two or more different antigens . Furthermore, these single domains have been shown to have a very short in vivo half-life. Therefore such domains are of limited therapeutic value.  
      It has been suggested to make bispecific antibody fragments by linking heavy chain variable domains of different specificity together (as described above). The disadvantage with this approach is that isolated antibody variable domains may have a hydrophobic interface that normally makes interactions with the light chain and is exposed to solvent and may be “sticky” allowing the single domain to bind to hydrophobic surfaces. Furthermore, in the absence of a partner light chain the combination of two or more different heavy chain variable domains and their association, possibly via their hydrophobic interfaces, may prevent them from binding to one in not both of the ligands they are able to bind in isolation. Moreover, in this case the heavy chain variable domains would not be associated with complementary light chain variable domains and thus may be less stable and readily unfold (Worn &amp; Pluckthun, 1998 Biochemistry 37, 13120-7).  
     SUMMARY OF THE INVENTION  
      The invention relates to antagonists of Tumor Necrosis Factor 1 (TNFR1, p55, CD 120a) and methods of using the antagonists. Preferred antagonists have efficacy in treating, suppressing or preventing a chronic inflammatory disease and do not substantially antagonize Tumor Necrosis Factor 2 (TNFR2). In some embodiments, the antagonist is monovalent.  
      In other embodiments, the antagonist is an antibody or antigen-binding fragment thereof, such as a monovalent antigen-binding fragment (e.g., Fab, Fab′, dAb) that has binding specificity for TNFR1.  
      Other preferred antagonists are ligands described herein that bind TNFR1. The ligands comprise an immunoglobulin single variable domain or domain antibody (dAb) that has binding specificity for TNFR1, or the complementarity determining regions of such a dAb in a suitable format. In some embodiments, the ligand is a dAb monomer that consists essentially of, or consists of, an immunoglobulin single variable domain or dAb that has binding specificity for TNFR1. In other embodiments, the ligand is a polypeptide that comprises a dAb (or the CDRs of a dAb) in a suitable format, such as an antibody format.  
      In certain embodiments, the ligand is a dual-specific ligand that comprises a first dAb that binds TNFR1 and a second dAb that has a different binding specificity from the first dAb. In one example, the dual-specific ligand comprises a first dAb that binds a first epitope on TNFR1 and a second dAb that binds an epitope on a different target. In another example, the second dAb binds an epitope on serum albumin.  
      In other embodiments, the ligand is a multispecific ligand that comprises a first epitope binding domain that has binding specificity for TNFR1 and at least one other epitope binding domain that has binding specificity different from the first epitope binding domain. For example, the first epitope binding domain can be a dAb that binds TNFR1 or can be a domain that comprises the CDRs of a dAb that binds TNFR1 (e.g., CDRs grafted onto a suitable protein scaffold or skeleton).  
      In certain embodiments, the ligand or dAb monomer is characterized by one or more of the following: 1) dissociates from human TNFR1 with a dissociation constant (K d ) of 50 nM to 20 pM, and a K off  rate constant of 5×10 −1  to 1×10 −7  s −1 ; 2) inhibits binding of Tumor Necrosis Factor Alpha (TNFα) to TNFR1 with an IC50 of 500 nM to 50 pM; 3) neutralizes human TNFR1 in a standard L929 cell assay with an ND50 of 500 nM to 50 pM; 4) antagonizes the activity of the TNFR1 in a standard cell assay with an ND50 of ≦100 nM, and at a concentration of ≦10 μM the dAb agonizes the activity of the TNFR1 by ≦5% in the assay; 5) inhibits lethality in the mouse LPS/D-galactosamine-induced septic shock model; 6) resists aggregation; 7) is secreted in a quantity of at least about 0.5 mg/L when expressed in  E. coli  or  Pichia  species (e.g.,  P. pastoris ); 8) unfolds reversibly; 9) has efficacy in a model of chronic inflammatory disease selected from the group consisting of mouse collagen-induced arthritis model, mouse ΔARE model of arthritis, mouse ΔARE model of inflammatory bowel disease, mouse dextran sulfate sodium-induced model of inflammatory bowel disease, mouse tobacco smoke model of chronic obstructive pulmonary disease, and suitable primate models (e.g., primate collagen-induced arthritis model); and/or 10) has efficacy in treating, suppressing or preventing a chronic inflammatory disease.  
      In particular embodiments, the ligand or dAb monomer dissociates from human TNFR1 with a dissociation constant (K d ) of 50 nM to 20 pM, and a K off  rate constant of 5×10 −1  to 1×10 −7  s −1 ; inhibits binding of Tumor Necrosis Factor Alpha (TNFα) to TNFR1 with an IC50 of 500 nM to 50 pM; and neutralizes human TNFR1 in a standard L929 cell assay with an ND50 of 500 nM to 50 pM. In other particular embodiments, the ligand or dAb monomer dissociates from human TNFR1 with a dissociation constant (K d ) of 50 nM to 20 pM, and a K off  rate constant of 5×10 −7  to 1×10 −7  s −1 ; inhibits binding of Tumor Necrosis Factor Alpha (TNFα) to TNFR1 with an IC50 of 500 nM to 50 pM; and has efficacy in a model of chronic inflammatory disease selected from the group consisting of mouse collagen-induced arthritis model, mouse ΔARE model of arthritis, mouse ΔARE model of inflammatory bowel disease, mouse dextran sulfate sodium-induced model of inflammatory bowel disease, mouse tobacco smoke model of chronic obstructive pulmonary disease, and suitable primate models (e.g., primate collagen-induced arthritis model). In other particular embodiments, the ligand or dAb monomer dissociates from human TNFR1 with a dissociation constant (K d ) of 50 nM to 20 pM, and a K off  rate constant of 5×10 −1  to 1×10−7 s −1 ; neutralizes human TNFR1 in a standard L929 cell assay with an ND50 of 500 nM to 50 pM; and antagonizes the activity of the TNFR1 in a standard cell assay with an ND 50  of ≦100 nM, and at a concentration of ≦10 μM the dAb agonizes the activity of the TNFR1 by ≦5% in the assay.  
      In more particular embodiment, the ligand or dAb monomer comprises an amino acid sequence that is at least about 90% homologous to an amino acid sequence of a dAb selected from the group consisting of TAR2h-12 (SEQ ID NO:32), TAR2h-13 (SEQ ID NO:33), TAR2h-14 (SEQ ID NO:34), TAR2h-16 (SEQ ID NO:35), TAR2h-17 (SEQ ID NO:36), TAR2h-18 (SEQ ID NO:37), TAR2h-19 (SEQ ID NO:38), TAR2h-20 (SEQ ID NO:39), TAR2h-21 (SEQ ID NO:40), TAR2h-22 (SEQ ID NO:41), TAR2h-23 (SEQ ID NO:42), TAR2h-24 (SEQ ID NO:43), TAR2h-25 (SEQ ID NO:44), TAR2h-26 (SEQ ID NO:45), TAR2h-27 (SEQ ID NO:46), TAR2h-29 (SEQ ID NO:47), TAR2h-30 (SEQ ID NO:48), TAR2h-32 (SEQ ID NO:49), TAR2h-33 (SEQ ID NO:50), TAR2h-10-1 (SEQ ID NO:51), TAR2h-10-2 (SEQ ID NO:52), TAR2h-10-3 (SEQ ID NO:53), TAR2h-10-4 (SEQ ID NO:54), TAR2h-10-5 (SEQ ID NO:55), TAR2h-10-6 (SEQ ID NO:56), TAR2h-10-7 (SEQ ID NO:57), TAR2h-10-8 (SEQ ID NO:58), TAR2h-10-9 (SEQ ID NO:59), TAR2h-10-10 (SEQ ID NO:60), TAR2h-10-11 (SEQ ID NO:61), TAR2h-10-12 (SEQ ID NO:62), TAR2h-10-13 (SEQ ID NO:63), TAR2h-10-14 (SEQ ID NO:64), TAR2h-10-15 (SEQ ID NO:65), TAR2h-10-16 (SEQ ID NO:66), TAR2h-10-17 (SEQ ID NO:67), TAR2h-10-18 (SEQ ID NO:68), TAR2h-10-19 (SEQ ID NO:69), TAR2h-10-20 (SEQ ID NO:70), TAR2h-10-21 (SEQ ID NO:71), TAR2h-10-22 (SEQ ID NO:72), TAR2h-10-27 (SEQ ID NO:73), TAR2h-10-29 (SEQ ID NO:74), TAR2h-10-31 (SEQ ID NO:75), TAR2h-10-35 (SEQ ID NO:76), TAR2h-10-36 (SEQ ID NO:77), TAR2h-10-37 (SEQ ID NO:78), TAR2h-10-38 (SEQ ID NO:79), TAR2h-10-45 (SEQ ID NO:80), TAR2h-10-47 (SEQ ID NO:81), TAR2h-10-48 (SEQ ID NO:82), TAR2h-10-57 (SEQ ID NO:83), TAR2h-10-56 (SEQ ID NO:84), TAR2h-10-58 (SEQ ID NO:85), TAR2h-10-66 (SEQ ID NO:86), TAR2h-10-64 (SEQ ID NO:87), TAR2h-10-65 (SEQ ID NO:88), TAR2h-10-68 (SEQ ID NO:89), TAR2h-10-69 (SEQ ID NO:90), TAR2h-10-67 (SEQ ID NO:91), TAR2h-10-61 (SEQ ID NO:92), TAR2h-10-62 (SEQ ID NO:93), TAR2h-10-63 (SEQ ID NO:94), TAR2h-10-60 (SEQ ID NO:95), TAR2h-10-55 (SEQ ID NO:96), TAR2h-10-59 (SEQ ID NO:97), TAR2h-10-70 (SEQ ID NO:98), TAR2h-34 (SEQ ID NO:373), TAR2h-35 (SEQ ID NO:374), TAR2h-36 (SEQ ID NO:375), TAR2h-37 (SEQ ID NO:376), TAR2h-38 (SEQ ID NO:377), TAR2h-39 (SEQ ID NO:378), TAR2h-40 (SEQ ID NO:379), TAR2h-41 (SEQ ID NO:380), TAR2h-42 (SEQ ID NO:381), TAR2h-43 (SEQ ID NO:382), TAR2h-44 (SEQ ID NO:383), TAR2h-45 (SEQ ID NO:384), TAR2h-47 (SEQ ID NO:385), TAR2h-48 (SEQ ID NO:386), TAR2h-50 (SEQ ID NO:387), TAR2h-51 (SEQ ID NO:388), TAR2h-66 (SEQ ID NO:389), TAR2h-67 (SEQ ID NO:390), TAR2h-68 (SEQ ID NO:391), TAR2h-70 (SEQ ID NO:392), TAR2h-71 (SEQ ID NO:393), TAR2h-72 (SEQ ID NO:394), TAR2h-73 (SEQ ID NO:395), TAR2h-74 (SEQ ID NO:396), TAR2h-75 (SEQ ID NO:397), TAR2h-76 (SEQ ID NO:398), TAR2h-77 (SEQ ID NO:399), TAR2h-78 (SEQ ID NO:400), TAR2h-79 (SEQ ID NO:401), and TAR2h-15 (SEQ ID NO:431).  
      The invention also relates to an antibody or antigen-binding fragment thereof that has binding specificity for TNFR1 and has efficacy in treating, suppressing or preventing a chronic inflammatory disease. In some embodiments, the antibody or antigen-binding fragment is a monovalent antigen-binding fragment.  
      The invention also provides a dAb monomer, and ligands comprising the dAb monomer, that has binding specificity for TNFR1 and inhibits TNFR-1-mediated signaling, but does not substantially inhibit binding of TNFα to TNFR1. In some embodiments the dAb monomer inhibits TNFα-induced crosslinking or clustering of TNFR1 on the surface of a cell.  
      The invention also provides isolated and/or recombinant nucleic acid molecules that encode the ligands of the invention, and vectors that comprise the recombinant nucleic acid molecules. Also provided are host cells comprising the recombinant nucleic acid molecules or vectors of the invention and methods for producing the ligands.  
      The invention also relates to pharmaceutical compositions comprising an antagonist or ligand of the invention and a pharmacologically, physiologically or pharmaceutically acceptable carrier.  
      The invention also relates to methods for treating, suppressing or preventing a disease or disorder (e.g., a chronic inflammatory disease, an autoimmune disorder, inflammatory disease, arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, pneumonia, septic shock), comprising administering to a mammal in need thereof a therapeutically effective amount or dose of an antagonist or ligand of the invention.  
      The invention also relates to an antagonist or ligand of the invention for use in therapy or diagnosis, and to the use of an antagonist or ligand of the invention for the manufacture of a medicament for treating, suppressing or preventing a disease or disorder as described herein (e.g., a chronic inflammatory disease, an autoimmune disorder, inflammatory disease, arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, pneumonia or septic shock).  
      The invention further relates to a pharmaceutical composition for treating, suppressing or preventing a disease or disorder described herein (e.g., a chronic inflammatory disease, an autoimmune disorder, inflammatory disease, arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, pneumonia or septic shock) comprising an antagonist or ligand of the invention as an active ingredient.  
      The single variable domains or domain antibodies (dAb) that have binding specificity for TNFR1 and ligands comprising these single variable domains or dAbs have several advantages. For example, the single variable domains or dAbs that have binding specificity for TNFR1 described herein antagonize TNFR1. Accordingly therapeutic agents that comprise an anti-TNFR1 immunoglobulin single variable domain or dAb of the invention can be administered (e.g., for therapeutic, diagnostic or prophylactic purposes) with substantially reduced risk of side effects caused by binding and/or antagonizing TNFR2 (e.g., immunosuppression). Therapeutic agents that target TNF alpha, such as ENBREL® (entarecept; Immunex Corporation) antagonize TNFR1 and TNFR2, and administering such agents can produce immunosuppression and related side effects (e.g., serious infections). These side effects can limit the use of such agents, particulary for chronic diseases where the tagent is administered over a long period. In contrast, because the ligands of the invention specifically antagonize TNFR1, they can be administered over long periods, on a chronic basis, with reduced risk of side effects and provide advantages for treating inflammatory conditions and chronic inflammatory conditions (including long duration diseases characterized by periods of quiescence and periods of active inflammation, such as inflammatory bowel disease and arthritis). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows the diversification of V H /HSA at positions H50, H52, H52a, H53, H55, H56, H58, H95, H96, H97, H98 (DVT or NNK encoded respectively) which are in the antigen binding site of V H  HSA. (SEQ ID NO: 1, nucleotide sequence; SEQ ID NO:2, amino acid sequence.) The sequence of V K  is diversified at positions L50, L53.  
       FIG. 2  is a schematic showing the structure of the plasmid pIT1/pIT2 used to prepare single chain Fv (scFv) libraries, and shows the nucleotide sequence of the plasmid across the expression control and cloning regions (SEQ ID NO:3) and the encoded amino acid sequence (SEQ ID NO:4). The plasmid was used to prepare 
          Library 1: Germline V K /DVT V H ,     Library 2: Germline V K /NNK V H ,     Library 3: Germline V H /DVT V K , and     Library 4: Germline V H /NNK V K  in phage display/ScFv format.        
      These libraries were pre-selected for binding to generic ligands protein A and protein L so that the majority of the clones and selected libraries are functional. Libraries were selected on HSA (first round) and β-gal (second round) or HSA β-gal selection or on β-gal (first round) and HSA (second round) β-gal HSA selection. Soluble scFv from these clones of PCR are amplified in the sequence. One clone encoding a dual specific antibody K8 was chosen for further work.  
       FIG. 3  shows an alignment of V H  chains (V H  dummy (SEQ ID NO:5), K8 (SEQ ID NO:6), VH2 (SEQ ID NO:7), VH4 (SEQ ID NO:8), VHC11 (SEQ ID NO:9), VHA10sd (SEQ ID NO:10), VHA1sd (SEQ ID NO:11), VHA5sd (SEQ ID NO:12), VHC5sd (SEQ ID NO:13), VHC11sd (SEQ ID NO:14), VHC11sd (SEQ ID NO:15)) and V ε  chains (Vk dummy (SEQ ID NO:16), K8 (SEQ ID NO:17), E5sc (SEQ ID NO:18), C3 (SEQ ID NO: 19)).  
       FIG. 4  shows the characterisation of the binding properties of the K8 antibody, the binding properties of the K8 antibody characterised by monoclonal phage ELISA, the dual specific K8 antibody was found to bind HSA and β-gal and displayed on the surface of the phage with absorbant signals greater than 1.0. No cross reactivity with other proteins was detected.  
       FIG. 5  shows soluble scFv ELISA performed using known concentrations of the K8 antibody fragment. A 96-well plate was coated with 100 μg of HSA, BSA and β-gal at 10 μg/ml and 100 μg/ml of Protein A at 1 μg/ml concentration. 50 μg of the serial dilutions of the K8 scFv was applied and the bound antibody fragments were detected with Protein L-HRP. ELISA results confirm the dual specific nature of the K8 antibody.  
       FIG. 6  shows the binding characteristics of the clone K8V K /dummy V H  analysed using soluble scFv ELISA. Production of the soluble scFv fragments was induced by IPTG as described by Harrison et al, Methods Enzymol. 1996;267:83-109 and the supernatant containing scFv assayed directly. Soluble scFv ELISA is performed as described in example 1 and the bound scFvs were detected with Protein L-HRP. The ELISA results revealed that this clone was still able to bind β-gal, whereas binding BSA was abolished.  
       FIG. 7  shows the sequence (SEQ ID NO:2 and SEQ ID NO:3) of variable domain vectors 1 and 2.  
       FIG. 8  is a map of the C H  vector used to construct a V H 1V H 2 multipsecific ligand.  
       FIG. 9  is a map of the C ε vector used to construct a V ε 1/V ε 2 multispecific ligand.  
       FIG. 10  shows a TNF receptor assay comparing TAR1-5 dimer 4, TAR1-5-19 dimer 4 and TAR1-5-19 monomer.  
       FIG. 11  shows a TNF receptor assay comparing TAR1-5 dimers 1-6. All dimers have been FPLC purified and the results for the optimal dimeric species are shown.  
       FIG. 12  shows a TNF receptor assay of TAR1-5 19 homodimers in different formats: dAb-linker-dAb format with 3U, 5U or 7U linker, Fab format and cysteine hinge linker format.  
       FIG. 13  shows Dummy VH sequence for library 1. (amino acid sequence ((SEQ ID NO:5; nucleotide sequences: coding strand (SEQ ID NO:20), noncoding strand (SEQ ID NO:21) The sequence of the VH framework based on germline sequence DP47-JH4b. Positions where NNK randomisation (N=A or T or C or G nucleotides; K=G or T nucleotides) has been incorporated into library 1 are indicated in bold underlined text.  
       FIG. 14  shows Dummy VH sequence for library 2. (amino acid sequence ((SEQ ID NO:22; nucleotide sequences: coding strand (SEQ ID NO:23), noncoding strand (SEQ ID NO:24) The sequence of the VH framework based on gernline sequence DP47-JH4b. Positions where NNK randomisation (N=A or T or C or G nucleotides; K=G or T nucleotides) has been incorporated into library 2 are indicated in bold underlined text.  
       FIG. 15  shows Dummy V K  sequence for library 3. (amino acid sequence ((SEQ ID NO: 16; nucleotide sequences: coding strand (SEQ ID NO:25), noncoding strand (SEQ ID NO:26) The sequence of the V K  framework based on germline sequence DP K 9-J  K 1. Positions where NNK randomisation (N=A or T or C or G nucleotides; K=G or T nucleotides) has been incorporated into library 3 are indicated in bold underlined text.  
       FIG. 16  shows nucleotide and amino acid sequence of anti MSA dAbs MSA 16 (nucleotide sequence (SEQ ID NO:27), amino acid sequence (SEQ ID NO:28) and MSA 26 (nucleotide sequence (SEQ ID NO:29), amino acid sequence (SEQ ID NO:30).  
       FIG. 17 ( a )- 17 ( b ) shows inhibition biacore of MSA 16 and 26. Purified dAbs MSA16 and MSA26 were analysed by inhibition biacore to determine K d . Briefly, the dAbs were tested to determine the concentration of dAb required to achieve 200RUs of response on a biacore CM5 chip coated with a high density of MSA. Once the required concentrations of dAb had been determined, MSA antigen at a range of concentrations around the expected K d  was premixed with the dAb and incubated overnight. Binding to the MSA coated biacore chip of dAb in each of the premixes was then measured at a high flow-rate of 30 μl/minute.  
       FIG. 18  shows serum levels of MSA16 following injection. Serum half life of the dAb MSA16 was determined in mouse. MSA16 was dosed as single i.v. injections at approx 1.5 mg/kg into CD1 mice. Modelling with a 2 compartment model showed MSA16 had a t½α of 0.98 hr, a t½β of 36.5 hr and an AUC of 913 hr.mg/ml. MSA16 had a considerably lengthened half life compared with HEL4 (an anti-hen egg white lysozyme dAb) which had a t½α of 0.06 hr and a t½β of 0.34 hr.  
       FIGS. 19   a - 19   c  shows an ELISA ( FIG. 19   a ) and TNF receptor assay ( FIG. 19   b ,  FIG. 19   19   c ) showing inhibition of TNF binding with a Fab-like fragment comprising MSA26Ck and TAR1-5-19CH. Addition of MSA with the Fab-like fragment reduces the level of inhibition. An ELISA plate coated with 1 μg/ml TNFA was probed with dual specific V K  C H  and V K  C K  Fab like fragment and also with a control TNFα binding dAb at a concentration calculated to give a similar signal on the ELISA. Both the dual specific and control dAb were used to probe the ELISA plate in the presence and in the absence of 2 mg/ml MSA. The signal in the dual specific well was reduced by more than 50% but the signal in the dAb well was not reduced at all (see  FIG. 19   a ). The same dual specific protein was also put into the receptor assay with and without MSA and competition by MSA was also shown (see  FIG. 19   c ). This demonstrates that binding of MSA to the dual specific is competitive with binding to TNFα.  
       FIG. 20  shows a TNF receptor assay showing inhibition of TNF binding with a disulphide bonded heterodimer of TAR1-5-19 dAb and MSA16 dAb. Addition of MSA with the dimer reduces the level of inhibition in a dose dependant manner. The TNF receptor assay ( FIG. 19 ( b )) was conducted in the presence of a constant concentration of heterodimer (18 nM) and a dilution series of MSA and HSA. The presence of HSA at a range of concentrations (up to 2 mg/ml) did not cause a reduction in the ability of the dimer to inhibit TNFα. However, the addition of MSA caused a dose dependant reduction in the ability of the dimer to inhibit TNFα ( FIG. 19   a ).This demonstrates that MSA and TNFα compete for binding to the cys bonded TAR1-5-19, MSA16 dimer. MSA and HSA alone did not have an effect on the TNF binding level in the assay.  
       FIG. 21A-21M  shows the amino acid sequences (SEQ ID NOS:31-98 and SEQ ID NOS:373-401 and 431) of several human immunoglobulin variable domains that have binding specificity for human TNFR1. The presented amino acid sequences are continuous with no gaps; the symbol ˜ has been inserted into the sequences to indicate the locations of the complementarity determining regions (CDRs). CDR1 is flanked by ˜, CDR2 is flanked by ˜˜, and CDR3 is flanked by ˜˜˜.  
       FIG. 22A-22T  shows the nucleotide sequences (SEQ ID NOS:99-166 and SEQ ID NOS:402-430 and 432) of several nucleic acids that encode the human immunoglobulin variable domains presented in  FIG. 21A-21M . The presented nucleotide sequences are continuous with no gaps; the symbol ˜ has been inserted into the sequences to indicate the location of the sequences encoding the CDRs. The sequences encoding CDR1 are flanked by ˜, the sequences encoding CDR2 are flanked by ˜˜, and the sequences encoding CDR3 are flanked by ˜˜˜.  
       FIG. 23A-23B  shows the amino acid sequences (SEQ ID NOS:167-179) of several human immunoglobulin variable domains that have binding specificity for mouse TNFR1. The presented amino acid sequences are continuous with no gaps. In some of the sequences the symbol ˜ has been inserted to indicate the location of the complementarity determining regions (CDRs). CDR1 is flanked by ˜, CDR2 is flanked by ˜˜, and CDR3 is flanked by ˜˜˜.  
       FIG. 24A-24C  shows the nucleotide sequences (SEQ ID NOS:180-192) of several nucleic acids that encode the human immunoglobulin variable domains presented in  FIG. 23A-23B .  
       FIG. 25A-25L  shows the nucleotide sequences encoding several human immunoglobulin variable domains and the amino acid sequences of the encoded human immunoglobulin variable domains (SEQ ID NOS:193-292).  
       FIG. 26  is a graph showing that anti-TNFR1 dAb formats do not substantially agonize TNFR1 in an L929 assay. L929 cells were cultured in media that contained a range of concentrations of anti-TNFR1 dAb monomer (TAR2m-21-23), TAR2m-21-23 monomer cross-linked by a commercially available anti-myc antibody (9E10), dual specific anti-TNFR1 dAb/anti-SA dAb (TAR2m-21-23 3U TAR7m-16), or pegylated anti-TNFR1 dAb monomer (TAR2m-21-23 40K PEG). In the case of TAR2m-21-23 monomer cross-linked by the anti-myc antibody, the dAb and antibody were mixed in a 2:1 ratio and pre-incubated for one hour at room-temperature to simulate the effects of in vivo immune cross-linking prior to culture. (The TAR2m-21-23 monomer includes a myc epitope.) TAR2m-21-23 monomer was incubated with the L929 cells at a concentration of 3,000 nM. TAR2m-21-23 monomer and anti-Myc antibody were incubated at a dAb concentration of 3,000 nM. TAR2m-21-23 3U TAR7m-16 was incubated with the cells at 25 nM, 83.3 nM, 250 nM, 833 nM and 2,500 nM concentrations. TAR2m-21-23 40K PEG was incubated with the cells at 158.25 nM, 527.5 nM, 1582.5 nM, 5,275 nM and 15,825 nM concentrations. After incubation overnight, cell viability was assessed. The results revealed that incubation of L929 cells with 10 nM, 1 nM or 0.1 nM of a commercially-available anti-TNFR1 IgG antibody that crosslinks and agonizes TNFR1 (Catalog No. AF-425-PB; R&amp;D Systems, Minneapolis, Minn.) resulted in a dose-dependent increase in non-viable cells, thereby demonstrating the sensitivity of these cells to agonists of TNFR1. In contrast, incubation with various amounts of anti-TNFR1 formats did not antagonize TNFR1 and did not result in an increase in the number of non-viable cells in the cultures, even when used at more than 1000 times the concentration of the commercially-available anti-TNFR1 IgG antibody. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Definitions  
      “Complementary” Two immunoglobulin domains are “complementary” where they belong to families of structures which form cognate pairs or groups or are derived from such families and retain this feature. For example, a V H  domain and a V L  domain of an antibody are complementary; two V H  domains are not complementary, and two V L  domains are not complementary. Complementary domains may be found in other members of the immunoglobulin superfamily, such as the V α  and V β  (or γ and δ) domains of the T-cell receptor. In the context of the second configuration of the present invention, non-complementary domains do not bind a target molecule cooperatively, but act independently on different target epitopes which may be on the same or different molecules. Domains which are artificial, such as domains based on protein scaffolds which do not bind epitopes unless engineered to do so, are non-complementary. Likewise, two domains based on (for example) an immunoglobulin domain and a fibronectin domain are not complementary.  
      “Immunoglobulin” This refers to a family of polypeptides which retain the immunoglobulin fold characteristic of antibody molecules, which contains two β sheets and, usually, a conserved disulphide bond. Members of the immunoglobulin superfamily are involved in many aspects of cellular and non-cellular interactions in vivo, including widespread roles in the immune system (for example, antibodies, T-cell receptor molecules and the like), involvement in cell adhesion (for example the ICAM molecules) and intracellular signalling (for example, receptor molecules, such as the PDGF receptor). The present invention is applicable to all immunoglobulin superfamily molecules which possess binding domains. Preferably, the present invention relates to antibodies.  
      “Combining” Variable domains according to the invention are combined to form a group of domains; for example, complementary domains may be combined, such as V L  domains being combined with V H  domains. Non-complementary domains may also be combined. Domains may be combined in a number of ways, involving linkage of the domains by covalent or non-covalent means.  
      “Domain” A domain is a folded protein structure which retains its tertiary structure independently of the rest of the protein. Generally, domains are responsible for discrete finctional properties of proteins, and in many cases may be added, removed or transferred to other proteins without loss of function of the remainder of the protein and/or of the domain. By single antibody variable domain is meant a folded polypeptide domain comprising sequences characteristic of antibody variable domains. It therefore includes complete antibody variable domains and modified variable domains, for example in which one or more loops have been replaced by sequences which are not characteristic of antibody variable domains, or antibody variable domains which have been truncated or comprise N- or C-terminal extensions, as well as folded fragments of variable domains which retain at least in part the binding activity and specificity of the full-length domain.  
      “Repertoire” A collection of diverse variants, for example polypeptide variants which differ in their primary sequence. A library used in the present invention will encompass a repertoire of polypeptides comprising at least 1000 members.  
      “Library” The term library refers to a mixture of heterogeneous polypeptides or nucleic acids. The library is composed of members, each of which have a single polypeptide or nucleic acid sequence. To this extent, library is synonymous with repertoire. Sequence differences between library members are responsible for the diversity present in the library. The library may take the form of a simple mixture of polypeptides or nucleic acids, or may be in the form of organisms or cells, for example bacteria, viruses, animal or plant cells and the like, transformed with a library of nucleic acids. Preferably, each individual organism or cell contains only one or a limited number of library members. Advantageously, the nucleic acids are incorporated into expression vectors, in order to allow expression of the polypeptides encoded by the nucleic acids. In a preferred aspect, therefore, a library may take the form of a population of host organisms, each organism containing one or more copies of an expression vector containing a single member of the library in nucleic acid form which can be expressed to produce its corresponding polypeptide member. Thus, the population of host organisms has the potential to encode a large repertoire of genetically diverse polypeptide variants.  
      A “closed conformation multi-specific ligand” describes a multi-specific ligand as herein defined comprising at least two epitope binding domains as herein defined. The term ‘closed conformation’ (multi-specific ligand) means that the epitope binding domains of the ligand are arranged such that epitope binding by one epitope binding domain competes with epitope binding by another epitope binding domain. That is, cognate epitopes may be bound by each epitope binding domain individually but not simultaneously. The closed conformation of the ligand can be achieved using methods herein described.  
      “Antibody” An antibody (for example IgG, IgM, IgA, IgD or IgE) or fragment (such as a Fab , F(ab′) 2 , Fv, disulphide linked Fv, scFv, closed conformation multispecific antibody, disulphide-linked scFv, diabody) whether derived from any species naturally producing an antibody, or created by recombinant DNA technology; whether isolated from serum, B-cells, hybridomas, transfectomas, yeast or bacteria).  
      “Dual-specific ligand” A ligand comprising a first immunoglobulin single variable domain and a second immunoglobulin single variable domain as herein defined, wherein the variable regions are capable of binding to two different antigens or two epitopes on the same antigen which are not normally bound by a monospecific immunoglobulin. For example, the two epitopes may be on the same hapten, but are not the same epitope or sufficiently adjacent to be bound by a monospecific ligand. The dual specific ligands according to the invention are composed of variable domains which have different specificities, and do not contain mutually complementary variable domain pairs which have the same specificity.  
      “Antigen” A molecule that is bound by a ligand according to the present invention. Typically, antigens are bound by antibody ligands and are capable of raising an antibody response in vivo. It may be a polypeptide, protein, nucleic acid or other molecule. Generally, the dual specific ligands according to the invention are selected for target specificity against a particular antigen. In the case of conventional antibodies and fragments thereof, the antibody binding site defined by the variable loops (L1, L2, L3 and H1, H2, H3) is capable of binding to the antigen.  
      “Epitope” A unit of structure conventionally bound by an immunoglobulin V H /N L  pair. Epitopes define the minimum binding site for an antibody, and thus represent the target of specificity of an antibody. In the case of a single domain antibody, an epitope represents the unit of structure bound by a variable domain in isolation.  
      “Generic ligand” A ligand that binds to all members of a repertoire. Generally, not bound through the antigen binding site as defined above. Non-limiting examples include protein A, protein L and protein G.  
      “Selecting” Derived by screening, or derived by a Darwinian selection process, in which binding interactions are made between a domain and the antigen or epitope or between an antibody and an antigen or epitope. Thus a first variable domain may be selected for binding to an antigen or epitope in the presence or in the absence of a complementary variable domain.  
      “Universal framework” A single antibody framework sequence corresponding to the regions of an antibody conserved in sequence as defined by Kabat (“Sequences of Proteins of Immunological Interest”, US Department of Health and Human Services) or corresponding to the human germline immunoglobulin repertoire or structure as defined by Chothia and Lesk, (1987) J. Mol. Biol. 196:910-917. The invention provides for the use of a single framework, or a set of such frameworks, which has been found to permit the derivation of virtually any binding specificity though variation in the hypervariable regions alone.  
      “Half-life” The time taken for the serum concentration of the ligand to reduce by 50%, in vivo, for example due to degradation of the ligand and/or clearance or sequestration of the ligand by natural mechanisms. The ligands of the invention are stabilised in vivo and their half-life increased by binding to molecules which resist degradation and/or clearance or sequestration. Typically, such molecules are naturally occurring proteins which themselves have a long half-life in vivo. The half-life of a ligand is increased if its functional activity persists, in vivo, for a longer period than a similar ligand which is not specific for the half-life increasing molecule. Thus, a ligand specific for HSA and a target molecule is compared with the same ligand wherein the specificity for HSA is not present, that it does not bind HSA but binds another molecule. For example, it may bind a second epitope on the target molecule. Typically, the half life is increased by 10%, 20%, 30%, 40%, 50% or more. Increases in the range of 2×, 3×, 4×, 5×, 10×, 20×, 30×, 40×, 50× or more of the half life are possible. Alternatively, or in addition, increases in the range of up to 30×, 40×, 50×, 60×, 70×, 80×, 90×, 100×, 150× of the half life are possible.  
      “Homogeneous immunoassay” An immunoassay in which analyte is detected without need for a step of separating bound and un-bound reagents.  
      “Substantially identical (or “substantially homologous”)” A first amino acid or nucleotide sequence that contains a sufficient number of identical or equivalent (e.g., with a similar side chain, e.g., conserved amino acid substitutions) amino acid residues or nucleotides to a second amino acid or nucleotide sequence such that the first and second amino acid or nucleotide sequences have similar activities. In the case of antibodies, the second antibody has the same binding specificity and has at least 50% of the affinity of the same.  
      As used herein, the terms “low stringency,” “medium stringency,” “high stringency,” or “very high stringency conditions” describe conditions for nucleic acid hybridization and washing. Guidance for performing hybridization reactions can be found in  Current Protocols in Molecular Biology , John Wiley &amp; Sons, N.Y. (1989), 6.3.1-6.3.6, which is incorporated herein by reference in its entirety. Aqueous and nonaqueous methods are described in that reference and either can be used. Specific hybridization conditions referred to herein are as follows: (1) low stringency hybridization conditions in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by two washes in 0.2× SSC, 0.1% SDS at least at 50° C. (the temperature of the washes can be increased to 55° C. for low stringency conditions); (2) medium stringency hybridization conditions in 6×SSC at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 60° C.; (3) high stringency hybridization conditions in 6×SSC at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 65° C.; and preferably (4) very high stringency hybridization conditions are 0.5M sodium phosphate, 7% SDS at 65° C., followed by one or more washes at 0.2×SSC, 1% SDS at 65° C. Very high stringency conditions (4) are the preferred conditions and the ones that should be used unless otherwise specified.  
      As herein defined the term “closed conformation” (multi-specific ligand) means that the epitope binding domains of the ligand are attached to or associated with each other, optionally by means of a protein skeleton, such that epitope binding by one epitope binding domain competes with epitope binding by another epitope binding domain. That is, cognate epitopes may be bound by each epitope binding domain individually but not simultaneously. The closed conformation of the ligand can be achieved using methods herein described.  
      “Open conformation” means that the epitope binding domains of the ligand are attached to or associated with each other, optionally by means of a protein skeleton, such that epitope binding by one epitope binding domain does not compete with epitope binding by another epitope binding domain.  
      As referred to herein, the term “competes” means that the binding of a first epitope to its cognate epitope binding domain is inhibited when a second epitope is bound to its cognate epitope binding domain. For example, binding may be inhibited sterically, for example by physical blocking of a binding domain or by alteration of the structure or environment of a binding domain such that its affinity or avidity for an epitope is reduced.  
      The phrase “immunoglobulin single variable domain” refers to an antibody variable region (V H , V HH , V L ) that specifically binds an antigen or epitope independently of other V regions or domains; however, as the term is used herein, an immunoglobulin single variable domain can be present in a format (e.g., homo- or hetero-multimer) with other variable regions or variable domains where the other regions or domains are not required for antigen binding by the single immunoglobulin variable domain (i.e., where the immunoglobulin single variable domain binds antigen independently of the additional variable domains). “Immunoglobulin single variable domain” encompasses not only an isolated antibody single variable domain polypeptide, but also larger polypeptides that comprise one or more monomers of an antibody single variable domain polypeptide sequence. A “domain antibody” or “dAb” is the same as an “immunoglobulin single variable domain” polypeptide as the term is used herein. An immunoglobulin single variable domain polypeptide, as used herein refers to a mammalian immunoglobulin single variable domain polypeptide, preferably human, but also includes rodent (for example, as disclosed in WO 00/29004, the contents of which are incorporated herein by reference in their entirety) or camelid V HH  dAbs. Camelid dAbs are immunoglobulin single variable domain polypeptides which are derived from species including camel, llama, alpaca, dromedary, and guanaco, and comprise heavy chain antibodies naturally devoid of light chain: V HH . V HH  molecules are about ten times smaller than IgG molecules, and as single polypeptides, they are very stable, resisting extreme pH and temperature conditions.  
      As used herein, the term “antagonist of Tumor Necrosis Factor Receptor 1 (TNFR1)” refers to an agent (e.g., a molecule, a compound) which binds TNFR1 and can inhibit a (i.e., one or more) finction of TNFR1. For example, an antagonist of TNFR1 can inhibit the binding of TNFα to TNFR1 and/or inhibit signal transduction mediated through TNFR1. Accordingly, TNFR1-mediated processes and cellular responses (e.g., TNFα-induced cell death in a standard L929 cytotoxicity assay) can be inhibited with an antagonist of TNFR1. An antagonist of TNFR1 can be, for example, a small organic molecule, natural product, protein, peptide or peptidomimetic. Antagonists of TNFR1 can be identified, for example, by screening libraries or collections of molecules, such as, the Chemical Repository of the National Cancer Institute, as described herein or using other suitable methods. Preferred antagonists of TNFR1 are antibodies, antigen-binding fragments of antibodies, ligands and dAb monomers described herein. Sequences similar or homologous (e.g., at least about 70% sequence identity) to the sequences disclosed herein are also part of the invention. In some embodiments, the sequence identity at the amino acid level can be about 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or higher. At the nucleic acid level, the sequence identity can be about 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or higher. Alternatively, substantial identity exists when the nucleic acid segments will hybridize under selective hybridization conditions (e.g., very high stringency hybridization conditions), to the complement of the strand. The nucleic acids may be present in whole cells, in a cell lysate, or in a partially purified or substantially pure form.  
      Calculations of “homology” or “sequence identity” or “similarity” between two sequences (the terms are used interchangeably herein) are performed as follows. The sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in one or both of a first and a second amino acid or nucleic acid sequence for optimal alignment and non-homologous sequences can be disregarded for comparison purposes). In a preferred embodiment, the length of a reference sequence aligned for comparison purposes is at least 30%, preferably at least 40%, more preferably at least 50%, even more preferably at least 60%, and even more preferably at least 70%, 80%, 90%, 100% of the length of the reference sequence. The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position (as used herein amino acid or nucleic acid “homology” is equivalent to amino acid or nucleic acid “identity”). The percent identity between the two sequences is a function of the number of identical positions shared by the sequences, taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment of the two sequences.  
      Advantageously, the BLAST algorithm (version 2.0) is employed for sequence alignment, with parameters set to default values. The BLAST algorithm is described in detail at the world wide web site (“www”) of the National Center for Biotechnology Information (“.ncbi”) of the National Institutes of Health (“nih”) of the U.S. government (“.gov”), in the “/Blast/” directory, in the “blast_help.html” file. The search parameters are defined as follows, and are advantageously set to the defined default parameters.  
      BLAST (Basic Local Alignment Search Tool) is the heuristic search algorithm employed by the programs blastp, blastn, blastx, tblastn, and tblastx; these programs ascribe significance to their findings using the statistical methods of Karlin and Altschul, 1990, Proc. Natl. Acad. Sci. USA 87(6):2264-8 (see the “blast_help.html” file, as described above) with a few enhancements. The BLAST programs were tailored for sequence similarity searching, for example to identify homologues to a query sequence. The programs are not generally useful for motif-style searching. For a discussion of basic issues in similarity searching of sequence databases, see Altschul et al. (1994). The five BLAST programs available at the National Center for Biotechnology Information web site perform the following tasks:  
      “blastp” compares an amino acid query sequence against a protein sequence database;  
      “blastn” compares a nucleotide query sequence against a nucleotide sequence database;  
      “blastx” compares the six-frame conceptual translation products of a nucleotide query sequence (both strands) against a protein sequence database;  
      “tblastn” compares a protein query sequence against a nucleotide sequence database dynamically translated in all six reading frames (both strands).  
      “tblastx” compares the six-frame translations of a nucleotide query sequence against the six-frame translations of a nucleotide sequence database.  
      BLAST uses the following search parameters:  
      HISTOGRAM Display a histogram of scores for each search; default is yes. (See parameter H in the BLAST Manual).  
      DESCRIPTIONS Restricts the number of short descriptions of matching sequences reported to the number specified; default limit is 100 descriptions. (See parameter V in the manual page). See also EXPECT and CUTOFF.  
      ALIGNMENTS Restricts database sequences to the number specified for which high-scoring segment pairs (HSPs) are reported; the default limit is 50. If more database sequences than this happen to satisfy the statistical significance threshold for reporting (see EXPECT and CUTOFF below), only the matches ascribed the greatest statistical significance are reported. (See parameter B in the BLAST Manual).  
      EXPECT The statistical significance threshold for reporting matches against database sequences; the default value is 10, such that 10 matches are expected to be found merely by chance, according to the stochastic model of Karlin and Altschul (1990). If the statistical significance ascribed to a match is greater than the EXPECT threshold, the match will not be reported. Lower EXPECT thresholds are more stringent, leading to fewer chance matches being reported. Fractional values are acceptable. (See parameter E in the BLAST Manual).  
      CUTOFF Cutoff score for reporting high-scoring segment pairs. The default value is calculated from the EXPECT value (see above). HSPs are reported for a database sequence only if the statistical significance ascribed to them is at least as high as would be ascribed to a lone HSP having a score equal to the CUTOFF value. Higher CUTOFF values are more stringent, leading to fewer chance matches being reported. (See parameter S in the BLAST Manual). Typically, significance thresholds can be more intuitively managed using EXPECT.  
      MATRIX Specify an alternate scoring matrix for BLASTP, BLASTX, TBLASTN and TBLASTX. The default matrix is BLOSUM62 (Henikoff &amp; Henikoff, 1992, Proc. Natl. Aacad. Sci. USA 89(22):10915-9). The valid alternative choices include: PAM40, PAM120, PAM250 and IDENTITY. No alternate scoring matrices are available for BLASTN; specifying the MATRIX directive in BLASTN requests returns an error response.  
      STRAND Restrict a TBLASTN search to just the top or bottom strand of the database sequences; or restrict a BLASTN, BLASTX or TBLASTX search to just reading frames on the top or bottom strand of the query sequence.  
      FILTER Mask off segments of the query sequence that have low compositional complexity, as determined by the SEG program of Wootton &amp; Federhen (1993) Computers and Chemistry 17:149-163, or segments consisting of short-periodicity internal repeats, as determined by the XNU program of Claverie &amp; States, 1993, Computers and Chemistry 17:191-201, or, for BLASTN, by the DUST program of Tatusov and Lipman (see the world wide web site of the NCBI). Filtering can eliminate statistically significant but biologically uninteresting reports from the blast output (e.g., hits against common acidic-, basic- or proline-rich regions), leaving the more biologically interesting regions of the query sequence available for specific matching against database sequences.  
      Low complexity sequence found by a filter program is substituted using the letter “N” in nucleotide sequence (e.g., “N” repeated 13 times) and the letter “X” in protein sequences (e.g., “X” repeated 9 times).  
      Filtering is only applied to the query sequence (or its translation products), not to database sequences. Default filtering is DUST for BLASTN, SEG for other programs.  
      It is not unusual for nothing at all to be masked by SEG, XNU, or both, when applied to sequences in SWISS-PROT, so filtering should not be expected to always yield an effect. Furthermore, in some cases, sequences are masked in their entirety, indicating that the statistical significance of any matches reported against the unfiltered query sequence should be suspect.  
      NCBI-gi Causes NCBI gi identifiers to be shown in the output, in addition to the accession and/or locus name.  
      Most preferably, sequence comparisons are conducted using the simple BLAST search algorithm provided at the NCBI world wide web site described above, in the “/BLAST” directory.  
      Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art (e.g., in cell culture, molecular genetics, nucleic acid chemistry, hybridization techniques and biochemistry). Standard techniques are used for molecular, genetic and biochemical methods (see generally, Sambrook et al., Molecular Cloning: A Laboratory Manual, 2d ed. (1989) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. and Ausubel et al., Short Protocols in Molecular Biology (1999) 4 th  Ed, John Wiley &amp; Sons, Inc. which are incorporated herein by reference) and chemical methods.  
      The invention relates to antagonists of TNFR1 (e.g., ligands described herein) that have binding specificity for Tumor Necrosis Factor Receptor 1 (TNFR1; p55; CD120a). Preferably the antagonists of the inventions do not have binding specificity for Tumor Necrosis Factor 2 (TNFR2), or do not substantially antagonize TNFR2. An antagonist of TNFR1 does not substantially antagonize TNFR2 when the antagonist (1 nM, 10 nM, 100 nM, 1 μM, 10 μM or 100 μM) results in no more than about 5% inhibition of TNFR2-mediated activity induced by TNFα (100 pg/ml) in a standard cell assay.  
      Particularly preferred antagonists of TNFR1 are effective therapeutics for treating chronic inflammatory disease (are efficacious, have therapeutic efficacy). For example, in some embodiments, the antagonist of TNFR1 is efficacious in a model of chronic inflammatory disease, such as the mouse collagen-induced arthritis model, mouse ΔARE model of arthritis, mouse dextran sulfate sodium-induced model of inflammatory bowel disease, mouse ΔARE model of inflammatory bowel disease, mouse tobacco smoke model of chronic obstructive pulmonary disease or a suitable primate model (e.g., primate collagen-induced arthritis).  
      In some embodiments, the antagonist is monovalent and contains one binding site that interacts with TNFR1. Monovalent antagonists bind one TNFR1 and do not induce cross-linking or clustering of TNFR1 on the surface of cells which can lead to activation of the receptor and signal transduction.  
      In other embodiments, the antagonist is an antibody that has binding specificity for TNFR1 or an antigen-binding fragment thereof, such as an Fab fragment, Fab′ fragment, F(ab′) 2  fragment or Fv fragment (e.g., scFV). In other embodiments, the antagonist is monovalent, such as a dAb or a monovalent antigen-binding fragment of an antibody, such as an Fab fragment, Fab′ fragment, or Fv fragment.  
      Preferably, the antagonist of TNFR1 is a ligand as described herein. The ligands comprise an immunoglobulin single variable domain or domain antibody (dAb) that has binding specificity for TNFR1 or the complementarity determining regions of such a dAb in a suitable format. The ligand can be a polypeptide that consists of such a dAb, or consists essentially of such a dAb. The ligand can also be a polypeptide that comprises a dAb (or the CDRs of a dAb) in a suitable format, such as an antibody format (e.g., IgG-like format, scFv, Fab, Fab′, F(ab′) 2 ), a dual specific ligand that comprises a dAb that binds TNFR1 and a second dAb that binds another target protein, antigen or epitope (e.g., serum albumin), or a multispecific ligand as described herein. Antagonists of TNFR1, including ligands according to any aspect of the present invention, as well as dAb monomers useful in constructing such ligands, may advantageously dissociate from their cognate target(s) with a K d  of 300 nM to 5 pM (ie, 3×10 −7  to 5×10 −12 M), preferably 50 nM to 20 pM, or 5 nM to 200 pM or 1 nM to 100 pM, 1×10 −7  M or less, 1×10 −8  M or less, 1×10 −9  M or less, 1×10 −10  M or less, 1×10 −11  M or less; and/or a K off  rate constant of 5×10 −1  s −1  to 1×10 −7  s −1 , preferably 1×10 −2  s −1  to 1×10 −6  s −1 , or 5×10 −3  s −1  to 1×10 −5  s −1 , or 5×10 −1  s −1  or less, or 1×10 −2  s −1  or less, or 1×10 −3  s −1  or less, or 1×10 −4  s −1  or less, or 1×10 −5  s −1  or less, or 1×10 −6  s −1  or less as determined by surface plasmon resonance. The K d  rate constant is defined as K off  /n on .  
      Ligands and dAb Monomers that Bind TNFR1  
      The invention provides ligands that comprise an anti-TNFRI dAb monomer, or (e.g., dual specific ligand comprising such a dAb) that binds to TNF Receptor I with a K d  of 300 nM to 5 pM (ie, 3×10 −7  to 5×10 −12 M), preferably 50 nM to 20 pM, more preferably 5 nM to 200 pM and most preferably 1 nM to 100 pM, for example 1×10 −7  M or less, preferably 1×10 −8  M or less, more preferably 1×10 −9  M or less, advantageously 1×10 −10  M or less and most preferably 1×10 −11  M or less; and/or a K off  rate constant of 5×10 −1  s −1  to 1×10 −7  s −1 , preferably 1×10 −2  s −1  to 1×10 −6  s −1 , more preferably 5×10 −3  s −1  to 1×10 −5  s −1 , for example 5×10 −1  s −1  or less, preferably 1×10 −2  s −1  or less, advantageously 1×10 −3  s −1  or less, more preferably 1×10 −4  s −1  or less, still more preferably 1×10 −5  s −1  or less, and most preferably 1×10 −6  s −1  or less as determined by surface plasmon resonance.  
      Preferably, the ligand or dAb monomer inhibits binding of TNF alpha to TNF alpha Receptor I (p55 receptor) with an inhibitory concentration 50 (IC50) of 500 nM to 50 pM, preferably 100 nM to 50 pM, more preferably 10 nM to 100 pM, advantageously 1 nM to 100 pM; for example 50 nM or less, preferably 5 nM or less, more preferably 500 pM or less, advantageously 200 pM or less, and most preferably 100 pM or less. Preferably, the TNF Receptor I target is Human TNFα.  
      Preferably, the ligand or dAb binds human TNFR1 and inhibits binding of human TNF alpha to human TNFR1, or inhibits signaling through TNFR1 in response to TNF alpha binding. For example, in certain embodiments, a ligand or dAb monomer can bind TNFR1 and inhibit TNFR-1-mediated signaling, but does not substantially inhibit binding of TNFa to TNFR 1. In some embodiments, the ligand or dAb monomer inhibits TNFα-induced crosslinking or clustering of TNFR1 on the surface of a cell. Such ligands or dAbs (e.g., TAR2m-21-23 described herein) are advantageous because they can antagonize cell surface TNFR1 but do not substantially reduce the inhibitory activity of endogenous soluble TNFR1. For example, the ligand or dAb can bind TNFR1, but inhibit binding of TNFα to TNFR1 in a receptor binding assay by no more that about 10%, no more that about 5%, no more than about 4%, no more than about 3%, no more than about 2%, or no more than about 1%. Also, in these embodiments, the ligand or dAb inhibits TNFα-induced crosslinking of TNFR1 and/or TNFR1-mediated signaling in a standard cell assay by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 99%.  
      Preferably, the ligand or dAb monomer neutralizes (inhibits the activity of) TNFA or TNFR1 in a standard assay (e.g., the standard L929 or standard HeLa IL-8 assays described herein) with a neutralizing dose 50 (ND50) of 500 nM to 50 pM, preferably 100 nM to 50 pM, more preferably 10 nM to 100 pM, advantageously 1 nM to 100 pM; for example 50 nM or less, preferably 5 nM or less, more preferably 500 pM or less, advantageously 200 pM or less, and most preferably 100 pM or less.  
      In certain embodiments, the ligand or dAb monomer specifically binds human Tumor Necrosis Factor Receptor 1 (TNFRI; p55), and dissociates from human TNFR1 with a dissociation constant (K d ) of 50 nM to 20 pM, and a K off  rate constant of 5×10 −1  s −1  to 1×10 −7  s −1 , as determined by surface plasmon resonance.  
      In other embodiments, the ligand or dAb monomer specifically binds TNFR1 with a K d  described herein and inhibits lethality in a standard mouse LPS/D-galactosamine-induced septic shock model (i.e., prevents lethality or reduces lethality by at least about 10%, as compared with a suitable control). Preferably, the dAb monomer inhibits lethality by at least about 25%, or by at least about 50%, as compared to a suitable control in a standard mouse LPS/D-galactosamine-induced septic shock model when administered at about 5 mg/kg or more preferably about 1 mg/kg.  
      In other embodiments, the ligand or dAb monomer binds TNFR1 and antagonizes the activity of the TNFR1 in a standard cell assay with an ND 50  of ≦100 nM, and at a concentration of ≦10 μM the dAb agonizes the activity of the TNFR1 by ≦5% in the assay.  
      In particular embodiments, ligand or dAb monomer does not substantially agonize TNFR1 (act as an agonist of TNFR1) in a standard cell assay (i.e., when present at a concentration of 1 nM, 10 nM, 100 nM, 1 μM, 10 μM, 100 μM, 1000 μM or 5,000 μM, results in no more than about 5% of the TNFR1-mediated activity induced by TNFα (100 pg/ml) in the assay).  
      In certain embodiments, the ligand or dAb monomer is substantially resistant to aggregation. For example, in some embodiments, less than about 10%, less than about 9%, less than about 8%, less than about 7%, less than about 6%, less than about 5%, less than about 4%, less than about 3%, less than about 2% or less than about 1% of the ligand or dAb monomer aggregates when a 1-5 mg/ml, 5-10 mg/ml, 10-20 mg/ml, 20-50 mg/ml, 50-100 mg/ml, 100-200 mg/ml or 200-500 mg/ml solution of ligand or dAb in a solvent that is routinely used for drug formulation such as saline, buffered saline, citrate buffer saline, water, an emulsion, and, any of these solvents with an acceptable excipient such as those approved by the FDA, is maintained at about 22° C., 22-25° C., 25-30° C., 30-37° C., 37-40° C., 40-50° C., 50-60° C., 60-70° C., 70-80° C., 15-20° C., 10-15° C., 5-10° C., 2-5° C., 0-2° C., −10° C. to 0° C., −20° C. to −10° C., −40° C. to −20° C., −60° C. to −40° C., or −80° C. to −60° C., for a period of about time, for example, 10 minutes, 1 hour, 8 hours, 24 hours, 2 days, 3 days, 4 days, 1 week, 2 weeks, 3 weeks, 1 month, 2 months, 3 months, 4 months, 6 months, 1 year, or 2 years.  
      Aggregation can be assessed using any suitable method, such as, by microscopy, assessing turbidity of a solution by visual inspection or spectroscopy or any other suitable method. Preferably, aggregation is assessed by dynamic light scattering. Ligands or dAb monomers that are resistant to aggregation provide several advantages. For example, such ligands or dAb monomers can readily be produced in high yield as soluble proteins by expression using a suitable biological production system, such as  E. coli , and can be formulated and/or stored at higher concentrations than conventional polypeptides, and with less aggregation and loss of activity.  
      In addition, ligands or dAb monomers that are resistant to aggregation can be produced more economically than other antigen- or epitope-binding polypeptides (e.g., conventional antibodies). For example, generally, preparation of antigen- or epitope-binding polypeptides intended for in vivo applications includes processes (e.g., gel filtration) that remove aggregated polypeptides. Failure to remove such aggregates can result in a preparation that is not suitable for in vivo applications because, for example, aggregates of an antigen-binding polypeptide that is intended to act as an antagonist can function as an agonist by inducing cross-linking or clustering of the target antigen. Protein aggregates can also reduce the efficacy of therapeutic polypeptide by inducing an immune response in the subject to which they are administered.  
      In contrast, the aggregation resistant ligands or dAb monomers of the invention can be prepared for in vivo applications without the need to include process steps that remove aggregates, and can be used in in vivo applications without the aforementioned disadvantages caused by polypeptide aggregates.  
      In some embodiments, the ligand or dAb monomer unfolds reversibly when heated to a temperature (Ts) and cooled to a temperature (Tc), wherein Ts is greater than the melting temperature (Tm) of the dAb, and Tc is lower than the melting temperature of the dAb. For example, the dAb monomer can unfold reversibly when heated to 80° C. and cooled to about room temperature. A polypeptide that unfolds reversibly loses function when unfolded but regains function upon refolding. Such polypeptides are distinguished from polypeptides that aggregate when unfolded or that improperly refold (misfolded polypeptides), i.e., do not regain finction.  
      Polypeptide unfolding and refolding can be assessed, for example, by directly or indirectly detecting polypeptide structure using any suitable method. For example, polypeptide structure can be detected by circular dichroism (CD) (e.g., far-UV CD, near-UV CD), fluorescence (e.g., fluorescence of tryptophan side chains), susceptibility to proteolysis, nuclear magnetic resonance (NMR), or by detecting or measuring a polypeptide finction that is dependent upon proper folding (e.g., binding to target ligand, binding to generic ligand). In one example, polypeptide unfolding is assessed using a functional assay in which loss of binding function (e.g., binding a generic and/or target ligand, binding a substrate) indicates that the polypeptide is unfolded.  
      The extent of unfolding and refolding of a ligand or dAb monomer can be determined using an unfolding or denaturation curve. An unfolding curve can be produced by plotting temperature as the ordinate and the relative concentration of folded polypeptide as the abscissa. The relative concentration of folded ligand or dAb monomer can be determined directly or indirectly using any suitable method (e.g., CD, fluorescence, binding assay). For example, a ligand or dAb monomer solution can be prepared and ellipticity of the solution determined by CD. The ellipticity value obtained represents a relative concentration of folded ligand or dAb monomer of 100%. The ligand or dAb monomer in the solution is then unfolded by incrementally raising the temperature of the solution and ellipticity is determined at suitable increments (e.g., after each increase of one degree in temperature). The ligand or dAb monomer in solution is then refolded by incrementally reducing the temperature of the solution and ellipticity is determined at suitable increments. The data can be plotted to produce an unfolding curve and a refolding curve. The unfolding and refolding curves have a characteristic sigmoidal shape that includes a portion in which the ligand or dAb monomer molecules are folded, an unfolding/refolding transition in which ligand or dAb monomer molecules are unfolded to various degrees, and a portion in which the ligand or dAb monomer molecules are unfolded. The y-axis intercept of the refolding curve is the relative amount of refolded ligand or dAb monomer recovered. A recovery of at least about 50%, or at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 85%, or at least about 90%, or at least about 95% is indicative that the ligand or dAb monomer unfolds reversibly.  
      In a preferred embodiment, reversibility of unfolding of the ligand or dAb monomer is determined by preparing a ligand or dAb monomer solution and plotting heat unfolding and refolding curves. The ligand or dAb monomer solution can be prepared in any suitable solvent, such as an aqueous buffer that has a pH suitable to allow the ligand or dAb monomer to dissolve (e.g., pH that is about 3. units above or below the isoelectric point (pI)). The ligand or dAb monomer solution is concentrated enough to allow unfolding/folding to be detected. For example, the ligand or dAb monomer solution can be about 0.1 μM to about 100 μM, or preferably about 1 μM to about 10 μM.  
      If the melting temperature (Tm) of the ligand or dAb monomer is known, the solution can be heated to about ten degrees below the Tm (Tm-10) and folding assessed by ellipticity or fluorescence (e.g., far-UV CD scan from 200 nm to 250 nm, fixed wavelength CD at 235 nm or 225 nm; tryptophan fluorescent emission spectra at 300 to 450 nm with excitation at 298 nm) to provide 100% relative folded ligand or dAb monomer. The solution is then heated to at least ten degrees above Tm (Tm+10) in predetermined increments (e.g., increases of about 0.1 to about 1 degree), and ellipticity or fluorescence is determined at each increment. Then, the ligand or dAb monomer is refolded by cooling to at least Tm-10 in predetermined increments and ellipticity or fluorescence determined at each increment. If the melting temperature of the ligand or dAb monomer is not known, the solution can be unfolded by incrementally heating from about 25° C. to about 100° C. and then refolded by incrementally cooling to at least about 25° C., and ellipticity or fluorescence at each heating and cooling increment is determined. The data obtained can be plotted to produce an unfolding curve and a refolding curve, in which the y-axis intercept of the refolding curve is the relative amount of refolded protein recovered.  
      In certain embodiments, the ligands or dAb monomers of the invention are efficacious in models of chronic inflammatory diseases when an effective amount is administered. Generally an effective amount is about 1 mg/kg to about 10 mg/kg (e.g., about 1 mg/kg, about 2 mg/kg, about 3 mg/kg, about 4 mg/kg, about 5 mg/kg, about 6 mg/kg, about 7 mg/kg, about 8 mg/kg, about 9 mg/kg, or about 10 mg/kg). The models of chronic inflammatory disease described herein are recognized by those skilled in the art as being predictive of therapeutic efficacy in humans. The prior art does not suggest using antagonists of TNFR1 (e.g., monovalent antagonists, ligands as described herein) in these models, or that they would be efficacious.  
      In particular embodiments, the ligand or dAb monomer is efficacious in the standard mouse collagen-induced arthritis model (Example 15A). For example, administering an effective amount of the ligand can reduce the average arthritic score of the summation of the four limbs in the standard mouse collagen-induced arthritis model, for example, by about 1 to about 16, about 3 to about 16, about 6 to about 16, about 9 to about 16, or about 12 to about 16, as compared to a suitable control. In another example, administering an effective amount of the ligand can delay the onset of symptoms of arthritis in the standard mouse collagen-induced arthritis model, for example, by about 1 day, about 2 days, about 3 days, about 4 days, about 5 days, about 6 days, about 7 days, about 10 days, about 14 days, about 21 days or about 28 days, as compared to a suitable control. In another example, administering an effective amount of the ligand can result in an average arthritic score of the summation of the four limbs in the standard mouse collagen-induced arthritis model of 0 to about 3, about 3 to about 5, about 5 to about 7, about 7 to about 15, about 9 to about 15, about 10 to about 15, about 12 to about 15, or about 14 to about 15.  
      In other embodiments, the ligand or dAb monomer is efficacious in the mouse ΔARE model of arthritis (Example 15B). For example, administering an effective amount of the ligand can reduce the average arthritic score in the mouse ΔARE model of arthritis, for example, by about 0.1 to about 2.5, about 0.5 to about 2.5, about 1 to about 2.5, about 1.5 to about 2.5, or about 2 to about 2.5, as compared to a suitable control. In another example, administering an effective amount of the ligand can delay the onset of symptoms of arthritis in the mouse ΔARE model of arthritis by, for example, about 1 day, about 2 days, about 3 days, about 4 days, about 5 days, about 6 days, about 7 days, about 10 days, about 14 days, about 21 days or about 28 days, as compared to a suitable control. In another example, administering an effective amount of the ligand can result in an average arthritic score in the mouse ΔARE model of arthritis of 0 to about 0.5, about 0.5 to about 1, about 1 to about 1.5, about 1.5 to about 2, or about 2 to about 2.5.  
      In other embodiments, the ligand or dAb monomer is efficacious in the mouse AARE model of inflammatory bowel disease (IBD) (Example 15B). For example, administering an effective amount of the ligand can reduce the average acute and/or chronic inflammation score in the mouse ΔARE model of IBD, for example, by about 0.1 to about 2.5, about 0.5 to about 2.5, about 1 to about 2.5, about 1.5 to about 2.5, or about 2 to about 2.5, as compared to a suitable control. In another example, administering an effective amount of the ligand can delay the onset of symptoms of IBD in the mouse ΔARE model of IBD by, for example, about 1 day, about 2 days, about 3 days, about 4 days, about 5 days, about 6 days, about 7 days, about 10 days, about 14 days, about 21 days or about 28 days, as compared to a suitable control. In another example, administering an effective amount of the ligand can result in an average acute and/or chronic inflammation score in the mouse ΔARE model of IBD of 0 to about 0.5, about 0.5 to about 1, about 1 to about 1.5, about 1.5 to about 2, or about 2 to about 2.5.  
      In other embodiments, the ligand or dAb monomer is efficacious in the mouse dextran sulfate sodium (DSS) induced model of IBD (Example 15C). For example, administering an effective amount of the ligand can reduce the average severity score in the mouse DSS model of IBD, for example, by about 0.1 to about 2.5, about 0.5 to about 2.5, about 1 to about 2.5, about 1.5 to about 2.5, or about 2 to about 2.5, as compared to a suitable control. In another example, administering an effective amount of the ligand can delay the onset of symptoms of IBD in the mouse DSS model of IBD by, for example, about 1 day, about 2 days, about 3 days, about 4 days, about 5 days, about 6 days, about 7 days, about 10 days, about 14 days, about 21 days or about 28 days, as compared to a suitable control. In another example, administering an effective amount of the ligand can result in an average severity score in the mouse DSS model of IBD of 0 to about 0.5, about 0.5 to about 1, about 1 to about 1.5, about 1.5 to about 2, or about 2 to about 2.5.  
      In particular embodiments, the ligand or dAb monomer is efficacious in the mouse tobacco smoke model of chronic obstructive pulmonary disease (COPD) (Example 15D). For example, administering an effective amount of the ligand can reduce or delay onset of the symptoms of COPD, as compared to a suitable control.  
      In particular embodiments, the ligand or dAb monomer specifically binds TNFR1 and comprises the amino acid sequence of TAR2-10 (SEQ ID NO:31) or a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% homologous thereto.  
      In particular embodiments, the ligand or dAb monomer specifically binds TNFR1 and comprises the amino acid sequence of TAR2-5 (SEQ ID NO:195) or a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% homologous thereto.  
      In other embodiments, the ligand comprises a domain antibody (dAb) monomer that specifically binds Tumor Necrosis Factor Receptor I (TNFR1, p55, CD120a) with a K d  of 300 nM to 5 pM, and comprises an amino acid sequence that is at least about 80%, at least about 85%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to the amino acid sequence or a dAb selected from the group consisting of TAR2h-12 (SEQ ID NO:32), TAR2h-13 (SEQ ID NO:33), TAR2h-14 (SEQ ID NO:34), TAR2h-16 (SEQ ID NO:35), TAR2h-17 (SEQ ID NO:36), TAR2h-18 (SEQ ID NO:37), TAR2h-19 (SEQ ID NO:38), TAR2h-20 (SEQ ID NO:39), TAR2h-21 (SEQ ID NO:40), TAR2h-22 (SEQ ID NO:41), TAR2h-23 (SEQ ID NO:42), TAR2h-24 (SEQ ID NO:43), TAR2h-25 (SEQ ID NO:44), TAR2h-26 (SEQ ID NO:45), TAR2h-27 (SEQ ID NO:46), TAR2h-29 (SEQ ID NO:47), TAR2h-30 (SEQ ID NO:48), TAR2h-32 (SEQ ID NO:49), TAR2h-33 (SEQ ID NO:50), TAR2h-10-1 (SEQ ID NO:51), TAR2h-10-2 (SEQ ID NO:52), TAR2h-10-3 (SEQ ID NO:53), TAR2h-10-4 (SEQ ID NO:54), TAR2h-10-5 (SEQ ID NO:55), TAR2h-10-6 (SEQ ID NO:56), TAR2h-10-7 (SEQ ID NO:57), TAR2h-10-8 (SEQ ID NO:58), TAR2h-10-9 (SEQ ID NO:59), TAR2h-10-10 (SEQ BD NO:60), TAR2h-10-11 (SEQ ID NO:61), TAR2h-10-12 (SEQ ID NO:62), TAR2h-10-13 (SEQ ID NO:63), TAR2h-10-14 (SEQ ID NO:64), TAR2h-10-15 (SEQ ID NO:65), TAR2h-10-16 (SEQ ID NO:66), TAR2h-10-17 (SEQ ID NO:67), TAR2h-10-18 (SEQ ID NO:68), TAR2h-10-19 (SEQ ID NO:69), TAR2h-10-20 (SEQ ID NO:70), TAR2h-10-21 (SEQ ID NO:71), TAR2h-10-22 (SEQ ID NO:72), TAR2h-10-27 (SEQ ID NO:73), TAR2h-10-29 (SEQ ID NO:74), TAR2h-10-31 (SEQ ID NO:75), TAR2h-10-35 (SEQ ID NO:76), TAR2h-10-36 (SEQ ID NO:77), TAR2h-10-37 (SEQ ID NO:78), TAR2h-10-38 (SEQ ID NO:79), TAR2h-10-45 (SEQ ID NO:80), TAR2h-10-47 (SEQ ID NO:81), TAR2h-10-48 (SEQ ID NO:82), TAR2h-10-57 (SEQ ID NO:83), TAR2h-10-56 (SEQ ID NO:84), TAR2h-10-58 (SEQ ID NO:85), TAR2h-10-66 (SEQ ID NO:86), TAR2h-10-64 (SEQ ID NO:87), TAR2h-10-65 (SEQ ID NO:88), TAR2h-10-68 (SEQ ID NO:89), TAR2h-10-69 (SEQ ID NO:90), TAR2h-10-67 (SEQ ID NO:91), TAR2h-10-61 (SEQ ID NO:92), TAR2h-10-62 (SEQ ID NO:93), TAR2h-10-63 (SEQ ID NO:94), TAR2h-10-60 (SEQ ID NO:95), TAR2h-10-55 (SEQ ID NO:96), TAR2h-10-59 (SEQ ID NO:97), TAR2h-10-70 (SEQ ID NO:98), TAR2h-34 (SEQ ID NO:373), TAR2h-35 (SEQ ID NO:374), TAR2h-36 (SEQ ID NO:375), TAR2h-37 (SEQ ID NO:376), TAR2h-38 (SEQ ID NO:377), TAR2h-39 (SEQ ID NO:378), TAR2h-40 (SEQ ID NO:379), TAR2h-41 (SEQ ID NO:380), TAR2h-42 (SEQ ID NO:381), TAR2h-43 (SEQ ID NO:382), TAR2h-44 (SEQ ID NO:383), TAR2h-45 (SEQ ID NO:384), TAR2h-47 (SEQ ID NO:385), TAR2h-48 (SEQ ID NO:386), TAR2h-50 (SEQ ID NO:387), TAR2h-51 (SEQ ID NO:388), TAR2h-66 (SEQ ID NO:389), TAR2h-67 (SEQ ID NO:390), TAR2h-68 (SEQ ID NO:391), TAR2h-70 (SEQ ID NO:392), TAR2h-71 (SEQ ID NO:393), TAR2h-72 (SEQ ID NO:394), TAR2h-73 (SEQ ID NO:395), TAR2h-74 (SEQ ID NO:396), TAR2h-75 (SEQ ID NO:397), TAR2h-76 (SEQ ID NO:398), TAR2h-77 (SEQ ID NO:399), TAR2h-78 (SEQ ID NO:400), TAR2h-79 (SEQ ID NO:401) and TAR2h-15 (SEQ ID NO:431).  
      In preferred embodiments, the ligands or dAbs comprise an amino acid sequence at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to an amino acid sequence of a dAb selected from the group consisting of TAR2h-10-27 (SEQ ID NO:73), TAR2h-10-57 (SEQ ID NO:83), TAR2h-10-56 (SEQ ID NO:84), TAR2h-10-58 (SEQ ID NO:85), TAR2h-10-66 (SEQ ID NO:86), TAR2h-10-64 (SEQ ID NO:87), TAR2h-10-65 (SEQ ID NO:88), TAR2h-10-68 (SEQ ID NO:89), TAR2h-10-69 (SEQ ID NO:90), TAR2h-10-67 (SEQ ID NO:91), TAR2h-10-61 (SEQ ID NO:92), TAR2h-10-62 (SEQ ID NO:93), TAR2h-10-63 (SEQ ID NO:94), TAR2h-10-60 (SEQ ID NO:95), TAR2h-10-55 (SEQ ID NO:96), TAR2h-10-59 (SEQ ID NO:97), and TAR2h-10-70 (SEQ ID NO:98). Particularly preferred ligands or dAbs comprise an amino acid sequence at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to the amino acid sequence of SEQ ID NO:73.  
      In other embodiments, the ligand comprises a domain antibody (dAb) monomer that specifically binds Tumor Necrosis Factor Receptor I (TNFR1, p55, CD120a) with a K d  of 300 nM to 5 pM and comprises an amino acid sequence that is at least about 80%, at least about 85%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to the amino acid sequence or a dAb selected from the group consisting of TAR2m-14 (SEQ ID NO: 167), TAR2m-15 (SEQ ID NO:168), TAR2m-19 (SEQ ID NO:169), TAR2m-20 (SEQ ID NO:170), TAR2m-21 (SEQ ID NO:171), TAR2m-24 (SEQ ID NO:172), TAR2m-21-23 (SEQ ID NO: 173), TAR2m-21-07 (SEQ ID NO: 174), TAR2m-21-43 (SEQ ID NO: 175), TAR2m-21-48 (SEQ ID NO:176), TAR2m-21-10 (SEQ ID NO:177), TAR2m-21-06 (SEQ ID NO: 1 78), TAR2m-21-17 (SEQ ID NO: 179).  
      Preferably, the ligand or dAb monomer is secreted in a quantity of at least about 0.5 mg/L when expressed in  E. coli  or in Pichia species (e.g.,  P. pastoris ). In other preferred embodiments, the dAb monomer is secreted in a quantity of at least about 0.75 mg/L, at least about 1 mg/L, at least about 4 mg/L, at least about 5 mg/L, at least about 10 mg/L, at least about 15 mg/L, at least about 20 mg/L, at least about 25 mg/L, at least about 30 mg/L, at least about 35 mg/L, at least about 40 mg/L, at least about 45 mg/L, or at least about 50 mg/L, or at least about 100 mg/L, or at least about 200 mg/L, or at least about 300 mg/L, or at least about 400 mg/L, or at least about 500 mg/L, or at least about 600 mg/L, or at least about 700 mg/L, or at least about 800 mg/L, at least about 900 mg/L, or at least about 1g/L when expressed in  E. coli  or in  Pichia  species (e.g.,  P. pastoris ). In other preferred embodiments, the dAb monomer is secreted in a quantity of at least about 1 mg/L to at least about 1 g/L, at least about 1 mg/L to at least about 750 mg/L, at least about 100 mg/L to at least about 1 g/L, at least about 200 mg/L to at least about 1 g/L, at least about 300 mg/L to at least about 1 g/L, at least about 400 mg/L to at least about 1 g/L, at least about 500 mg/L to at least about lg/L, at least about 600 mg/L to at least about 1 g/L, at least about 700 mg/L to at least about 1 g/L, at least about 800 mg/L to at least about 1 g/L, or at least about 900 mg/L to at least about 1 g/L when expressed in  E. coli  or in  Pichia  species (e.g.,  P. pastoris ). Although, the ligands and dAb monomers described herein can be secretable when expressed in  E. coli  or in  Pichia  species (e.g.,  P. pastoris ), they can be produced using any suitable method, such as synthetic chemical methods or biological production methods that do not employ  E. coli  or  Pichia  species.  
      The dAb monomer can comprise any suitable immunoglobulin variable domain, and preferably comprises a human variable domain or a variable domain that comprises human framework regions. In certain embodiments, the dAb monomer comprises a universal framework, as described herein.  
      The universal framework can be a V L  framework (Vλ or Vκ) , such as a framework that comprises the framework amino acid sequences encoded by the human germuline DPK1, DPK2, DPK3, DPK4, DPK5, DPK6, DPK7, DPK8, DPK9, DPK10, DPK12, DPK13, DPK15, DPK16, DPK18, DPK19, DPK20, DPK21, DPK22, DPK23, DPK24, DPK25, DPK26 or DPK 28 immunoglobulin gene segment. If desired, the V L  framework can further comprises the framework amino acid sequence encoded by the human germline J κ 1, J κ 2, J κ 3, J κ 4, or J κ 5 immunoglobulin gene segment.  
      In other embodiments the universal framework can be a V H  framework, such as a framework that comprises the framework amino acid sequences encoded by the human germline DP4, DP7, DP8, DP9, DP10, DP31, DP33, DP38, DP45, DP46, DP47, DP49, DP50, DP5 1, DP53, DP54, DP65, DP66, DP67, DP68 or DP69 immunoglobulin gene segment. If desired, the V H  framework can further comprises the framework amino acid sequence encoded by the human germline J H 1, J H 2, J H 3, J H 4, J H 4b, J H 5 and J H 6 immunoglobulin gene segment.  
      In particular embodiments, the dAb monomer ligand comprises the DPK9 V L  framework, or a V H  framework selected from the group consisting of DP47, DP45 and DP38.  
      The dAb monomer can comprises a binding site for a generic ligand, such as protein A, protein L and protein G.  
      In certain embodiments, the dAb monomer comprises one or more framework regions comprising an amino acid sequence that is the same as the amino acid sequence of a corresponding framework region encoded by a human germline antibody gene segment, or the amino acid sequences of one or more of said framework regions collectively comprise up to 5 amino acid differences relative to the amino acid sequence of said corresponding framework region encoded by a human germline antibody gene segment.  
      In other embodiments, the amino acid sequences of FW1, FW2, FW3 and FW4 of the dAb monomer are the same as the amino acid sequences of corresponding framework regions encoded by a human germline antibody gene segment, or the amino acid sequences of FW1, FW2, FW3 and FW4 collectively contain up to 10 amino acid differences relative to the amino acid sequences of corresponding framework regions encoded by said human germline antibody gene segment.  
      In other embodiments, the dAb monomer comprises FW1, FW2 and FW3 regions, and the amino acid sequence of said FW1, FW2 and FW3 regions are the same as the amino acid sequences of corresponding framework regions encoded by human germline antibody gene segments.  
      In some embodiments, the dAb monomer does not comprise a Camelid immunoglobulin variable domain, or one or more framework amino acids that are unique to immunoglobulin variable domains encoded by Camelid germline antibody gene segments.  
      Ligands and dAb Monomers that Bind Serum Albumin  
      The invention provides a ligand or dAb monomer (e.g., dual specific ligand comprising such a dAb) that binds to serum albumin (SA) with a K d  of 1 nM to 500 μM (ie, ×10 −9  to 5×10 −4 ), preferably 100 nM to 10 μM. Preferably, for a dual specific ligand comprising a first anti-SA dAb and a second dAb to another target, the affinity (eg K d  and/or K off  as measured by surface plasmon resonance, eg using BiaCore) of the second dAb for its target is from 1 to 100000 times (preferably 100 to 100000, more preferably 1000 to 100000, or 10000 to 100000 times) the affinity of the first dAb for SA. For example, the first dAb binds SA with an affinity of approximately 10 μM, while the second dAb binds its target with an affinity of 100 pM. Preferably, the serum albumin is human serum albumin (HSA). In one embodiment, the first dAb (or a dAb monomer) binds SA (eg, HSA) with a K d  of approximately 50, preferably 70, and more preferably 100, 150 or 200 nM.  
      In certain embodiments, the dAb monomer specific for SA comprises the amino acid sequence of MSA-16 (SEQ ID NO:28) or a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% homologous thereto.  
      In other embodiments, the dAb monomer specific for SA comprises the amino acid sequence of MSA-26 (SEQ ID NO:30) or a sequence that is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% homologous thereto.  
      In certain embodiments, the dAb monomer that binds SA resists aggregation, unfolds reversibly and/or comprises a framework region as described above for dAb monomers that bind TNFR1.  
      Nucleic Acid Molecules, Vectors and Host Cells  
      The invention also provides isolated and/or recombinant nucleic acid molecules that encode the ligands and dAb monomers described herein. In certain embodiments, the isolated and/or recombinant nucleic acid comprises a nucleotide sequence that encodes a domain antibody (dAb) monomer that specifically binds Tumor Necrosis Factor Receptor I (TNFR1), wherein said nucleotide sequence is at least about 80%, at least about 85%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to a nucleotide sequence selected from the group consisting of TAR2h-12 (SEQ ID NO:32), TAR2h-13 (SEQ ID NO:33), TAR2h-14 (SEQ ID NO:34), TAR2h-16 (SEQ ID NO:35), TAR2h-17 (SEQ ID NO:36), TAR2h-18 (SEQ ID NO:37), TAR2h-19 (SEQ ID NO:38), TAR2h-20 (SEQ ID NO:39), TAR2h-21 (SEQ ID NO:40), TAR2h-22 (SEQ ID NO:41), TAR2h-23 (SEQ ID NO:42), TAR2h-24 (SEQ ID NO:43), TAR2h-25 (SEQ ID NO:44), TAR2h-26 (SEQ ID NO:45), TAR2h-27 (SEQ ID NO:46), TAR2h-29 (SEQ ID NO:47), TAR2h-30 (SEQ ID NO:48), TAR2h-32 (SEQ ID NO:49), TAR2h-33 (SEQ ID NO:50), TAR2h-10-1 (SEQ ID NO:51), TAR2h-10-2 (SEQ ID NO:52), TAR2h-10-3 (SEQ ID NO:53), TAR2h-10-4 (SEQ ID NO:54), TAR2h-10-5 (SEQ ID NO:55), TAR2h-10-6 (SEQ ID NO:56), TAR2h-10-7 (SEQ ID NO:57), TAR2h-10-8 (SEQ ID NO:58), TAR2h-10-9 (SEQ ID NO:59), TAR2h-10-10 (SEQ ID NO:60), TAR2h-10-11 (SEQ ID NO:61), TAR2h-10-12 (SEQ ID NO:62), TAR2h-10-13 (SEQ ID NO:63), TAR2h-10-14 (SEQ ID NO:64), TAR2h-10-15 (SEQ ID NO:65), TAR2h-10-16 (SEQ ID NO:66), TAR2h-10-17 (SEQ ID NO:67), TAR2h-10-18 (SEQ ID NO:68), TAR2h-10-19 (SEQ ID NO:69), TAR2h-10-20 (SEQ ID NO:70), TAR2h-10-21 (SEQ ID NO:71), TAR2h-10-22 (SEQ ID NO:72), TAR2h-10-27 (SEQ ID NO:73), TAR2h-10-29 (SEQ ID NO:74), TAR2h-10-31 (SEQ ID NO:75), TAR2h-10-35 (SEQ ID NO:76), TAR2h-10-36 (SEQ ID NO:77), TAR2h-10-37 (SEQ ID NO:78), TAR2h-10-38 (SEQ ID NO:79), TAR2h-10-45 (SEQ ID NO:80), TAR2h-10-47 (SEQ ID NO:81), TAR2h-10-48 (SEQ ID NO:82), TAR2h-10-57 (SEQ ID NO:83), TAR2h-10-56 (SEQ ID NO:84), TAR2h-10-58 (SEQ ID NO:85), TAR2h-10-66 (SEQ ID NO:86), TAR2h-10-64 (SEQ ID NO:87), TAR2h-10-65 (SEQ ID NO:88), TAR2h-10-68 (SEQ ID NO:89), TAR2h-10-69 (SEQ ID NO:90), TAR2h-10-67 (SEQ ID NO:91), TAR2h-10-61 (SEQ ID NO:92), TAR2h-10-62 (SEQ ID NO:93), TAR2h-10-63 (SEQ ID NO:94), TAR2h-10-60 (SEQ ID NO:95), TAR2h-10-55 (SEQ ID NO:96), TAR2h-10-59 (SEQ ID NO:97), TAR2h-10-70 (SEQ ID NO:98), TAR2h-34 (SEQ ID NO:402), TAR2h -35 (SEQ ID NO:403), TAR2h-36 (SEQ ID NO:404), TAR2h-37 (SEQ ID NO:405), TAR2h-38 (SEQ ID NO:406), TAR2h-39 (SEQ ID NO:407), TAR2h-40 (SEQ ID NO:408), TAR2h-41 (SEQ ID NO:409), TAR2h-42 (SEQ ID NO:410), TAR2h-43 (SEQ ID NO:411), TAR2h-44 (SEQ ID NO:412), TAR2h-45 (SEQ ID NO:413), TAR2h-47 (SEQ ID NO:414), TAR2h-48 (SEQ ID NO:415), TAR2h-50 (SEQ ID NO:416), TAR2h-51 (SEQ ID NO:417), TAR2h-66 (SEQ ID NO:418), TAR2h-67 (SEQ ID NO:419), TAR2h-68 (SEQ ID NO:420), TAR2h-70 (SEQ ID NO:421), TAR2h-71 (SEQ ID NO:422), TAR2h-72 (SEQ ID NO:423), TAR2h-73 (SEQ ID NO:424), TAR2h-74 (SEQ ID NO:425), TAR2h-75 (SEQ ID NO:426), TAR2h-76 (SEQ ID NO:427), TAR2h-77 (SEQ ID NO:428), TAR2h-78 (SEQ ID NO:429), TAR2h-79 (SEQ ID NO:430), and TAR2h-15 (SEQ ID NO:432).  
      In a preferred embodiment, the isolated and/or recombinant nucleic acid comprise a nucleotide sequence that is at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to a nucleotide sequence selected from the group consisting of TAR2h-10-27 (SEQ ID NO:141), TAR2h-10-57 (SEQ ID NO:151), TAR2h-10-56 (SEQ ID NO:152), TAR2h-10-58 (SEQ ID NO:153), TAR2h-10-66 (SEQ ID NO:154), TAR2h-10-64 (SEQ ID NO:155), TAR2h-10-65 (SEQ ID NO:156), TAR2h-10-68 (SEQ ID NO:157), TAR2h-10-69 (SEQ ID NO:158), TAR2h-10-67 (SEQ ID NO:159), TAR2h-10-61 (SEQ ID NO:160), TAR2h-10-62 (SEQ ID NO:161), TAR2h-10-63 (SEQ ID NO:162), TAR2h-10-60 (SEQ ID NO:163), TAR2h-10-55 (SEQ ID NO:164), TAR2h-10-59 (SEQ ID NO:165), and TAR2h-10-70 (SEQ ID NO:166).  
      In other embodiments, the isolated and/or recombinant nucleic acid comprises a nucleotide sequence that encodes a domain antibody (dAb) monomer that specifically binds Tumor Necrosis Factor Receptor I (TNFR1), wherein said nucleotide sequence is at least about 80%, at least about 85%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% homologous to a nucleotide sequence selected from the group consisting of TAR2m-14 (SEQ ID NO:180), TAR2m-15 (SEQ ID NO:181), TAR2m-19 (SEQ ID NO:182), TAR2m-20 (SEQ ID NO:183), TAR2m-21 (SEQ ID NO:184), TAR2m-24 (SEQ ID NO:185), TAR2m-21-23 (SEQ ID NO:186), TAR2m-21-07 (SEQ ID NO:187), TAR2m-21-43 (SEQ ID NO: 188), TAR2m-21-48 (SEQ ID NO: 1 89), TAR2m-21-10 (SEQ ID NO: 190), TAR2m-21-06 (SEQ ID NO: 191), and TAR2m-21-17 (SEQ ID NO: 1 92).  
      The invention also provides a vector comprising a recombinant nucleic acid molecule of the invention. In certain embodiments, the vector is an expression vector comprising one or more expression control elements or sequences that are operably linked to the recombinant nucleic acid of the invention. Suitable vectors (e.g., plasmids, phagmids) and expression control elements are further described below.  
      The invention also provides a recombinant host cell comprising a recombinant nucleic acid moleculer or vector of the invention. Suitable host cells and methods for producing the recombinant host cell of the invention are further described below.  
      The invention also provides a method for producing a ligand (e.g., dAb monomer, dual-specific ligand, multispecific ligand) of the invention, comprising maintaining a recombinant host cell comprising a recombinant nucleic acid of the invention under conditions suitable for expression of the recombinant nucleic acid, whereby the recombinant nucleic acid is expressed and a ligand is produced. In some embodiments, the method further comprises isolating the ligand.  
      Ligand Formats  
      Ligands according to the invention can be formatted as mono or multispecific antibodies or antibody fragments or into mono or multispecific non-immunoglobulin structures. Suitable formats include, any suitable polypeptide structure in which an antibody variable domain or the CDR thereof can be incorporated so as to confer binding specificity for antigen on the structure. A variety of suitable antibody formats are known in the art, such as, IgG-like formats, chimeric antibodies, humanized antibodies, human antibodies, single chain antibodies, bispecific antibodies, antibody heavy chains, antibody light chains, homodimers and heterodimers of antibody heavy chains and/or light chains, antigen-binding fragments of any of the foregoing (e.g., a Fv fragment (e.g., single chain Fv (scFv), a disulfide bonded Fv), a Fab fragment, a Fab′ fragment, a F(ab′) 2  fragment), a single variable domain (e.g., V H , V L ), a dAb, and modified versions of any of the foregoing (e.g., modified by the covalent attachment of polyalkylene glycol (e.g., polyethylene glycol, polypropylene glycol, polybutylene glycol) or other suitable polymer). See, PCT/GB03/002804, filed Jun. 30, 2003, which designated the United States, (WO 2004/081026) regarding PEGylated of single variable domains and dAbs, suitable methods for preparing same, increased in vivo half life of the PEGylated single variable domains and dAb monomers and multimers, suitable PEGs, preferred hydrodynamic sizes of PEGs, and preferred hydrodynamic sizes of PEGylated single variable domains and dAb monomers and multimers. The entire teaching of PCT/GBO3/002804 (WO 2004/081026), including the portions referred to above, are incorporated herein by reference.  
      In some embodiments, the ligand is an IgG-like format. Such formats have the conventional four chain structure of an IgG molecule (2 heavy chains and two light chains), in which one or more of the variable regions (V H  and or V L ) have been replaced with a dAb or single variable domain of a desired specificity. Preferably, each of the variable regions (2 V H  regions and 2 V L  regions) is replaced with a dAb or single variable domain. The dAb(s) or single variable domain(s) that are included in an IgG-like format can have the same specificity or different specificities. In some embodiments, the IgG-like format is tetravalent and can have one, two, three or four specificities. For example, the IgG-like format can be monospecific and comprises 4 dAbs that have the same specificity; bispecific and comprises 3 dAbs that have the same specificity and another dAb that has a different specificity; bispecific and comprise two dAbs that have the same specificity and two dAbs that have a common but different specificity; trispecific and comprises first and second dAbs that have the same specificity, a third dAbs with a different specificity and a fourth dAb with a different specificity from the first, second and third dAbs; or tetraspecific and comprise four dAbs that each have a different specificity. Antigen-binding fragments of IgG-like formats (e.g., Fab, F(ab′) 2 , Fab′, Fv, scFv) can be prepared. Preferably, the IgG-like formats or antigen-binding fragments thereof do not crosslink TNFR1.  
      Ligands according to the invention, including dAb monomers, dimers and trimers, can be linked to an antibody Fc region, comprising one or both of C H 2 and C H 3 domains, and optionally a hinge region. For example, vectors encoding ligands linked as a single nucleotide sequence to an Fc region may be used to prepare such polypeptides.  
      The invention moreover provides dimers, trimers and polymers of the aforementioned dAb monomers, in accordance with the following aspects of the present invention.  
      Ligands according to the invention may be combined and/or formatted into non-immunoglobulin multi-ligand structures to form multivalent complexes, which bind target molecules with the same antigen, thereby providing superior avidity. In some embodiments, at least one variable domain binds an antigen to increase the half life of the multimer. For example natural bacterial receptors such as SpA have been used as scaffolds for the grafting of CDRs to generate ligands which bind specifically to one or more epitopes. Details of this procedure are described in U.S. Pat. No. 5,831,012. Other suitable scaffolds include those based on fibronectin and affibodies. Details of suitable procedures are described in WO 98/58965. Other suitable scaffolds include lipocallin and CTLA4, as described in van den Beuken et al., J. Mol. Biol. (2001) 310, 591-601, and scaffolds such as those described in WO 00/69907 (Medical Research Council), which are based for example on the ring structure of bacterial GroEL or other chaperone polypeptides.  
      Protein scaffolds may be combined; for example, CDRs may be grafted on to a CTLA4 scaffold and used together with immunoglobulin V H  or V L  domains to form a ligand. Likewise, fibronectin, lipocallin and other scaffolds may be combined.  
      Dual- and Multi-Specific Ligands  
      The inventors have described, in their copending international patent application WO 03/002609 as well as copending unpublished UK patent application 0230203.2, dual specific immunoglobulin ligands which comprise immunoglobulin single variable domains which each have different specificities. The domains may act in competition with each other or independently to bind antigens or epitopes on target molecules.  
      Dual-Specific ligands according to the present invention preferably comprise combinations of heavy and light chain domains. For example, the dual specific ligand may comprise a V H  domain and a V L  domain, which may be linked together in the form of an scFv. In addition, the ligands may comprise one or more C H  or C L  domains. For example, the ligands may comprise a C H 1 domain, C H 2 or C H 3 domain, and/or a C L  domain, Cμ1, Cμ2, Cμ3 or Cμ4 domains, or any combination thereof. A hinge region domain may also be included. Such combinations of domains may, for example, mimic natural antibodies, such as IgG or IgM, or fragments thereof, such as Fv, scFv, Fab or F(ab′) 2  molecules. Other structures, such as a single arm of an IgG molecule comprising V H , V L , C H 1 and C L  domains, are envisaged.  
      In a preferred embodiment of the invention, the variable regions are selected from single domain V gene repertoires. Generally the repertoire of single antibody domains is displayed on the surface of filamentous bacteriophage. In a preferred embodiment each single antibody domain is selected by binding of a phage repertoire to antigen.  
      In a preferred embodiment of the invention each single variable domain may be selected for binding to its target antigen or epitope in the absence of a complementary variable region. In an alternative embodiment, the single variable domains may be selected for binding to its target antigen or epitope in the presence of a complementary variable region. Thus the first single variable domain may be selected in the presence of a third complementary variable domain, and the second variable domain may be selected in the presence of a fourth complementary variable domain. The complementary third or fourth variable domain may be the natural cognate variable domain having the same specificity as the single domain being tested, or a non-cognate complementary domain—such as a “dummy” variable domain.  
      Preferably, the dual specific ligand of the invention comprises only two variable domains although several such ligands may be incorporated together into the same protein, for example two such ligands can be incorporated into an IgG or a multimeric immunoglobulin, such as IgM. Alternatively, in another embodiment a plurality of dual specific ligands are combined to form a multimer. For example, two different dual specific ligands are combined to create a tetra-specific molecule.  
      It will be appreciated by one skilled in the art that the light and heavy variable regions of a dual-specific ligand produced according to the method of the present invention may be on the same polypeptide chain, or alternatively, on different polypeptide chains. In the case that the variable regions are on different polypeptide chains, then they may be linked via a linker, generally a flexible linker (such as a polypeptide chain), a chemical linking group, or any other method known in the art.  
      In a first configuration, the present invention provides a further improvement in dual specific ligands as developed by the present inventors, in which one specificity of the ligand is directed towards a protein or polypeptide present in vivo in an organism which can act to increase the half-life of the ligand by binding to it.  
      Accordingly, in a first aspect, there is provided a dual-specific ligand comprising a first immunoglobulin single variable domain having a binding specificity to a first antigen or epitope and a second complementary immunoglobulin single variable domain having a binding activity to a second antigen or epitope, wherein one or both of said antigens or epitopes acts to increase the half-life of the ligand in vivo and wherein said first and second domains lack mutually complementary domains which share the same specificity, provided that said dual specific ligand does not consist of an anti-HSA V H  domain and an anti-β galactosidase V κ  domain. Preferably, that neither of the first or second variable domains binds to human serum albumin (HSA).  
      Antigens or epitopes which increase the half-life of a ligand as described herein are advantageously present on proteins or polypeptides found in an organism in vivo. Examples include extracellular matrix proteins, blood proteins, and proteins present in various tissues in the organism. The proteins act to reduce the rate of ligand clearance from the blood, for example by acting as bulking agents, or by anchoring the ligand to a desired site of action. Examples of antigens/epitopes which increase half-life in vivo are given in Annex 1 below.  
      Increased half-life is useful in in vivo applications of immunoglobulins, especially antibodies and most especially antibody fragments of small size. Such fragments (Fvs, disulphide bonded Fvs, Fabs, scFvs, dAbs) suffer from rapid clearance from the body; thus, whilst they are able to reach most parts of the body rapidly, and are quick to produce and easier to handle, their in vivo applications have been limited by their only brief persistence in vivo. The invention solves this problem by providing increased half-life of the ligands in vivo and consequently longer persistence times in the body of the functional activity of the ligand.  
      Methods for pharmacokinetic analysis and determination of ligand half-life will be familiar to those skilled in the art. Details may be found in Kenneth, A et al: Chemical Stability of Pharmaceuticals: A Handbook for Pharmacists and in Peters et al, Pharmacokinetc analysis: A Practical Approach (1996). Reference is also made to “Pharmacokinetics”, M Gibaldi &amp; D Perron, published by Marcel Dekker, 2 nd  Rev. ex edition (1982), which describes pharmacokinetic parameters such as t alpha and t beta half lives and area under the curve (AUC). Half lives (t½ alpha and t½ beta) and AUC can be determined from a curve of serum concentration of ligand against time. The WinNonlin analysis package (available from Pharsight Corp., Mountain View, Calif. 94040, USA) can be used, for example, to model the curve. In a first phase (the alpha phase) the ligand is undergoing mainly distribution in the patient, with some elimination. A second phase (beta phase) is the terminal phase when the ligand has been distributed and the serum concentration is decreasing as the ligand is cleared from the patient. The t alpha half life is the half life of the first phase and the t beta half life is the half life of the second phase. Thus, advantageously, the present invention provides a ligand or a composition comprising a ligand according to the invention having a tα half-life in the range of 15 minutes or more. In one embodiment, the lower end of the range is 30 minutes, 45 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 10 hours, 11 hours or 12 hours. In addition, or alternatively, a ligand or composition according to the invention will have a tα half life in the range of up to and including 12 hours. In one embodiment, the upper end of the range is 11, 10, 9, 8, 7, 6 or 5 hours. An example of a suitable range is 1 to 6 hours, 2 to 5 hours or 3 to 4 hours.  
      Advantageously, the present invention provides a ligand or a composition comprising a ligand according to the invention having a tβ half-life in the range of 2.5 hours or more. In one embodiment, the lower end of the range is 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 10 hours, 11 hours, or 12 hours. In addition, or alternatively, a ligand or composition according to the invention has a tβ half-life in the range of up to and including 21 days. In one embodiment, the upper end of the range is 12 hours, 24 hours, 2 days, 3 days, 5 days, 10 days, 15 days or 20 days. Advantageously a ligand or composition according to the invention will have a tβ half life in the range 12 to 60 hours. In a further embodiment, it will be in the range 12 to 48 hours. In a further embodiment still, it will be in the range 12 to 26 hours.  
      In addition, or alternatively to the above criteria, the present invention provides a ligand or a composition comprising a ligand according to the invention having an AUC value (area under the curve) in the range of 1 mg.min/ml or more. In one embodiment, the lower end of the range is 5, 10, 15, 20, 30, 100, 200 or 300 mg.min/ml. In addition, or alternatively, a ligand or composition according to the invention has an AUC in the range of up to 600 mg.min/ml. In one embodiment, the upper end of the range is 500, 400, 300, 200, 150, 100, 75 or 50 mg.min/ml. Advantageously a ligand according to the invention will have a AUC in the range selected from the group consisting of the following: 15 to 150 mg.min/ml, 15 to 100 mg.min/ml, 15 to 75 mg.min/ml, and 15 to 50 mg.min/ml.  
      In a first embodiment, the dual specific ligand comprises two complementary variable domains, i.e. two variable domains that, in their natural environment, are capable of operating together as a cognate pair or group even if in the context of the present invention they bind separately to their cognate epitopes. For example, the complementary variable domains may be immunoglobulin heavy chain and light chain variable domains (V H  and V L ). V H  and V L  domains are advantageously provided by scFv or Fab antibody fragments. Variable domains may be linked together to form multivalent ligands by, for example: provision of a hinge region at the C-terminus of each V domain and disulphide bonding between cysteines in the hinge regions; or provision of dAbs each with a cysteine at the C-terminus of the domain, the cysteines being disulphide bonded together; or production of V—CH &amp; V—CL to produce a Fab format; or use of peptide linkers (for example Gly 4 Ser linkers discussed hereinbelow) to produce dimers, trimers and further multimers.  
      The inventors have found that the use of complementary variable domains allows the two domain surfaces to pack together and be sequestered from the solvent. Furthermore the complementary domains are able to stabilise each other. In addition, it allows the creation of dual-specific IgG antibodies without the disadvantages of hybrid hybridomas as used in the prior art, or the need to engineer heavy or light chains at the sub-unit interfaces. The dual-specific ligands of the first aspect of the present invention have at least one V H /V L  pair. A bispecific IgG according to this invention will therefore comprise two such pairs, one pair on each arm of the Y-shaped molecule. Unlike conventional bispecific antibodies or diabodies, therefore, where the ratio of chains used is determinative in the success of the preparation thereof and leads to practical difficulties, the dual specific ligands of the invention are free from issues of chain balance. Chain imbalance in conventional bi-specific antibodies results from the association of two different V L  chains with two different V H  chains, where V L  chain 1 together with V H  chain 1 is able to bind to antigen or epitope 1 and V L  chain 2 together with V H  chain 2 is able to bind to antigen or epitope 2 and the two correct pairings are in some way linked to one another. Thus, only when V L  chain 1 is paired with V H  chain 1 and V L  chain 2 is paired with V H  chain 2 in a single molecule is bi-specificity created. Such bi-specific molecules can be created in two different ways. Firstly, they can be created by association of two existing V H /V L  pairings that each bind to a different antigen or epitope (for example, in a bi-specific IgG). In this case the V H /V L  pairings must come all together in a 1:1 ratio in order to create a population of molecules all of which are bi-specific. This never occurs (even when complementary CH domain is enhanced by “knobs into holes” engineering) leading to a mixture of bi-specific molecules and molecules that are only able to bind to one antigen or epitope but not the other. The second way of creating a bi-specific antibody is by the simultaneous association of two different V H  chain with two different V L  chains (for example in a bi-specific diabody). In this case, although there tends to be a preference for V L  chain 1 to pair with V H  chain 1 and V L  chain 2 to pair with V H  chain 2 (which can be enhanced by “knobs into holes” engineering of the V L  and V H  domains), this paring is never achieved in all molecules, leading to a mixed formulation whereby incorrect pairings occur that are unable to bind to either antigen or epitope.  
      Bi-specific antibodies constructed according to the dual-specific ligand approach according to the first aspect of the present invention overcome all of these problems because the binding to antigen or epitope 1 resides within the V H  or V L  domain and the binding to antigen or epitope 2 resides with the complementary V L  or V H  domain, respectively. Since V H  and V L  domains pair on a 1:1 basis all V H /V L  pairings will be bi-specific and thus all formats constructed using these V H /V L  pairings (Fv, scFvs, Fabs, minibodies, IgGs etc) will have 100% bi-specific activity.  
      In the context of the present invention, first and second “epitopes” are understood to be epitopes which are not the same and are not bound by a single monospecific ligand. In the first configuration of the invention, they are advantageously on different antigens, one of which acts to increase the half-life of the ligand in vivo. Likewise, the first and second antigens are advantageously not the same.  
      The dual specific ligands of the invention do not include ligands as described in WO 02/02773. Thus, the ligands of the present invention do not comprise complementary V H /V L  pairs which bind any one or more antigens or epitopes co-operatively. Instead, the ligands according to the first aspect of the invention comprise a V H /V L  complementary pair, wherein the V domains have different specificities. Moreover, the ligands according to the first aspect of the invention comprise V H /V L  complementary pairs having different specificities for non-structurally related epitopes or antigens. Structurally related epitopes or antigens are epitopes or antigens which possess sufficient structural similarity to be bound by a conventional V H /V L  complementary pair which acts in a co-operative manner to bind an antigen or epitope; in the case of structurally related epitopes, the epitopes are sufficiently similar in structure that they “fit” into the same binding pocket formed at the antigen binding site of the V H /V L  dimer.  
      In a second aspect, the present invention provides a ligand comprising a first immunoglobulin variable domain having a first antigen or epitope binding specificity and a second immunoglobulin variable domain having a second antigen or epitope binding specificity wherein one or both of said first and second variable domains bind to an antigen which increases the half-life of the ligand in vivo, and the variable domains are not complementary to one another.  
      In one embodiment, binding via one variable domain modulates the binding of the ligand via the second variable domain.  
      In this embodiment, the variable domains may be, for example, pairs of V H  domains or pairs of V L  domains. Binding of antigen at the first site may modulate, such as enhance or inhibit, binding of an antigen at the second site. For example, binding at the first site at least partially inhibits binding of an antigen at a second site. In such an embodiment, the ligand may for example be maintained in the body of a subject organism in vivo through binding to a protein which increases the half-life of the ligand until such a time as it becomes bound to the second target antigen and dissociates from the half-life increasing protein.  
      Modulation of binding in the above context is achieved as a consequence of the structural proximity of the antigen binding sites relative to one another. Such structural proximity can be achieved by the nature of the structural components linking the two or more antigen binding sites, e.g. by the provision of a ligand with a relatively rigid structure that holds the antigen binding sites in close proximity. Advantageously, the two or more antigen binding sites are in physically close proximity to one another such that one site modulates the binding of antigen at another site by a process which involves steric hindrance and/or conformational changes within the immunoglobulin molecule.  
      The first and the second antigen binding domains may be associated either covalently or non-covalently. In the case that the domains are covalently associated, then the association may be mediated for example by disulphide bonds or by a polypeptide, linker such as (Gly 4 Ser) n , where n=from 1 to 8, e.g., 2, 3, 4, 5 or 7.  
      In the case that the variable domains are selected from V-gene repertoires selected for instance using phage display technology as herein described, then these variable domains can comprise a universal framework region, such that they may be recognised by a specific generic ligand as herein defined. The use of universal frameworks, generic ligands and the like is described in WO 99/20749. In the present invention, reference to phage display includes the use of both phage and/or phagemids.  
      Where V-gene repertoires are used variation in polypeptide sequence is preferably located within the structural loops of the variable domains. The polypeptide sequences of either variable domain may be altered by DNA shuffling or by mutation in order to enhance the interaction of each variable domain with its complementary pair.  
      In a preferred embodiment of the invention the ‘dual-specific ligand’ is a single chain Fv fragment. In an alternative embodiment of the invention, the ‘dual-specific ligand’ consists of a Fab region of an antibody. The term “Fab region” includes a Fab-like region where two VH or two VL domains are used.  
      The variable regions may be derived from antibodies directed against target antigens or epitopes. Alternatively they may be derived from a repertoire of single antibody domains such as those expressed on the surface of filamentous bacteriophage. Selection may be performed as described below.  
      In a further aspect, the present invention provides one or more nucleic acid molecules encoding at least a dual-specific ligand as herein defined. The dual specific ligand may be encoded on a single nucleic acid molecule; alternatively, each domain may be encoded by a separate nucleic acid molecule. Where the ligand is encoded by a single nucleic acid molecule, the domains may be expressed as a fusion polypeptide, in the manner of a scFv molecule, or may be separately expressed and subsequently linked together, for example using chemical linking agents. Ligands expressed from separate nucleic acids will be linked together by appropriate means.  
      The nucleic acid may further encode a signal sequence for export of the polypeptides from a host cell upon expression and may be fused with a surface component of a filamentous bacteriophage particle (or other component of a selection display system) upon expression.  
      In a further aspect the present invention provides a vector comprising nucleic acid encoding a dual specific ligand according to the present invention.  
      In a yet further aspect, the present invention provides a host cell transfected with a vector encoding a dual specific ligand according to the present invention.  
      Expression from such a vector may be configured to produce, for example on the surface of a bacteriophage particle, variable domains for selection. This allows selection of displayed variable regions and thus selection of ‘dual-specific ligands’ using the method of the present invention.  
      The present invention further provides a kit comprising at least a dual-specific ligand according to the present invention.  
      In a third aspect, the invention provides a method for producing a ligand comprising a first immunoglobulin single variable domain having a first binding specificity and a second single immunoglobulin single variable domain having a second (different) binding specificity, one or both of the binding specificities being specific for an antigen which increases the half-life of the ligand in vivo, the method comprising the steps of: 
          (a) selecting a first variable domain by its ability to bind to a first epitope,     (b) selecting a second variable region by its ability to bind to a second epitope,     (c) combining the variable domains; and     (d) selecting the ligand by its ability to bind to said first epitope and to said second epitope.        

      The ligand can bind to the first and second epitopes either simultaneously or, where there is competition between the binding domains for epitope binding, the binding of one domain may preclude the binding of another domain to its cognate epitope. In one embodiment, therefore, step (d) above requires simultaneous binding to both first and second (and possibly further) epitopes; in another embodiment, the binding to the first and second epitopes is not simultaneous.  
      The epitopes are preferably on separate antigens.  
      Ligands advantageously comprise V H /V L  combinations, or V H /V H  or V L /V L  combinations of immunoglobulin variable domains, as described above. The ligands may moreover comprise camelid V HH  domains, provided that the V HH  domain which is specific for an antigen which increases the half-life of the ligand in vivo does not bind Hen egg white lysozyme (HEL), porcine pancreatic alpha-amylase or NmC-A; hcg, BSA-linked RR6 azo dye or  S. mutans  HG982 cells, as described in Conrath et al., (2001) JBC 276:7346-7350 and WO99/23221, neither of which describe the use of a specificity for an antigen which increases half-life to increase the half life of the ligand in vivo.  
      In one embodiment, said first variable domain is selected for binding to said first epitope in absence of a complementary variable domain. In a further embodiment, said first variable domain is selected for binding to said first epitope/antigen in the presence of a third variable domain in which said third variable domain is different from said second variable domain and is complementary to the first domain. Similarly, the second domain may be selected in the absence or presence of a complementary variable domain.  
      The antigens or epitopes targeted by the ligands of the invention, in addition to the half-life enhancing protein, may be any antigen or epitope but advantageously is an antigen or epitope that is targeted with therapeutic benefit. The invention provides ligands, including open conformation, closed conformation and isolated dAb monomer ligands, specific for any such target, particularly those targets further identified herein. Such targets may be, or be part of, polypeptides, proteins or nucleic acids, which may be naturally occurring or synthetic. In this respect, the ligand of the invention may bind the epitope or antigen and act as an antagonist or agonist (eg, EPO receptor agonist). One skilled in the art will appreciate that the choice is large and varied. They may be for instance human or animal proteins, cytokines, cytokine receptors, enzymes co-factors for enzymes or DNA binding proteins. Suitable cytokines and growth factors include but are not limited to: ApoE, Apo-SAA, BDNF, Cardiotrophin-1, EGF, EGF receptor, ENA-78, Eotaxin, Eotaxin-2, Exodus-2, EpoR, FGF-acidic, FGF-basic, fibroblast growth factor-10, FLT3 ligand, Fractalkine (CX3C), GDNF, G-CSF, GM-CSF, GF-β1, insulin, IFN-γ, IGF-I, IGF-II, IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8 (72 a.a.), IL-8 (77 a.a.), IL-9, IL-10, IL-11, IL-12, IL-13, IL-15, IL-16, IL-17, IL-18 (IGIF), Inhibin a, inhibin β, IP-10, keratinocyte growth factor-2 (KGF-2), KGF, Leptin, LIF, Lymphotactin, Mullerian inhibitory substance, monocyte colony inhibitory factor, monocyte attractant protein, M-CSF, MDC (67 a.a.), MDC (69 a.a.), MCP-1 (MCAF), MCP-2, MCP-3, MCP-4, MDC (67 a.a.), MDC (69 a.a.), MIG, MIP-1α, MIP-1β, MIP-3α, MIP-3β, MIP-4, myeloid progenitor inhibitor factor-1 (MPIF-1), NAP-2, Neurturin, Nerve growth factor, β-NGF, NT-3, NT-4, Oncostatin M, PDGF-AA, PDGF-AB, PDGF-BB, PF-4, RANTES, SDF1α, SDF1β, SCF, SCGF, stem cell factor (SCF), TARC, TGF-α, TGF-β, TGF-β2, TGF-β3, tumour necrosis factor (TNF), TNF-α, TNF-β, TNF receptor I, TNF receptor II, TNIL-1, TPO, VEGF, VEGF receptor 1, VEGF receptor 2, VEGF receptor 3, GCP-2, GRO/MGSA, GRO-β, GRO-γ, HCC1, 1-309, HER 1, HER 2, HER 3 and HER 4. Cytokine receptors include receptors for the foregoing cytokines. It will be appreciated that this list is by no means exhaustive.  
      In one embodiment of the invention, the variable domains are derived from a respective antibody directed against the antigen or epitope. In a preferred embodiment the variable domains are derived from a repertoire of single variable antibody domains.  
      In a second configuration, the present invention provides multispecific ligands. According to the present invention the term “multi-specific ligand” refers to a ligand which possesses more than one epitope binding specificity as herein defined. Generally, the multi-specific ligand comprises two or more epitope binding domains.  
      Epitope binding domains according to the present invention comprise a protein scaffold and epitope interaction sites (which are advantageously on the surface of the protein scaffold). According to the present invention, advantageously, each epitope binding domain is of a different epitope binding specificity.  
      In the context of the present invention, first and second “epitopes” are understood to be epitopes which are not the same and are not bound by a single monospecific ligand. They may be on different antigens or on the same antigen, but separated by a sufficient distance that they do not form a single entity that could be bound by a single mono-specific V H /V L  binding pair of a conventional antibody. Experimentally, if both of the individual variable domains in single chain antibody form (domain antibodies or dAbs) are separately competed by a monospecific V H /V L  ligand against two epitopes then those two epitopes are not sufficiently far apart to be considered separate epitopes according to the present invention.  
      According to the present invention, advantageously, each epitope binding domain comprises an immunoglobulin variable domain. More advantageously, each immunoglobulin variable domain will be either a variable light chain domain (V L ) or a variable heavy chain domain V H . In the second configuration of the present invention, the immunoglobulin domains when present on a ligand according to the present invention are non-complementary, that is they do not associate to form a V H /V L  antigen binding site. Thus, multi-specific ligands as defined in the second configuration of the invention comprise immunoglobulin domains of the same sub-type, that is either variable light chain domains (V L ) or variable heavy chain domains (V H ). Moreover, where the ligand according to the invention is in the closed conformation, the immunoglobulin domains may be of the camelid V HH  type.  
      In an alternative embodiment, the ligand(s) according to the invention do not comprise a camelid V HH  domain. More particularly, the ligand(s) of the invention do not comprise one or more amino acid residues that are specific to canelid V HH  domains as compared to human V H  domains.  
      Advantageously, the single variable domains are derived from antibodies selected for binding activity against different antigens or epitopes. For example, the variable domains may be isolated at least in part by human immunisation. Alternative methods are known in the art, including isolation from human antibody libraries and synthesis of artificial antibody genes.  
      The variable domains advantageously bind superantigens, such as protein A or protein L. Binding to superantigens is a property of correctly folded antibody variable domains, and allows such domains to be isolated from, for example, libraries of recombinant or mutant domains.  
      Epitope binding domains may also be based on protein scaffolds or skeletons other than immunoglobulin domains. For example natural bacterial receptors such as SpA have been used as scaffolds for the grafting of CDRs to generate ligands which bind specifically to one or more epitopes. Details of this procedure are described in U.S. Pat. No. 5,831,012. Other suitable scaffolds include those based on fibronectin and affibodies. Details of suitable procedures are described in WO 98/58965. Other suitable scaffolds include lipocallin and CTLA4, as described in van den Beuken et al., J. Mol. Biol. (2001) 310, 591-601, and scaffolds such as those described in WO0069907 (Medical Research Council), which are based for example on the ring structure of bacterial GroEL or other chaperone polypeptides.  
      Protein scaffolds may be combined; for example, CDRs may be grafted on to a CTLA4 scaffold and used together with immunoglobulin V H  or V L  domains to form a multivalent ligand. Likewise, fibronectin, lipocallin and other scaffolds may be combined.  
      In one embodiment, the multispecific ligand comprises an epitope binding domain that comprises the CDRs of a single immunoglobulin domain (dAb) that binds TNFR1 described herein grafted to a suitable protein scaffold or skeleton.  
      It will be appreciated by one skilled in the art that the epitope binding domains of a closed conformation multispecific ligand produced according to the method of the present invention may be on the same polypeptide chain, or alternatively, on different polypeptide chains. In the case that the variable regions are on different polypeptide chains, then they may be linked via a linker, advantageously a flexible linker (such as a polypeptide chain), a chemical linking group, or any other method known in the art.  
      The first and the second epitope binding domains may be associated either covalently or non-covalently. In the case that the domains are covalently associated, then the association may be mediated for example by disulphide bonds.  
      In certain embodiments of the second configuration of the invention, the epitopes may displace each other on binding. For example, a first epitope may be present on an antigen which, on binding to its cognate first binding domain, causes steric hindrance of a second binding domain, or a coformational change therein, which displaces the epitope bound to the second binding domain.  
      Advantageously, binding is reduced by 25% or more, advantageously 40%, 50%, 60%, 70%, 80%, 90% or more, and preferably up to 100% or nearly so, such that binding is completely inhibited. Binding of epitopes can be measured by conventional antigen binding assays, such as ELISA, by fluorescence based techniques, including FRET, or by techniques such as surface plasmon resonance which measure the mass of molecules. Moreover, the invention provides a closed conformation multi-specific ligand comprising a first epitope binding domain having a first epitope binding specificity and a non-complementary second epitope binding domain having a second epitope binding specificity, wherein the first and second binding specificities compete for epitope binding such that the closed conformation multi-specific ligand may not bind both epitopes simultaneously.  
      The closed conformation multispecific ligands of the invention do not include ligands as described in WO 02/02773. Thus, the ligands of the present invention do not comprise complementary V H /V L  pairs which bind any one or more antigens or epitopes co-operatively. Instead, the ligands according to the invention preferably comprise non-complementary V H -V H  or V L -V L  pairs. Advantageously, each V H  or V L  domain in each V H -V H  or V L -V L  pair has a different epitope binding specificity, and the epitope binding sites are so arranged that the binding of an epitope at one site competes with the binding of an epitope at another site.  
      Advantageously, the closed conformation multispecific ligand may comprise a first domain capable of binding a target molecule, and a second domain capable of binding a molecule or group which extends the half-life of the ligand. For example, the molecule or group may be a bulky agent, such as HSA or a cell matrix protein. As used herein, the phrase “molecule or group which extends the half-life of a ligand” refers to a molecule or chemical group which, when bound by a dual-specific.ligand as described herein increases the in vivo half-life of such dual specific ligand when administered to an animal, relative to a ligand that does not bind that molecule or group. Examples of molecules or groups that extend the half-life of a ligand are described hereinbelow. In a preferred embodiment, the closed conformation multispecific ligand may be capable of binding the target molecule only on displacement of the half-life enhancing molecule or group. Thus, for example, a closed conformation multispecific ligand is maintained in circulation in the bloodstream of a subject by a bulky molecule such as HSA. When a target molecule is encountered, competition between the binding domains of the closed conformation multispecific ligand results in displacement of the HSA and binding of the target.  
      In a preferred embodiment of the second configuration of the invention, the epitope binding domains are immunoglobulin variable regions and are selected from single domain V gene repertoires. Generally the repertoire of single antibody domains is displayed on the surface of filamentous bacteriophage. In a preferred embodiment each single antibody domain is selected by binding of a phage repertoire to antigen. In a preferred embodiment of the second configuration of the invention, the epitope binding domains are immunoglobulin variable regions and are selected from single domain V gene repertoires. Generally the repertoire of single antibody domains is displayed on the surface of filamentous bacteriophage. In a preferred embodiment each single antibody domain is selected by binding of a phage repertoire to antigen.  
      In one aspect, the multispecific ligand comprises at least two non-complementary variable domains. For example, the ligands may comprise a pair of V H  domains or a pair of V L  domains. Advantageously, the domains are of non-camelid origin; preferably they are human domains or comprise human framework regions (FWs) and one or more heterologous CDRs. CDRs and framework regions are those regions of an immunoglobulin variable domain as defined in the Kabat database of Sequences of Proteins of Immunological Interest.  
      Preferred human framework regions are those encoded by germline gene segments DP47 and DPK9. Advantageously, FW1, FW2 and FW3 of a V H  or V L  domain have the sequence of FW1, FW2 or FW3 from DP47 or DPK9. The human frameworks may optionally contain mutations, for example up to about 5 amino acid changes or up to about 10 amino acid changes collectively in the human frameworks used in the ligands of the invention.  
      The variable domains in the multispecific ligands according to the second configuration of the invention may be arranged in an open or a closed conformation; that is, they may be arranged such that the variable domains can bind their cognate ligands independently and simultaneously, or such that only one of the variable domains may bind its cognate ligand at any one time.  
      The inventors have realised that under certain structural conditions, non-complementary variable domains (for example two light chain variable domains or two heavy chain variable domains) may be present in a ligand such that binding of a first epitope to a first variable domain inhibits the binding of a second epitope to a second variable domain, even though such non-complementary domains do not operate together as a cognate pair.  
      Advantageously, the ligand comprises two or more pairs of variable domains; that is, it comprises at least four variable domains. Advantageously, the four variable domains comprise frameworks of human origin.  
      In a preferred embodiment, the human frameworks are identical to those of human germline sequences.  
      The present inventors consider that such antibodies will be of particular use in ligand binding assays for therapeutic and other uses.  
      In one embodiment of the second configuration of the invention, the variable domains are derived from an antibody directed against the first and/or second antigen or epitope. In a preferred embodiment the variable domains are derived from a repertoire of single variable antibody domains. In one example, the repertoire is a repertoire that is not created in an animal or a synthetic repertoire. In another example, the single variable domains are not isolated (at least in part) by animal immunisation. Thus, the single domains can be isolated from a naive library.  
      The second configuration of the invention, in another aspect, provides a multi-specific ligand comprising a first epitope binding domain having a first epitope binding specificity and a non-complementary second epitope binding domain having a second epitope binding specificity. The first and second binding specificities may be the same or different.  
      In a further aspect, the present invention provides a closed conformation multi-specific ligand comprising a first epitope binding domain having a first epitope binding specificity and a non-complementary second epitope binding domain having a second epitope binding specificity wherein the first and second binding specificities are capable of competing for epitope binding such that the closed conformation multi-specific ligand cannot bind both epitopes simultaneously.  
      In a still further aspect, the invention provides open conformation ligands comprising non-complementary binding domains, wherein the domains are specific for a different epitope on the same target. Such ligands bind to targets with increased avidity. Similarly, the invention provides multivalent ligands comprising non-complementary binding domains specific for the same epitope and directed to targets which comprise multiple copies of said epitope, such as IL-5, PDGF-AA, PDGF-BB, TGF beta, TGF beta2, TGF beta3 and TNFα, for eample human TNF Receptor 1 and human TNFa. In a similar aspect, ligands according to the invention can be configured to bind individual epitopes with low affinity, such that binding to individual epitopes is not therapeutically significant; but the increased avidity resulting from binding to two epitopes provides a therapeutic benefit. In a particular example, epitopes may be targeted which are present individually on normal cell types, but present together only on abnormal or diseased cells, such as tumour cells. In such a situation, only the abnormal or diseased cells are effectively targeted by the bispecific ligands according to the invention.  
      Ligand specific for multiple copies of the same epitope, or adjacent epitopes, on the same target (known as chelating dAbs) may also be trimeric or polymeric (tertrameric or more) ligands comprising three, four or more non-complementary binding domains. For example, ligands may be constructed comprising three or four VH domains or VL domains.  
      Moreover, ligands are provided which bind to multisubunit targets, wherein each binding domain is specific for a subunit of said target. The ligand may be dimeric, trimeric or polymeric.  
      Preferably, the multi-specific ligands according to the above aspects of the invention are obtainable by the method of the first aspect of the invention.  
      According to the above aspect of the second configuration of the invention, advantageously the first epitope binding domain and the second epitope binding domains are non-complementary immunoglobulin variable domains, as herein defined. That is either V H -V H  or V L -V L  variable domains.  
      Chelating dabs in particular may be prepared according to a preferred aspect of the invention, namely the use of anchor dAbs, in which a library of dimeric, trimeric or multimeric dAbs is constructed using a vector which comprises a constant dAb upstream or downstream of a linker sequence, with a repertoire of second, third and further dAbs being inserted on the other side of the linker. For example, the anchor or guiding dAb may be TAR1-5 (Vκ), TAR1-27(Vκ), TAR2h-5(VH) or TAR2h-6(Vκ).  
      In alternative methodologies, the use of linkers may be avoided, for example by the use of non-covalent bonding or natural affinity between binding domains such as V H  and V κ . The invention accordingly provides a method for preparing a chelating multimeric ligand comprising the steps of: 
      (a) providing a vector comprising a nucleic acid sequence encoding a single binding domain specific for a first epitope on a target;     (b) providing a vector encoding a repertoire comprising second binding domains specific for a second epitope on said target, which epitope can be the same or different to the first epitope, said second epitope being adjacent to said first epitope; and     (c) expressing said first and second binding domains; and     (d) isolating those combinations of first and second binding domains which combine together to produce a target-binding dimer.    

      The first and second epitopes are adjacent such that a multimeric ligand is capable of binding to both epitopes simultaneously. This provides the ligand with the advantages of increased avidity if binding. Where the epitopes are the same, the increased avidity is obtained by the presence of multiple copies of the epitope on the target, allowing at least two copies to be simultaneously bound in order to obtain the increased avidity effect.  
      The binding domains may be associated by several methods, as well as the use of linkers. For example, the binding domains may comprise cys residues, avidin and streptavidin groups or other means for non-covalent attachment post-synthesis; those combinations which bind to the target efficiently will be isolated. Alternatively, a linker may be present between the first and second binding domains, which are expressed as a single polypeptide from a single vector, which comprises the first binding domain, the linker and a repertoire of second binding domains, for instance as described above.  
      In a preferred aspect, the first and second binding domains associate naturally when bound to antigen; for example, V H  and V κ  domains, when bound to adjacent epitopes, will naturally associate in a three-way interaction to form a stable dimer. Such associated proteins can be isolated in a target binding assay. An advantage of this procedure is that only binding domains which bind to closely adjacent epitopes, in the correct conformation, will associate and thus be isolated as a result of their increased avidity for the target.  
      In an alternative embodiment of the above aspect of the second configuration of the invention, at least one epitope binding domain comprises a non-immunoglobulin “protein scaffold” or “protein skeleton” as herein defined. Suitable non-immunoglobulin protein scaffolds include but are not limited to any of those selected from the group consisting of: SpA, fibronectin, GroEL and other chaperones, lipocallin, CCTLA4 and affibodies, as set forth above.  
      According to the above aspect of the second configuration of the invention, advantageously, the epitope binding domains are attached to a protein skeleton. Advantageously, a protein skeleton according to the invention is an immunoglobulin skeleton.  
      According to the present invention, the term “immunoglobulin skeleton” refers to a protein which comprises at least one immunoglobulin fold and which acts as a nucleus for one or more epitope binding domains, as defined herein.  
      Preferred immunoglobulin skeletons as herein defined includes any one or more of those selected from the following: an immunoglobulin molecule comprising at least (i) the CL (kappa or lambda subclass) domain of an antibody; or (ii) the CH1 domain of an antibody heavy chain; an immunoglobulin molecule comprising the CH1 and CH2 domains of an antibody heavy chain; an immunoglobulin molecule comprising the CH1, CH2 and CH3 domains of an antibody heavy chain; or any of the subset (ii) in conjunction with the CL (kappa or lambda subclass) domain of an antibody. A hinge region domain may also be included. Such combinations of domains may, for example, mimic natural antibodies, such as IgG or IgM, or fragments thereof, such as Fv, scFv, Fab or F(ab′) 2  molecules. Those skilled in the art will be aware that this list is not intended to be exhaustive.  
      Linking of the skeleton to the epitope binding domains, as herein defined may be achieved at the polypeptide level, that is after expression of the nucleic acid encoding the skeleton and/or the epitope binding domains. Alternatively, the linking step may be performed at the nucleic acid level. Methods of linking a protein skeleton according to the present invention, to the one or more epitope binding domains include the use of protein chemistry and/or molecular biology techniques which will be familiar to those skilled in the art and are described herein.  
      Advantageously, the closed conformation multispecific ligand may comprise a first domain capable of binding a target molecule, and a second domain capable of binding a molecule or group which extends the half-life of the ligand. For example, the molecule or group may be a bulky agent, such as HSA or a cell matrix protein. As used herein, the phrase “molecule or group which extends the half-life of a ligand” refers to a molecule or chemical group which, when bound by a dual-specific ligand as described herein increases the in vivo half-life of such dual specific ligand when administered to an animal, relative to a ligand that does not bind that molecule or group. Examples of molecules or groups that extend the half-life of a ligand are described hereinbelow. In a preferred embodiment, the closed conformation multispecific ligand may be capable of binding the target molecule only on displacement of the half-life enhancing molecule or group. Thus, for example, a closed conformation multispecific ligand is maintained in circulation in the bloodstream of a subject by a bulky molecule such as HSA. When a target molecule is encountered, competition between the binding domains of the closed conformation multispecific ligand results in displacement of the HSA and binding of the target.  
      In a further aspect of the second configuration of the invention, the present invention provides one or more nucleic acid molecules encoding at least a multispecific ligand as herein defined. In one embodiment, the ligand is a closed conformation ligand. In another embodiment, it is an open conformation ligand. The multispecific ligand may be encoded on a single nucleic acid molecule; alternatively, each epitope binding domain may be encoded by a separate nucleic acid molecule. Where the ligand is encoded by a single nucleic acid molecule, the domains may be expressed as a fusion polypeptide, or may be separately expressed and subsequently linked together, for example using chemical linking agents. Ligands expressed from separate nucleic acids will be linked together by appropriate means.  
      The nucleic acid may further encode a signal sequence for export of the polypeptides from a host cell upon expression and may be fused with a surface component of a filamentous bacteriophage particle (or other component of a selection display system) upon expression. Leader sequences, which may be used in bacterial expression and/or phage or phagemid display, include pelB, stII, ompA, phoA, bla and pelA.  
      In a further aspect of the second configuration of the invention the present invention provides a vector comprising nucleic acid according to the present invention.  
      In a yet further aspect, the present invention provides a host cell transfected with a vector according to the present invention.  
      Expression from such a vector may be configured to produce, for example on the surface of a bacteriophage particle, epitope binding domains for selection. This allows selection of displayed domains and thus selection of ‘multispecific ligands’ using the method of the present invention.  
      The present invention further provides a kit comprising at least a multispecific ligand according to the present invention, which may be an open conformation or closed conformation ligand. Kits according to the invention may be, for example, diagnostic kits, therapeutic kits, kits for the detection of chemical or biological species, and the like.  
      The present invention provides a method for producing a multispecific ligand comprising the steps of: 
      a) selecting a first epitope binding domain by its ability to bind to a first epitope,     b) selecting a second epitope binding domain by its ability to bind to a second epitope,     c) combining the epitope binding domains; and     d) selecting the closed conformation multispecific ligand by its ability to bind to said first second epitope and said second epitope.    

      In a further aspect of the second configuration, the invention provides a method for preparing a closed conformation multi-specific ligand comprising a first epitope binding domain having a first epitope binding specificity and a non-complementary second epitope binding domain having a second epitope binding specificity, wherein the first and second binding specificities compete for epitope binding such that the closed conformation multi-specific ligand may not bind both epitopes simultaneously, said method comprising the steps of: 
      a) selecting a first epitope binding domain by its ability to bind to a first epitope,     b) selecting a second epitope binding domain by its ability to bind to a second epitope,     c) combining the epitope binding domains such that the domains are in a closed conformation; and     d) selecting the closed conformation multispecific ligand by its ability to bind to said first second epitope and said second epitope, but not to both said first and second epitopes simultaneously.    

      An alternative embodiment of the above aspect of the of the second configuration of the invention optionally comprises a further step (b1) comprising selecting a third or further epitope binding domain. In this way the multi-specific ligand produced, whether of open or closed conformation, comprises more than two epitope binding specificities. In a preferred aspect of the second configuration of the invention, where the multi-specific ligand comprises more than two epitope binding domains, at least two of said domains are in a closed conformation and compete for binding; other domains may compete for binding or may be free to associate independently with their cognate epitope(s).  
      In the second configuration of the invention, the first and the second epitopes are preferably different. They may be, or be part of, polypeptides, proteins or nucleic acids, which may be naturally occurring or synthetic. In this respect, the ligand of the invention may bind an epitope or antigen and act as an antagonist or agonist (eg, EPO receptor agonist). The epitope binding domains of the ligand in one embodiment have the same epitope specificity, and may for example simultaneously bind their epitope when multiple copies of the epitope are present on the same antigen. In another embodiment, these epitopes are provided on different antigens such that the ligand can bind the epitopes and bridge the antigens. One skilled in the art will appreciate that the choice of epitopes and antigens is large and varied. They may be for instance human or animal proteins, cytokines, cytokine receptors, enzymes co-factors for enzymes or DNA binding proteins. Suitable cytokines and growth factors include but are not limited to: ApoE, Apo-SAA, BDNF, Cardiotrophin-1, EGF, EGF receptor, ENA-78, Eotaxin, Eotaxin-2, Exodus-2, EpoR, FGF-acidic, FGF-basic, fibroblast growth factor-10, FLT3 ligand, Fractalkine (CX3C), GDNF, G-CSF, GM-CSF, GF-β1, insulin, IFN-γ, IGF-I, IGF-II, IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8 (72 a.a.), IL-8 (77 a.a.), IL-9, IL-10, IL-11, IL-12, IL-13, IL-15, IL-16, IL-17, IL-18 (IGIF), Inhibin α, Inhibin β, IP-10, keratinocyte growth factor-2 (KGF-2), KGF, Leptin, LIF, Lymphotactin, Mullerian inhibitory substance, monocyte colony inhibitory factor, monocyte attractant protein, M-CSF, MDC (67 a.a.), MDC (69 a.a.), MCP-1 (MCAF), MCP-2, MCP-3, MCP-4, MDC (67 a.a.), MDC (69 a.a.), MIG, MIP-1α, MIP-1β, MIP-3α, MIP-3β, MIP-4, myeloid progenitor inhibitor factor-1 (MPIF-1), NAP-2, Neurturin, Nerve growth factor, β-NGF, NT-3, NT-4, Oncostatin M, PDGF-AA, PDGF-AB, PDGF-BB, PF-4, RANTES, SDF1α, SDF1β, SCF, SCGF, stem cell factor (SCF), TARC, TGF-α, TGF-β, TGF-β2, TGF-β3, tumour necrosis factor (TNF), TNF-α, TNF-β, TNF receptor I, TNF receptor II, TNIL-1, TPO, VEGF, VEGF receptor 1, VEGF receptor 2, VEGF receptor 3, GCP-2, GRO/MGSA, GRO-β, GRO-γ, HCC1, 1-309, HER 1, HER 2, HER 3, HER 4, TACE recognition site, TNF BP-I and TNF BP-II, as well as any target disclosed in Annex 2 or Annex 3 hereto, whether in combination as set forth in the Annexes, in a different combination or individually. Cytokine receptors include receptors for the foregoing cytokines, e.g. IL-1 R1; IL-6R; IL-10R; IL-18R, as well as receptors for cytokines set forth in Annex 2 or Annex 3 and also receptors disclosed in Annex 2 and 3. It will be appreciated that this list is by no means exhaustive. Where the multispecific ligand binds to two epitopes (on the same or different antigens), the antigen(s) may be selected from this list. In particular embodiments, the ligand comprises a dAb that binds TNFR1 and a second dAb or epitope binding domain that binds any one of the these antigens. In such embodiments, the multispecific ligand can comprise any combination of immunoglobulin variable domains (e.g., V H V H , V H V L , V L V L ).  
      Preparation of Immunoglobulin Based Multi-specific Ligands Dual specific ligands according to the invention, whether open or closed in conformation according to the desired configuration of the invention, may be prepared according to previously established techniques, used in the field of antibody engineering, for the preparation of scFv, “phage” antibodies and other engineered antibody molecules. Techniques for the preparation of antibodies, and in particular bispecific antibodies, are for example described in the following reviews and the references cited therein: Winter &amp; Milstein, (1991) Nature 349:293-299; Pluckthun (1992) Immunological Reviews 130:151-188; Wright et al., (1992) Crti. Rev. Immunol.12:125-168; Holliger, P. &amp; Winter, G. (1993) Curr. Op. Biotechn. 4, 446-449; Carter, et al. (1995) J. Hematother. 4, 463-470; Chester, K. A. &amp; Hawkins, R. E. (1995) Trends Biotechn. 13, 294-300; Hoogenboom, H. R. (1997) Nature Biotechnol. 15, 125-126; Fearon, D. (1997) Nature Biotechnol. 15, 618-619; Pückthun, A. &amp; Pack, P. (1997) Immunotechnology 3, 83-105; Carter, P. &amp; Merchant, A. M. (1997) Curr. Opin. Biotechnol. 8, 449-454; Holliger, P. &amp; Winter, G. (1997) Cancer Immunol. Immunother. 45,128-130.  
      The invention provides for the selection of variable domains against two different antigens or epitopes, and subsequent combination of the variable domains.  
      The techniques employed for selection of the variable domains employ libraries and selection procedures which are known in the art. Natural libraries (Marks et al. (1991)  J. Mol. Biol.,  222: 581; Vaughan et al. (1996)  Nature Biotech.,  14: 309) which use rearranged V genes harvested from human B cells are well known to those skilled in the art. Synthetic libraries (Hoogenboom &amp; Winter (1992)  J. Mol. Biol.,  227: 381; Barbas et al. (1992)  Proc. Natl. Acad. Sci. USA,  89: 4457; Nissim et al. (1994)  EMBO J.,  13: 692; Griffiths et al. (1994)  EMBO J.,  13: 3245; De Kruif et al. (1995)  J. Mol. Biol.,  248: 97) are prepared by cloning immunoglobulin V genes, usually using PCR. Errors in the PCR process can lead to a high degree of randomisation. V H  and/or V L  libraries may be selected against target antigens or epitopes separately, in which case single domain binding is directly selected for, or together.  
      A preferred method for making a dual specific ligand according to the present invention comprises using a selection system in which a repertoire of variable domains is selected for binding to a first antigen or epitope and a repertoire of variable domains is selected for binding to a second antigen or epitope. The selected first and second variable domains are then combined and the dual-specific ligand selected for binding to both first and second antigen or epitope. Closed conformation ligands are selected for binding both first and second antigen or epitope in isolation but not simultaneously.  
      A. Library Vector Systems  
      A variety of selection systems are known in the art which are suitable for use in the present invention. Examples of such systems are described below. Bacteriophage lambda expression systems may be screened directly as bacteriophage plaques or as colonies of lysogens, both as previously described (Huse et al. (1989)  Science,  246: 1275; Caton and Koprowski (1990)  Proc. Natl. Acad. Sci. US.A.,  87; Mullinax et al. (1990)  Proc. Natl. Acad. Sci. U.S.A.,  87: 8095; Persson et al. (1991)  Proc. Natl. Acad. Sci. US.A.,  88: 2432) and are of use in the invention. Whilst such expression systems can be used to screen up to 10 6  different members of a library, they are not really suited to screening of larger numbers (greater than 10 6  members).  
      Of particular use in the construction of libraries are selection display systems, which enable a nucleic acid to be linked to the polypeptide it expresses. As used herein, a selection display system is a system that permits the selection, by suitable display means, of the individual members of the library by binding the generic and/or target ligands.  
      Selection protocols for isolating desired members of large libraries are known in the art, as typified by phage display techniques. Such systems, in which diverse peptide sequences are displayed on the surface of filamentous bacteriophage (Scott and Smith (1990)  Science,  249: 386), have proven useful for creating libraries of antibody fragments (and the nucleotide sequences that encoding them) for the in vitro selection and amplification of specific antibody fragments that bind a target antigen (McCafferty et al., WO 92/01047). The nucleotide sequences encoding the V H  and V L  regions are linked to gene fragments which encode leader signals that direct them to the periplasmic space of  E. coli  and as a result the resultant antibody fragments are displayed on the surface of the bacteriophage, typically as fusions to bacteriophage coat proteins (e.g., pIII or pVIII). Alternatively, antibody fragments are displayed externally on lambda phage capsids (phagebodies). An advantage of phage-based display systems is that, because they are biological systems, selected library members can be amplified simply by growing the phage containing the selected library member in bacterial cells. Furthermore, since the nucleotide sequence that encode the polypeptide library member is contained on a phage or phagemid vector, sequencing, expression and subsequent genetic manipulation is relatively straightforward.  
      Methods for the construction of bacteriophage antibody display libraries and lambda phage expression libraries are well known in the art (McCafferty et al. (1990)  Nature,  348: 552; Kang et al. (1991)  Proc. Natl. Acad. Sci. US.A.,  88: 4363; Clackson et al. (1991)  Nature,  352: 624; Lowman et al. (1991)  Biochemistry,  30: 10832; Burton et al. (1991)  Proc. Natl. Acad. Sci U.S.A.,  88: 10134; Hoogenboom et al. (1991) Nucleic Acids Res., 19: 4133; Chang et al. (1991)  J. Immunol.,  147: 3610; Breitling et al. (1991)  Gene,  104: 147; Marks et al. (1991) supra; Barbas et al. (1992) supra; Hawkins and Winter (1992)  J. Immunol.,  22: 867; Marks et al., 1992,  J. Biol. Chem.,  267: 16007; Lerner et al. (1992)  Science,  258: 1313, incorporated herein by reference).  
      One particularly advantageous approach has been the use of scFv phage-libraries (Huston et al., 1988, Proc. Natl. Acad. Sci U.S.A., 85: 5879-5883; Chaudhary et al. (1990) Proc. Natl. Acad. Sci U.S.A., 87: 1066-1070; McCafferty et al. (1990) supra; Clackson et al. (1991)  Nature,  352: 624; Marks et al. (1991)  J. Mol. Biol.,  222: 581; Chiswell et al. (1992) Trends Biotech., 10: 80; Marks et al. (1992)  J. Biol. Chem.,  267). Various embodiments of scFv libraries displayed on bacteriophage coat proteins have been described. Refinements of phage display approaches are also known, for example as described in WO96/06213 and WO92/01047 (Medical Research Council et al.) and WO97/08320 (Morphosys), which are incorporated herein by reference.  
      Other systems for generating libraries of polypeptides involve the use of cell-free enzymatic machinery for the in vitro synthesis of the library members. In one method, RNA molecules are selected by alternate rounds of selection against a target ligand and PCR amplification (Tuerk and Gold (1990)  Science,  249: 505; Ellington and Szostak (1990)  Nature,  346: 818). A similar technique may be used to identify DNA sequences which bind a predetermined human transcription factor (Thiesen and Bach (1990)  Nucleic Acids Res.,  18: 3203; Beaudry and Joyce (1992)  Science,  257: 635; WO92/05258 and WO92/14843). In a similar way, in vitro translation can be used to synthesise polypeptides as a method for generating large libraries. These methods which generally comprise stabilised polysome complexes, are described further in WO88/08453, WO90/05785, WO90/07003, WO91/02076, WO91/05058, and WO92/02536. Alternative display systems which are not phage-based, such as those disclosed in WO95/22625 and WO95/11922 (Affymax) use the polysomes to display polypeptides for selection.  
      A still further category of techniques involves the selection of repertoires in artificial compartments, which allow the linkage of a gene with its gene product. For example, a selection system in which nucleic acids encoding desirable gene products may be selected in microcapsules formed by water-in-oil emulsions is described in WO99/02671, WO00/40712 and Tawfik &amp; Griffiths (1998)  Nature Biotechnol  16(7), 652-6. Genetic elements encoding a gene product having a desired activity are compartmentalised into microcapsules and then transcribed and/or translated to produce their respective gene products (RNA or protein) within the microcapsules. Genetic elements which produce gene product having desired activity are subsequently sorted. This approach selects gene products of interest by detecting the desired activity by a variety of means.  
      B. Library Construction  
      Libraries intended for selection, may be constructed using techniques known in the art, for example as set forth above, or may be purchased from commercial sources. Libraries which are useful in the present invention are described, for example, in WO99/20749. Once a vector system is chosen and one or more nucleic acid sequences encoding polypeptides of interest are cloned into the library vector, one may generate diversity within the cloned molecules by undertaking mutagenesis prior to expression; alternatively, the encoded proteins may be expressed and selected, as described above, before mutagenesis and additional rounds of selection are performed. Mutagenesis of nucleic acid sequences encoding structurally optimised polypeptides is carried out by standard molecular methods. Of particular use is the polymerase chain reaction, or PCR, (Mullis and Faloona (1987)  Methods Enzymol.,  155: 335, herein incorporated by reference). PCR, which uses multiple cycles of DNA replication catalysed by a thermostable, DNA-dependent DNA polymerase to amplify the target sequence of interest, is well known in the art. The construction of various antibody libraries has been discussed in Winter et al. (1994) Ann. Rev. Immunology 12, 433-55, and references cited therein.  
      PCR is performed using template DNA (at least lfg; more usefully, 1-1000 ng) and at least 25 pmol of oligonucleotide primers; it may be advantageous to use a larger amount of primer when the primer pool is heavily heterogeneous, as each sequence is represented by only a small fraction of the molecules of the pool, and amounts become limiting in the later amplification cycles. A typical reaction mixture includes: 2 μl of DNA, 25 pmol of oligonucleotide primer, 2.5 μl of 10×PCR buffer 1 (Perkin-Elmer, Foster City, Calif.), 0.4 μl of 1.25 μM dNTP, 0.15 μl (or 2.5 units) of Taq DNA polymerase (Perkin Elmer, Foster City, Calif.) and deionized water to a total volume of 25 μl. Mineral oil is overlaid and the PCR is performed using a programmable thermal cycler. The length and temperature of each step of a PCR cycle, as well as the number of cycles, is adjusted in accordance to the stringency requirements in effect. Annealing temperature and timing are determined both by the efficiency with which a primer is expected to anneal to a template and the degree of mismatch that is to be tolerated; obviously, when nucleic acid molecules are simultaneously amplified and mutagenised, mismatch is required, at least in the first round of synthesis. The ability to optimise the stringency of primer annealing conditions is well within the knowledge of one of moderate skill in the art. An annealing temperature of between 30° C. and 72° C. is used. Initial denaturation of the template molecules normally occurs at between 92° C. and 99° C. for 4 minutes, followed by 20-40 cycles consisting of denaturation (94-99° C. for 15 seconds to 1 minute), annealing (temperature determined as discussed above; 1-2 minutes), and extension (72° C. for 1-5 minutes, depending on the length of the amplified product). Final extension is generally for 4 minutes at 72° C., and may be followed by an indefinite (0-24 hour) step at 4° C.  
      C. Combining Single Variable Domains  
      Domains useful in the invention, once selected, may be combined by a variety of methods known in the art, including covalent and non-covalent methods.  
      Preferred methods include the use of polypeptide linkers, as described, for example, in connection with scFv molecules (Bird et al., (1988) Science 242:423-426). Discussion of suitable linkers is provided in Bird et al. Science 242, 423-426; Hudson et al, Journal Immunol Methods 231 (1999) 177-189; Hudson et al, Proc Nat Acad Sci USA 85, 5879-5883. Linkers are preferably flexible, allowing the two single domains to interact. One linker example is a (Gly 4  Ser) n  linker, where n=1 to 8, eg, 2, 3, 4, 5 or 7. The linkers used in diabodies, which are less flexible, may also be employed (Holliger et al., (1993) PNAS (USA) 90:6444-6448).  
      In one embodiment, the linker employed is not an immunoglobulin hinge region.  
      Variable domains may be combined using methods other than linkers. For example, the use of disulphide bridges, provided through naturally-occurring or engineered cysteine residues, may be exploited to stabilise V H -V H ,V L -V L  or V H -V L  dimers (Reiter et al., (1994) Protein Eng. 7:697-704) or by remodelling the interface between the variable domains to improve the “fit” and thus the stability of interaction (Ridgeway et al., (1996) Protein Eng. 7:617-621; Zhu et al., (1997) Protein Science 6:781-788). Other techniques for joining or stabilising variable domains of immunoglobulins, and in particular antibody V H  domains, may be employed as appropriate.  
      In accordance with the present invention, dual specific ligands can be in “closed” conformations in solution. A “closed” configuration is that in which the two domains (for example V H  and V L ) are present in associated form, such as that of an associated V H -V L  pair which forms an antibody binding site. For example, scFv may be in a closed conformation, depending on the arrangement of the linker used to link the V H  and V L  domains. If this is sufficiently flexible to allow the domains to associate, or rigidly holds them in the associated position, it is likely that the domains will adopt a closed conformation.  
      Similarly, V H  domain pairs and V L  domain pairs may exist in a closed conformation. Generally, this will be a function of close association of the domains, such as by a rigid linker, in the ligand molecule. Ligands in a closed conformation will be unable to bind both the molecule which increases the half-life of the ligand and a second target molecule. Thus, the ligand will typically only bind the second target molecule on dissociation from the molecule which increases the half-life of the ligand.  
      Moreover, the construction of V H /V H , V L /V L  or V H /V L  dimers without linkers provides for competition between the domains.  
      Ligands according to the invention may moreover be in an open conformation. In such a conformation, the ligands will be able to simultaneously bind both the molecule which increases the half-life of the ligand and the second target molecule. Typically, variable domains in an open configuration are (in the case of V H -V L  pairs) held far enough apart for the domains not to interact and form an antibody binding site and not to compete for binding to their respective epitopes. In the case of V H /V H  or V L /V L  dimers, the domains are not forced together by rigid linkers. Naturally, such domain pairings will not compete for antigen binding or form an antibody binding site.  
      Fab fragments and whole antibodies will exist primarily in the closed conformation, although it will be appreciated that open and closed dual specific ligands are likely to exist in a variety of equilibria under different circumstances. Binding of the ligand to a target is likely to shift the balance of the equilibrium towards the open configuration. Thus, certain ligands according to the invention can exist in two conformations in solution, one of which (the open form) can bind two antigens or epitopes independently, whilst the alternative conformation (the closed form) can only bind one antigen or epitope; antigens or epitopes thus compete for binding to the ligand in this conformation.  
      Although the open form of the dual specific ligand may thus exist in equilibrium with the closed form in solution, it is envisaged that the equilibrium will favour the closed form; moreover, the open form can be sequestered by target binding into a closed conformation. Preferably, therefore, certain dual specific ligands of the invention are present in an equilibrium between two (open and closed) conformations.  
      Dual specific ligands according to the invention may be modified in order to favour an open or closed conformation. For example, stabilisation of V H -V L  interactions with disulphide bonds stabilises the closed conformation. Moreover, linkers used to join the domains, including V H  domain and V L  domain pairs, may be constructed such that the open from is favoured; for example, the linkers may sterically hinder the association of the domains, such as by incorporation of large amino acid residues in opportune locations, or the designing of a suitable rigid structure which will keep the domains physically spaced apart.  
      D. Characterisation of the Dual-Specific Ligand  
      The binding of the dual-specific ligand to its specific antigens or epitopes can be tested by methods which will be familiar to those skilled in the art and include ELISA. In a preferred embodiment of the invention binding is tested using monoclonal phage ELISA.  
      Phage ELISA may be performed according to any suitable procedure: an exemplary protocol is set forth below.  
      Populations of phage produced at each round of selection can be screened for binding by ELISA to the selected antigen or epitope, to identify “polyclonal” phage antibodies. Phage from single infected bacterial colonies from these populations can then be screened by ELISA to identify “monoclonal” phage antibodies. It is also desirable to screen soluble antibody fragments for binding to antigen or epitope, and this can also be undertaken by ELISA using reagents, for example, against a C- or N-terminal tag (see for example Winter et al. (1994) Ann. Rev. Immunology 12, 433-55 and references cited therein.  
      The diversity of the selected phage monoclonal antibodies may also be assessed by gel electrophoresis of PCR products (Marks et al. 1991, supra; Nissim et al. 1994 supra), probing (Tomlinson et al., 1992) J. Mol. Biol. 227, 776) or by sequencing of the vector DNA.  
      E. Structure of Dual-Specific Ligands  
      As described above, an antibody is herein defined as an antibody (for example IgG, IgM, IgA, IgA, IgE) or fragment (Fab, Fv, disulphide linked Fv, scFv, diabody) which comprises at least one heavy and a light chain variable domain, at least two heavy chain variable domains or at least two light chain variable domains. It may be at least partly derived from any species naturally producing an antibody, or created by recombinant DNA technology; whether isolated from serum, B-cells, hybridomas, transfectomas, yeast or bacteria).  
      In a preferred embodiment of the invention the dual-specific ligand comprises at least one single heavy chain variable domain of an antibody and one single light chain variable domain of an antibody, or two single heavy or light chain variable domains. For example, the ligand may comprise a V H /V L  pair, a pair of V H  domains or a pair of V L  domains.  
      The first and the second variable domains of such a ligand may be on the same polypeptide chain. Alternatively they may be on separate polypeptide chains. In the case that they are on the same polypeptide chain they may be linked by a linker, which is preferentially a peptide sequence, as described above.  
      The first and second variable domains may be covalently or non-covalently associated.  
      In the case that they are covalently associated, the covalent bonds may be disulphide bonds.  
      In the case that the variable domains are selected from V-gene repertoires selected for instance using phage display technology as herein described, then these variable domains comprise a universal framework region, such that is they may be recognised by a specific generic ligand as herein defined. The use of universal frameworks, generic ligands and the like is described in WO99/20749.  
      Where V-gene repertoires are used variation in polypeptide sequence is preferably located within the structural loops of the variable domains. The polypeptide sequences of either variable domain may be altered by DNA shuffling or by mutation in order to enhance the interaction of each variable domain with its complementary pair. DNA shuffling is known in the art and taught, for example, by Stemmer, 1994, Nature 370: 389-391 and U.S. Pat. No. 6,297,053, both of which are incorporated herein by reference. Other methods of mutagenesis are well known to those of skill in the art.  
      In a preferred embodiment of the invention the ‘dual-specific ligand’ is a single chain Fv fragment. In an alternative embodiment of the invention, the ‘dual-specific ligand’ consists of a Fab format.  
      In a further aspect, the present invention provides nucleic acid encoding at least a ‘dual-specific ligand’ as herein defined.  
      One skilled in the art will appreciate that, depending on the aspect of the invention, both antigens or epitopes may bind simultaneously to the same antibody molecule. Alternatively, they may compete for binding to the same antibody molecule. For example, where both epitopes are bound simultaneously, both variable domains of a dual specific ligand are able to independently bind their target epitopes. Where the domains compete, the one variable domain is capable of binding its target, but not at the same time as the other variable domain binds its cognate target; or the first variable domain is capable of binding its target, but not at the same time as the second variable domain binds its cognate target.  
      The variable regions may be derived from antibodies directed against target antigens or epitopes. Alternatively they may be derived from a repertoire of single antibody domains such as those expressed on the surface of filamentous bacteriophage. Selection may be performed as described below.  
      In general, the nucleic acid molecules and vector constructs required for the performance of the present invention may be constructed and manipulated as set forth in standard laboratory manuals, such as Sambrook et al. (1989)  Molecular Cloning: A Laboratory Manual , Cold Spring Harbor, USA.  
      The manipulation of nucleic acids useful in the present invention is typically carried out in recombinant vectors.  
      Thus in a further aspect, the present invention provides a vector comprising nucleic acid encoding at least a ‘dual-specific ligand’ as herein defined.  
      As used herein, vector refers to a discrete element that is used to introduce heterologous DNA into cells for the expression and/or replication thereof. Methods by which to select or construct and, subsequently, use such vectors are well known to one of ordinary skill in the art. Numerous vectors are publicly available, including bacterial plasmids, bacteriophage, artificial chromosomes and episomal vectors. Such vectors may be used for simple cloning and mutagenesis; alternatively gene expression vector is employed. A vector of use according to the invention may be selected to accommodate a polypeptide coding sequence of a desired size, typically from 0.25 kilobase (kb) to 40 kb or more in length A suitable host cell is transformed with the vector after in vitro cloning manipulations. Each vector contains various functional components, which generally include a cloning (or “polylinker”) site, an origin of replication and at least one selectable marker gene. If given vector is an expression vector, it additionally possesses one or more of the following: enhancer element, promoter, transcription termination and signal sequences, each positioned in the vicinity of the cloning site, such that they are operatively linked to the gene encoding a ligand according to the invention.  
      Both cloning and expression vectors generally contain nucleic acid sequences that enable the vector to replicate in one or more selected host cells. Typically in cloning vectors, this sequence is one that enables the vector to replicate independently of the host chromosomal DNA and includes origins of replication or autonomously replicating sequences. Such sequences are well known for a variety of bacteria, yeast and viruses. The origin of replication from the plasmid pBR322 is suitable for most Gram-negative bacteria, the 2 micron plasmid origin is suitable for yeast, and various viral origins (e.g. SV 40, adenovirus) are useful for cloning vectors in mammalian cells. Generally, the origin of replication is not needed for mammalian expression vectors unless these are used in mammalian cells able to replicate high levels of DNA, such as COS cells.  
      Advantageously, a cloning or expression vector may contain a selection gene also referred to as selectable marker. This gene encodes a protein necessary for the survival or growth of transformed host cells grown in a selective culture medium. Host cells not transformed with the vector containing the selection gene will therefore not survive in the culture medium. Typical selection genes encode proteins that confer resistance to antibiotics and other toxins, e.g. ampicillin, neomycin, methotrexate or tetracycline, complement auxotrophic deficiencies, or supply critical nutrients not available in the growth media.  
      Since the replication of vectors encoding a ligand according to the present invention is most conveniently performed in  E. coli , an  E. coli -selectable marker, for example, the β-lactamase gene that confers resistance to the antibiotic ampicillin, is of use. These can be obtained from  E. coli  plasmids, such as pBR322 or a pUC plasmid such as pUC18 or pUC19.  
      Expression vectors usually contain a promoter that is recognised by the host organism and is operably linked to the coding sequence of interest. Such a promoter may be inducible or constitutive. The term “operably linked” refers to a juxtaposition wherein the components described are in a relationship permitting them to function in their intended manner. A control sequence “operably linked” to a coding sequence is ligated in such a way that expression of the coding sequence is achieved under conditions compatible with the control sequences.  
      Promoters suitable for use with prokaryotic hosts include, for example, the β-lactamase and lactose promoter systems, alkaline phosphatase, the tryptophan (trp) promoter system and hybrid promoters such as the tac promoter. Promoters for use in bacterial systems will also generally contain a Shine-Delgamo sequence operably linked to the coding sequence.  
      The preferred vectors are expression vectors that enables the expression of a nucleotide sequence corresponding to a polypeptide library member. Thus, selection with the first and/or second antigen or epitope can be performed by separate propagation and expression of a single clone expressing the polypeptide library member or by use of any selection display system. As described above, the preferred selection display system is bacteriophage display. Thus, phage or phagemid vectors may be used, eg pIT1 or pIT2. Leader sequences useful in the invention include pelB, stII, ompA, phoA, bla and pelA. One example are phagemid vectors which have an  E. coli . origin of replication (for double stranded replication) and also a phage origin of replication (for production of single-stranded DNA). The manipulation and expression of such vectors is well known in the art (Hoogenboom and Winter (1992) supra; Nissim et al. (1994) supra). Briefly, the vector contains a β-lactamase gene to confer selectivity on the phagemid and a lac promoter upstream of a expression cassette that consists (N to C terminal) of a pelB leader sequence (which directs the expressed polypeptide to the periplasmic space), a multiple cloning site (for cloning the nucleotide version of the library member), optionally, one or more peptide tag (for detection), optionally, one or more TAG stop codon and the phage protein pIII. Thus, using various suppressor and non-suppressor strains of  E. coli  and with the addition of glucose, iso-propyl thio-β-D-galactoside (IPTG) or a helper phage, such as VCS M13, the vector is able to replicate as a plasmid with no expression, produce large quantities of the polypeptide library member only or produce phage, some of which contain at least one copy .of the polypeptide-pIII fusion on their surface.  
      Construction of vectors encoding ligands according to the invention employs conventional ligation techniques. Isolated vectors or DNA fragments are cleaved, tailored, and religated in the form desired to generate the required vector. If desired, analysis to confirm that the correct sequences are present in the constructed vector can be performed in a known fashion. Suitable methods for constructing expression vectors, preparing in vitro transcripts, introducing DNA into host cells, and performing analyses for assessing expression and function are known to those skilled in the art. The presence of a gene sequence in a sample is detected, or its amplification and/or expression quantified by conventional methods, such as Southern or Northern analysis, Western blotting, dot blotting of DNA, RNA or protein, in situ hybridisation, immunocytochemistry or sequence analysis of nucleic acid or protein molecules. Those skilled in the art will readily envisage how these methods may be modified, if desired.  
      Structure of Closed Conformation Multispecific Ligands  
      According to one aspect of the second configuration of the invention present invention, the two or more non-complementary epitope binding domains are linked so that they are in a closed conformation as herein defined. Advantageously, they may be further attached to a skeleton which may, as a alternative, or on addition to a linker described herein, facilitate the formation and/or maintenance of the closed conformation of the epitope binding sites with respect to one another.  
      (I) Skeletons  
      Skeletons may be based on immunoglobulin molecules or may be non-immunoglobulin in origin as set forth above. Preferred immunoglobulin skeletons as herein defined includes any one or more of those selected from the following: an immunoglobulin molecule comprising at least (i) the CL (kappa or lambda subclass) domain of an antibody; or (ii) the CH1 domain of an antibody heavy chain; an immunoglobulin molecule comprising the CH1 and CH2 domains of an antibody heavy chain; an immunoglobulin molecule comprising the CH1, CH2 and CH3 domains of an antibody heavy chain; or any of the subset (ii) in conjunction with the CL (kappa or lambda subclass) domain of an antibody. A hinge region domain may also be included. Such combinations of domains may, for example, mimic natural antibodies, such as IgG or IgM, or fragments thereof, such as Fv, scFv, Fab or F(ab′) 2  molecules. Those skilled in the art will be aware that this list is not intended to be exhaustive.  
      (II) Protein Scaffolds  
      Each epitope binding domain comprises a protein scaffold and one or more CDRs which are involved in the specific interaction of the domain with one or more epitopes. Advantageously, an epitope binding domain according to the present invention comprises three CDRs. Suitable protein scaffolds include any of those selected from the group consisting of the following: those based on immunoglobulin domains, those based on fibronectin, those based on affibodies, those based on CTLA4, those based on chaperones such as GroEL, those based on lipocallin and those based on the bacterial Fc receptors SpA and SpD. Those skilled in the art will appreciate that this list is not intended to be exhaustive.  
      F: Scaffolds for Use in Constructing Dual Specific Ligands  
      i. Selection of the Main-Chain Conformation  
      The members of the immunoglobulin superfamily all share a similar fold for their polypeptide chain. For example, although antibodies are highly diverse in terms of their primary sequence, comparison of sequences and crystallographic structures has revealed that, contrary to expectation, five of the six antigen binding loops of antibodies (H1, H2, L1, L2, L3) adopt a limited number of main-chain conformations, or canonical structures (Chothia and Lesk (1987)  J. Mol. Biol.,  196: 901; Chothia et al. (1989)  Nature,  342: 877). Analysis of loop lengths and key residues has therefore enabled prediction of the main-chain conformations of H1, H2, L1, L2 and L3 found in the majority of human antibodies (Chothia et al. (1992)  J. Mol. Biol.,  227: 799; Tomlinson et al. (1995)  EMBO J.,  14: 4628; Williams et al. (1996)  J. Mol. Biol.,  264: 220). Although the H3 region is much more diverse in terms of sequence, length and structure (due to the use of D segments), it also forms a limited number of main-chain conformations for short loop lengths which depend on the length and the presence of particular residues, or types of residue, at key positions in the loop and the antibody framework (Martin et al. (1996)  J. Mol. Biol.,  263: 800; Shirai et al. (1996)  FEBS Letters,  399: 1).  
      The dual specific ligands of the present invention are advantageously assembled from libraries of domains, such as libraries of V H  domains and/or libraries of V L  domains. Moreover, the dual specific ligands of the invention may themselves be provided in the form of libraries. In one aspect of the present invention, libraries of dual specific ligands and/or domains are designed in which certain loop lengths and key residues have been chosen to ensure that the main-chain conformation of the members is known. Advantageously, these are real conformations of immunoglobulin superfamily molecules found in nature, to minimise the chances that they are non-finctional, as discussed above. Germline V gene segments serve as one suitable basic framework for constructing antibody or T-cell receptor libraries; other sequences are also of use. Variations may occur at a low frequency, such that a small number of finctional members may possess an altered main-chain conformation, which does not affect its function.  
      Canonical structure theory is also of use to assess the number of different main-chain conformations encoded by ligands, to predict the main-chain conformation based on ligand sequences and to chose residues for diversification which do not affect the canonical structure. It is known that, in the human V κ  domain, the L1 loop can adopt one of four canonical structures, the L2 loop has a single canonical structure and that 90% of human V κ  domains adopt one of four or five canonical structures for the L3 loop (Tomlinson et al. (1995) supra); thus, in the V κ  domain alone, different canonical structures can combine to create a range of different main-chain conformations. Given that the V λ  domain encodes a different range of canonical structures for the L1, L2 and L3 loops and that V κ  and V λ  domains can pair with any V H  domain which can encode several canonical structures for the H 1  and H2 loops, the number of canonical structure combinations observed for these five loops is very large. This implies that the generation of diversity in the main-chain conformation may be essential for the production of a wide range of binding specificities. However, by constructing an antibody library based on a single known main-chain conformation it has been found, contrary to expectation, that diversity in the main-chain conformation is not required to generate sufficient diversity to target substantially all antigens. Even more surprisingly, the single main-chain conformation need not be a consensus structure—a single naturally occurring conformation can be used as the basis for an entire library. Thus, in a preferred aspect, the dual-specific ligands of the invention possess a single known main-chain conformation.  
      The single main-chain conformation that is chosen is preferably commonplace among molecules of the immunoglobulin superfamily type in question. A conformation is commonplace when a significant number of naturally occurring molecules are observed to adopt it. Accordingly, in a preferred aspect of the invention, the natural occurrence of the different main-chain conformations for each binding loop of an immunoglobulin domain are considered separately and then a naturally occurring variable domain is chosen which possesses the desired combination of main-chain conformations for the different loops. If none is available, the nearest equivalent may be chosen. It is preferable that the desired combination of main-chain conformations for the different loops is created by selecting germline gene segments which encode the desired main-chain conformations. It is more preferable, that the selected germline gene segments are frequently expressed in nature, and most preferable that they are the most frequently expressed of all natural germline gene segments.  
      In designing dual specific ligands or libraries thereof the incidence of the different main-chain conformations for each of the six antigen binding loops may be considered separately. For H1, H2, L1, L2 and L3, a given conformation that is adopted by between 20% and 100% of the antigen binding loops of naturally occurring molecules is chosen. Typically, its observed incidence is above 35% (i.e. between 35% and 100%) and, ideally, above 50% or even above 65%. Since the vast majority of H3 loops do not have canonical structures, it is preferable to select a main-chain conformation which is commonplace among those loops which do display canonical structures. For each of the loops, the conformation which is observed most often in the natural repertoire is therefore selected. In human antibodies, the most popular canonical structures (CS) for each loop are as follows: H1-CS1 (79% of the expressed repertoire), H2-CS3 (46%), L1-CS2 of V κ  (39%), L2-CS1 (100%), L3-CS1 of V κ  (36%) (calculation assumes a κ:λ ratio of 70:30, Hood et al. (1967)  Cold Spring Harbor Symp. Quant. Biol.,  48: 133). For H3 loops that have canonical structures, a CDR3 length (Kabat et al. (1991)  Sequences of proteins of immunological interest , U.S. Department of Health and Human Services) of seven residues with a salt-bridge from residue 94 to residue 101 appears to be the most common. There are at least 16 human antibody sequences in the EMBL data library with the required H3 length and key residues to form this conformation and at least two crystallographic structures in the protein data bank which can be used as a basis for antibody modelling (2cgr and Itet). The most frequently expressed germline gene segments that this combination of canonical structures are the V H  segment 3-23 DP-47), the J H  segment JH4b, the V κ  segment O2/O12 (DPK9) and the J κ  segment J κ 1. V H  segments DP45 and DP38 are also suitable. These segments can therefore be used in combination as a basis to construct a library with the desired single main-chain conformation.  
      Alternatively, instead of choosing the single main-chain conformation based on the natural occurrence of the different main-chain conformations for each of the binding loops in isolation, the natural occurrence of combinations of main-chain conformations is used as the basis for choosing the single main-chain conformation. In the case of antibodies, for example, the natural occurrence of canonical structure combinations for any two, three, four, five or for all six of the antigen binding loops can be determined. Here, it is preferable that the chosen conformation is commonplace in naturally occurring antibodies and most preferable that it observed most frequently in the natural repertoire. Thus, in human antibodies, for example, when natural combinations of the five antigen binding loops, H1, H2, L1, L2 and L3, are considered, the most frequent combination of canonical structures is determined and then combined with the most popular conformation for the H3 loop, as a basis for choosing the single main-chain conformation.  
      ii. Diversification of the Canonical Sequence  
      Having selected several known main-chain conformations or, preferably a single known main-chain conformation, dual specific ligands according to the invention or libraries for use in the invention can be constructed by varying the binding site of the molecule in order to generate a repertoire with structural and/or functional diversity. This means that variants are generated such that they possess sufficient diversity in their structure and/or in their function so that they are capable of providing a range of activities.  
      The desired diversity is typically generated by varying the selected molecule at one or more positions. The positions to be changed can be chosen at random or are preferably selected. The variation can then be achieved either by randomisation, during which the resident amino acid is replaced by any amino acid or analogue thereof, natural or synthetic, producing a very large number of variants or by replacing the resident amino acid with one or more of a defined subset of amino acids, producing a more limited number of variants.  
      Various methods have been reported for introducing such diversity. Error-prone PCR (Hawkins et al. (1992)  J. Mol. Biol.,  226: 889), chemical mutagenesis (Deng et al. (1994)  J. Biol. Chem.,  269: 9533) or bacterial mutator strains (Low et al. (1996)  J. Mol. Biol.,  260: 359) can be used to introduce random mutations into the genes that encode the molecule. Methods for mutating selected positions are also well known in the art and include the use of mismatched oligonucleotides or degenerate oligonucleotides, with or without the use of PCR. For example, several synthetic antibody libraries have been created by targeting mutations to the antigen binding loops. The H3 region of a human tetanus toxoid-binding Fab has been randomised to create a range of new binding specificities (Barbas et al. (1992)  Proc. Natl. Acad. Sci. USA,  89: 4457). Random or semi-random H3 and L3 regions have been appended to germline V gene segments to produce large libraries with unmutated framework regions (Hoogenboom &amp; Winter (1992)  J. Mol. Biol.,  227: 381; Barbas et al. (1992)  Proc. Natl. Acad. Sci. USA,  89: 4457; Nissim et al. (1994)  EMBO J.,  13: 692; Griffiths et al. (1994)  EMBO J.,  13: 3245; De Kruif et al. (1995)  J. Mol. Biol.,  248: 97). Such diversification has been extended to include some or all of the other antigen binding loops (Crameri et al. (1996)  Nature Med.,  2: 100; Riechmann et al. (1995)  Bio/Technology,  13: 475; Morphosys, WO97/08320, supra).  
      Since loop randomisation has the potential to create approximately more than 10 15  structures for H3 alone and a similarly large number of variants for the other five loops, it is not feasible using current transformation technology or even by using cell free systems to produce a library representing all possible combinations. For example, in one of the largest libraries constructed to date, 6×10 10  different antibodies, which is only a fraction of the potential diversity for a library of this design, were generated (Griffiths et al. (1994) supra). In a preferred embodiment, only those residues which are directly involved in creating or modifying the desired function of the molecule are diversified. For many molecules, the function will be to bind a target and therefore diversity should be concentrated in the target binding site, while avoiding changing residues which are crucial to the overall packing of the molecule or to maintaining the chosen main-chain conformation.  
      Diversification of the Canonical Sequence as it Applies to Antibody Domains  
      In the case of antibody dual-specific ligands, the binding site for the target is most often the antigen binding site. Thus, in a highly preferred aspect, the invention provides libraries of or for the assembly of antibody dual-specific ligands in which only those residues in the antigen binding site are varied. These residues are extremely diverse in the human antibody repertoire and are known to make contacts in high-resolution antibody/antigen complexes. For example, in L2 it is known that positions 50 and 53 are diverse in naturally occurring antibodies and are observed to make contact with the antigen. In contrast, the conventional approach would have been to diversify all the residues in the corresponding Complementarity Determining Region (CDR1) as defined by Kabat et al. (1991, supra), some seven residues compared to the two diversified in the library for use according to the invention. This represents a significant improvement in terms of the functional diversity required to create a range of antigen binding specificities.  
      In nature, antibody diversity is the result of two processes: somatic recombination of germline V, D and J gene segments to create a naive primary repertoire (so called germline and junctional diversity) and somatic hypermutation of the resulting rearranged V genes. Analysis of human antibody sequences has shown that diversity in the primary repertoire is focused at the centre of the antigen binding site whereas somatic hypermutation spreads diversity to regions at the periphery of the antigen binding site that are highly conserved in the primary repertoire (see Tomlinson et al. (1996)  J. Mol. Biol.,  256: 813). This complementarity has probably evolved as an efficient strategy for searching sequence space and, although apparently unique to antibodies, it can easily be applied to other polypeptide repertoires. The residues which are varied are a subset of those that form the binding site for the target. Different (including overlapping) subsets of residues in the target binding site are diversified at different stages during selection, if desired.  
      In the case of an antibody repertoire, an initial ‘naive’ repertoire is created where some, but not all, of the residues in the antigen binding site are diversified. As used herein in this context, the term “naive” refers to antibody molecules that have no pre-determined target. These molecules resemble those which are encoded by the immunoglobulin genes of an individual who has not undergone immune diversification, as is the case with fetal and newborn individuals, whose immune systems have not yet been challenged by a wide variety of antigenic stimuli. This repertoire is then selected against a range of antigens or epitopes. If required, further diversity can then be introduced outside the region diversified in the initial repertoire. This matured repertoire can be selected for modified function, specificity or affinity.  
      The invention provides two different naive repertoires of binding domains for the construction of dual specific ligands, or a naïve library of dual specific ligands, in which some or all of the residues in the antigen binding site are varied. The “primary” library mimics the natural primary repertoire, with diversity restricted to residues at the centre of the antigen binding site that are diverse in the germline V gene segments (germline diversity) or diversified during the recombination process (junctional diversity). Those residues which are diversified include, but are not limited to, H50, H52, H52a, H53, H55, H56, H58, H95, H96, H97, H98, L50, L53, L91, L92, L93, L94 and L96. In the “somatic” library, diversity is restricted to residues that are diversified during the recombination process (junctional diversity) or are highly somatically mutated). Those residues which are diversified include, but are not limited to: H31, H33, H35, H95, H96, H97, H98, L30, L31, L32, L34 and L96. All the residues listed above as suitable for diversification in these libraries are known to make contacts in one or more antibody-antigen complexes. Since in both libraries, not all of the residues in the antigen binding site are varied, additional diversity is incorporated during selection by varying the remaining residues, if it is desired to do so. It shall be apparent to one skilled in the art that any subset of any of these residues (or additional residues which comprise the antigen binding site) can be used for the initial and/or subsequent diversification of the antigen binding site.  
      In the construction of libraries for use in the invention, diversification of chosen positions is typically achieved at the nucleic acid level, by altering the coding sequence which specifies the sequence of the polypeptide such that a number of possible amino acids (all 20 or a subset thereof) can be incorporated at that position. Using the IUPAC nomenclature, the most versatile codon is NNK, which encodes all amino acids as well as the TAG stop codon. The NNK codon is preferably used in order to introduce the required diversity. Other codons which achieve the same ends are also of use, including the NNN codon, which leads to the production of the additional stop codons TGA and TAA.  
      A feature of side-chain diversity in the antigen binding site of human antibodies is a pronounced bias which favours certain amino acid residues. If the amino acid composition of the ten most diverse positions in each of the V H , V κ  and V λ  regions are summed, more than 76% of the side-chain diversity comes from only seven different residues, these being, serine (24%), tyrosine (14%), asparagine (11%), glycine (9%), alanine (7%), aspartate (6%) and threonine (6%). This bias towards hydrophilic residues and small residues which can provide main-chain flexibility probably reflects the evolution of surfaces which are predisposed to binding a wide range of antigens or epitopes and may help to explain the required promiscuity of antibodies in the primary repertoire.  
      Since it is preferable to mimic this distribution of amino acids, the distribution of amino acids at the positions to be varied preferably mimics that seen in the antigen binding site of antibodies. Such bias in the substitution of amino acids that permits selection of certain polypeptides (not just antibody polypeptides) against a range of target antigens is easily applied to any polypeptide repertoire. There are various methods for biasing the amino acid distribution at the position to be varied (including the use of tri-nucleotide mutagenesis, see WO97/08320), of which the preferred method, due to ease of synthesis, is the use of conventional degenerate codons. By comparing the amino acid profile encoded by all combinations of degenerate codons (with single, double, triple and quadruple degeneracy in equal ratios at each position) with the natural amino acid use it is possible to calculate the most representative codon. The codons (AGT)(AGC)T, (AGT)(AGC)C and (AGT)(AGC)(CT)—that is, DVT, DVC and DVY, respectively using IUPAC nomenclature—are those closest to the desired amino acid profile: they encode 22% serine and 11% tyrosine, asparagine, glycine, alanine, aspartate, threonine and cysteine. Preferably, therefore, libraries are constructed using either the DVT, DVC or DVY codon at each of the diversified positions.  
      G: Antigens Capable of Increasing Ligand Half-Life  
      The dual specific ligands according to the invention, in one configuration thereof, are capable of binding to one or more molecules which can increase the half-life of the ligand in vivo. Typically, such molecules are polypeptides which occur naturally in vivo and which resist degradation or removal by endogenous mechanisms which remove unwanted material from the organism. For example, the molecule which increases the half-life of the organism may be selected from the following:  
      Proteins from the extracellular matrix; for example collagen, laminins, integrins and fibronectin. Collagens are the major proteins of the extracellular matrix. About 15 types of collagen molecules are currently known, found in different parts of the body, eg type I collagen (accounting for 90% of body collagen) found in bone, skin, tendon, ligaments, cornea, internal organs or type II collagen found in cartilage, invertebral disc, notochord, vitreous humour of the eye.  
      Proteins found in blood, including:  
      Plasma proteins such as fibrin, α-2 macroglobulin, serum albumin, fibrinogen A, fibrinogen B, serum amyloid protein A, heptaglobin, profilin, ubiquitin, uteroglobulin and β-2-microglobulin;  
      Enzymes and inhibitors such as plasminogen, lysozyme, cystatin C, alpha-1-antitrypsin and pancreatic trypsin inhibitor. Plasminogen is the inactive precursor of the trypsin-like serine protease plasmin. It is normally found circulating through the blood stream. When plasminogen becomes activated and is converted to plasmin, it unfolds a potent enzymatic domain that dissolves the fibrinogen fibers that entangle the blood cells in a blood clot. This is called fibrinolysis.  
      Immune system proteins, such as IgE, IgG, IgM.  
      Transport proteins such as retinol binding protein, α-1 microglobulin.  
      Defensins such as beta-defensin 1, Neutrophil defensins 1, 2 and 3.  
      Proteins found at the blood brain barrier or in neural tissues, such as melanocortin receptor, myelin, ascorbate transporter.  
      Transferrin receptor specific ligand-neuropharmaceutical agent fusion proteins (see U.S. Pat. No. 5,977,307);  
      brain capillary endothelial cell receptor, transferrin, transferrin receptor, insulin, insulin-like growth factor 1 (IGF 1) receptor, insulin-like growth factor 2 (IGF 2) receptor, insulin receptor.  
      Proteins localised to the kidney, such as polycystin, type IV collagen, organic anion transporter K1, Heymann&#39;s antigen.  
      Proteins localised to the liver, for example alcohol dehydrogenase, G250.  
      Blood coagulation factor X  
      α1 antitrypsin  
      HNF 1α 
      Proteins localised to the lung, such as secretory component (binds IgA).  
      Proteins localised to the Heart, for example HSP 27. This is associated with dilated cardiomyopathy.  
      Proteins localised to the skin, for example keratin.  
      Bone specific proteins, such as bone morphogenic proteins (BMPs), which are a subset of the transforming growth factor β superfamily that demonstrate osteogenic activity. Examples include BMP-2, -4, -5, -6, -7 (also referred to as osteogenic protein (OP-1) and -8 (OP-2).  
      Tumour specific proteins, including human trophoblast antigen, herceptin receptor, oestrogen receptor, cathepsins eg cathepsin B (found in liver and spleen).  
      Disease-specific proteins, such as antigens expressed only on activated T-cells: including  
      LAG-3 (lymphocyte activation gene), osteoprotegerin ligand (OPGL) see  Nature  402, 304-309; 1999, OX40 (a member of the TNF receptor family, expressed on activated T cells and the only costimulatory T cell molecule known to be specifically up-regulated human T cell leukaemia virus type-I (HTLV-I)-producing cells.) See  J Immunol.  2000 Jul. 1;165(1):263-70; Metalloproteases (associated with arthritis/cancers), including CG6512  Drosophila , human paraplegin, human FtsH, human AFG3L2, murine ftsH; angiogenic growth factors, including acidic fibroblast growth factor (FGF-1), basic fibroblast growth factor (FGF-2), Vascular endothelial growth factor /vascular permeability factor (VEGF/VPF), transforming growth factor-a (TGF a), tumor necrosis factor-alpha (TNF-α), angiogenin, interleukin-3 (IL-3), interleukin-8 (IL-8), platelet-derived endothelial growth factor (PD-ECGF), placental growth factor (PlGF), midkine platelet-derived growth factor-BB (PDGF), fractalkine.  
      Stress Proteins (Heat Shock Proteins)  
      HSPs are normally found intracellularly. When they are found extracellularly, it is an indicator that a cell has died and spilled out its contents. This unprogrammed cell death (necrosis) only occurs when as a result of trauma, disease or injury and therefore in vivo, extracellular HSPs trigger a response from the immune system that will fight infection and disease. A dual specific which binds to extracellular HSP can be localised to a disease site. 
      Proteins involved in Fc transport     Brambell receptor (also known as FcRB)     This Fc receptor has two functions, both of which are potentially useful for delivery     The functions are     The transport of IgG from mother to child across the placenta     the protection of IgG from degradation thereby prolonging its serum half life of IgG. It is thought that the receptor recycles IgG from endosome.    

      See Holliger et al, Nat Biotechnol 1997 Jul;15(7):632-6.  
      Ligands according to the invention may designed to be specific for the above targets without requiring any increase in or increasing half life in vivo. For example, ligands according to the invention can be specific for targets selected from the foregoing which are tissue-specific, thereby enabling tissue-specific targeting of the dual specific ligand, or a dAb monomer that binds a tissue-specific therapeutically relevant target, irrespective of any increase in half-life, although this may result. Moreover, where the ligand or dAb monomer targets kidney or liver, this may redirect the ligand or dAb monomer to an alternative clearance pathway in vivo (for example, the ligand may be directed away from liver clearance to kidney clearance).  
      H: Use of Multispecific Ligands According to the Second Configuration of the Invention  
      Multispecific ligands according to the method of the second configuration of the present invention may be employed in in vivo therapeutic and prophylactic applications, in vitro and in vivo diagnostic applications, in vitro assay and reagent applications, and the like. For example antibody molecules may be used in antibody based assay techniques, such as ELISA techniques, according to methods known to those skilled in the art.  
      As alluded to above, the multispecific ligands according to the invention are of use in diagnostic, prophylactic and therapeutic procedures. Multispecific antibodies according to the invention are of use diagnostically in Western analysis and in situ protein detection by standard immunohistochemical procedures; for use in these applications, the ligands may be labelled in accordance with techniques known to the art. In addition, such antibody polypeptides may be used preparatively in affinity chromatography procedures, when complexed to a chromatographic support, such as a resin. All such techniques are well known to one of skill in the art.  
      Diagnostic uses of the closed conformation multispecific ligands according to the invention include homogenous assays for analytes which exploit the ability of closed conformation multispecific ligands to bind two targets in competition, such that two targets cannot bind simultaneously (a closed conformation), or alternatively their ability to bind two targets simultaneously (an open conformation).  
      In a further aspect still of the second configuration of the invention, the present invention provides a homogenous immunoassay using a ligand according to the present invention.  
      A true homogenous immunoassay format has been avidly sought by manufacturers of diagnostics and research assay systems used in drug discovery and development. The main diagnostics markets include human testing in hospitals, doctor&#39;s offices and clinics, commercial reference laboratories, blood banks, and the home, non-human diagnostics (for example food testing, water testing, environmental testing, bio-defence, and veterinary testing), and finally research (including drug development; basic research and academic research).  
      At present all these markets utilise immunoassay systems that are built around chemiluminescent, ELISA, fluorescence or in rare cases radio-immunoassay technologies. Each of these assay formats requires a separation step (separating bound from un-bound reagents). In some cases, several separation steps are required. Adding these additional steps adds reagents and automation, takes time, and affects the ultimate outcome of the assays. In human diagnostics, the separation step may be automated, which masks the problem, but does not remove it. The robotics, additional reagents, additional incubation times, and the like add considerable cost and complexity. In drug development, such as high throughput screening, where literally millions of samples are tested at once, with very low levels of test molecule, adding additional separation steps can eliminate the ability to perform a screen. However, avoiding the separation creates too much noise in the read out. Thus, there is a need for a true homogenous format that provides sensitivities at the range obtainable from present assay formats.  
      Advantageously, an assay possesses fully quantitative read-outs with high sensitivity and a large dynamic range. Sensitivity is an important requirement, as is reducing the amount of sample required. Both of these features are features that a homogenous system offers. This is very important in point of care testing, and in drug development where samples are precious. Heterogenous systems, as currently available in the art, require large quantities of sample and expensive reagents  
      Applications for homogenous assays include cancer testing, where the biggest assay is that for Prostate Specific Antigen, used in screening men for prostate cancer. Other applications include fertility testing, which provides a series of tests for women attempting to conceive including beta-hcg for pregnancy. Tests for infectious diseases, including hepatitis, HIV, rubella, and other viruses and microorganisms and sexually transmitted diseases. Tests are used by blood banks, especially tests for HIV, hepatitis A, B, C, non A non B. Therapeutic drug monitoring tests include monitoring levels of prescribed drugs in patients for efficacy and to avoid toxicity, for example digoxin for arrhythmia, and phenobarbital levels in psychotic cases; theophylline for asthma. Diagnostic tests are moreover useful in abused drug testing, such as testing for cocaine, marijuana and the like. Metabolic tests are used for measuring thyroid function, anaemia and other physiological disorders and functions.  
      The homogenous immunoassay format is moreover useful in the manufacture of standard clinical chemistry assays. The inclusion of immunoassays and chemistry assays on the same instrument is highly advantageous in diagnostic testing. Suitable chemical assays include tests for glucose, cholesterol, potassium, and the like.  
      A further major application for homogenous immunoassays is drug discovery and development: high throughput screening includes testing combinatorial chemistry libraries versus targets in ultra high volume. Signal is detected, and positive groups then split into smaller groups, and eventually tested in cells and then animals. Homogenous assays may be used in all these types of test. In drug development, especially animal studies and clinical trials heavy use of immunoassays is made. Homogenous assays greatly accelerate and simplify these procedures. Other Applications include food and beverage testing: testing meat and other foods for  E. coli , salmonella, etc; water testing, including testing at water plants for all types of contaminants including  E. coli ; and veterinary testing.  
      In a broad embodiment, the invention provides a binding assay comprising a detectable agent which is bound to a closed conformation multispecific ligand according to the invention, and whose detectable properties are altered by the binding of an analyte to said closed conformation multispecific ligand. Such an assay may be configured in several different ways, each exploiting the above properties of closed conformation multispecific ligands.  
      The assay relies on the direct or indirect displacement of an agent by the analyte, resulting in a change in the detectable properties of the agent. For example, where the agent is an enzyme which is capable of catalysing a reaction which has a detectable end-point, said enzyme can be bound by the ligand such as to obstruct its active site, thereby inactivating the enzyme. The analyte, which is also bound by the closed conformation multispecific ligand, displaces the enzyme, rendering it active through freeing of the active site. The enzyme is then able to react with a substrate, to give rise to a detectable event. In an alternative embodiment, the ligand may bind the enzyme outside of the active site, influencing the conformation of the enzyme and thus altering its activity. For example, the structure of the active site may be constrained by the binding of the ligand, or the binding of cofactors necessary for activity may be prevented.  
      The physical implementation of the assay may take any form known in the art. For example, the closed conformation multispecific ligand/enzyme complex may be provided on a test strip; the substrate may be provided in a different region of the test strip, and a solvent containing the analyte allowed to migrate through the ligand/enzyme complex, displacing the enzyme, and carrying it to the substrate region to produce a signal. Alternatively, the ligand/enzyme complex may be provided on a test stick or other solid phase, and dipped into an analyte/substrate solution, releasing enzyme into the solution in response to the presence of analyte.  
      Since each molecule of analyte potentially releases one enzyme molecule, the assay is quantitative, with the strength of the signal generated in a given time being dependent on the concentration of analyte in the solution.  
      Further configurations using the analyte in a closed conformation are possible. For example, the closed conformation multispecific ligand may be configured to bind an enzyme in an allosteric site, thereby activating the enzyme. In such an embodiment, the enzyme is active in the absence of analyte. Addition of the analyte displaces the enzyme and removes allosteric activation, thus inactivating the enzyme.  
      In the context of the above embodiments which employ enzyme activity as a measure of the analyte concentration, activation or inactivation of the enzyme refers to an increase or decrease in the activity of the enzyme, measured as the ability of the enzyme to catalyse a signal-generating reaction. For example, the enzyme may catalyse the conversion of an undetectable substrate to a detectable form thereof. For example, horseradish peroxidase is widely used in the art together with chromogenic or chemiluminescent substrates, which are available commercially. The level of increase or decrease of the activity of the enzyme may between 10% and 100%, such as 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%; in the case of an increase in activity, the increase may be more than 100%, i.e. 200%, 300%, 500% or more, or may not be measurable as a percentage if the baseline activity of the inhibited enzyme is undetectable.  
      In a further configuration, the closed conformation multispecific ligand may bind the substrate of an enzyme/substrate pair, rather than the enzyme. The substrate is therefore unavailable to the enzyme until released from the closed conformation multispecific ligand through binding of the analyte. The implementations for this configuration are as for the configurations which bind enzyme.  
      Moreover, the assay may be configured to bind a fluorescent molecule, such as a fluorescein or another fluorophore, in a conformation such that the fluorescence is quenched on binding to the ligand. In this case, binding of the analyte to the ligand will displace the fluorescent molecule, thus producing a signal. Alternatives to fluorescent molecules which are useful in the present invention include luminescent agents, such as luciferin/luciferase, and chromogenic agents, including agents commonly used in immunoassays such as HRP.  
      Therapeutic and Diagnostic Compositions and Uses  
      The invention provides compositions comprising an antagonist of TNFR1 (e.g. ligand) of the invention (e.g., dual-specific ligand, multi-specific ligand, dAb monomer) and a pharmaceutically acceptable carrier, diluent or excipient, and therapeutic and diagnostic methods that employ the ligands or compositions of the invention. Antagonists and ligands (e.g., dual-specific ligands, multispecific ligands, dAb monomers) according to the method of the present invention may be employed in in vivo therapeutic and prophylactic applications, in vivo diagnostic applications and the like.  
      Therapeutic and prophylactic uses of antagonists and ligands (e.g., multispecific ligands, dual-specific ligands, dAb monomers) of the invention involve the administration of antoagonists and/or ligands according to the invention to a recipient mammal, such as a human. Dual-specific and Multi-specific ligands (e.g., dual-specific antibody formats) to bind to multimeric antigen with great avidity. Dual- or Multispecific ligands can allow the cross-linking of two antigens, for example in recruiting cytotoxic T-cells to mediate the killing of tumour cell lines.  
      Substantially pure ligands or binding proteins thereof, for example dAb monomers, of at least 90 to 95% homogeneity are preferred for administration to a mammal, and 98 to 99% or more homogeneity is most preferred for pharmaceutical uses, especially when the mammal is a human. Once purified, partially or to homogeneity as desired, the ligands may be used diagnostically or therapeutically (including extracorporeally) or in developing and performing assay procedures, immunofluorescent stainings and the like (Lefkovite and Pemis, (1979 and 1981) Immunological Methods, Volumes I and II, Academic Press, NY).  
      For example, the ligands or binding proteins thereof, for example dAb monomers, of the present invention will typically find use in preventing, suppressing or treating inflammatory states including acute and chronic inflammatory diseases. For example, the antagonists and/or ligands can be administered to treat, suppress or prevent a chronic inflammatory disease; allergic hypersensitivity, cancer, bacterial or viral infection, autoimmune disorders (which include, but are not limited to, Type I diabetes, asthma, multiple sclerosis, rheumatoid arthritis, juvenile rheumatoid arthritis, psoriatic arthritis, spondylarthropathy (e.g., ankylosing spondylitis), systemic lupus erythematosus, inflammatory bowel disease (e.g., Crohn&#39;s disease, ulcerative colitis), myasthenia gravis and Behcet&#39;s syndrome), psoriasis, endometriosis, and abdominal adhesions (e.g., post abdominal surgery).  
      Antagonists (e.g., ligands) according to the invention (e.g, dual-specific ligands, multispecific ligands, dAb monomers) which able to bind to extracellular targets involved in endocytosis (e.g. Clathrin) can be endocytosed, enabling access to intracellular targets. In addition, dual or multispecific ligands, provide a means by which a binding domain (e.g., a dAb monomer) that is specificity able to bind to an ntracellular target can be delivered to an intracellular environment. This strategy requires, for example, a dual-specific ligand with physical properties that enable it to remain functional inside the cell. Alternatively, if the final destination intracellular compartment is oxidising, a well folding ligand may not need to be disulphide free.  
      In the instant application, the term “prevention” involves administration of the protective composition prior to the induction of the disease. “Suppression” refers to administration of the composition after an inductive event, but prior to the clinical appearance of the disease. “Treatment” involves administration of the protective composition after disease symptoms become manifest.  
      Advantageously, dual- or multi-specific ligands may be used to target cytokines and other molecules which cooperate synergistically in therapeutic situations in the body of an organism. The invention therefore provides a method for synergising the activity of two or more binding domains (e.g., dAbs) that bind cytokines or other molecules, comprising administering a dual- or multi-specific ligand capable of binding to said two or more molecules (e.g., cytokines). In this aspect of the invention, the dual- or multi-specific ligand may be any dual- or multi-specific ligand, including a ligand composed of complementary and/or non-complementary domains, a ligand in an open conformation, and a ligand in a closed conformation. For example, this aspect of the invention relates to combinations of V H  domains and V L  domains, V H  domains only and V L  domains only.  
      Synergy in a therapeutic context may be achieved in a number of ways. For example, target combinations may be therapeutically active only if both targets are targeted by the ligand, whereas targeting one target alone is not therapeutically effective. In another embodiment, one target alone may provide some low or minimal therapeutic effect, but together with a second target the combination provides a synergistic increase in therapeutic effect. Preferably, the cytokines bound by the dual- or multi-specific ligands of this aspect of the invention are selected from the list shown in Annex 2.  
      Moreover, dual- or multi-specific ligands may be used in oncology applications, where one specificity targets CD89, which is expressed by cytotoxic cells, and the other is tumour specific. Examples of tumour antigens which may be targetted are given in Annex 3.  
      Animal model systems which can be used to screen the effectiveness of the antagonists of TNFR1 (e.g, ligands, antibodies or binding proteins thereof) in protecting against or treating the disease are available. Methods for the testing of systemic lupus erythematosus (SLE) in susceptible mice are known in the art (Knight et al. (1978)  J. Exp. Med.,  147: 1653; Reinersten et al. (1978)  New Eng. J. Med.,  299: 515). Myasthenia Gravis (MG) is tested in SJL/J female mice by inducing the disease with soluble AchR protein from another species (Lindstrom et al. (1988)  Adv. Immunol.,  42: 233). Arthritis is induced in a susceptible strain of mice by injection of Type II collagen (Stuart et al. (1984)  Ann. Rev. Immunol.,  42: 233). A model by which adjuvant arthritis is induced in susceptible rats by injection of mycobacterial heat shock protein has been described (Van Eden et al. (1988)  Nature,  331: 171). Thyroiditis is induced in mice by administration of thyroglobulin as described (Maron et al. (1980)  J. Exp. Med.,  152: 1115). Insulin dependent diabetes mellitus (IDDM) occurs naturally or can be induced in certain strains of mice such as those described by Kanasawa et al. (1984)  Diabetologia,  27: 113. EAE in mouse and rat serves as a model for MS in human. In this model, the demyelinating disease is induced by administration of myelin basic protein (see Paterson (1986)  Textbook of Immunopathology , Mischer et al., eds., Grune and Stratton, New York, pp. 179-213; McFarlin et al. (1973)  Science,  179: 478: and Satoh et al. (1987)  J. Immunol.,  138: 179).  
      Generally, the present antagonists (e.g., ligands) will be utilised in purified form together with pharmacologically appropriate carriers. Typically, these carriers include aqueous or alcoholic/aqueous solutions, emulsions or suspensions, any including saline and/or buffered media. Parenteral vehicles include sodium chloride solution, Ringer&#39;s dextrose, dextrose and sodium chloride and lactated Ringer&#39;s. Suitable physiologically-acceptable adjuvants, if necessary to keep a polypeptide complex in suspension, may be chosen from thickeners such as carboxymethylcellulose, polyvinylpyrrolidone, gelatin and alginates.  
      Intravenous vehicles include fluid and nutrient replenishers and electrolyte replenishers, such as those based on Ringer&#39;s dextrose. Preservatives and other additives, such as antimicrobials, antioxidants, chelating agents and inert gases, may also be present (Mack (1982)  Remington&#39;s Pharmaceutical Sciences,  16th Edition). A variety of suitable formulations can be used, including extended release formulations.  
      The antagonists (e.g., ligands) of the present invention may be used as separately administered compositions or in conjunction with other agents. These can include various immunotherapeutic drugs, such as cylcosporine, methotrexate, adriamycin or cisplatinum, and immunotoxins. Pharmaceutical compositions can include “cocktails” of various cytotoxic or other agents in conjunction with the antagonists (e.g., ligands) of the present invention, or even combinations of ligands according to the present invention having different specificities, such as ligands selected using different target antigens or epitopes, whether or not they are pooled prior to administration.  
      The route of administration of pharmaceutical compositions according to the invention may be any of those commonly known to those of ordinary skill in the art. For therapy, including without limitation immunotherapy, the selected ligands thereof of the invention can be administered to any patient in accordance with standard techniques. The administration can be by any appropriate mode, including parenterally, intravenously, intramuscularly, intraperitoneally, transdermally, via the pulmonary route, or also, appropriately, by direct infusion with a catheter. The dosage and frequency of administration will depend on the age, sex and condition of the patient, concurrent administration of other drugs, counterindications and other parameters to be taken into account by the clinician.  
      The ligands of this invention can be lyophilised for storage and reconstituted in a suitable carrier prior to use. This technique has been shown to be effective with conventional immunoglobulins and art-known lyophilisation and reconstitution techniques can be employed. It will be appreciated by those skilled in the art that lyophilisation and reconstitution can lead to varying degrees of antibody activity loss (e.g. with conventional immunoglobulins, IgM antibodies tend to have greater activity loss than IgG antibodies) and that use levels may have to be adjusted upward to compensate.  
      The compositions containing the present antagonists (e.g., ligands) or a cocktail thereof can be administered for prophylactic and/or therapeutic treatments. In certain therapeutic applications, an adequate amount to accomplish at least partial inhibition, suppression, modulation, killing, or some other measurable parameter, of a population of selected cells is defined as a “therapeutically-effective dose”. Amounts needed to achieve this dosage will depend upon the severity of the disease and the general state of the patient&#39;s own immune system, but generally range from 0.005 to 5.0 mg of ligand, e.g. antibody, receptor (e.g. a T-cell receptor) or binding protein thereofper kilogram of body weight, with doses of 0.05 to 2.0 mg/kg/dose being more commonly used. For prophylactic applications, compositions containing the present ligands or cocktails thereof may also be administered in similar or slightly lower dosages, to prevent, inhibit or delay onset of disease (e.g., to sustain remission or quiescence, or to prevent acute phase). The skilled clinician will be able to determine the appropriate dosing interval to treat, suppress or prevent disease. When an antagonist of TNFR1 (e.g., ligand) is administered to treat, suppress or prevent a chronic inflammatory disease, it can be administered up to four times per day, twice weekly, once weekly, once every two weeks, once a month, or once every two months, at a dose off, for example, about 10 μg/kg to about 80 mg/kg, about 100 μg/kg to about 80 mg/kg, about 1 mg/kg to about 80 mg/kg, about 1 mg/kg to about 70 mg/kg, about 1 mg/kg to about 60 mg/kg, about 1 mg/kg to about 50 mg/kg, about 1 mg/kg to about 40 mg/kg, about 1 mg/kg to about 30 mg/kg, about 1 mg/kg to about 20 mg/kg, about 1 mg/kg to about 10 mg/kg, about 10 μg/kg to about 10 mg/kg, about 10 μg/kg to about 5 mg/kg, about 10 μg/kg to about 2.5 mg/kg, about 1 mg/kg, about 2 mg/kg, about 3 mg/kg, about 4 mg/kg, about 5 mg/kg, about 6 mg/kg, about 7 mg/kg, about 8 mg/kg, about 9 mg/kg or about 10 mg/kg. In particular embodiments, the antagonist of TNFR1 (e.g., ligand) is administered to treat, suppress or prevent a chronic inflammatory disease once every two weeks or once a month at a dose of about 10 μg/kg to about 10 mg/kg (e.g., about 10 μg/kg, about 100 μg/kg, about 1 mg/kg, about 2 mg/kg, about 3 mg/kg, about 4 mg/kg, about 5 mg/kg, about 6 mg/kg, about 7 mg/kg, about 8 mg/kg, about 9 mg/kg or about 10 mg/kg.)  
      Treatment or therapy performed using the compositions described herein is considered “effective” if one or more symptoms are reduced (e.g., by at least 10% or at least one point on a clinical assessment scale), relative to such symptoms present before treatment, or relative to such symptoms in an individual (human or model animal) not treated with such composition or other suitable control. Symptoms will obviously vary depending upon the disease or disorder targeted, but can be measured by an ordinarily skilled clinician or technician. Such symptoms can be measured, for example, by monitoring the level of one or more biochemical indicators of the disease or disorder (e.g., levels of an enzyme or metabolite correlated with the disease, affected cell numbers, etc.), by monitoring physical manifestations (e.g., inflammation, tumor size, etc.), or by an accepted clinical assessment scale, for example, the Expanded Disability Status Scale (for multiple sclerosis), the Irvine Inflammatory Bowel Disease Questionnaire (32 point assessment evaluates quality of life with respect to bowel function, systemic symptoms, social function and emotional status—score ranges from 32 to 224, with higher scores indicating a better quality of life), the Quality of Life Rheumatoid Arthritis Scale, or other accepted clinical assessment scale as known in the field. A sustained (e.g., one day or more, preferably longer) reduction in disease or disorder symptoms by at least 10% or by one or more points on a given clinical scale is indicative of “effective” treatment. Similarly, prophylaxis performed using a composition as described herein is “effective” if the onset or severity of one or more symptoms is delayed, reduced or abolished relative to such symptoms in a similar individual (human or animal model) not treated with the composition.  
      A composition containing an antagonists (e.g., ligand) or cocktail thereof according to the present invention may be utilised in prophylactic and therapeutic settings to aid in the alteration, inactivation, killing or removal of a select target cell population in a mammal. In addition, the selected repertoires of polypeptides described herein may be used extracorporeally or in vitro selectively to kill, deplete or otherwise effectively remove a target cell population from a heterogeneous collection of cells. Blood from a mammal may be combined extracorporeally with the ligands, e.g. antibodies, cell-surface receptors or binding proteins thereof whereby the undesired cells are killed or otherwise removed from the blood for return to the mammal in accordance with standard techniques.  
      A composition containing an antagonist (e.g., ligand) according to the present invention may be utilised in prophylactic and therapeutic settings to aid in the alteration, inactivation, killing or removal of a select target cell population in a mammal.  
      The antagonists of TNFR1 (e.g., ligands, dAb monomers) can be administered and or formulated together with one or more additional therapeutic or active agents. When an antagonist of TNFR1 (e.g,, ligand, dAb monomer) is administered with an additional therapeutic agent , the antagonist of TNFR1 can be administered before, simultaneously with or subsequent to administration of the additional agent. Generally, the antagonist of TNFR1 (e.g., ligand, dAb monomer) and additional agent are administered in a manner that provides an overlap of therapeutic effect.  
      In one embodiment, the invention is a method for treating, suppressing or preventing a chronic inflammatory disease, comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In one embodiment, the invention is a method for treating, suppressing or preventing arthritis (e.g., rheumatoid arthritis, juvenile rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis) comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In another embodiment, the invention is a method for treating, suppressing or preventing psoriasis comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In another embodiment, the invention is a method for treating, suppressing or preventing inflammatory bowel disease (e.g., Crohn&#39;s disease, ulcerative colitis) comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In another embodiment, the invention is a method for treating, suppressing or preventing chronic obstructive pulmonary disease (e.g., chronic bronchitis, chronic obstructive bronchitis, emphysema), comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In another embodiment, the invention is a method for treating, suppressing or preventing pneumonia (e.g., bacterial pneumonia, such as Staphylococcal pneumonia) comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In another embodiment, the invention is a method treating, suppressing or preventing septic shock comprising administering to a mammal in need thereof a therapeutically-effective dose or amount of an antagonist of TNFR1 (e.g., a ligand that comprises a dAb monomer that binds TNFR1).  
      In a further aspect still of the second configuration of the invention, the present invention provides a composition comprising a closed conformation multispecific ligand, obtainable by a method of the present invention, and a pharmaceutically acceptable carrier, diluent or excipient.  
      Moreover, the present invention provides a method for the treatment of disease using a “closed conformation multispecific ligand” or a composition according to the present invention.  
      In a preferred embodiment of the invention the disease is cancer or an inflammatory disease, eg rheumatoid arthritis, asthma or Crohn&#39;s disease.  
      In a further aspect of the second configuration of the invention, the present invention provides a method for the diagnosis, including diagnosis of disease using a closed conformation multispecific ligand, or a composition according to the present invention. Thus in general the binding of an analyte to a closed conformation multispecific ligand may be exploited to displace an agent, which leads to the generation of a signal on displacement. For example, binding of analyte (second antigen) could displace an enzyme (first antigen) bound to the antibody providing the basis for an immunoassay, especially if the enzyme were held to the antibody through its active site.  
      Thus, the present invention provides a method for detecting the presence of a target molecule, comprising: 
      (a) providing a closed conformation multispecific ligand bound to an agent, said ligand being specific for the target molecule and the agent, wherein the agent which is bound by the ligand leads to the generation of a detectable signal on displacement from the ligand;     (b) exposing the closed conformation multispecific ligand to the target molecule; and     (c) detecting the signal generated as a result of the displacement of the agent.    

      According to the above aspect of the second configuration of the invention, advantageously, the agent is an enzyme, which is inactive when bound by the closed conformation multi-specific ligand. Alternatively, the agent may be any one or more selected from the group consisting of the following: the substrate for an enzyme, and a fluorescent, luminescent or chromogenic molecule which is inactive or quenched when bound by the ligand.  
      In addition, the selected repertoires of polypeptides described herein may be used extracorporeally or in vitro selectively to kill, deplete or otherwise effectively remove a target cell population from a heterogeneous collection of cells. Blood from a mammal may be combined extracorporeally with the ligands, e.g. antibodies, cell- surface receptors or binding proteins thereof whereby the undesired cells are killed or otherwise removed from the blood for return to the mammal in accordance with standard techniques.  
     EXAMPLES  
      The invention is further described, for the purposes of illustration only, in the following examples. As used herein, for the purposes of dAb nomenclature, human TNFα is referred to as TAR1 and human TNFα receptor 1 (p55 receptor) is referred to as TAR2.  
     Example 1  
     Selection of a Dual Specific scFv Antibody (K8) Directed against Human Serum Albumin (HSA) and β-galactosidase (β-gal)  
      This example explains a method for making a dual specific antibody directed against β-gal and HSA in which a repertoire of V κ  variable domains linked to a germline (dummy) V H  domain is selected for binding to β-gal and a repertoire of V H  variable domains linked to a germline (dummy) V κ  domain is selected for binding to HSA. The selected variable V H  HSA and V κ  β-gal domains are then combined and the antibodies selected for binding to β-gal and HSA. HSA is a half-life increasing protein found in human blood.  
      Four human phage antibody libraries were used in this experiment.  
                                                          Library 1   Germline V κ /DVT V H     8.46 × 10 7             Library 2   Germline V κ /NNK V H     9.64 × 10 7             Library 3   Germline V H /DVT V κ     1.47 × 10 8             Library 4   Germline V H /NNK V κ     1.45 × 10 8                        
 
      All libraries are based on a single human framework for V H  (V3-23/DP47 and J H 4b) and V κ  (O12/O2/DPK9 and J κ 1) with side chain diversity incorporated in complementarity determining regions (CDR2 and CDR3).  
      Library 1 and Library 2 contain a dummy V κ  sequence, whereas the sequence of V H  is diversified at positions H50, H52, H52a, H53, H55, H56, H58, H95, H96, H97 and H98 (DVT or NNK encoded, respectively) ( FIG. 1 ). Library 3 and Library 4 contain a dummy V H  sequence, whereas the sequence of V K  is diversified at positions L50, L53, L91, L92, L93, L94 and L96 (DVT or NNK encoded, respectively) ( FIG. 1 ). The libraries are in phagemid pIT2/ScFv format ( FIG. 2 ) and have been preselected for binding to generic ligands, Protein A and Protein L, so that the majority of clones in the unselected libraries are functional. The sizes of the libraries shown above correspond to the sizes after preselection. Library 1 and Library 2 were mixed prior to selections on antigen to yield a single V H /dummy V κ  library and Library 3 and Library 4 were mixed to form a single V κ /dummy V H  library.  
      Three rounds of selections were performed on β-gal using V κ /dummy V H  library and three rounds of selections were performed on HSA using V H /dummy V K  library. In the case of β-gal the phage titres went up from 1.1×10 6  in the first round to 2.0×10 8  in the third round. In the case of HSA the phage titres went up from 2×10 4  in the first round to 1.4×10 9  in the third round. The selections were performed as described by Griffith et al., (1993), except that KM13 helper phage (which contains a pIII protein with a protease cleavage site between the D2 and D3 domains) was used and phage were eluted with 1 mg/ml trypsin in PBS. The addition of trypsin cleaves the pIII proteins derived from the helper phage (but not those from the phagemid) and elutes bound scFv-phage fusions by cleavage in the c-myc tag ( FIG. 2 ), thereby providing a further enrichment for phages expressing functional scFvs and a corresponding reduction in background (Kristensen &amp; Winter, Folding &amp; Design 3: 321-328, Jul 9, 1998). Selections were performed using immunotubes coated with either HSA or β-gal at 100 μg/ml concentration.  
      To check for binding, 24 colonies from the third round of each selection were screened by monoclonal phage ELISA. Phage particles were produced as described by Harrison et al., Methods Enzymol. 1996;267:83-109. 96-well ELISA plates were coated with 100 μl of HSA or β-gal at 10 μg/ml concentration in PBS overnight at 4° C. A standard ELISA protocol was followed (Hoogenboom et al., 1991) using detection of bound phage with anti-M13-HRP conjugate. A selection of clones gave ELISA signals of greater than 1.0 with 50 μl supernatant.  
      Next, DNA preps were made from V H /dummy V κ  library selected on HSA and from V κ /dummy V H  library selected on β-gal using the QIAprep Spin Miniprep kit (Qiagen). To access most of the diversity, DNA preps were made from each of the three rounds of selections and then pulled together for each of the antigens. DNA preps were then digested with SalI/NotI overnight at 37° C. Following gel purification of the fragments, V κ  chains from the V κ /dummy V H  library selected on β-gal were ligated in place of a dummy V κ  chain of the V H /dummy V κ  library selected on HSA creating a library of 3.3×10 9  clones.  
      This library was then either selected on HSA (first round) and β-gal (second round), HSA/β-gal selection, or on β-gal (first round) and HSA (second round), β-gal/HSA selection. Selections were performed as described above. In each case after the second round 48 clones were tested for binding to HSA and β-gal by the monoclonal phage ELISA (as described above) and by ELISA of the soluble scFv fragments. Soluble antibody fragments were produced as described by Harrison et al., (1996), and standard ELISA protocol was followed Hoogenboom et al. (1991) Nucleic Acids Res., 19: 4133, except that 2% Tween/PBS was used as a blocking buffer and bound scFvs were detected with Protein L-HRP. Three clones (E4, E5 and E8) from the HSA/β-gal selection and two clones (K8 and K10) from the β-gal/HSA selection were able to bind both antigens. scFvs from these clones were PCR amplified and sequenced as described by Ignatovich et al., (1999) J Mol Biol 1999 Nov. 26;294(2):457-65, using the primers LMB3 and pHENseq. Sequence analysis revealed that all clones were identical. Therefore, only one clone encoding a dual specific antibody (K8) was chosen for further work ( FIG. 3 ).  
     Example 2  
     Characterisation of the Binding Properties of the K8 Antibody  
      Firstly, the binding properties of the K8 antibody were characterised by the monoclonal phage ELISA. A 96-well plate was coated with 100 μl of HSA and β-gal alongside with alkaline phosphatase (APS), bovine serum albumin (BSA), peanut agglutinin, lysozyme and cytochrome c (to check for cross-reactivity) at 10 μg/ml concentration in PBS overnight at 4° C. The phagemid from K8 clone was rescued with KM13 as described by Harrison et al., (1996) and the supernatant (50 μl) containing phage assayed directly. A standard ELISA protocol was followed (Hoogenboom et al., 1991) using detection of bound phage with anti-M13-HRP conjugate. The dual specific K8 antibody was found to bind to HSA and β-gal when displayed on the surface of the phage with absorbance signals greater than 1.0 ( FIG. 4 ). Strong binding to BSA was also observed ( FIG. 4 ). Since HSA and BSA are 76% homologous on the amino acid level, it is not surprising that K8 antibody recognised both of these structurally related proteins. No cross-reactivity with other proteins was detected ( FIG. 4 ).  
      Secondly, the binding properties of the K8 antibody were tested in a soluble scFv ELISA. Production of the soluble scFv fragment was induced by IPTG as described by Harrison et al., (1996). To determine the expression levels of K8 scFv, the soluble antibody fragments were purified from the supernatant of 50 ml inductions using Protein A-Sepharose columns as described by Harlow and Lane, Antibodies: a Laboratory Manual, (1988) Cold Spring Harbor. OD 280  was then measured and the protein concentration calculated as described by Sambrook et al., (1989). K8 scFv was produced in supernatant at 19 mg/l.  
      A soluble scFv ELISA was then performed using known concentrations of the K8 antibody fragment. A 96-well plate was coated with 100 μl of HSA, BSA and μ-gal at 10 μg/ml and 100 μl of Protein A at 1 μg/ml concentration. 50 μl of the serial dilutions of the K8 scFv was applied and the bound antibody fragments were detected with Protein L-HRP. ELISA results confirmed the dual specific nature of the K8 antibody ( FIG. 5 ).  
      To confirm that binding to β-gal is determined by the V κ  domain and binding to HSA/BSA by the V H  domain of the K8 scFv antibody, the V κ  domain was cut out from K8 scFv DNA by Sa 1 I/NotI digestion and ligated into a SalI/NotI digested pIT2 vector containing dummy V H  chain ( FIGS. 1 and 2 ). Binding characteristics of the resulting clone K8V κ /dummy V H  were analysed by soluble scFv ELISA. Production of the soluble scFv fragments was induced by IPTG as described by Harrison et al., (1996) and the supernatant (50μ) containing scFvs assayed directly. Soluble scFv ELISA was performed as described in Example 1 and the bound scFvs were detected with Protein L-HRP. The ELISA results revealed that this clone was still able to bind μ-gal, whereas binding to BSA was abolished ( FIG. 6 ).  
     Example 3  
     Selection of Single V H  Domain Antibodies Antigens A and B and Single V κ  Domain Antibodies Directed Against Antigens C and D  
      This example describes a method for making single V H  domain antibodies directed against antigens A and B and single V κ  domain antibodies directed against antigens C and D by selecting repertoires of virgin single antibody variable domains for binding to these antigens in the absence of the complementary variable domains.  
      Selections and characterisation of the binding clones is performed as described previously (see Example 5, PCT/GB 02/003014). Four clones are chosen for further work: 
          VH1—Anti A V H       VH2—Anti B V H       VK1—Anti C V κ      VK2—Anti D V κ         

      The procedures described above in Examples 1-3 may be used, in a similar manner as that described, to produce dimer molecules comprising combinations of V H  domains (i.e., V H -V H  ligands) and combinations of V L  domains (V L -V L  ligands).  
     Example 4  
     Creation and Characterisation of the Dual Specific ScFv Antibodies (VH1/VH2 Directed against Antigens A and B and VK1/VK2 Directed against Antigens C and D).  
      This example demonstrates that dual specific ScFv antibodies (VH1/VH2 directed against antigens A and B and VK1/VK2 directed against antigens C and D) could be created by combining V κ  and V H  single domains selected against respective antigens in a ScFv vector.  
      To create dual specific antibody VH1/VH2, VH1 single domain is excised from variable domain vector 1 ( FIG. 7 ) by NcoI/XhoI digestion and ligated into NcoI/XhoI digested variable domain vector 2 ( FIG. 7 ) to create VH1/variable domain vector 2. VH2 single domain is PCR amplified from variable domain vector 1 using primers to introduce SalI restriction site to the 5′ end and NotI restriction site to the 3′ end. The PCR product is then digested with SalI/NotI and ligated into SalI/NotI digested VH1/variable domain vector 2 to create VH1/VH2/variable domain vector 2.  
      VK1/VK2/variable domain vector 2 is created in a similar way. The dual specific nature of the produced VH1/VH2 ScFv and VK1/VK2 ScFv is tested in a soluble ScFv ELISA as described previously (see Example 6, PCT/GB 02/003014). Competition ELISA is performed as described previously (see Example 8, PCT/GB 02/003014).  
      Possible outcomes: 
          VH1/VH2 ScFv is able to bind antigens A and B simultaneously     VK1/VK2 ScFv is able to bind antigens C and D simultaneously     VH1/VH2 ScFv binding is competitive (when bound to antigen A, VH1/VH2 ScFv cannot bind to antigen B)     VK1/VK2 ScFv binding is competitive (when bound to antigen C, VK1/VK2 ScFv cannot bind to antigen D)        

     Example 5  
     Construction of Dual Specific VH1/VH2 Fab and VK1NK2 Fab and Analysis of their Binding Properties  
      To create VH1/VH2 Fab, VH1 single domain is ligated into NcoI/XhoI digested CH vector ( FIG. 8 ) to create VH1/CH and VH2 single domain is ligated into SalI/NotI digested CK vector ( FIG. 9 ) to create VH2/CK. Plasmid DNA from VH1/CH and VH2/CK is used to co-transform competent  E. coli  cells as described previously (see Example 8, PCT/GB02/003014).  
      The clone containing VH1/CH and VH2/CK plasmids is then induced by IPTG to produce soluble VH1/VH2 Fab as described previously (see Example 8, PCT/GB 02/003014).  
      VK1/VK2 Fab is produced in a similar way.  
      Binding properties of the produced Fabs are tested by competition ELISA as described previously (see Example 8, PCT/GB 02/003014).  
      Possible outcomes: 
          VH1/VH2 Fab is able to bind antigens A and B simultaneously     VK1/VK2 Fab is able to bind antigens C and D simultaneously     VH1/VH2 Fab binding is competitive (when bound to antigen A, VH1NH2 Fab cannot bind to antigen B)     VK1/VK2 Fab binding is competitive (when bound to antigen C, VK1/VK2 Fab cannot bind to antigen D)        

     Example 6  
     Chelating dAb Dimers  
     SUMMARY  
      VH and VK homo-dimers are created in a dAb-linker-dAb format using flexible polypeptide linkers. Vectors were created in the dAb linker-dab format containing glycine-serine linkers of different lengths 3U:(Gly 4 Ser) 3 , 5U:(Gly 4 Ser) 5 , 7U:(Gly 4 Ser) 7 . Dimer libraries were created using guiding dAbs upstream of the linker: TAR1-5 (VK), TAR1-27(VK), TAR2-5(VH) or TAR2-6(VK) and a library of corresponding second dAbs after the linker. Using this method, novel dimeric dAbs were selected. The effect of dimerisation on antigen binding was determined by ELISA and BIAcore studies and in cell neutralisation and receptor binding assays. Dimerisation of both TAR1-5 and TAR1-27 resulted in significant improvement in binding affinity and neutralisation levels.  
      1.0 Methods  
      1.1 Library Generation  
      1.1.1 Vectors  
      pEDA3U, pEDA5U and pEDA7U vectors were designed to introduce different linker lengths compatible with the dAb-linker-dAb format. For pEDA3U, sense and anti-sense 73-base pair oligo linkers were annealed using a slow annealing program (95° C.-5 mins, 80° C.-10 mins, 70° C.-15 mins, 56° C-15 mins, 42° C. until use) in buffer containing 0.1M NaCl, 10 mM Tris-HCl pH7.4 and cloned using the Xhol and Notl restriction sites. The linkers encompassed 3 (Gly 4 Ser) units and a stuffer region housed between Sal1 and Not1 cloning sites (scheme 1). In order to reduce the possibility of monomeric dAbs being selected for by phage display, the stuffer region was designed to include 3 stop codons, a Sacl restriction site and a frame shift mutation to put the region out of frame when no second dAb was present. For pEDA5U and 7U due to the length of the linkers required, overlapping oligo-linkers were designed for each vector, annealed and elongated using Klenow. The fragment was then purified and digested using the appropriate enzymes before cloning using the Xhol and Notl restriction sites.  
                 
 
 1.1.2 Library Preparation 
 
      The N-terminal V gene corresponding to the guiding dAb was cloned upstream of the linker using Ncol and Xhol restriction sites. VH genes have existing compatible sites, however cloning VK genes required the introduction of suitable restriction sites. This was achieved by using modifying PCR primers (VK-DLIBF: 5′ cggccatggcgtcaacggacat (SEQ ID NO:377); VKXho1R: 5′ atgtgcgctcgagcgtttgattt 3′ (SEQ ID NO:378)) in 30 cycles of PCR amplification using a 2:1 mixture of SuperTaq (HTBiotechnology Ltd)and pfu turbo (Stratagene). This maintained the Ncol site at the 5′ end while destroying the adjacent Sall site and introduced the Xhol site at the 3′ end. 5 guiding dAbs were cloned into each of the 3 dimer vectors: TAR1-5 (VK), TAR1-27(VK), TAR2-5(VH), TAR2-6(VK) and TAR2-7(VK). All constructs were verified by sequence analysis.  
      Having cloned the guiding dAbs upstream of the linker in each of the vectors (pEDA3U, 5U and 7U): TAR1-5 (VK), TAR1-27(VK), TAR2-5(VH) or TAR2-6(VK) a library of corresponding second dAbs were cloned after the linker. To achieve this, the complimentary dAb libraries were PCR amplified from phage recovered from round 1 selections of either a VK library against Human TNFα (at approximately 1×10 6  diversity after round 1) when TAR1-5 or TAR1-27 are the guiding dAbs, or a VH or VK library against human p55 TNF receptor (both at approximately 1 x 105 diversity after round 1) when TAR2-5 or TAR2-6 respectively are the guiding dAbs. For VK libraries PCR amplification was conducted using primers in 30 cycles of PCR amplification using a 2:1 mixture of SuperTaq and pfu turbo. VH libraries were PCR amplified using primers in order to introduce a Sal1 restriction site at the 5′ end of the gene. The dAb library PCRs were digested with the appropriate restriction enzymes, ligated into the corresponding vectors down stream of the linker, using Sal1/Not1 restriction sites and electroporated into freshly prepared competent TG1 cells.  
      The titres achieved for each library are as follows: 
      TAR1-5: pEDA3U=4×10 8 , pEDA5U=8×10 7 , pEDA7U=1×10 8       TAR1-27: pEDA3U=6.2×10 8 , pEDA5U=1×10 8 , pEDA7U=1×9     TAR2h-5: pEDA3U=4×10 7 , pEDA5U=2×10 8 , pEDA7U=8×10 7       TAR2h-6: pEDA3U=7.4×10 8 , pEDA5U=1.2×10 8 , pEDA7U=2.2×10 8  
 
 1.2 Selections 
 
 1.2.1 TNFα
   

      Selections were conducted using human TNFα passively coated on immunotubes. Briefly, Immunotubes are coated overnight with 1-4 mls of the required antigen. The immunotubes were then washed 3 times with PBS and blocked with 2% milk powder in PBS for 1-2 hrs and washed a further 3 times with PBS. The phage solution is diluted in 2% milk powder in PBS and incubated at room temperature for 2 hrs. The tubes are then washed with PBS and the phage eluted with lmg/ml trypsin-PBS. Three selection strategies were investigated for the TAR1-5 dimer libraries. The first round selections were carried out in immunotubes using human TNFA coated at 1 μg/ml or 20 μg/ml with 20 washes in PBS 0.1%Tween. TG1 cells are infected with the eluted phage and the titres are determined (eg, Marks et al J Mol Biol. 1991 Dec. 5; 222(3):581-97, Richmann et al Biochemistry. 1993 Aug. 31; 32(34):8848-55).  
      The titres recovered were: 
          pEDA3U=2.8×10 7  (1 μg/ml TNF) 1.5×10 8  (20 μg/mlTNF),     pEDA5U=1.8×10 7  (1 μg/ml TNF), 1.6×10 8  (20 μg/ml TNF)     pEDA7U  32  8×10 6  (1 μg/ml TNF), 7×10 7  (20 μg/ml TNF).        

      The second round selections were carried out using 3 different methods. 
          1. In immunotubes, 20 washes with overnight incubation followed by a further 10 washes.     2. In immunotubes, 20 washes followed by lhr incubation at RT in wash buffer with (1 g/ml TNFα) and 10 further washes.        

      3. Selection on streptavidin beads using 33 pmoles biotinylated human TNFα (Henderikx et al., 2002 , Selection of antibodies against biotinylated antigens . Antibody Phage Display : Methods and protocols, Ed. O&#39;Brien and Atkin, Humana Press). Single clones from round 2 selections were picked into 96 well plates and crude supernatant preps were made in 2 ml 96 well plate format.  
                                   TABLE 1                                   Round 1                       Human           TNFαimmuno   Round 2   Round 2   Round 2           tube coating   selection   selection   selection           concentration   method 1   method 2   method 3                                                        pEDA3U    1 μg/ml     1 × 10 9     1.8 × 10 9     2.4 × 10 10         pEDA3U   20 μg/ml     6 × 10 9     1.8 × 10 10     8.5 × 10 10         pEDA5U    1 μg/ml     9 × 10 8     1.4 × 10 9     2.8 × 10 10         pEDA5U   20 μg/ml   9.5 × 10 9     8.5 × 10 9     2.8 × 10 10         pEDA7U    1 μg/ml   7.8 × 10 8     1.6 × 10 8       4 × 10 10         pEDA7U   20 μg/ml     1 × 10 10       8 × 10 9     1.5 × 10 10                    
 
 For TARI-27, selections were carried out as described previously with the following modifications. The first round selections were carried out in immunotubes using human TNFα coated at 1 μg/ml or 20 μg/ml with 20 washes in PBS 0.1%Tween. The second round selections were carried out in immunotubes using 20 washes with overnight incubation followed by a further 20 washes. Single clones from round 2 selections were picked into 96 well plates and crude supernatant preps were made in 2 ml 96 well plate format. 
 
      TAR1-27 titres are as follows:  
                               TABLE 2                                   Human                   TNFαimmunotube           coating conc   Round 1   Round 2                                                            pEDA3U    1 μg/ml     4 × 10 9       6 × 10 9             pEDA3U   20 μg/ml     5 × 10 9     4.4 × 10 10             pEDA5U    1 μg/ml   1.5 × 10 9     1.9 × 10 10             pEDA5U   20 μg/ml   3.4 × 10 9     3.5 × 10 10             pEDA7U    1 μg/ml   2.6 × 10 9       5 × 10 9             pEDA7U   20 μg/ml     7 × 10 9     1.4 × 10 10                        
 
 1.2.2 TNF RECEPTOR 1 (p55 RECEPTOR; TAR2) 
 
      Selections were conducted as described previously for the TAR2h-5 libraries only. 3 rounds of selections were carried out in immunotubes using either 1 μg/ml human p55 TNF receptor or 10 μg/ml human p55 TNF receptor with 20 washes in PBS 0.1%Tween with overnight incubation followed by a further 20 washes. Single clones from round 2 and 3 selections were picked into 96 well plates and crude supernatant preps were made in 2 ml 96 well plate format.  
      TAR2h-5 Titres are as Follows:  
                                   TABLE 3                                   Round 1 human                       p55 TNF           receptor           immunotube           coating           concentration   Round 1   Round 2   Round 3                                                        pEDA3U    1 μg/ml   2.4 × 10 6     1.2 × 10 7     1.9 × 10 9         pEDA3U   10 μg/ml   3.1 × 10 7       7 × 10 7       1 × 10 9         pEDA5U    1 μg/ml   2.5 × 10 6     1.1 × 10 7     5.7 × 10 8         pEDA5U   10 μg/ml   3.7 × 10 7     2.3 × 10 8     2.9 × 10 9         pEDA7U    1 μg/ml   1.3 × 10 6     1.3 × 10 7     1.4 × 10 9         pEDA7U   10 μg/ml   1.6 × 10 7     1.9 × 10 7       3 × 10 10                    
 
 1.3 Screening 
 
      Single clones from round 2 or 3 selections were picked from each of the 3U, 5U and 7U libraries from the different selections methods, where appropriate. Clones were grown in 2×TY with 100 μg/ml ampicillin and 1% glucose overnight at 37° C. A 1/100 dilution of this culture was inoculated into 2 mls of 2×TY with 100 μg/ml ampicillin and 0.1% glucose in 2 ml, 96 well plate format and grown at 37° C. shaking until OD600 was approximately 0.9. The culture was then induced with 1 mM IPTG overnight at 30° C. The supernatants were clarified by centrifugation at 4000 rpm for 15 mins in a sorval plate centrifuge. The supernatant preps the used for initial screening.  
      1.3.1 ELISA  
      Binding activity of dimeric recombinant proteins was compared to monomer by Protein A/L ELISA or by antigen ELISA. Briefly, a 96 well plate is coated with antigen or Protein A/L overnight at 4° C. The plate washed with 0.05% Tween-PBS, blocked for 2 hrs with 2% Tween-PBS. The sample is added to the plate incubated for 1 hr at room temperature. The plate is washed and incubated with the secondary reagent for 1 hr at room temperature. The plate is washed and developed with TMB substrate. Protein A/L-HRP or India-HRP was used as a secondary reagent. For antigen ELISAs, the antigen concentrations used were 1 g/ml in PBS for Human TNFα and human THF receptor 1. Due to the presence of the guiding dAb in most cases dimers gave a positive ELISA signal therefore off rate determination was examined by BlAcore.  
      1.3.2 BIAcore  
      BIAcore analysys was conducted for TAR1-5 and TAR2h-5 clones. For screening, Human TNFα was coupled to a CM5 chip at high density (approximately 10000 RUs). 50 μl of Human TNFα (50 μg/ml) was coupled to the chip at 5 μl/min in acetate buffer—pH5.5. Regeneration of the chip following analysis using the standard methods is not possible due to the instability of Human TNFα, therefore after each sample was analysed, the chip was washed for lOmins with buffer.  
      For TAR1-5, clones supernatants from the round 2 selection were screened by BIAcore. 48 clones were screened from each of the 3U, 5U and 7U libraries obtained using the following selection methods: 
      R1: 1 μg/ml human TNFα immunotube, R2 1 μg/ml human TNFα immunotube, overnight wash.     R1: 20 μg/ml human TNFa immunotube, R2 20 μg/ml human TNFα immunotube, overnight wash.     R1: 1 μg/ml human TNFA immunotube, R2 33 pmoles biotinylated human TNFα on beads.     R1: 20 μg/ml human TNFA immunotube, R2 33 pmoles biotinylated human TNFα beads.    

      For screening, human p55 TNF receptor was coupled to a CM5 chip at high density (approximately 4000 RUs). 100 μl of human p55 TNF receptor (10 μg/ml) was coupled to the chip at 5 μl/min in acetate buffer—pH5.5. Standard regeneration conditions were examined (glycine pH2 or pH3) but in each case antigen was removed from the surface of the chip therefore as with TNFα, therefore after each sample was analysed, the chip was washed for 10 mins with buffer.  
      For TAR2-5, clones supernatants from the round 2 selection were screened. 48 clones were screened from each of the 3U, 5U and 7U libraries, using the following selection methods: 
      R1: 1 μg/ml human p55 TNF receptor immunotube, R2 1 μg/ml human p55 TNF receptor immunotube, overnight wash.     R1: 10 μg/ml human p55 TNF receptor immunotube, R2 10 μg/ml human p55 TNF receptor immunotube, overnight wash. 
 
 1.3.3 Receptor and Cell Assays 
   

      The ability of the dimers to neutralise in the receptor assay was conducted as follows:  
      Receptor Binding  
      Anti-TNF dAbs were tested for the ability to inhibit the binding of TNF to recombinant TNF receptor 1 (p55). Briefly, Maxisorp plates were incubated overnight with 30 mg/ml anti-human Fc mouse monoclonal antibody (Zymed, San Francisco, USA). The wells were washed with phosphate buffered saline (PBS) containing 0.05% Tween-20 and then blocked with 1% BSA in PBS before being incubated with 100 ng/ml TNF receptor 1 Fc fusion protein (R&amp;D Systems, Minneapolis, USA). Anti-TNF dAb was mixed with TNF which was added to the washed wells at a final concentration of 10 ng/ml. TNF binding was detected with 0.2 mg/ml biotinylated anti-TNF antibody (HyCult biotechnology, Uben, Netherlands) followed by 1 in 500 dilution of horse radish peroxidase labelled streptavidin (Amersham Biosciences, UK) and then incubation with TMB substrate (KPL, Gaithersburg, USA). The reaction was stopped by the addition of HCl and the absorbance was read at 450 nm. Anti-TNF dAb activity lead to a decrease in TNF binding and therefore a decrease in absorbance compared with the TNF only control.  
      L929 Cytotoxicity Assay Anti-TNF dAbs were also tested for the ability to neutralise the cytotoxic activity of TNF on mouse L929 fibroblasts (Evans, T. (2000) Molecular Biotechnology 15, 243-248). Briefly, L929 cells plated in microtitre plates were incubated overnight with anti-TNF dAb, 100 pg/ml TNF and 1 mg/ml actinomycin D (Sigma, Poole, UK). Cell viability was measured by reading absorbance at 490 nm following an incubation with [3-(4,5-dimethylthiazol-2-yl)-5-(3-carbboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (Promega, Madison, USA). Anti-TNF dAb activity lead to a decrease in TNF cytotoxicity and therefore an increase in absorbance compared with the TNF only control.  
      In the initial screen, supernatants prepared for BIAcore analysis, described above, were also used in the receptor assay. Further analysis of selected dimers was also conducted in the receptor and cell assays using purified proteins.  
      HeLa IL-8 Assay  
      Anti-TNFR1 or anti-TNF alpha dAbs were tested for the ability to neutralise the induction of IL-8 secretion by TNF in HeLa cells (method adapted from that of Akeson, L. et al (1996) Journal of Biological Chemistry 271, 30517-30523, describing the induction of IL-8 by IL-1 in HUVEC; here we look at induction by human TNF alpha and we use HeLa cells instead of the HUVEC cell line). Briefly, HeLa cells plated in microtitre plates were incubated overnight with dAb and 300 pg/ml TNF. Post incubation the supernatant was aspirated off the cells and IL-8 concentration measured via a sandwich ELISA (R&amp;D Systems). Anti-TNFR1 dAb activity lead to a decrease in IL-8 secretion into the supernatant compared with the TNF only control.  
      The L929 assay is used throughout the following experiments; however, the use of the HeLa IL-8 assay is preferred to measure anti-TNF receptor 1 (p55) ligands; the presence of mouse p55 in the L929 assay poses certain limitations in its use.  
      1.4 Sequence Analysis  
      Dimers that proved to have interesting properties in the BIAcore and the receptor assay screens were sequenced. Sequences are detailed in the sequence listing.  
      1.5 Formatting  
      1.5.1 TAR1-5-19 dimers  
      The TAR1-5 dimers that were shown to have good neutralisation properties were re-formatted and analysed in the cell and receptor assays. The TAR1-5 guiding dab was substituted with the affinity matured clone TAR1-5-19. To achieve this TAR1-5 was cloned out of the individual dimer pair and substituted with TAR1-5-19 that had been amplified by PCR. In addition, TAR1-5-19 homodimers were also constructed in the 3U, 5U and 7U vectors. The N terminal copy of the gene was amplified by PCR and cloned as described above and the C-terminal gene fragment was cloned using existing Sal1 and Not1 restriction sites.  
      1.5.2 Mutagenesis  
      The amber stop codon present in dAb2, one of the C-terminal dAbs in the TAR1-5 dimer pairs was mutated to a glutamine by site-directed mutagenesis.  
      1.5.3 Fabs  
      The dimers containing TAR1-5 or TAR1-5-19 were re-formatted into Fab expression vectors. dAbs were cloned into expression vectors containing either the CK or CH genes using Sfi1 and Not1 restriction sites and verified by sequence analysis. The CK vector is derived from a pUC based ampicillin resistant vector and the CH vector is derived from a pACYC chloramphenicol resistant vector. For Fab expression the dAb-CH and dAb-CK constructs were co-transformed into HB2151 cells and grown in 2×TY containing 0.1% glucose, 100 μg/ml ampicillin and 10 μg/ml chloramphenicol.  
      1.5.3 Hinge Dimerisation  
      Dimerisation of dAbs via cystine bond formation was examined. A short sequence of amino acids EPKSGDKTHTCPPCP (SEQ ID NO:379) a modified form of the human IgGC1 hinge was engineered at the C terminal region on the dAb. An oligo linker encoding for this sequence was synthesised and annealed, as described previously. The linker was cloned into the pEDA vector containing TAR1-5-19 using Xho1 and Not1 restriction sites. Dimerisation occurs in situ in the periplasm.  
      1.6 Expression and Purification  
      1.6.1 Expression  
      Supernatants were prepared in the 2 ml, 96-well plate format for the initial screening as described previously. Following the initial screening process selected dimers were analysed further. Dimer constructs were expressed in TOP10F′ or HB2151 cells as supernatants. Briefly, an individual colony from a freshly streaked plate was grown overnight at 37° C. in 2×TY with 100 μg/ml ampicillin and 1% glucose. A 1/100 dilution of this culture was inoculated into 2×TY with 100 μg/ml ampicillin and 0.1% glucose and grown at 37° C. shaking until OD600 was approximately 0.9. The culture was then induced with ImM IPTG overnight at 30° C. The cells were removed by centrifugation and the supernatant purified with protein A or L agarose.  
      Fab and cysteine hinge dimers were expressed as periplasmic proteins in HB2152 cells. A 1/100 dilution of an overnight culture was inoculated into 2×TY with 0.1% glucose and the appropriate antibiotics and grown at 30° C. shaking until OD600 was approximately 0.9. The culture was then induced with 1 mM IPTG for 3-4 hours at 25° C. The cells were harvested by centrifugation and the pellet resuspended in periplasmic preparation buffer (30 mM Tris-HCl pH8.0, 1 mM EDTA, 20% sucrose). Following centrifugation the supernatant was retained and the pellet resuspended in 5 mM MgSO 4 . The supernatant was harvested again by centrifugation, pooled and purified.  
      1.6.2 Protein A/L Purification  
      Optimisation of the purification of dimer proteins from Protein L agarose (Affitech, Norway) or Protein A agarose (Sigma, UK) was examined. Protein was eluted by batch or by column elution using a peristaltic pump. Three buffers were examined 0.1M Phosphate-citrate buffer pH2.6, 0.2M Glycine pH2.5 and 0.1M Glycine pH2.5. The optimal condition was determined to be under peristaltic pump conditions using 0.1M Glycine pH2.5 over 10 column volumes. Purification from protein A was conducted peristaltic pump conditions using 0.1M Glycine pH2.5.  
      1.6.3 FPLC Purification  
      Further purification was carried out by FPLC analysis on the AKTA Explorer 100 system (Amersham Biosciences Ltd). TAR1-5 and TAR1-5-19 dimers were fractionated by cation exchange chromatography (1 ml Resource S—Amersham Biosciences Ltd) eluted with a 0-1M NaCl gradient in 50 mM acetate buffer pH4. Hinge dimers were purified by ion exchange (Iml Resource Q Amersham Biosciences Ltd) eluted with a 0-1M NaCl gradient in 25 mMTris HCl pH 8.0. Fabs were purified by size exclusion chromatography using a superose 12 (Amersham Biosciences Ltd ) column run at a flow rate of 0.5 ml/min in PBS with 0.05% tween. Following purification samples were concentrated using vivaspin 5K cut off concentrators (Vivascience Ltd).  
      2.0 Results  
      2.1 TAR1-5 Dimers  
      6×96 clones were picked from the round 2 selection encompassing all the libraries and selection conditions. Supernatant preps were made and assayed by antigen and Protein L ELISA, BlAcore and in the receptor assays. In ELISAs, positive binding clones were identified from each selection method and were distributed between 3U, 5U and 7U libraries. However, as the guiding dAb is always present it was not possible to discriminate between high and low affinity binders by this method therefore BIAcore analysis was conducted.  
      BlAcore analysis was conducted using the 2 ml supernatants. BIAcore analysis revealed that the dimer Koff rates were vastly improved compared to monomeric TAR1-5. Monomer Koff rate was in the range of 10 −1 M compared with dimer Koff rates which were in the range of 10 −3 -10 −4 M. 16 clones that appeared to have very slow off rates were selected, these came from the 3U, 5U and 7U libraries and were sequenced. In addition the supernatants were analysed for the ability to neutralise human TNFa in the receptor assay.  
      6 lead clones (d1-d6 below) that neutralised in these assays and have been sequenced. The results shows that out of the 6 clones obtained there are only 3 different second dAbs (dAb1, dAb2 and dAb3) however where the second dAb is found more than once they are linked with different length linkers. 
      TAR1-5d1: 3U linker  2   nd  dAb=dAb1−1 μg/ml Ag immunotube overnight wash     TAR1-5d2: 3U linker 2 nd  dAb=dAb2−1 μg/ml Ag immunotube overnight wash     TAR1-5d3: 5U linker 2 nd  dAb=dAb2−1 μg/ml Ag immunotube overnight wash     TAR1-5d4: 5U linker 2 nd  dAb=dAb3−20 g/ml Ag immunotube overnight wash     TAR1-5d5: 5U linker 2 nd  dAb=dAb−20 μg/ml Ag immunotube overnight wash     TAR1-5d6: 7U linker 2 nd  dAb=dAb1−R1:1 μg/ml Ag immunotube ove rnight wash , R2:beads    

      The 6 lead clones were examined further. Protein was produced from the periplasm and supernatant, purified with protein L agarose and examined in the cell and receptor assays. The levels of neutralisation were variable (Table 1). The optimal conditions for protein preparation were determined. Protein produced from HB2151 cells as supernatants gave the highest yield (approximately 10 mgs/L of culture). The supernatants were incubated with protein L agarose for 2 hrs at room temperature or overnight at 4° C. The beads were washed with PBS/NaCl and packed onto an FPLC column using a peristaltic pump. The beads were washed with 10 column volumes of PBS/NaCl and eluted with 0.1M glycine pH2.5. In general, dimeric protein is eluted after the monomer.  
      TAR1-5d1-6 dimers were purified by FPLC. Three species were obtained, by FPLC purification and were identified by SDS PAGE. One species corresponds to monomer and the other two species corresponds to dimers of different sizes. The larger of the two species is possibly due to the presence of C terminal tags. These proteins were examined in the receptor assay. The data presented in table 1 represents the optimum results obtained from the two dimeric species ( FIG. 11 )  
      The three second dAbs from the dimer pairs (ie, dAb1, dAb2 and dAb3) were cloned as monomers and examined by ELISA and in the cell and receptor assay. All three dAbs bind specifically to TNF by antigen ELISA and do not cross react with plastic or BSA. As monomers, none of the dAbs neutralise in the cell or receptor assays.  
      2.1.2 TAR1-5-19 dimers  
      TAR1-5-19 was substituted for TAR1-5 in the 6 lead clones. Analysis of all TAR1-5-19 dimers in the cell and receptor assays was conducted using total protein (protein L purified only) unless otherwise stated (Table 2). TAR1-5-19d4 and TARl-5-19d3 have the best ND 50  (˜5 nM) in the cell assay, this is consistent with the receptor assay results and is an improvement over TAR1-5-19 monomer (ND 50 ˜30 nM). Although purified TAR1-5 dimers give variable results in the receptor and cell assays TAR1-5-19 dimers were more consistent. Variability was shown when using different elution buffers during the protein purification. Elution using 0.1M Phosphate-citrate buffer pH2.6 or 0.2M Glycine pH2.5 although removing all protein from the protein L agarose in most cases rendered it less functional.  
      TAR1-5-19d4 was expressed in the fermenter and purified on cation exchange FPLC to yield a completely pure dimer. As with TAR1-5d4 three species were obtained, by FPLC purification corresponding to monomer and two dimer species. This dimer was amino acid sequenced. TAR1-5-19 monomer and TAR1-5-19d4 were then examined in the receptor assay and the resulting IC50 for monomer was 30 nM and for dimer was 8 nM. The results of the receptor assay comparing TAR1-5-19 monomer, TAR1-5-19d4 and TAR1-5d4 is shown in  FIG. 10 .  
      TAR1-5-19 homodimers were made in the 3U, 5U and 7U vectors, expressed and purified on Protein L. The proteins were examined in the cell and receptor assays and the resulting IC 50 s (for receptor assay) and ND 50 s (for cell assay) were determined (table 3,  FIG. 12 ).  
      2.2 Fabs  
      TAR1-5 and TAR1-5-19 dimers were also cloned into Fab format, expressed and purified on protein L agarose. Fabs were assessed in the receptor assays (Table 4). The results showed that for both TAR1-5-19 and TAR1-5 dimers the neutralisation levels were similar to the original Gly 4 Ser linker dimers from which they were derived. A TAR1-5-19 Fab where TAR1-5-19 was displayed on both CH and CK was expressed, protein L purified and assessed in the receptor assay. The resulting IC50 was approximately 1 nM.  
      2.3 TAR1-27 Dimers  
      3×96 clones were picked from the round 2 selection encompassing all the libraries and selection conditions. 2ml supernatant preps were made for analysis in ELISA and bioassays. Antigen ELISA gave 71 positive clones. The receptor assay of crude supernatants yielded 42 clones with inhibitory properties (TNF binding 0-60%). In the majority of cases inhibitory properties correlated with a strong ELISA signal. 42 clones were sequenced, 39 of these have unique second dAb sequences. The 12 dimers that gave the best inhibitory properties were analysed further.  
      The 12 neutralising clones were expressed as 200 ml supernatant preps and purified on protein L. These were assessed by protein L and antigen ELISA, BIAcore and in the receptor assay. Strong positive ELISA signals were obtained in all cases. BIAcore analysis revealed all clones to have fast on and off rates. The off rates were improved compared to monomeric TAR1-27, however the off rate of TAR1-27 dimers was faster (Koff is approximately in the range of 10 −1  and 10 −2 M) than the TAR1-5 dimers examined previously (Koff is approximately in the range of 10 −3 - 10 −4 M). The stability of the purified dimers was questioned and therefore in order to improve stability, the addition on 5% glycerol, 0.5% Triton X100 or 0.5% NP40 (Sigrna) was included in the purification of 2 TAR1-27 dimers (d2 and d16). Addition of NP40 or Triton X100 ™ improved the yield of purified product approximately 2 fold. Both dimers were assessed in the receptor assay. TAR1-27d2 gave IC50 of ˜30 nM under all purification conditions. TAR1-27d16 showed no neutralisation effect when purified without the use of stabilising agents but gave an IC50 of ˜50 nM when purified under stabilising conditions. No further analysis was conducted.  
      2.4 TAR2-5 Dimers  
      3×96 clones were picked from the second round selections encompassing all the libraries and selection conditions. 2 ml supernatant preps were made for analysis. Protein A and antigen ELISAs were conducted for each plate. 30 interesting clones were identified as having good off-rates by BIAcore (Koff ranges between 10 −2 -10 −3 M). The clones were sequenced and 13 unique dimers were identified by sequence analysis.  
               TABLE 4                          TAR1-5 dimers.                                                 Protein   Elution   Receptor/       Dimer   Cell type   Purification   Fraction   conditions   Cell assay               TAR1-5d1   HB2151   Protein L + FPLC   small dimeric   0.1M glycine   RA˜30 nM                   species   pH 2.5       TAR1-5d2   HB2151   Protein L + FPLC   small dimeric   0.1M glycine   RA˜50 nM                   species   pH 2.5       TAR1-5d3   HB2151   Protein L + FPLC   large dimeric   0.1M glycine   RA˜300 nM                   species   pH 2.5       TAR1-5d4   HB2151   Protein L + FPLC   small dimeric   0.1M glycine   RA˜3 nM                   species   pH 2.5       TAR1-5d5   HB2151   Protein L + FPLC   large dimeric   0.1M glycine   RA˜200 nM                   species   pH 2.5       TAR1-5d6   HB2151   Protein L + FPLC   Large dimeric   0.1M glycine   RA˜100 nM                   species   pH 2.5                 *note dimer 2 and dimer 3 have the same second dAb (called dAb2), however have different linker lengths (d2 = (Gly 4 Ser) 3 , d3 = (Gly 4 Ser) 3 ). dAb1 is the partner dAb to dimers 1, 5 and 6. dAb3 is the partner dAb to dimer4. None of the partner dAbs neutralise alone. FPLC purification is by cation exchange unless otherwise stated. The optimal dimeric species for each dimer obtained by FPLC was determined in these assays.             
 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                   
               
               
                 TAR1-5-19 dimers 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Protein 
                 Elution 
                 Receptor/ 
               
               
                 Dimer 
                 Cell type 
                 Purification 
                 Fraction 
                 conditions 
                 Cell assay 
               
               
                   
               
               
                 TAR1-5-19 d1 
                 TOP10F′ 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜15 nM 
               
               
                   
                   
                   
                 protein 
                 pH 2.0 
               
               
                 TAR1-5-19 d2 
                 TOP10F′ 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜2 nM 
               
               
                 (no stop codon) 
                   
                   
                 protein 
                 pH 2.0 + 0.05% 
               
               
                   
                   
                   
                   
                 NP40 
               
               
                 TAR1-5-19d3 
                 TOP10F′ 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜8 nM 
               
               
                 (no stop codon) 
                   
                   
                 protein 
                 pH 2.5 + 0.05% 
               
               
                   
                   
                   
                   
                 NP40 
               
               
                 TAR1-5-19d4 
                 TOP10F′ 
                 Protein L + FPLC 
                 FPLC 
                 0.1M glycine 
                 RA˜2-5 nM 
               
               
                   
                   
                   
                 purified 
                 pH 2.0 
                 CA˜12 nM 
               
               
                   
                   
                   
                 fraction 
               
               
                 TAR1-5-19d5 
                 TOP10F′ 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜8 nM 
               
               
                   
                   
                   
                 protein 
                 pH 2.0 + NP40 
                 CA˜10 nM 
               
               
                 TAR1-5-19 d6 
                 TOP10F′ 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜10 nM 
               
               
                   
                   
                   
                 protein 
                 pH 2.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                   
               
               
                 TAR1-5-19 homodimers 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Protein 
                 Elution 
                 Receptor/Cell 
               
               
                 Dimer 
                 Cell type 
                 Purification 
                 Fraction 
                 conditions 
                 assay 
               
               
                   
               
               
                 TAR1-5-19 3U 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜20 nM 
               
               
                 homodimer 
                   
                   
                 protein 
                 pH 2.5 
                 CA˜30 nM 
               
               
                 TAR1-5-19 5U 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜2 nM 
               
               
                 homodimer 
                   
                   
                 protein 
                 pH 2.5 
                 CA˜3 nM 
               
               
                 TAR1-5-19 7U 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜10 nM 
               
               
                 homodimer 
                   
                   
                 protein 
                 pH 2.5 
                 CA˜15 nM 
               
               
                 TAR1-5-19 cys 
                 HB2151 
                 Protein L + FPLC 
                 FPLC 
                 0.1M glycine 
                 RA˜2 nM 
               
               
                 hinge 
                   
                   
                 purified 
                 pH 2.5 
               
               
                   
                   
                   
                 dimer 
               
               
                   
                   
                   
                 fraction 
               
               
                 TAR1-5-19CH/ 
                 HB2151 
                 Protein 
                 Total 
                 0.1M glycine 
                 RA˜1 nM 
               
               
                 TAR1-5-19 CK 
                   
                   
                 protein 
                 pH 2.5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                   
               
               
                 TAR1-5/TAR1-5-19 Fabs 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Cell 
                 Purifi- 
                 Protein 
                 Elution 
                 Receptor/ 
               
               
                 Dimer 
                 type 
                 cation 
                 Fraction 
                 conditions 
                 Cell assay 
               
               
                   
               
               
                 TAR1-5CH/ 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M citrate 
                 RA˜90 nM 
               
               
                 dAb1 CK 
                   
                   
                 protein 
                 pH 2.6 
               
               
                 TAR1-5CH/ 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜30 nM 
               
               
                 dAb2 CK 
                   
                   
                 protein 
                 pH 2.5 
                 CA˜60 nM 
               
               
                 dAb3CH/ 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M citrate 
                 RA˜100 nM 
               
               
                 TAR1-5CK 
                   
                   
                 protein 
                 pH 2.6 
               
               
                 TAR1-5- 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜6 nM 
               
               
                 19CH/dAb1 
                   
                   
                 protein 
                 pH 2.0 
               
               
                 CK 
               
               
                 dAb1 CH/ 
                 HB2151 
                 Protein L 
                 0.1M 
                 Myc/flag 
                 RA˜6 nM 
               
               
                 TAR1-5- 
                   
                   
                 glycine 
               
               
                 19CK 
                   
                   
                 pH 2.0 
               
               
                 TAR1-5- 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜8 nM 
               
               
                 19CH/dAb2 
                   
                   
                 protein 
                 pH 2.0 
                 CA˜12 nM 
               
               
                 CK 
               
               
                 TAR1-5- 
                 HB2151 
                 Protein L 
                 Total 
                 0.1M glycine 
                 RA˜3 nM 
               
               
                 9CH/ 
                   
                   
                 protein 
                 pH 2.0 
               
               
                 dAb3CK 
               
               
                   
               
            
           
         
       
     
     Example 7  
     dAb Dimerisation by Terminal Cysteine Linkage  
      Summary  
      For dAb dimerisation, a free cysteine has been engineered at the C-terminus of the protein. When expressed the protein forms a dimer which can be purified by a two step purification method.  
      PCR Construction of TAR1-5-19CYS Dimer  
      See example 8 describing the dAb trimer. The trimer protocol gives rise to a mixture of monomer, dimer and trimer.  
      Expression and Purification of TAR1-5-19CYS Dimer  
      The dimer was purified from the supernatant of the culture by capture on Protein L agarose as outlined in the example 8.  
      Separation of TAR1-5-19CYS Monomer from the TAR1-5-19CYS Dimer  
      Prior to cation exchange separation, the mixed monomer/dimer sample was buffer exchanged into 50 mM sodium acetate buffer pH 4.0 using a PD-10 column (Amersham Pharmacia), following the manufacturer&#39;s guidelines. The sample was then applied to a 1 mL Resource S cation exchange column (Amersham Pharmacia), which had been pre-equilibrated with 50 mM sodium acetate pH 4.0. The monomer and dimer were separated using the following salt gradient in 50 mM sodium acetate pH 4.0: 
      150 to 200 mM sodium chloride over 15 column volumes     200 to 450 mM sodium chloride over 10 column volumes     450 to 1000 mM sodium chloride over 15 column volumes    

      Fractions containing dimer only were identified using SDS-PAGE and then pooled and the pH increased to 8 by the addition of ⅕ volume of 1M Tris pH 8.0.  
      In Vitro Functional Binding Assay: TNF Receptor Assay and Cell Assay  
      The affinity of the dimer for human TNFα was determined using the TNF receptor and cell assay. IC50 in the receptor assay was approximately 0.3-0.8 nM; ND50 in the cell assay was approximately 3-8 nM.  
      Other Possible TAR1-5-19CYS Dimer Formats  
      PEG Dimers and Custom Synthetic Maleimide Dimers  
      Nektar (Shearwater) offer a range of bi-maleimide PEGs [mPEG2-(MAL)2 or mPEG-(MAL)2] which would allow the monomer to be formatted as a dimer, with a small linker separating the dAbs and both being linked to a PEG ranging in size from 5 to 40 kDa. It has been shown that the 5 kDa mPEG-(MAL)2 (ie, [TAR1-5-19]-Cys-maleimide-PEG×2, wherein the maleimides are linked together in the dimer) has an affinity in the TNF receptor assay of ˜1-3 nM. Also the dimer can also be produced using TMEA (Tris[2-maleimidoethyl]amine) (Pierce Biotechnology) or other bi-functional linkers.  
      It is also possible to produce the disulphide dimer using a chemical coupling procedure using 2,2′-dithiodipyridine (Sigma Aldrich) and the reduced monomer.  
      Addition of a Polypeptide Linker or Hinge to the C-Terminus of the dAb.  
      A small linker, either (Gly 4 Ser) n  where n=1 to 10, eg, 1, 2, 3, 4, 5, 6 or 7, an immunoglobulin (eg, IgG hinge region or random peptide sequence (eg, selected from a library of random peptide sequences) can be engineered between the dAb and the terminal cysteine residue. This can then be used to make dimers as outlined above.  
     Example 8  
     dAb Trimerisation  
      Summary  
      For dAb trimerisation, a free cysteine is required at the C-terminus of the protein. The cysteine residue, once reduced to give the free thiol, can then be used to specifically couple the protein to a trimeric maleimide molecule, for example TMEA (Tris[2-maleimidoethyl]amine).  
      PCR Construction of TAR1-5-19CYS  
      The following oligonucleotides were used to specifically PCR TAR1-5-19 with a SalI and BamHI sites for cloning and also to introduce a C-terrninal cysteine residue:  
                                                         SalI                         ˜˜˜˜˜˜˜˜       1   Trp Ser Ala Ser Thr Asp* Ile Gln Met Thr Gln Ser Pro Ser Ser Leu Ser Ala Ser Val           TGG AGC GCG TCG ACG GAC ATC CAG ATG ACC CAG TCT CCA TCC TCT CTG TCT GCA TCT GTA           ACC TCG CGC AGC TGC CTG TAG GTC TAC TGG GTC AGA GGT AGG AGA GAC AGA CGT AGA CAT               61   Gly Asp Arg Val Thr Ile Thr Cys Arg Ala Ser Gln Ser Ile Asp Ser Tyr Leu His Trp           GGA GAC CGT GTC ACC ATC ACT TGC CGG GCA AGT CAG AGC ATT GAT AGT TAT TTA CAT TGG           CCT CTG GCA CAG TGG TAG TGA ACG GCC CGT TCA GTC TCG TAA CTA TCA ATA AAT GTA ACC               121   Tyr Gln Gln Lys Pro Gly Lys Ala Pro Lys Leu Leu Ile Tyr Ser Ala Ser Glu Leu Gln           TAC CAG GAG AAA CCA GGG AAA GCC CCT AAG CTC CTG ATC TAT AGT GCA TCC GAG TTG CAA           ATG GTC GTC TTT GGT CCC TTT CGG GGA TTC GAG GAC TAG ATA TCA CGT AGG CTC AAC GTT               181   Ser Gly Val Pro Ser Arg Phe Ser Gly Ser Gly Ser Gly Thr Asp Phe Thr Leu Thr Ile           AGT GGG GTC CCA TCA CGT TTC AGT GGC AGT GGA TCT GGG ACA GAT TTC ACT CTC ACC ATC           TCA CCC CAG GGT AGT GCA AAG TCA CCG TCA CCT AGA CCC TGT CTA AAG TGA GAG TGG TAG               241   Ser Ser Leu Gln Pro Glu Asp Phe Ala Thr Tyr Tyr Cys Gln Gln Val Val Trp Arg Pro           AGC AGT CTG CAA CCT GAA GAT TTT GCT ACG TAC TAC TGT CAA CAG GTT GTG TGG CGT CCT           TCG TCA GAC GTT GGA CTT CTA AAA CGA TGC ATG ATG ACA GTT GTC CAA CAC ACC GCA GGA                                                                                   BamHI                                                                           ˜˜˜˜˜˜˜˜       301   Phe Thr Phe Gly Gln Gly Thr Lys Val Glu Ile Lys Arg Cys *** *** Gly Ser Gly           TTT ACG TTC GGC CAA GGG ACC AAG GTG GAA ATC AAA CGG TGC TAA TAA GGA TCC GGC           AAA TGC AAG CCG GTT CCC TGG TTC CAC CTT TAG TTT GCC ACG ATT ATT CCT AGG CCG                 (* start of TAR1-5-19CYS sequence; TAR1-5-19CYS amino acid sequence (SEQ ID NO:293; TAR1-5-19CYS nucleotide sequences (SEQ ID NO:294, coding strand; SEQ ID NO:295, noncoding strand))             
 
     
       
         
           
               
               
               
            
               
                   
                   
               
               
                   
                 Forward primer 
                   
               
            
           
           
               
               
               
            
               
                   
                 (SEQ ID NO:296) 
                   
               
            
           
           
               
               
               
            
               
                   
                 5′-TGGAGCGCGTCGACGGACATCCAGATGACCCAGTCTCCA-3′ 
                   
               
               
                   
                   
               
               
                   
                 Reverse primer 
               
            
           
           
               
               
               
            
               
                   
                 (SEQ ID NO:297) 
                   
               
            
           
           
               
               
               
            
               
                   
                 5′-TTAGCAGCCGGATCCTTATTAGCACCGTTTGATTTCCAC-3′ 
                   
               
            
           
         
       
     
      The PCR reaction (50 μL volume) was set up as follows: 200 μM dNTPs, 0.4 μM of each primer, 5 μL of 10×PfuTurbo buffer (Stratagene), 100 ng of template plasmid (encoding TAR1-5-19), 1 μL of PfuTurbo enzyme (Stratagene) and the volume adjusted to 50 μL using sterile water. The following PCR conditions were used: initial denaturing step 94° C. for 2 mins, then 25 cycles of 94° C. for 30 secs, 64° C. for 30 sec and 72° C. for 30 sec. A final extension step was also included of 72° C. for 5 mins. The PCR product was purified and digested with SalI and BamHI and ligated into the vector which had also been cut with the same restriction enzymes. Correct clones were verified by DNA sequencing.  
      Expression and Purification of TAR1-5-19CYS  
      TAR1-5-19CYS vector was transformed into BL21 (DE3) pLysS chemically competent cells (Novagen) following the manufacturer&#39;s protocol. Cells carrying the dAb plasmid were selected for using 100 g/mL carbenicillin and 37 μg/mL chloramphenicol. Cultures were set up in 2L baffled flasks containing 500 mL of terrific broth (Sigma-Aldrich), 100 μg/mL carbenicillin and 37 μg/mL chloramphenicol. The cultures were grown at 30° C. at 200 rpm to an O.D.600 of 1-1.5 and then induced with 1 mM IPTG (isopropyl-beta-D-thiogalactopyranoside, from Melford Laboratories). The expression of the dAb was allowed to continue for 12-16 hrs at 30° C. It was found that most of the dAb was present in the culture media. Therefore, the cells were separated from the media by centrifugation (8,000×g for 30 mins), and the supernatant used to purify the dAb. Per litre of supernatant, 30 mL of Protein L agarose (Affitech) was added and the dAb allowed to batch bind with stirring for 2 hours. The resin was then allowed to settle under gravity for a further hour before the supernatant was siphoned off. The agarose was then packed into a XK 50 column (Amersham Phamacia) and was washed with 10 column volumes of PBS. The bound dAb was eluted with 100 mM glycine pH 2.0 and protein containing fractions were then neutralized by the addition of ⅕ volume of 1 M Tris pH 8.0. Per litre of culture supernatant 20 mg of pure protein was isolated, which contained a 50:50 ratio of monomer to dimer.  
      Trimerisation of TAR1-5-19CYS  
      2.5 ml of 100 μM TAR1-5-19CYS was reduce with 5 mM dithiothreitol and left at room temperature for 20 minutes. The sample was then buffer exchanged using a PD-10 column (Amersham Pharmacia). The column had been pre-equilibrated with 5 mM EDTA, 50 mM sodium phosphate pH 6.5, and the sample applied and eluted following the manufactures guidelines. The sample was placed on ice until required. TMEA (Tris[2-maleimidoethyl]amine) was purchased from Pierce Biotechnology. A 20 mM stock solution of TMEA was made in 100% DMSO (dimethyl sulphoxide). It was found that a concentration of TMEA greater than 3:1 (molar ratio of dAb:TMEA) caused the rapid precipitation and cross-linking of the protein. Also the rate of precipitation and cross-linking was greater as the pH increased. Therefore using 100 μM reduced TAR1-5-19CYS, 25 μM TMEA was added to trimerise the protein and the reaction allowed to proceed at room temperature for two hours. It was found that the addition of additives such as glycerol or ethylene glycol to 20% (v/v), significantly reduced the precipitation of the trimer as the coupling reaction proceeded. After coupling, SDS-PAGE analysis showed the presence of monomer, dimer and trimer in solution.  
      Purification of the Trimeric TAR1-5-19CYS  
      40 μL of 40% glacial acetic acid was added per mL of the TMEA-TAR1-5-19cys reaction to reduce the pH to ˜4. The sample was then applied to a lmL Resource S cation exchange column (Amersham Pharmacia), which had been pre-equilibrated with 50 mM sodium acetate pH 4.0. The dimer and trimer were partially separated using a salt gradient of 340 to 450 mM Sodium chloride, 50 mM sodium acetate pH 4.0 over 30 column volumes. Fractions containing trimer only were identified using SDS-PAGE and then pooled and the pH increased to 8 by the addition of ⅕ volume of 1M Tris pH 8.0. To prevent precipitation of the trimer during concentration steps (using 5K cut off Viva spin concentrators; Vivascience), 10% glycerol was added to the sample.  
      In Vitro Functional Binding Assay: TNF Receptor Assay and Cell Assay  
      The affinity of the trimer for human TNFα was determined using the TNF receptor and cell assay. IC50 in the receptor assay was 0.3 nM; ND50 in the cell assay was in the range of 3 to 10 nM (eg, 3 nM).  
      Other Possible TAR1-5-19CYS Trimer Formats  
      TAR1-5-19CYS may also be formatted into a trimer using the following reagents:  
      PEG Trimers and Custom Synthetic Maleimide Trimers  
      Nektar (Shearwater) offer a range of multi arm PEGs, which can be chemically modified at the terminal end of the PEG. Therefore using a PEG trimer with a maleimide functional group at the end of each arm would allow the trimerisation of the dAb in a manner similar to that outlined above using TMEA. The PEG may also have the advantage in increasing the solubility of the trimer thus preventing the problem of aggregation. Thus, one could produce a dAb trimer in which each dAb has a C-terminal cysteine that is linked to a maleimide functional group, the maleimide functional groups being linked to a PEG trimer.  
      Addition of a Polypeptide Linker or Hinge to the C-Terminus of the dAb  
      A small linker, either (Gly 4 Ser) n  where n=1 to 10, eg, 1, 2, 3, 4, 5, 6 or 7 , an immunoglobulin (eg, IgG hinge region or random peptide sequence (eg, selected from a library of random peptide sequences) could be engineered between the dAb and the terminal cysteine residue. When used to make multimers (eg, dimers or trimers), this again would introduce a greater degree of flexibility and distance between the individual monomers, which may improve the binding characteristics to the target, eg a multisubunit target such as human TNFα.  
     Example 9  
     Selection of a Collection of Single Domain Antibodies (dAbs) Directed Against Human Serum Albumin (HSA) and Mouse Serum Albumin (MSA).  
      This example explains a method for making a single domain antibody (dAb) directed against serum albumin. Selection of dAbs against both mouse serum albumin (MSA) and human serum albumin (HSA) is described. Three human phage display antibody libraries were used in this experiment, each based on a single human framework for V H  (see  FIG. 13 : sequence of dummy V H  based on V3-23/DP47 and JH4b) or V K  (see  FIG. 15 : sequence of dummy V K  based on o12/o2/DPK9 and Jk1) with side chain diversity encoded by NNK codons incorporated in complementarity determining regions (CDR1, CDR2 and CDR3).  
      Library 1 (V H ):  
     
         
          Diversity at positions: H30, H31, H33, H35, H50, H52, H52a, H53, H55, H56, H58, H95, H97, H98.  
          Library size: 6.2×10 9  
 
 Library 2 (V H ): 
 
          Diversity at positions: H30, H31, H33, H35, H50, H52, H52a, H53, H55, H56, H58, H95, H97, H98, H99, H100, H100a, H100b.  
          Library size: 4.3×10 9  
 
 Library 3 (V K ): 
 
          Diversity at positions: L30, L31, L32, L34, L50, L53, L91, L92, L93, L94, L96  
          Library size: 2×10 9    
       
    
      The V H  and V K  libraries have been preselected for binding to generic ligands protein A and protein L respectively so that the majority of clones in the unselected libraries are functional. The sizes of the libraries shown above correspond to the sizes after preselection.  
      Two rounds of selection were performed on serum albumin using each of the libraries separately. For each selection, antigen was coated on immunotube (nunc) in 4 ml of PBS at a concentration of 100 μg/ml. In the first round of selection, each of the three libraries was panned separately against HSA (Sigma) and MSA (Sigma). In the second round of selection, phage from each of the six first round selections was panned against (i) the same antigen again (eg 1 st  round MSA, 2 nd  round MSA) and (ii) against the reciprocal antigen (eg 1 st  round MSA, 2 nd  round HSA) resulting in a total of twelve 2 nd  round selections. In each case, after the second round of selection 48 clones were tested for binding to HSA and MSA. Soluble dAb fragments were produced as described for scFv fragments by Harrison et al, Methods Enzymol. 1996;267:83-109 and standard ELISA protocol was followed (Hoogenboom et al. (1991) Nucleic Acids Res., 19: 4133) except that 2% tween PBS was used as a blocking buffer and bound dAbs were detected with either protein L-HRP (Sigma) (for the V KS ) and protein A -HRP (Amersham Pharmacia Biotech) (for the V H s).  
      dAbs that gave a signal above background indicating binding to MSA, HSA or both were tested in ELISA insoluble form for binding to plastic alone but all were specific for serum albumin. Clones were then sequenced (see table below) revealing that 21 unique dAb sequences had been identified. The minimum similarity (at the amino acid level) between the V K  dAb clones selected was 86.25% ((69/80)×100; the result when all the diversified residues are different, eg clones 24 and 34). The minimum similarity between the VHdAb clones selected was 94% ((127/136)×100).  
      Next, the serum albumin binding dAbs were tested for their ability to capture biotinylated antigen from solution. ELISA protocol (as above) was followed except that ELISA plate was coated with 1 μg/ml protein L (for the V K  clones) and 1 μg/ml protein A (for the V H  clones). Soluble dAb was captured from solution as in the protocol and detection was with biotinylated MSA or HSA and streptavidin HRP. The biotinylated MSA and HSA had been prepared according to the manufacturer&#39;s instructions, with the aim of achieving an average of 2 biotins per serum albumin molecule. Twenty four clones were identified that captured biotinylated MSA from solution in the ELISA. Two of these (clones 2 and 38 below) also captured biotinylated HSA. Next, the dAbs were tested for their ability to bind MSA coated on a CM5 biacore chip. Eight clones were found that bound MSA on the biacore.  
                                           TABLE 8                                                           dAb (all                   Binds           capture                   MSA   Captures       biotinylated   H               in   biotinylated       MSA)   or κ   CDR1   CDR2   CDR3   biacore?   HSA?                                                                            Vκ library 3   κ   XXXLX   (SEQ ID   XASXLQS   (SEQ ID   QQXXXXPXT   (SEQ ID                   template   XXLX           NO:298)       NO:299)       NO:300)       (dummy)               2, 4, 7, 41,   κ   SSYLN   (SEQ ID   RASPLQS   (SEQ ID   QQTYSVPPT   (SEQ ID       ✓ all 4 bind                   NO:301)       NO:302)       NO:303)               38, 54   κ   SSYLN   (SEQ ID   RASPLQS   (SEQ ID   QQTYRIPPT   (SEQ ID       ✓ both bind                   NO:304)       NO:305)       NO:306)               46, 47, 52, 56   κ   FKSLK   (SEQ ID   NASYLQS   (SEQ ID   QQVVYWPVT   (SEQ ID                   NO:307)       NO:308)       NO:309)               13, 15   κ   YYHLK   (SEQ ID   KASTLQS   (SEQ ID   QQVRKVPRT   (SEQ ID                   NO:310)       NO:311)       NO:312)               30, 35   κ   RRYLK   (SEQ ID   QASVLQS   (SEQ ID   QQGLYPPIT   (SEQ ID                   NO:313)       NO:314)       NO:315)               19,   κ   YNWLK   (SEQ ID   RASSLQS   (SEQ ID   QQNVVIPRT   (SEQ ID                   NO:316)       NO:317)       NO:318)               22,   κ   LWHLR   (SEQ ID   HASLLQS   (SEQ ID   QQSAVYPKT   (SEQ ID                   NO:319)       NO:320)       NO:321)               23,   κ   FRYLA   (SEQ ID   HASHLQS   (SEQ ID   QQRLLYPKT   (SEQ ID                   NO:322)       NO:323)       NO:324)               24,   κ   FYHLA   (SEQ ID   PASKLQS   (SEQ ID   QQRARWPRT   (SEQ ID                   NO:325)       NO:326)       NO:327)               31,   κ   IWHLN   (SEQ ID   RASRLQS   (SEQ ID   QQVARVPRT   (SEQ ID                   NO:328)       NO:329)       NO:330)               33,   κ   YRYLR   (SEQ ID   KASSLQS   (SEQ ID   QQYVGYPRT   (SEQ ID                   NO:331)       NO:332)       NO:333)               34,   κ   LKYLK   (SEQ ID   NASHLQS   (SEQ ID   QQTTYYPIT   (SEQ ID                   NO:334)       NO:335)       NO:336)               53,   κ   LRYLR   (SEQ ID   KASWLQS   (SEQ ID   QQVLYYPQT   (SEQ ID                   NO:337)       NO:338)       NO:339)               11,   κ   LRSLK   (SEQ ID   AASRLQS   (SEQ ID   QQVVYWPAT   (SEQ ID   ✓                   NO:340)       NO:341)       NO:342)               12,   κ   FRHLK   (SEQ ID   AASRLQS   (SEQ ID   QQVALYPKT   (SEQ ID   ✓                   NO:343)       NO:344)       NO:345)               17,   κ   RKYLR   (SEQ ID   TASSLQS   (SEQ ID   QQNLFWPRT   (SEQ ID   ✓                   NO:346)       NO:347)       NO:348)               18,   κ   RRYLN   (SEQ ID   AASSLQS   (SEQ ID   QQMLFYPKT   (SEQ ID   ✓                   NO:349)       NO:350)       NO:351)               16, 21   κ   IKHLK   (SEQ ID   GASRLQS   (SEQ ID   QQGARWPQT   (SEQ ID   ✓                   NO:352)       NO:353)       NO:354)               25, 26   κ   YYHLK   (SEQ ID   KASTLQS   (SEQ ID   QQVRKVPRT   (SEQ ID   ✓                   NO:355)       NO:356)       NO:357)               27,   κ   YKHLK   (SEQ ID   NASHLQS   (SEQ ID   QQVGRYPKT   (SEQ ID   ✓                   NO:358)       NO:359)       NO:360)               55,   κ   FKSLK   (SEQ ID   NASYLQS   (SEQ ID   QQVVYWPVT   (SEQ ID   ✓                   NO:361)       NO:362)       NO:363)               V H  library 1   H   XXYXXX   (SEQ ID   XIXXXGXXTXYADSVKG   (SEQ ID   XXXX(XXXX)FDY   (SEQ ID       (and 2)           NO:364)       NO:365)       NO:366)       template       (dummy)               8, 10   H   WVYQMD   (SEQ ID   SISAFGAKTLYADSVKG   (SEQ ID   LSGKFDY   (SEQ ID                   NO:367)       NO:368)       NO:369)               36,   H   WSYQMT   (SEQ ID   SISSFGSSTLYADSVKG   (SEQ ID   GRDHNYSLFDY   (SEQ ID                   NO:370)       NO:371)       NO:372)                  
 
      In all cases the frameworks were identical to the frameworks in the corresponding dummy sequence, with diversity in the CDRs as indicated in the table above.  
      Of the eight clones that bound MSA on the biacore, two clones that are highly expressed in  E. coli  (clones MSA16 and MSA26) were chosen for further study (see example 10). Full nucleotide and amino acid sequences for MSA16 and 26 are given in  FIG. 16 .  
     Example 10  
     Determination of Affinity and Serum Half-Life in Mouse of MSA Binding dAbs MSA16 and MSA26.  
      dAbs MSA16 and MSA26 were expressed in the periplasm of  E. coli  and purified using batch absorbtion to protein L-agarose affinity resin (Affitech, Norway) followed by elution with glycine at pH 2.2. The purified dAbs were then analysed by inhibition biacore to determine K d . Briefly, purified MSA16 and MSA26 were tested to determine the concentration of dAb required to achieve 200RUs of response on a biacore CM5 chip coated with a high density of MSA. Once the required concentrations of dAb had been determined, MSA antigen at a range of concentrations around the expected K d  was premixed with the dAb and incubated overnight. Binding to the MSA coated biacore chip of dAb in each of the premixes was then measured at a high flow-rate of 30 μl/minute. The resulting curves were used to create Klotz plots, which gave an estimated K d  of 200 nM for MSA16 and 70 nM for MSA 26 ( FIG. 17A  &amp; B).  
      Next, clones MSA16 and MSA26 were cloned into an expression vector with the HA tag (nucleic acid sequence: TATCCTTATGATGTTCCTGATTATGCA (SEQ ID NO: 373) and amino acid sequence: YPYDVPDYA (SEQ ID NO:374)) and 2-10 mg quantities were expressed in  E. coli  and purified from the supernatant with protein L-agarose affinity resin (Affitech, Norway) and eluted with glycine at pH2.2. Serum half life of the dAbs was determined in mouse. MSA26 and MSA16 were dosed as single i.v. injections at approx 1.5 mg/kg into CD1 mice. Analysis of serum levels was by goat anti-HA (Abcam, UK) capture and protein L-HRP (invitrogen) detection ELISA which was blocked with 4% Marvel. Washing was with 0.05% tween PBS. Standard curves of known concentrations of dAb were set up in the presence of lxmouse serum to ensure comparability with the test samples. Modelling with a 2 compartment model showed MSA-26 had a t½α of 0.16 hr, a t½β of 14.5 hr and an area under the curve (AUC) of 465 hr.mg/ml (data not shown) and MSA-16 had a t½α of 0.98 hr, a t½β of 36.5 hr and an AUC of 913hr.mg/ml ( FIG. 18 ). Both anti-MSA clones had considerably lengthened half life compared with HEL4 (an anti-hen egg white lysozyme dAb) which had a t½α of 0.06 hr, and a t½β of 0.34 hr.  
     Example 11  
     Creation of V H -V H  and V K -V K  Dual Specific Fab Like Fragments  
      This example describes a method for making V H -V H  and V K -V K  dual specifics as Fab like fragments. Before constructing each of the Fab like fragments described, dAbs that bind to targets of choice were first selected from dAb libraries similar to those described in example 9. A V H  dAb, HEL4, that binds to hen egg lysozyme (Sigma) was isolated and a second V H  dAb (TAR2h-5) that binds to TNFt receptor (R and D systems) was also isolated. The sequences of these are given in the sequence listing. A V K  dAb that binds TNFα (TAR1-5-19) was isolated by selection and affinity maturation and the sequence is also set forth in the sequence listing. A second V K  dAb (MSA 26) described in example 9 whose sequence is in  FIG. 17B  was also used in these experiments.  
      DNA from expression vectors containing the four dAbs described above was digested with enzymes SalI and NotI to excise the DNA coding for the dAb. A band of the expected size (300-400 bp) was purified by running the digest on an agarose gel and excising the band, followed by gel purification using the Qiagen gel purification kit (Qiagen, UK). The DNA coding for the dAbs was then inserted into either the C H  or C K  vectors ( FIGS. 8 and 9 ) as indicated in the table below.  
                                   TABLE 9                               dAb V H     Inserted                   Target   or dAb   into   tag (C   Antibiotic       dAb   antigen   Vκ   vector   terminal)   resistance                  HEL4   Hen egg   V H     C H     myc   Chloramphenicol           lysozyme       TAR2-5   TNF   V H     Cκ   flag   Ampicillin           receptor       TAR1-5-   TNF α   Vκ   C H     myc   Chloramphenicol       19       MSA 26   Mouse   Vκ   Cκ   flag   Ampicillin           serum           albumin                  
 
      The V H  C H  and V H  C K  constructs were cotransformed into HB2151 cells. Separately, the V K  C H  and V K  C K  constructs were cotransformed into HB2151 cells. Cultures of each of the cotransformed cell lines were grown overnight (in 2×Ty containing 5% glucose, 10 μg/ml chloramphenicol and 100 μg/ml ampicillin to maintain antibiotic selection for both C H  and C K  plasmids). The overnight cultures were used to inoculate fresh media (2×Ty, 10 μg/ml chloramphenicol and 100 g/ml ampicillin) and grown to OD 0.7-0.9 before induction by the addition of IPTG to express their C H  and C K  constructs. Expressed Fab like fragment was then purified from the periplasm by protein A purification (for the contransformed V H  C H  and V H  C K ) and MSA affinity resin purification (for the contransformed V K  C H  and V K  C K ).  
      V H -V H  Dual Specific  
      Expression of the V H  C H  and V H  C K  dual specific was tested by running the protein on a gel. The gel was blotted and a band the expected size for the Fab fragment could be detected on the Western blot via both the myc tag and the flag tag, indicating that both the V H  C H  and V H  C K  parts of the Fab like fragment were present. Next, in order to determine whether the two halves of the dual specific were present in the same Fab-like fragment, an ELISA plate was coated overnight at 4° C. with 100 μl per well of hen egg lysozyme (HEL) at 3 mg/ml in sodium bicarbonate buffer. The plate was then blocked (as described in example 1) with 2% tween PBS followed by incubation with the V H  C H /V H  C K  dual specific Fab like fragment. Detection of binding of the dual specific to the HEL was via the non cognate chain using 9e10 (a monoclonal antibody that binds the myc tag, Roche) and anti mouse IgG-HRP (Amersham Pharmacia Biotech). The signal for the V H  C H /V H  C K  dual specific Fab like fragment was 0.154 compared to a background signal of 0.069 for the V H  C K  chain expressed alone. This demonstrates that the Fab like fragment has binding specificity for target antigen.  
      V K -V K  Dual Specific  
      After purifying the contransformed V K  C H  and V K  C K  dual specific Fab like fragment on an MSA affinity resin, the resulting protein was used to probe an ELISA plate coated with 1 μg/ml TNFα and an ELISA plate coated with 10 μg/ml MSA. As predicted, there was signal above background when detected with protein L-HRP on both ELISA plates (data not shown). This indicated that the fraction of protein able to bind to MSA (and therefore purified on the MSA affinity column) was also able to bind TNFα in a subsequent ELISA, confirming the dual specificity of the antibody fragment. This fraction of protein was then used for two subsequent experiments. Firstly, an ELISA plate coated with 1 μg/ml TNFα was probed with dual specific V K  C H  and V K  C K  Fab like fragment and also with a control TNFα binding dAb at a concentration calculated to give a similar signal on the ELISA. Both the dual specific and control dAb were used to probe the ELISA plate in the presence and in the absence of 2 mg/ml MSA. The signal in the dual specific well was reduced by more than 50% but the signal in the dAb well was not reduced at all (see  FIG. 19   a ). The same protein was also put into the receptor assay with and without MSA and competition by MSA was also shown (see  FIG. 19   c ). This demonstrates that binding of MSA to the dual specific is competitive with binding to TNFα.  
     Example 12  
     Creation of a V K -V K  Dual Specific cys Bonded Ddual Specific with Specificity for Mouse Serum Albumin and TNFα 
      This example describes a method for making a dual specific antibody fragment specific for both mouse serum albumin and TNFα by chemical coupling via a disulphide bond. Both MSA16 (from example 1) and TAR1-5-19 dAbs were recloned into a pET based vector with a C terminal cysteine and no tags. The two dAbs were expressed at 4-10 mg levels and purified from the supernatant using protein L-agarose affinity resin (Affitiech, Norway). The cysteine tagged dabs were then reduced with dithiothreitol. The TAR1-5-19 dAb was then coupled with dithiodipyridine to block reformation of disulphide bonds resulting in the formation of PEP 1-5-19 homodimers. The two different dAbs were then mixed at pH 6.5 to promote disulphide bond formation and the generation of TAR1-5-19, MSA16 cys bonded heterodimers. This method for producing conjugates of two unlike proteins was originally described by King et al. (King TP, Li Y Kochoumian L Biochemistry. 1978 voll7:1499-506 Preparation of protein conjugates via intermolecular disulfide bond formation.) Heterodimers were separated from monomeric species by cation exchange. Separation was confirmed by the presence of a band of the expected size on a SDS gel. The resulting heterodimeric species was tested in the TNF receptor assay and found to have an IC50 for neutralising TNF of approximately 18 nM. Next, the receptor assay was repeated with a constant concentration of heterodimer (18 nM) and a dilution series of MSA and HSA. The presence of HSA at a range of concentrations (up to 2 mg/ml) did not cause a reduction in the ability of the dimer to inhibit TNFα. However, the addition of MSA caused a dose dependant reduction in the ability of the dimer to inhibit TNFα ( FIG. 20 ).This demonstrates that MSA and TNFα compete for binding to the cys bonded TAR1-5-19, MSA16 dimer.  
      Data Summary  
      A summary of data obtained in the experiments set forth in the foregoing examples is set forth in Annex 4.  
     Example 13  
     Activity of Anti-Mouse TNFR1 dAbs and Anti-Human TNFR1 dAbs  
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                   
               
               
                 Activity of Anti-mouse TNFR1 dAbs 
               
            
           
           
               
               
               
            
               
                   
                 Activity (IC50) 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 dAb 
                 L929 Cell Assay 
                 Receptor Binding Assay 
               
               
                   
                   
               
               
                   
                 TAR2m-19 
                  10 μM 
                  2 μM 
               
               
                   
                 TAR2m-20 
                 n/d 
                 150 nM 
               
               
                   
                 TAR2m-21 
                 400 nM 
                 n/d 
               
               
                   
                 TAR2m-24 
                  1 μM 
                  1.3 μM  
               
               
                   
                 TAR2m-21-23 
                  1 nM 
                 n/d 
               
               
                   
                 TAR2m-21-07 
                  10 nM 
                 n/d 
               
               
                   
                 TAR2m-21-43 
                  6 nM 
                 n/d 
               
               
                   
                 TAR2m-21-48 
                  6 nM 
                 n/d 
               
               
                   
                 TAR2m-21-10 
                  30 nM 
                 n/d 
               
               
                   
                 TAR2m-21-06 
                 100 nM 
                 n/d 
               
               
                   
                 TAR2m-21-17 
                 300 nM 
                 n/d 
               
               
                   
                   
               
               
                   
                   n/d, not determined    
               
            
           
         
       
     
                     TABLE 11                          Activity of Anti-human TNFR1 dAbs                         Activity (IC50)                         dAb   HeLa IL-8 Cell Assay   Receptor Binding Assay               TAR2h-10    50 nM    30 nM       TAR2h-12   100 nM   n/d       TAR2h-13   300 nM   n/d       TAR2h-14   300 nM    30 nM       TAR2h-15   n/d    5 nM       TAR2h-16   200 nM    30 nM       TAR2h-17   n/d   100 nM       TAR2h-18   400 nM   n/d       TAR2h-22   n/d   200 nM       TAR2h-27   3000 nM     30 nM       TAR2h-29   300 nM   300 nM       TAR2h-32   100 nM   n/d       TAR2h-34   n/d   300 nM       TAR2h-35   800 nM   n/d       TAR2h-41    30 nM    8 nM       TAR2h-42    10 nM    15 nM       TAR2h-44   300 nM    10 nM       TAR2h-47   n/d    8 nM       TAR2h-51   n/d    80 nM       TAR2h-67   300 nM   n/d       TAR2h-10-1   n/d    10 nM       TAR2h-10-2   n/d    11 nM       TAR2h-10-3   n/d    11 nM       TAR2h-10-4   n/d    8 nM       TAR2h-10-5   n/d    11 nM       TAR2h-10-7    30 nM   n/d       TAR2h-10-27    10 nM    2 nM       TAR2h-10-55    20 nM   n/d                 n/d, not determined               
 MRC-5 IL-8 Release Assay 
 
      The activities of certain dAbs that bind human TNFR1 were assessed in the following MRC-5 cell assay. The assay is based on the induction of IL-8 secretion by TNF in MRC-5 cells and is adapted from the method described in Alceson, L. et al.  Journal of Biological Chemistry  271:30517-30523 (1996), describing the induction of IL-8 by IL-1 in HUVEC. The activity of the dabs was assayed by assessing IL-8 induction by human TNFα using MRC-5 cells instead of the HUVEC cell line. Briefly, MRC-5 cells were plated in microtitre plates and the plates were incubated overnight with dAb and human TNFα (300 pg/ml). Following incubation, the culture supernatant was aspirated and the IL-8 concentration in the supernatant was measured via a sandwich ELISA (R&amp;D Systems). Anti-TNFR1 dAb activity resulted in a decrease in IL-8 secretion into the supernatant compared with control wells that were incubated with TNFα only.  
     Example 14  
     Mouse Septic Shock Model  
      The in vivo efficacy of an anti-TNFR1 dAb was assessed in a well-established experimental model for septic shock syndrome (Rothe et al.,  Circulatory Shock  44:51-56, (1995)). LPS-induced death in this model is dependent upon TNFR-1 (p55) activation. In this model mice were sensitized to the toxicity of LPS using D-galactosamine (D-GaIN). The lethal LPS dose for wild-type animals in this study was about 10 ng.  
      LPS ( Salmonella enteritidis , Sigma, USA) and D-Galactosamine (D-GaIN, Sigma, USA) were injected intraperitoneally. D-Ga1N-sensitized (10 mg/mouse) control mice died within 18 hour following challenge with LPS (10 ng). Mortality of non-sensitized mice was recorded over a period of 1 day after challenge.  
      Mice were administered a dual specific ligand that binds mouse TNFR1 and mouse serum albumin (TAR2m-21-23 3U TAR7m-16; TAR7m-16 is also referred to herein as MSA16) or ENBREL® (entarecept; Immunex Corporation) by intraperitoneal injections 4 hours prior to the administration of LPS. (See, Table 12). Survival was monitored at 4-6 hour intervals over a period of 48 hours. Efficacy of anti-mouse TNFR1 dAbs was demonstrated by survival.  
                               TABLE 12                               LPS dose   Number   Number of       Treatment       per mouse   of   Survivors at       Group   Agent and Dose   (ng)   animals   24 hours                                                    1   Saline   10   8   0/8       2    10 mg/kg   10   8   8/8           ENBREL ® (entarecept;           Immunex Corporation)       3   5.4 mg/kg   10   8   4/8           TAR2m-21-23 3U           TAR7m-16       4     1 mg/kg   10   8   2/8           TAR2m-21-23 3U           TAR7m-16       5   5.4 mg/kg   0   2   2/2           TAR2m-21-23 3U           TAR7m-16                  
 
      TAR2m-21-23 3U TAR7m-16 is a dual specific ligand that contains a dAb that binds mouse TNFR1 that is joined through a peptide linker to a dAb that binds mouse serum albumin. A nucleotide sequence encoding TAR2m-21-23 3U TAR7m-16 and the amino acid sequence of the dual specific ligand are presented below as SEQ ID NO: 375 and SEQ ID NO:376, respectively.  
                              GAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGCGTC   (SEQ ID NO:375)                   TCTCCTGTGCAGCCTCCGGATTCACCTTTAATAGGTATAGTATGGGGTGGCTCCGCCA               GGCTCCAGGGAAGGGTCTAGAGTGGGTCTCACGGATTGATTCTTATGGTCGTGGTACA               TACTACGAAGACCCCGTGAAGGGCCGGTTCAGCATCTCCCGCGACAATTCCAAGAACA               CGCTGTATCTGCAAATGAACAGCCTGCGTGCCGAGGACACCGCCGTATATTACTGTGC               GAAAATTTCTCAGTTTGGGTCAAATGCGTTTGACTACTGGGGTCAGGGAACCCAGGTC               ACCGTCTCGAGCGGTGGAGGCGGTTCAGGCGGAGGTGGCAGCGGCGGTGGCGGGTCGA               CGGACATCCAGATGACCCAGTCTCCATCCTCCCTGTCTGCATCTGTAGGAGACCGTGT               CACCATCACTTGCCGGGCAAGTCAGAGCATTATTAAGCATTTAAAGTGGTACCAGCAG               AAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGGTGCATCCCGGTTGCAAAGTGGGG               TCCCATCACGTTTCAGTGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAG               TCTGCAACCTGAAGATTTTGCTACGTACTACTGTCAACAGGGGGCTCGGTGGCCTCAG               ACGTTCGGCCAAGGGACCAAGGTGGAAATCAAACGGGCGGCCGCAGAACAAAAACTCA               TCTCAGAAGAGGATCTGAAT               EVQLLESGGGLVQPGGSLRLSCAASGFTFNRYSMGWLRQAPGKGLEWVSRIDSYGRGT   (SEQ ID NO:376)               YYEDPVKGRFSISRDNSKNTLYLQMNSLRAEDTAVYYCAKISQFGSNAFDYWGQGTQV               TVSSGGGGSGGGGSGGGGSTDIQMTQSPSSLSASVGDRVTITCRASQSIIKHLKWYQQ               KPGKAPKLLIYGASRLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGARWPQ               TFGQGTKVEIKRAAAEQKLISEEDLN          
 
      The presence of survivors in the TAR2m-21-23 3U TAR7m-16 treatment groups demonstrates that the anti-TNFR1 dAb was efficacious in inhibiting the activity of the receptor in vivo, and the results demonstrate that the effect was dose dependent. Moreover, the efficacy of the TAR2m-21-23 3U TAR7m-16 treatment compared favorably with the efficacy of ENBREL® (entarecept; Immunex Corporation). The survival of the animals which were treated with TAR2m-21-23 3U TAR7m-16 alone (Group 5, no LPS challenge) also demonstrates that TAR2m-21-23 3U TAR7m-16 was not toxic and did not agonise the receptor in vivo by receptor cross-linking.  
      Further studies confirmed that anti-TNFR1 dAbs do not agonise TNFR1 (act as TNFR1 agonists) in the absence of TNFα. L929 cells were cultured in media that contained a range of concentrations of either TAR2m-21-23 monomer, TAR2m-21-23 monomer cross-linked to a commercially available anti-myc antibody (9E10), TAR2m-21-23 3U TAR7m-16 or TAR2m-21-23 40K PEG. In the case of TAR2m-21-23 monomer cross-linked with the anti-myc antibody, the dAb and antibody were mixed in a 2:1 ratio and pre-incubated for one hour at room-temperature to simulate the effects of in vivo immune cross-linking prior to culture. TAR2m-21-23 monomer was incubated with the L929 cells at a concentration of 3000 nM. TAR2m-21-23 monomer and anti-Myc antibody were incubated at a dAb concentration of 3000 nM. TAR2m-21-23 3U TAR7m-16 was incubated with the cells at 25 nM, 83.3 nM, 250 nM, 833 nM and 2500 nM concentrations. TAR2m-21-23 40K PEG was incubated with the cells at 158.25 nM, 527.5 nM, 1582.5 nM, 5275 nM and 15825 nM concentrations. After incubation overnight, cell viability was assessed as described for the L929 cell cytotoxicity assay. The results revealed that incubation with various amounts of dAbs did not result in an increase in the number of non-viable cells in the cultures. The incubation of L929 cells with 10 nM, 1 nM and 0.1 nM of a commercially-available anti-TNFR1 IgG antibody resulted in a dose-dependent increase in non-viable cells thereby demonstrating the sensitivity of these cells to TNFR1-mediated agonism. ( FIG. 26 ).  
     Example 15  
     Models of Chronic Inflammatory Diseases  
      A. Mouse Collagen-Induced Arthritis Model  
      DBA/1 mice were injected once with an emulsion of Arthrogen-CIA adjuvant and Arthrogen-CIA collagen (MD-biosciences). At day 21, animals with high arthritic scores were removed from the study and the remainder of the animals were divided into groups of 10 with equal numbers of male and female animals. At day 21 treatments commenced with intraperitoneal injections of either saline, ENBREL® (entarecept; Immunex Corporation) or TAR2m-21-23 40k PEG and continued for 28 days. Clinical arthritic scores on a scale of 0 to 4 were measured for each of the 4 limbs of the animals, a score of 0 was assigned for a normal limb and a score of 4 was assigned for a maximally inflamed limb with involvement of multiple joints.  
      A reduction of the summation of the arthritic scores of the four limbs from the maximum of 16 to (a) 14-15, (b) 12-15, (c) 10-15, (d) 9-15, (e) 7-15, (f) 5-15, (g), 3-15, or (h) 1-15 is a beneficial effect in this model. A beneficial effect can result is a summation of the arthritic scores of the four limbs of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15. A delay in the onset of arthritis, compared with the untreated control group, is also a beneficial effect in this model.  
      The clinical scores clearly demonstrated that treatment with TAR2m-21-23 40k PEG had a very favourable impact of inhibition of the development of arthritis when compared with the saline control, and moreover the TAR2m-21-23 40k PEG treatment compared favourably with ENBREL® (entarecept; Immunex Corporation). This is the first demonstration of inhibition of TNFR1 being efficacious in the treatment of a chronic inflammatory disease model.  
      B. Mouse ΔARE Model of IBD and Arthritis  
      Mice that bear a targeted deletion in the 3′ AU-rich elements (AREs) of the TNF mRNA (referred to as Tnf ΔARE  mice) overproduce TNF and develop an inflammatory bowel disease that is histopathologically similar to Crohn&#39;s disease. (Kontoyiannis et al.,  J Exp Med  196:1563-74 (2002).) In these mice, the Crohn&#39;s-like disease develops between 4 and 8 weeks of age, and the animals also develop clinical signs of rheumatoid arthritis.  
      dAbs that bind mouse TNFR-1 were assessed for efficacy in inhibiting Crohn&#39;s-like pathology and arthritis in Tnf ΔARE  mice. ENBREL® (entarecept; Immunex Corporation) was used as a positive control. The agents were administered by intraperitoneal injections according to the administration and dosing regiment presented in Table 13.  
      The dAbs that were studied include: 
      1) TAR2m-21-23 PEGylated with one 40 kD PEG moiety;    

      2) dual specific TAR2m-21-23 3U TAR7m-16 which binds mouse TNFR-1 and mouse serum albumin.  
                               TABLE 13                                   Number of   Number of       Group   Treatment   Dose   Doses   Animals                  6   ENBREL ® (entarecept;   10 mg/kg   8   10           Immunex Corporation)           (administered 3           times/week)       5   TAR2m21-23 40 kD    1 mg/kg   8   10           PEG           (administered           twice/week)       4   TAR2m21-23 40 kD   10 mg/kg   8   10           PEG           (administered           twice/week)       3   TAR2m-21-23 3U    1 mg/kg   8   10           TAR7m-16           (administered           twice/week)       2   TAR2m-21-23 3U   10 mg/kg   8   10           TAR7m-16           (administered           twice/week)       1   Saline   NA   8   10                  
 
 At the conclusion of the dosing period, the mice were sacrificed and the terminal ileums and proximal colons were removed for analysis. 
 
      For histological analysis, the tissue samples will be sectioned and stained with hematoxylin and eosin, and acute and chronic inflammation will be scored using a semi-quantitive scoring system. The scores will be assigned as follows: acute inflammation score 0=0-1 polymorphonuclear (PMN) cell per high powered field (PMN/hpf); 1=2-10 PMN/hpf within mucosa; 2=11-20 PMN/hpf within mucosa; 3=21-30 PMN/hpf within mucosa or 11-20 PMN/hpf with extension below muscularis mucosae; 4=&gt;30 PMN/hpf within mucosa or &gt;20 PMN/hpf with extension below muscularis mucosae; chronic inflammation score 0=0-10 mononuclear leukocytes (ML) per hpf (ML/hpf) within mucosa; 1=11-20 ML/hpf within mucosa; 2=21-30 ML/hpf within mucosa or 11-20 ML/hpf with extension below muscularis mucosae; 3=31-40 ML/hpf within mucosa or follicular hyperplasia; and 4=&gt;40 ML/hpf within mucosa or &gt;30 ML/hpf with extension below muscularis mucosae or follicular hyperplasia.  
      The macrophenotypic signs of arthritis were scored weekly according to the following system: 0=no arthritis (normal appearance and flexion); 1=mild arthritis Ooint distortion); 2=moderate arthritis (swelling, joint deformation); 3=heavy arthritis (severely impaired movement).  
      The TAR2m-21-23 dAb demonstrated good in vivo efficacy in the delta ARE mouse model of arthritis as both a 40 kD PEGylated monomer (TAR2m21-23-40 kD PEG) and as a dual specific anti-TNFR1/anti-SA format (TAR2m-21-23 3U TAR7m-16). At week 9 the mean arthritic scores of both the TAR2m-21-23 and the TAR2m-21-23 3U TAR7m-16 treated groups were less than 0.4. In contrast the saline control group had moderate to severe arthritis with an average arthritic score that was &gt;1.0. The group treated with ENBREL® (entarecept; Immunex Corporation), which was administered 3 times per week as compared with TAR2m-21-23 and the TAR2m-21-23 3U TAR7m-16 which were administered twice per week, had an average score of 0.5-1.0. These results indicate that therapy with dAb formats that bind TNFR1 is a highly efficacious anti-arthritis therapy, and that both the PEGylated and dual specificity dAb formats studied are highly effective drugs for chronic inflammatory disease. Moreover these results further demonstrate that dAbs that bind TNFR1 engage the receptor only in an antagonistic manner.  
      C. Mouse DSS model of IBD.  
      IBD will be induced in mice by administering dextran sulfate sodium (DSS) in the drinking water. (See, e.g., Okayasu I. et al.,  Gastroenterology  98:694-702 (1990); Podolsky K.,  J Gasteroenterol.  38 suppl XV:63-66 (2003).) Adult BDF1 mice that are  H. pylori  free will be housed for 2 weeks to stabilize their circadian rhythms. All mice will be held in individually ventilated cages in a specific pathogen free (SPF) barrier unit on a 12 hour light:dark cycle. Animals will be allowed food and water ad libitum throughout.  
      The study will run for 7 days. The drinking water will contain 5% DSS for the duration of the study. All animals will be treated on days 1-7 in the morning (0900-1000) and evening (1600-1700). (See Table 14.) Day 1 is equivalent to a singe prophylactic dose. All animals to be weighed daily and any diarrhoea incidence will be noted. All animals will be sacrifices 24 hours following the last treatment, and will be administered a pulse of bromodeoxyuridine 40 minutes prior to sacrifice. The distal large intestines will be removed from the animals. A small sample of the distal large intestine will be placed into “RNAlater”, and the remainder will be fixed in Carnoy&#39;s fixative, embedded in paraffin, sectioned (non-serial sections per slide) and stained with hematoxylin and eosin. Sections will be visually assessed for IBD severity and assigned a severity score. Histometric analyses will be performed and mean lesion area (ulcer area), mean epithelial area, and mean intramural inflammatory area will be determined.  
      H&amp;E cross sections of the large intestine will be used to record a series of tissue dimensions using a Zeiss Axiohome microscope, which enables accurate quantification of areas. For each cross section, the area of epithelium plus lamina propria and the area of connective tissue will be measured. The epithelial area will then be measured separately, the difference being the area of lamina propria. In normal tissue the relative contribution of this tissue to the area is about 10%, but this increases as inflammation increases. The relative proportion of epithelium:lamina propria therefore changes.  
      With increasing severity the depth of this area narrows (contributing to the ulceration) and length of the colon shortens. Together these phenomena cause the cross-sectional area of the lumen to increase. This parameter can therefore also be a useful measurement of disease severity.  
      The tissue samples will be observed microscopically and assigned a severity score where 0=no inflammation; 1=mild inflammation around crypt base; 2=massive inflammatory infiltration, and disrupted mucosal architecture; 3=massive inflammatory infiltration, and disrupted mucosal architecture plus ulceration.  
      Efficacy is indicated in this model when the treatment produces a reduction of in severity score, relative to the severity score of the saline control group. For example the severity score of the treatment group can be reduced by 0.1 to about 1, 1 to about 2, or 2 to about 3. Efficacy would be indicated by a score of about 2 or less, 1 to about 2, or 1 or less.  
      9 groups of 6 animals will be treated as follows:  
                   TABLE 14                       Group                      1   DSS in drinking water       2   DSS in drinking water + ip PEG TAR2m-21-23, 10 mg/kg 1x/d       3   DSS in drinking water + ip PEG TAR2m-21-23, 1 mg/kg 1x/d       4   DSS in drinking water + ip saline       5   DSS in drinking water + oral gavage PEG TAR2m-21-23, 0.25           mg/animal 2x/d       6   DSS in drinking water + oral gavage saline       7   DSS in drinking water + ip dosing +ve control e.g. steroid       8   DSS in drinking water + oral gavage +ve control e.g. 5′           aminosalicylic acid or similar       9   Untreated animals                 Oral gavages will be given with ZANTAC ® (ranitidine hydrochloride; GlaxoSmithKline).             
 
 D. Mouse Model of Chronic Obstructive Pulmonary Disease (COPD) 
 
      Efficacy of anti-TNFR1 dAbs in progression of disease in the mouse sub-chronic tobacco smoke (TS) model will be assessed. (See, e.g., Wright J L and Churg A.  Chest  122:306S-309S (2002).) Anti-mouse TNFR1 domain antibodies will be administered by intraperitoneal injections every 48 hours (starting 24 hours before the first exposure to TS) and will be given as extended serum half life formats. ENBREL® (entarecept; Immunex Corporation) will be used as a positive control. TS exposure will be daily and will escalate to a daily observed tolerance for a total of 11 days. Following a further 24 hours, BALs will be analysed for total and differential cell counts and for KC chemokine and protein levels.  
      Female A/J mice (5 per exposure chamber) will be exposed daily to TS generated from cigarettes (Ref. 1R1, supplied by University of Kentucky) or TO air for 11 consecutive days. Initial exposure will be to 2 cigarettes on day 2 increasing to a maximum of 6 cigarettes by day 7/8. Exposure thereafter to day 12 will be 6 cigarettes. The rate of increase will be regulated with regard to the daily observed tolerance of the mice.  
      Therapeutic agents (dAbs, ENBREL® (entarecept; Immunex Corporation)) will be administered 24 hours before the first exposure to TS (see timeline below). The dAbs will be administered by intraperitoneal injections at 10 mg/kg every 48 hours. The study will use 40 mice (FOUR groups of 10 mice) (Table 15).  
                                                                               
 
     
       
         
           
               
               
               
             
               
                 TABLE 15 
               
               
                   
               
               
                   
               
               
                 Group 
                 Exposure 
                 Treatment 
               
               
                   
               
             
            
               
                 A 
                 Air 
                 Saline 
               
               
                 B 
                 TS 
                 Saline 
               
               
                 C 
                 TS 
                 ENBREL ® (entarecept; Immunex Corporation) 
               
               
                 D 
                 TS 
                 TAR2m21-23 40 kD PEG (10 mg/kg) 
               
               
                   
               
            
           
         
       
     
      Animals will be killed by anaesthetic overdose (pentobarbitone Na, 100 mg/kg i.p.) 24 hours following the 11th and final TS exposure. BAL will be performed using 0.4 ml of heparinised phosphate buffered saline (PBS). Cells recovered from the BAL will be used for total and differential cell counts (cytospin preparation). BAL supernatants will be frozen for subsequent analysis of protein levels. The remaining BAL fluid will be analyzed for KC chemokine (ELISA), MCR1 levels and total protein levels (Pearce assay), or a multi analyte assay will be performed. A reduction in the symptoms or diagnostics of COPD, such as a reduction in amount of KC chemokine in BAL fluid compared to control, is indicative of efficacy in this model.  
      All publications mentioned in the present specification, and references cited in said publications, are herein incorporated by reference. Various modifications and variations of the described methods and system of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in molecular biology or related fields are intended to be within the scope of the following claims.  
      Annex 1; polypeptides which enhance half-life in vivo. 
      Alpha-1 Glycoprotein (Orosomucoid) (AAG)     Alpha-1 Antichyromotrypsin (ACT)     Alpha-1 Antitrypsin (AAT)     Alpha-1 Microglobulin (Protein HC) (AIM)     Alpha-2 Macroglobulin (A2M)     Antithrombin III (AT III)     Apolipoprotein A-1 (Apo A-1)     Apoliprotein B (Apo B)     Beta-2-microglobulin (B2M)     Ceruloplasmin (Cp)     Complement Component (C3)     Complement Component (C4)     C1 Esterase Inhibitor (C1NH)     C-Reactive Protein (CRP)     Cystatin C (Cys C)     Ferritin (FER)     Fibrinogen (FIB)     Fibronectin (FN)     Haptoglobin (Hp)     Hemopexin (HPX)     Immunoglobulin A (IgA)     Immunoglobulin D (IgD)     Immunoglobulin E (IgE)     Immunoglobulin G (IgG)     Immunoglobulin M (IgM)     Immunoglobulin Light Chains (kapa/lambda)     Lipoprotein(a) [Lp(a)]    Mannose-bindign protein (MBP)     Myoglobin (Myo)     Plasminogen (PSM)     Prealbumin (Transthyretin) (PAL)     Retinol-binding protein (RBP)     Rheomatoid Factor (RF)     Serum Amyloid A (SAA)     Soluble Tranferrin Receptor (sTfR)     Transferrin (Tf)    

      Annex 2  
                                   Pairing   Therapeutic relevant references.                  TNF   TGF-b and TNF when injected into the ankle joint of collagen       ALPHA/TGF-β   induced arthritis model significantly enhanced joint           inflammation. In non-collagen challenged mice there was no           effect.       TNF   TNF and IL-1 synergize in the pathology of uveitis.       ALPHA/IL-1   TNF and IL-1 synergize in the pathology of malaria           (hypoglycaemia, NO).           TNF and IL-1 synergize in the induction of           polymorphonuclear (PMN) cells migration in inflammation.           IL-1 and TNF synergize to induce PMN infiltration into the           peritoneum.           IL-1 and TNF synergize to induce the secretion of IL-1 by           endothelial cells. Important in inflammation.           IL-1 or TNF alone induced some cellular infiltration into knee           synovium. IL-1 induced PMNs, TNF - monocytes. Together           they induced a more severe infiltration due to increased PMNs.           Circulating myocardial depressant substance (present in sepsis)           is low levels of IL-1 and TNFacting synergistically.       TNF   Most relating to synergisitic activation of killer T-cells.       ALPHA/IL-2       TNF   Synergy of interleukin 3 and tumor necrosis factor alpha in       ALPHA/IL-3   stimulating clonal growth of acute myelogenous leukemia           blasts is the result of induction of secondary hematopoietic           cytokines by tumor necrosis factor alpha.           Cancer Res. 1992 Apr 15; 52(8): 2197-201.       TNF   IL-4 and TNF synergize to induce VCAM expression on       ALPHA/IL-4   endothelial cells. Implied to have a role in asthma. Same for           synovium - implicated in RA.           TNF and IL-4 synergize to induce IL-6 expression in           keratinocytes.           Sustained elevated levels of VCAM-1 in cultured fibroblast-           like synoviocytes can be achieved by TNF-alpha in           combination with either IL-4 or IL-13 through increased           mRNA stability. Am J Pathol. 1999 Apr; 154(4): 1149-58       TNF   Relationship between the tumor necrosis factor system and the       ALPHA/IL-5   serum interleukin-4, interleukin-5, interleukin-8, eosinophil           cationic protein, and immunoglobulin E levels in the bronchial           hyperreactivity of adults and their children. Allergy Asthma           Proc. 2003 Mar-Apr; 24(2): 111-8.       TNF   TNF and IL-6 are potent growth factors for OH-2, a novel       ALPHA/IL-6   human myeloma cell line. Eur J Haematol. 1994 Jul; 53(1): 31-7.       TNF   TNF and IL-8 synergized with PMNs to activate platelets.       ALPHA/IL-8   Implicated in Acute Respiratory Distress Syndrome.           See IL-5/TNF (asthma). Synergism between interleukin-8 and           tumor necrosis factor-alpha for neutrophil-mediated platelet           activation. Eur Cytokine Netw. 1994 Sep-Oct; 5(5): 455-60.           (adult respiratory distress syndrome (ARDS))       TNF       ALPHA/IL-9       TNF   IL-10 induces and synergizes with TNF in the induction of       ALPHA/IL-10   HIV expression in chronically infected T-cells.       TNF   Cytokines synergistically induce osteoclast differentiation:       ALPHA/IL-11   support by immortalized or normal calvarial cells. Am J           Physiol Cell Physiol. 2002 Sep; 283(3): C679-87. (Bone loss)       TNF       ALPHA/IL-12       TNF   Sustained elevated levels of VCAM-1 in cultured fibroblast-       ALPHA/IL-13   like synoviocytes can be achieved by TNF-alpha in           combination with either IL-4 or IL-13 through increased           mRNA stability. Am J Pathol. 1999 Apr; 154(4): 1149-58.           Interleukin-13 and tumour necrosis factor-alpha synergistically           induce eotaxin production in human nasal fibroblasts. Clin Exp           Allergy. 2000 Mar; 30(3): 348-55.           Interleukin-13 and tumour necrosis factor-alpha synergistically           induce eotaxin production in human nasal fibroblasts. Clin Exp           Allergy. 2000 Mar; 30(3): 348-55 (allergic inflammation)           Implications of serum TNF-beta and IL-13 in the treatment           response of childhood nephrotic syndrome. Cytokine. 2003 Feb 7;           21(3): 155-9.       TNF   Effects of inhaled tumour necrosis factor alpha in subjects with       ALPHA/IL-14   mild asthma. Thorax. 2002 Sep; 57(9): 774-8.       TNF   Effects of inhaled tumour necrosis factor alpha in subjects with       ALPHA/IL-15   mild asthma. Thorax. 2002 Sep; 57(9): 774-8.       TNF   Tumor necrosis factor-alpha-induced synthesis of interleukin-       ALPHA/IL-16   16 in airway epithelial cells: priming for serotonin stimulation.           Am J Respir Cell Mol Biol. 2003 Mar; 28(3): 354-62. (airway           inflammation)           Correlation of circulating interleukin 16 with proinflammatory           cytokines in patients with rheumatoid arthritis. Rheumatology           (Oxford). 2001 Apr; 40(4): 474-5. No abstract available.           Interleukin 16 is up-regulated in Crohn&#39;s disease and           participates in TNBS colitis in mice. Gastroenterology. 2000           Oct; 119(4): 972-82.       TNF   Inhibition of interleukin-17 prevents the development of       ALPHA/IL-17   arthritis in vaccinated mice challenged with  Borrelia               burgdorferi . Infect Immun. 2003 Jun; 71(6): 3437-42.           Interleukin 17 synergises with tumour necrosis factor alpha to           induce cartilage destruction in vitro. Ann Rheum Dis. 2002           Oct; 61(10): 870-6.           A role of GM-CSF in the accumulation of neutrophils in the           airways caused by IL-17 and TNF-alpha. Eur Respir J. 2003           Mar; 21(3): 387-93. (Airway inflammation)           Abstract Interleukin-1, tumor necrosis factor alpha, and           interleukin-17 synergistically up-regulate nitric oxide and           prostaglandin E2 production in explants of human           osteoarthritic knee menisci. Arthritis Rheum. 2001           Sep; 44(9): 2078-83.       TNF   Association of interleukin-18 expression with enhanced levels       ALPHA/IL-18   of both interleukin-1beta and tumor necrosis factor alpha in           knee synovial tissue of patients with rheumatoid arthritis.           Arthritis Rheum. 2003 Feb; 48(2): 339-47.           Abstract Elevated levels of interleukin-18 and tumor necrosis           factor-alpha in serum of patients with type 2 diabetes mellitus:           relationship with diabetic nephropathy. Metabolism. 2003           May; 52(5): 605-8.       TNF   Abstract IL-19 induces production of IL-6 and TNF-alpha and       ALPHA/IL-19   results in cell apoptosis through TNF-alpha. J Immunol. 2002 Oct 15;           169(8): 4288-97.       TNF   Abstract Cytokines: IL-20 - a new effector in skin       ALPHA/IL-20   inflammation. Curr Biol. 2001 Jul 10; 11(13): R531-4       TNF   Inflammation and coagulation: implications for the septic       ALPHA/Complement   patient. Clin Infect Dis. 2003 May 15; 36(10): 1259-65. Epub           2003 May 08. Review.       TNF   MHC induction in the brain.       ALPHA/IFN-γ   Synergize in anti-viral response/IFN-β induction.           Neutrophil activation/respiratory burst.           Endothelial cell activation           Toxicities noted when patients treated with TNF/IFN-γ as anti-           viral therapy           Fractalkine expression by human astrocytes.           Many papers on inflammatory responses - i.e. LPS, also           macrophage activation.           Anti-TNF and anti-IFN-γ synergize to protect mice from lethal           endotoxemia.       TGF-β/IL-1   Prostaglndin synthesis by osteoblasts           IL-6 production by intestinal epithelial cells (inflammation model)           Stimulates IL-11 and IL-6 in lung fibroblasts (inflammation           model)           IL-6 and IL-8 production in the retina       TGF-β/IL-6   Chondrocarcoma proliferation       IL-1/IL-2   B-cell activation           LAK cell activation           T-cell activation           IL-1 synergy with IL-2 in the generation of lymphokine           activated killer cells is mediated by TNF-alpha and beta           (lymphotoxin). Cytokine. 1992 Nov; 4(6): 479-87.       IL-1/IL-3       IL-1/IL-4   B-cell activation           IL-4 induces IL-1 expression in endothelial cell activation.       1/5 IL-1/IL-5       IL-1/IL-6   B cell activation           T cell activation (can replace accessory cells)           IL-1 induces IL-6 expression           C3 and serum amyloid expression (acute phase response)           HIV expression           Cartilage collagen breakdown.       IL-1/IL-7   IL-7 is requisite for IL-1-induced thymocyte proliferation.           Involvement of IL-7 in the synergistic effects of granulocyte-           macrophage colony-stimulating factor or tumor necrosis factor           with IL-1. J Immunol. 1992 Jan 1; 148(1): 99-105.       IL-1/IL-8       IL-1/IL-10       IL-1/IL-11   Cytokines synergistically induce osteoclast differentiation:           support by immortalized or normal calvarial cells. Am J           Physiol Cell Physiol. 2002 Sep; 283(3): C679-87. (Bone loss)       IL-1/IL-16   Correlation of circulating interleukin 16 with proinflammatory           cytokines in patients with rheumatoid arthritis. Rheumatology           (Oxford). 2001 Apr; 40(4): 474-5. No abstract available.       IL-1/IL-17   Inhibition of interleukin-17 prevents the development of           arthritis in vaccinated mice challenged with Borrelia           burgdorferi. Infect Immun. 2003 Jun; 71(6): 3437-42.           Contribution of interleukin 17 to human cartilage degradation           and synovial inflammation in osteoarthritis. Osteoarthritis           Cartilage. 2002 Oct; 10(10): 799-807.           Abstract Interleukin-1, tumor necrosis factor alpha, and           interleukin-17 synergistically up-regulate nitric oxide and           prostaglandin E2 production in explants of human           osteoarthritic knee menisci. Arthritis Rheum. 2001           Sep; 44(9): 2078-83.       IL-1/IL-18   Association of interleukin-18 expression with enhanced levels           of both interleukin-1beta and tumor necrosis factor alpha in           knee synovial tissue of patients with rheumatoid arthritis.           Arthritis Rheum. 2003 Feb; 48(2): 339-47.       IL-1/IFN-g       IL-2/IL-3   T-cell proliferation           B cell proliferation       IL-2/IL-4   B-cell proliferation           T-cell proliferation           (selectively inducing activation of CD8 and NK           lymphocytes)IL-2R beta agonist P1-30 acts in synergy with           IL-2, IL-4, IL-9, and IL-15: biological and molecular effects. J           Immunol. 2000 Oct 15; 165(8): 4312-8.       IL-2/IL-5   B-cell proliferation/Ig secretion           IL-5 induces IL-2 receptors on B-cells       IL-2/IL-6   Development of cytotoxic T-cells       IL-2/IL-7       IL-2/IL-9   See IL-2/IL-4 (NK-cells)       IL-2/IL-10   B-cell activation       IL-2/IL-12   IL-12 synergizes with IL-2 to induce lymphokine-activated           cytotoxicity and perforin and granzyme gene expression in           fresh human NK cells. Cell Immunol. 1995 Oct 1; 165(1): 33-43.           (T-cell activation)       IL-2/IL-15   See IL-2/IL-4 (NK cells)           (T cell activation and proliferation) IL-15 and IL-2: a matter of           life and death for T cells in vivo. Nat Med. 2001 Jan; 7(1): 114-8.       IL-2/IL-16   Synergistic activation of CD4+ T cells by IL-16 and IL-2. J           Immunol. 1998 Mar 1; 160(5): 2115-20.       IL-2/IL-17   Evidence for the early involvement of interleukin 17 in human           and experimental renal allograft rejection. J Pathol. 2002           Jul; 197(3): 322-32.       IL-2/IL-18   Interleukin 18 (IL-18) in synergy with IL-2 induces lethal lung           injury in mice: a potential role for cytokines, chemokines, and           natural killer cells in the pathogenesis of interstitial           pneumonia. Blood. 2002 Feb 15; 99(4): 1289-98.       IL-2/TGF-β   Control of CD4 effector fate: transforming growth factor beta           1 and interleukin 2 synergize to prevent apoptosis and promote           effector expansion. J Exp Med. 1995 Sep 1; 182(3): 699-709.       IL-2/IFN-γ   Ig secretion by B-cells           IL-2 induces IFN-γ expression by T-cells       IL-2/IFN-α/β   None       IL-3/IL-4   Synergize in mast cell growth           Synergistic effects of IL-4 and either GM-CSF or IL-3 on the           induction of CD23 expression by human monocytes:           regulatory effects of IFN-alpha and IFN-gamma. Cytokine.           1994 Jul; 6(4): 407-13.       IL-3/IL-5       IL-3/IL-6       IL-3/IFN-γ   IL-4 and IFN-gamma synergistically increase total polymeric           IgA receptor levels in human intestinal epithelial cells. Role of           protein tyrosine kinases. J Immunol. 1996 Jun 15;           156(12): 4807-14.       IL-3/GM-CSF   Differential regulation of human eosinophil IL-3, IL-5, and           GM-CSF receptor alpha-chain expression by cytokines: IL-3,           IL-5, and GM-CSF down-regulate IL-5 receptor alpha           expression with loss of IL-5 responsiveness, but up-regulate           IL-3 receptor alpha expression. J Immunol. 2003 Jun 1;           170(11): 5359-66. (allergic inflammation)       IL-4/IL-2   IL-4 synergistically enhances both IL-2- and IL-12-induced           IFN-{gamma} expression in murine NK cells. Blood. 2003 Mar 13           [Epub ahead of print]       IL-4/IL-5   Enhanced mast cell histamine etc. secretion in response to IgE           A Th2-like cytokine response is involved in bullous           pemphigoid. the role of IL-4 and IL-5 in the pathogenesis of           the disease. Int J Immunopathol Pharmacol. 1999 May-Aug;           12(2): 55-61.       IL-4/IL-6       IL-4/IL-10       IL-4/IL-11   Synergistic interactions between interleukin-11 and           interleukin-4 in support of proliferation of primitive           hematopoietic progenitors of mice. Blood. 1991 Sep 15;           78(6): 1448-51.       IL-4/IL-12   Synergistic effects of IL-4 and IL-18 on IL-12-dependent IFN-           gamma production by dendritic cells. J Immunol. 2000 Jan 1;           164(1): 64-71. (increase Th1/Th2 differentiation)           IL-4 synergistically enhances both IL-2- and IL-12-induced           IFN-{gamma} expression in murine NK cells. Blood. 2003 Mar 13           [Epub ahead of print]       IL-4/IL-13   Abstract Interleukin-4 and interleukin-13 signaling           connections maps. Science. 2003 Jun 6; 300(5625): 1527-8.           (allergy, asthma)           Inhibition of the IL-4/IL-13 receptor system prevents allergic           sensitization without affecting established allergy in a mouse           model for allergic asthma. J Allergy Clin Immunol. 2003           Jun; 111(6): 1361-1369.       IL-4/IL-16   (asthma) Interleukin (IL)-4/IL-9 and exogenous IL-16 induce           IL-16 production by BEAS-2B cells, a bronchial epithelial cell           line. Cell Immunol. 2001 Feb 1; 207(2): 75-80       IL-4/IL-17   Interleukin (IL)-4 and IL-17 synergistically stimulate IL-6           secretion in human colonic myofibroblasts. Int J Mol Med.           2002 Nov; 10(5): 631-4. (Gut inflammation)       IL-4/IL-24   IL-24 is expressed by rat and human macrophages.           Immunobiology. 2002 Jul; 205(3): 321-34.       IL-4/IL-25   Abstract New IL-17 family members promote Th1 or Th2           responses in the lung: in vivo function of the novel cytokine           IL-25. J Immunol. 2002 Jul 1; 169(1): 443-53. (allergic           inflammation)           Abstract Mast cells produce interleukin-25 upon Fcepsilon RI-           mediated activation. Blood. 2003 May 1; 101(9): 3594-6. Epub           2003 Jan 02. (allergic inflammation)       IL-4/IFN-γ   Abstract Interleukin 4 induces interleukin 6 production by           endothelial cells: synergy with interferon-gamma. Eur J           Immunol. 1991 Jan; 21(1): 97-101.       IL-4/SCF   Regulation of human intestinal mast cells by stem cell factor           and IL-4. Immunol Rev. 2001 Feb; 179: 57-60. Review.       IL-5/IL-3   Differential regulation of human eosinophil IL-3, IL-5, and           GM-CSF receptor alpha-chain expression by cytokines: IL-3,           IL-5, and GM-CSF down-regulate IL-5 receptor alpha           expression with loss of IL-5 responsiveness, but up-regulate           IL-3 receptor alpha expression. J Immunol. 2003 Jun 1;           170(11): 5359-66. (Allergic inflammation see abstract)       IL-5/IL-6       IL-5/IL-13   Inhibition of allergic airways inflammation and airway           hyperresponsiveness in mice by dexamethasone: role of           eosinophils, IL-5, eotaxin, and IL-13. J Allergy Clin Immunol.           2003 May; 111(5): 1049-61.       IL-5/IL-17   Interleukin-17 orchestrates the granulocyte influx into airways           after allergen inhalation in a mouse model of allergic asthma.           Am J Respir Cell Mol Biol. 2003 Jan; 28(1): 42-50.       IL-5/IL-25   Abstract New IL-17 family members promote Th1 or Th2           responses in the lung: in vivo function of the novel cytokine           IL-25. J Immunol. 2002 Jul 1; 169(1): 443-53. (allergic           inflammation)           Abstract Mast cells produce interleukin-25 upon Fcepsilon RI-           mediated activation. Blood. 2003 May 1; 101(9): 3594-6. Epub           2003 Jan 02. (allergic inflammation)       IL-5/IFN-γ       IL-5/GM-CSF   Differential regulation of human eosinophil IL-3, IL-5, and           GM-CSF receptor alpha-chain expression by cytokines: IL-3,           IL-5, and GM-CSF down-regulate IL-5 receptor alpha           expression with loss of IL-S responsiveness, but up-regulate           IL-3 receptor alpha expression. J Immunol. 2003 Jun 1;           170(11): 5359-66. (Allergic inflammation)       IL-6/IL-10       IL-6/IL-11       IL-6/IL-16   Interleukin-16 stimulates the expression and production of pro-           inflammatory cytokines by human monocytes. Immunology.           2000 May; 100(1): 63-9.       IL-6/IL-17   Stimulation of airway mucin gene expression by interleukin           (IL)-17 through IL-6 paracrine/autocrine loop. J Biol Chem.           2003 May 9; 278(19): 17036-43. Epub 2003 Mar 06. (airway           inflammation, asthma)       IL-6/IL-19   Abstract IL-19 induces production of IL-6 and TNF-alpha and           results in cell apoptosis through TNF-alpha. J Immunol. 2002 Oct 15;           169(8): 4288-97.       IL-6/IFN-g       IL-7/IL-2   Interleukin 7 worsens graft-versus-host disease. Blood. 2002 Oct 1;           100(7): 2642-9.       IL-7/IL-12   Synergistic effects of IL-7 and IL-12 on human T cell           activation. J Immunol. 1995 May 15; 154(10): 5093-102.       IL-7/IL-15   Interleukin-7 and interleukin-15 regulate the expression of the           bcl-2 and c-myb genes in cutaneous T-cell lymphoma cells.           Blood. 2001 Nov 1; 98(9): 2778-83. (growth factor)       IL-8/IL-11   Abnormal production of interleukin (IL)-11 and IL-8 in           polycythaemia vera. Cytokine. 2002 Nov 21; 20(4): 178-83.       IL-8/IL-17   The Role of IL-17 in Joint Destruction. Drug News Perspect.           2002 Jan; 15(1): 17-23. (arthritis)           Abstract Interleukin-17 stimulates the expression of           interleukin-8, growth-related oncogene-alpha, and           granulocyte-colony-stimulating factor by human airway           epithelial cells. Am J Respir Cell Mol Biol. 2002           Jun; 26(6): 748-53. (airway inflammation)       IL-8/GSF   Interleukin-8: an autocrine/paracrine growth factor for human           hematopoietic progenitors acting in synergy with colony           stimulating factor-1 to promote monocyte-macrophage growth           and differentiation. Exp Hematol. 1999 Jan; 27(1): 28-36.       IL-8/VGEF   Intracavitary VEGF, bFGF, IL-8, IL-12 levels in primary and           recurrent malignant glioma. J Neurooncol. 2003           May; 62(3): 297-303.       IL-9/IL-4   Anti-interleukin-9 antibody treatment inhibits airway           inflammation and hyperreactivity in mouse asthma model. Am           J Respir Crit Care Med. 2002 Aug 1; 166(3): 409-16.       IL-9/IL-5   Pulmonary overexpression of IL-9 induces Th2 cytokine           expression, leading to immune pathology. J Clin Invest. 2002           Jan; 109(1): 29-39.           Th2 cytokines and asthma. Interleukin-9 as a therapeutic target           for asthma. Respir Res. 2001; 2(2): 80-4. Epub 2001 Feb 15           Review.           Abstract Interleukin-9 enhances interleukin-5 receptor           expression, differentiation, and survival of human eosinophils.           Blood. 2000 Sep 15; 96(6): 2163-71 (asthma)       IL-9/IL-13   Anti-interleukin-9 antibody treatment inhibits airway           inflammation and hyperreactivity in mouse asthma model. Am           J Respir Crit Care Med. 2002 Aug 1; 166(3): 409-16.           Direct effects of interleukin-13 on epithelial cells cause airway           hyperreactivity and mucus overproduction in asthma. Nat Med.           2002 Aug; 8(8): 885-9.       IL-9/IL-16   See IL-4/IL-16       IL-10/IL-2   The interplay of interleukin-10 (IL-10) and interleukin-2 (IL-           2) in humoral immune responses: IL-10 synergizes with IL-2           to enhance responses of human B lymphocytes in a mechanism           which is different from upregulation of CD25 expression. Cell           Immunol. 1994 Sep; 157(2): 478-88.       IL-10/IL-12       IL-10/TGF-β   IL-10 and TGF-beta cooperate in the regulatory T cell           response to mucosal allergens in normal immunity and specific           immunotherapy. Eur J Immunol. 2003 May; 33(5): 1205-14.       IL-10/IFN-γ       IL-11/IL-6   Interleukin-6 and interleukin-11 support human osteoclast           formation by a RANKL-independent mechanism. Bone. 2003           Jan; 32(1): 1-7. (bone resorption in inflammation)       IL-11/IL-17   Polarized in vivo expression of IL-11 and IL-17 between acute           and chronic skin lesions. J Allergy Clin Immunol. 2003           Apr; 111(4): 875-81. (allergic dermatitis)           IL-17 promotes bone erosion in murine collagen-induced           arthritis through loss of the receptor activator of NF-kappa B           ligand/osteoprotegerin balance. J Immunol. 2003 Mar 1;           170(5): 2655-62.       IL-11/TGF-β   Polarized in vivo expression of IL-11 and IL-17 between acute           and chronic skin lesions. J Allergy Clin Immunol. 2003           Apr; 111(4): 875-81. (allergic dermatitis)       IL-12/IL-13   Relationship of Interleukin-12 and Interleukin-13 imbalance           with class-specific rheumatoid factors and anticardiolipin           antibodies in systemic lupus erythematosus. Clin Rheumatol.           2003 May; 22(2): 107-11.       IL-12/IL-17   Upregulation of interleukin-12 and -17 in active inflammatory           bowel disease. Scand J Gastroenterol. 2003 Feb; 38(2): 180-5.       IL-12/IL-18   Synergistic proliferation and activation of natural killer cells           by interleukin 12 and interleukin 18. Cytokine. 1999           Nov; 11(11): 822-30.           Inflammatory Liver Steatosis Caused by IL-12 and IL-18. J           Interferon Cytokine Res. 2003 Mar; 23(3): 155-62.       IL-12/IL-23   nterleukin-23 rather than interleukin-12 is the critical cytokine           for autoimmune inflammation of the brain. Nature. 2003 Feb 13;           421(6924): 744-8.           Abstract A unique role for IL-23 in promoting cellular           immunity. J Leukoc Biol. 2003 Jan; 73(1): 49-56. Review.       IL-12/IL-27   Abstract IL-27, a heterodimeric cytokine composed of EBI3           and p28 protein, induces proliferation of naive CD4(+) T cells.           Immunity. 2002 Jun; 16(6): 779-90.       IL-12/IFN-γ   IL-12 induces IFN-γ expression by B and T-cells as part of           immune stimulation.       IL-13/IL-5   See IL-5/IL-13       IL-13/IL-25   Abstract New IL-17 family members promote Th1 or Th2           responses in the lung: in vivo function of the novel cytokine           IL-25. J Immunol. 2002 Jul 1; 169(1): 443-53. (allergic           inflammation)           Abstract Mast cells produce interleukin-25 upon Fcepsilon RI-           mediated activation. Blood. 2003 May 1; 101(9): 3594-6. Epub           2003 Jan 02. (allergic inflammation)       IL-15/IL-13   Differential expression of interleukins (IL)-13 and IL-15 in           ectopic and eutopic endometrium of women with           endometriosis and normal fertile women. Am J Reprod           Immunol. 2003 Feb; 49(2): 75-83.       IL-15/IL-16   IL-15 and IL-16 overexpression in cutaneous T-cell           lymphomas: stage-dependent increase in mycosis fungoides           progression. Exp Dermatol. 2000 Aug; 9(4): 248-51.       IL-15/IL-17   Abstract IL-17, produced by lymphocytes and neutrophils, is           necessary for lipopolysaccharide-induced airway neutrophilia:           IL-15 as a possible trigger. J Immunol. 2003 Feb 15;           170(4): 2106-12. (airway inflammation)       IL-15/IL-21   IL-21 in Synergy with IL-15 or IL-18 Enhances IFN-gamma           Production in Human NK and T Cells. J Immunol. 2003 Jun 1;           170(11): 5464-9.       IL-17/IL-23   Interleukin-23 promotes a distinct CD4 T cell activation state           characterized by the production of interleukin-17. J Biol           Chem. 2003 Jan 17; 278(3): 1910-4. Epub 2002 Nov 03       IL-17/TGF-β   Polarized in vivo expression of IL-11 and IL-17 between acute           and chronic skin lesions. J Allergy Clin Immunol. 2003           Apr; 111(4): 875-81. (allergic dermatitis)       IL-18/IL-12   Synergistic proliferation and activation of natural killer cells           by interleukin 12 and interleukin 18. Cytokine. 1999           Nov; 11(11): 822-30.           Abstract Inhibition of in vitro immunoglobulin production by           IL-12 in murine chronic graft-vs.-host disease: synergism with           IL-18. Eur J Immunol. 1998 Jun; 28(6): 2017-24.       IL-18/IL-21   IL-21 in Synergy with IL-15 or IL-18 Enhances IFN-gamma           Production in Human NK and T Cells. J Immunol. 2003 Jun 1;           170(11): 5464-9.       IL-18/TGF-β   Interleukin 18 and transforming growth factor betal in the           serum of patients with Graves′ ophthalmopathy treated with           corticosteroids. Int Immunopharmacol. 2003 Apr; 3(4): 549-52.       IL-18/IFN-γ       Anti-TNF   Synergistic therapeutic effect in DBA/1 arthritic mice.       ALPHA/anti-       CD4                  
 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
               
               
                   
                 Target 
                 Disease 
                 Pair with 
               
               
                   
                   
               
             
            
               
                   
                 CD89* 
                 Use as cytotoxic cell 
                 All 
               
               
                   
                   
                 recruiter 
               
               
                   
                 CD19 
                 B cell lymphomas 
                 HLA-DR 
               
               
                   
                   
                   
                 CD5 
               
               
                   
                 HLA-DR 
                 B cell lymphomas 
                 CD89 
               
               
                   
                   
                   
                 CD19 
               
               
                   
                   
                   
                 CD5 
               
               
                   
                 CD38 
                 Multiple myeloma 
                 CD138 
               
               
                   
                   
                   
                 CD56 
               
               
                   
                   
                   
                 HLA-DR 
               
               
                   
                 CD138 
                 Multiple myeloma 
                 CD38 
               
               
                   
                   
                   
                 CD56 
               
               
                   
                   
                   
                 HLA-DR 
               
               
                   
                 CD138 
                 Lung cancer 
                 CD56 
               
               
                   
                   
                   
                 CEA 
               
               
                   
                 CD33 
                 Acute myelod lymphoma 
                 CD34 
               
               
                   
                   
                   
                 HLA-DR 
               
               
                   
                 CD56 
                 Lung cancer 
                 CD138 
               
               
                   
                   
                   
                 CEA 
               
               
                   
                 CEA 
                 Pan carcinoma 
                 MET receptor 
               
               
                   
                 VEGF 
                 Pan carcinoma 
                 MET receptor 
               
               
                   
                 VEGF 
                 Pan carcinoma 
                 MET receptor 
               
               
                   
                 receptor 
               
               
                   
                 IL-13 
                 Asthma/pulmonary 
                 IL-4 
               
               
                   
                   
                 inflammation 
                 IL-5 
               
               
                   
                   
                   
                 Eotaxin(s) 
               
               
                   
                   
                   
                 MDC 
               
               
                   
                   
                   
                 TARC 
               
               
                   
                   
                   
                 TNFα 
               
               
                   
                   
                   
                 IL-9 
               
               
                   
                   
                   
                 EGFR 
               
               
                   
                   
                   
                 CD40L 
               
               
                   
                   
                   
                 IL-25 
               
               
                   
                   
                   
                 MCP-1 
               
               
                   
                   
                   
                 TGFβ 
               
               
                   
                 IL-4 
                 Asthma 
                 IL-13 
               
               
                   
                   
                   
                 IL-5 
               
               
                   
                   
                   
                 Eotaxin(s) 
               
               
                   
                   
                   
                 MDC 
               
               
                   
                   
                   
                 TARC 
               
               
                   
                   
                   
                 TNFα 
               
               
                   
                   
                   
                 IL-9 
               
               
                   
                   
                   
                 EGFR 
               
               
                   
                   
                   
                 CD40L 
               
               
                   
                   
                   
                 IL-25 
               
               
                   
                   
                   
                 MCP-1 
               
               
                   
                   
                   
                 TGFβ 
               
               
                   
                 Eotaxin 
                 Asthma 
                 IL-5 
               
               
                   
                   
                   
                 Eotaxin-2 
               
               
                   
                   
                   
                 Eotaxin-3 
               
               
                   
                 EGFR 
                 cancer 
                 HER2/neu 
               
               
                   
                   
                   
                 HER3 
               
               
                   
                   
                   
                 HER4 
               
               
                   
                 HER2 
                 cancer 
                 HER3 
               
               
                   
                   
                   
                 HER4 
               
               
                   
                 TNFR1 
                 RA/Crohn&#39;s disease 
                 IL-1R 
               
               
                   
                   
                   
                 IL-6R 
               
               
                   
                   
                   
                 IL-18R 
               
               
                   
                 TNFα 
                 RA/Crohn&#39;s disease 
                 IL-1α/β 
               
               
                   
                   
                   
                 IL-6 
               
               
                   
                   
                   
                 IL-18 
               
               
                   
                   
                   
                 ICAM-1 
               
               
                   
                   
                   
                 IL-15 
               
               
                   
                   
                   
                 IL-17 
               
               
                   
                 IL-1R 
                 RA/Crohn&#39;s disease 
                 IL-6R 
               
               
                   
                   
                   
                 IL-18R 
               
               
                   
                 IL-18R 
                 RA/Crohn&#39;s disease 
                 IL-6R 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
            
               
                   
               
               
                   
               
               
                 Data Summary 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Equilibrium 
                   
                 IC50 for 
                 ND50 for cell 
               
               
                   
                   
                 dissocation constant 
                   
                 ligand 
                 based neutralisn 
               
               
                 TARGET 
                 dAb 
                 (Kd = Koff/Kon) 
                 Koff 
                 assay 
                 assay 
               
               
                   
               
               
                 TAR1 
                 TAR1 
                 300 nM to 5 pM 
                 5 × 10 −1  to 
                 500 nM to 
                 500 nM to 50 pM 
               
               
                   
                 monomers 
                 (ie, 3 × 10 −7  to 
                 1 × 10 −7   
                 100 pM 
               
               
                   
                   
                 5 × 10 −12 ), preferably 
               
               
                   
                   
                 50 nM to 20 pM 
               
               
                   
                 TAR1 
                 As TAR1 monomer 
                 As TAR1 
                 As TAR1 
                 As TAR1 
               
               
                   
                 dimers 
                   
                 monomer 
                 monomer 
                 monomer 
               
               
                   
                 TAR1 
                 As TAR1 monomer 
                 As TAR1 
                 As TAR1 
                 As TAR1 
               
               
                   
                 trimers 
                   
                 monomer 
                 monomer 
                 monomer 
               
               
                   
                 TAR1-5 
               
               
                   
                 TAR1-27 
               
               
                   
                 TAR1-5-19 
                 30 nM 
               
               
                   
                 monomer 
               
               
                   
                 TAR1-5-19 
                   
                   
                 With 
                 =30 nM 
               
               
                   
                 homodimer 
                   
                   
                 (Gly 4 Ser) 3   
                 =3 nM 
               
               
                   
                   
                   
                   
                 linker = 20 nm 
                 =15 nM 
               
               
                   
                   
                   
                   
                 With 
               
               
                   
                   
                   
                   
                 (Gly 4 Ser) 5   
               
               
                   
                   
                   
                   
                 linker = 2 nm 
               
               
                   
                   
                   
                   
                 With 
               
               
                   
                   
                   
                   
                 (Gly 4 Ser) 7   
               
               
                   
                   
                   
                   
                 linker = 10 nm 
               
               
                   
                   
                   
                   
                 In Fab 
               
               
                   
                   
                   
                   
                 format = 1 nM 
               
               
                   
                 TAR1-5-19 
                   
                   
                 With 
                 =12 nM 
               
               
                   
                 heterodimers 
                   
                   
                 (Gly 4 Ser) n   
                 =10 nM 
               
               
                   
                   
                   
                   
                 linker 
                 =12 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19 d2 = 2 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19 d3 = 8 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19 d4 = 2-5 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19 d5 = 8 nM 
               
               
                   
                   
                   
                   
                 In Fab 
               
               
                   
                   
                   
                   
                 format 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19CH 
               
               
                   
                   
                   
                   
                 d1CK = 6 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19CK 
               
               
                   
                   
                   
                   
                 d1CH = 6 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19CH 
               
               
                   
                   
                   
                   
                 d2CK = 8 nM 
               
               
                   
                   
                   
                   
                 TAR1-5- 
               
               
                   
                   
                   
                   
                 19CH 
               
               
                   
                   
                   
                   
                 d3CK = 3 nM 
               
               
                   
                 TAR1-5 
                   
                   
                 With 
                 =60 nM 
               
               
                   
                 heterodimers 
                   
                   
                 (Gly 4 Ser) n   
               
               
                   
                   
                   
                   
                 linker 
               
               
                   
                   
                   
                   
                 TAR1-5d1 = 30 nM 
               
               
                   
                   
                   
                   
                 TAR1-5d2 = 50 nM 
               
               
                   
                   
                   
                   
                 TAR1-5d3 = 300 nM 
               
               
                   
                   
                   
                   
                 TAR1-5d4 = 3 nM 
               
               
                   
                   
                   
                   
                 TAR1-5d5 = 200 nM 
               
               
                   
                   
                   
                   
                 TAR1-5d6 = 100 nM 
               
               
                   
                   
                   
                   
                 In Fab 
               
               
                   
                   
                   
                   
                 format 
               
               
                   
                   
                   
                   
                 TAR1- 
               
               
                   
                   
                   
                   
                 5CH 
               
               
                   
                   
                   
                   
                 d2CK = 30 nM 
               
               
                   
                   
                   
                   
                 TAR1- 
               
               
                   
                   
                   
                   
                 5CK 
               
               
                   
                   
                   
                   
                 d3CH = 100 nM 
               
               
                   
                 TAR1-5-19 
                   
                   
                 0.3 nM 
                 3-10 nM (eg, 
               
               
                   
                 homotrimer 
                   
                   
                   
                 3 nM) 
               
               
                 TAR2 
                 TAR2 
                 As TAR1 monomer 
                 As TAR1 
                 500 nM to 
                 500 nM to 50 pM 
               
               
                   
                 monomers 
                   
                 monomer 
                 100 pM 
               
               
                   
                 TAR2-10 
               
               
                   
                 TAR2-5 
               
               
                 Serum 
                 Anti-SA 
                 1 nM to 500 μM, 
                   
                 1 nM to 
               
               
                 Albumin 
                 monomers 
                 preferably 100 nM to 
                   
                 500 μM, 
               
               
                   
                   
                 10 μM 
                   
                 preferably 
               
               
                   
                   
                 In Dual Specific 
                   
                 100 nM to 
               
               
                   
                   
                 format, target affinity 
                   
                 10 μM 
               
               
                   
                   
                 is 1 to 100,000 x 
                   
                 In Dual 
               
               
                   
                   
                 affinity of SA dAb 
                   
                 Specific 
               
               
                   
                   
                 affinity, eg 100 pM 
                   
                 format, 
               
               
                   
                   
                 (target) and 10 μM 
                   
                 target 
               
               
                   
                   
                 SA affinity. 
                   
                 affinity is 
               
               
                   
                   
                   
                   
                 1 to 
               
               
                   
                   
                   
                   
                 100,000 x 
               
               
                   
                   
                   
                   
                 affinity of 
               
               
                   
                   
                   
                   
                 SA dAb 
               
               
                   
                   
                   
                   
                 affinity, eg 
               
               
                   
                   
                   
                   
                 100 pM 
               
               
                   
                   
                   
                   
                 (target) 
               
               
                   
                   
                   
                   
                 and 10 μM 
               
               
                   
                   
                   
                   
                 SA 
               
               
                   
                   
                   
                   
                 affinity. 
               
               
                   
                 MSA-16 
                 200 nM 
               
               
                   
                 MSA-26 
                 70 nM