Patent Publication Number: US-7915218-B2

Title: Polypeptides for oligomeric assembly of antigens

Description:
RELATED APPLICATIONS 
     This application is the U.S. National Phase of International Application No. PCT/IB2005/002528, filed Jul. 22, 2005 and published in English, which claims priority to U.S. Provisional Application No. 60/590,648, filed Jul. 23, 2004. The teachings of the above applications are incorporated herein in their entirety by reference. 
    
    
     All documents cited herein are incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     This invention is in the field of antigen presentation. More particularly, it concerns the modification of proteins to allow their expression in oligomeric form e.g. on the surface of a cell. 
     BACKGROUND OF THE INVENTION 
     Many polypeptides that are naturally immunogenic lose this property when expressed recombinantly. In some cases the native polypeptide has structural features which do not form during expression in a heterologous host e.g. post-translational modifications may be incorrect, intermolecular interactions which influence conformation may be lost, etc. A further cause of lost immunogenicity is where a polypeptide (e.g. a surface-exposed polypeptide) is naturally oligomeric, and where this quaternary structure is required for immunogenicity (e.g. where the polypeptide has epitopes that are displayed only when a specific quaternary oligomeric structure is present). Loss of oligomeric structure can mean that the monomeric protein is less immunogenic than its native oligomeric counterpart. 
     In other cases the native polypeptide may be a transmembrane polypeptide that is not amenable to expression in a recombinant host. These problems are often seen when eukaryotic polypeptides (including those of eukaryotic viruses) are to be expressed in prokaryotes. One way of improving expression of viral transmembrane polypeptides is to remove their transmembrane domains and express only the antigenic extracellular domains {1}. However, this “soluble receptor” technology again suffers from loss of quaternary structure. If a native receptor exists in an oligomeric form on the surface of a virus, and the oligomerisation arises from sequences in the transmembrane region, the soluble receptor will lose its ability to oligomerise, and this loss can have functional consequences e.g. loss of signalling or of avidity. Loss of binding avidity, even though binding affinity may be retained, is a particular problem for antigens e.g. those used in vaccines. 
     Techniques for oligomerising proteins have been disclosed in references 2 and 3. 
     It is an object of the invention to provide ways of improving the expression of polypeptides, and particularly of antigenic polypeptides e.g. to retain their oligomeric structure. 
     SUMMARY OF THE INVENTION 
     The invention is based on a system for expressing antigenic polypeptides in oligomeric form. The antigenic polypeptide is fused to an oligomerisation polypeptide such that the oligomerisation polypeptide can interact with other oligomerisation polypeptides and bring multiple copies of the antigenic polypeptide into close proximity in the form of an oligomer. Expressing the polypeptides in oligomeric form in this way can improve their immunogenicity compared to a monomeric form. 
     Thus the invention provides a method for expressing a polypeptide of interest in a recombinant oligomeric form, wherein the polypeptide of interest is fused to an oligomerisation polypeptide such that a plurality of oligomerisation domains can associate in order to present the polypeptide of interest in oligomeric form. In particular, the method can be applied (a) to present the oligomerised polypeptide on the surface of a membrane, but including a transmembrane sequence in the structure, and (b) to present the oligomerised polypeptide by using structural features of an adhesin, such as a bacterial adhesin e.g. the NadA adhesin {4} from  Neisseria meningitidis.    
     The invention can be applied to any antigenic polypeptide, including viral and non-viral antigens. It is particularly suitable for expressing surface polypeptides in an oligomeric form, such as the extracellular portions of surface proteins that are naturally found in an oligomeric form. The polypeptide of interest may be the full-length polypeptide or, alternatively, it may be a fragment of a full-length polypeptide e.g. it may comprise one or more domains of the full-length polypeptide. 
     The invention provides a polypeptide comprising: (a) a antigenic domain; (b) an oligomerisation domain; and (c) a transmembrane domain, wherein domains (a), (b) and (c) are not all found together in the same polypeptide in nature (and, in particular, wherein domains (a) and (b) are not found together in the same polypeptide in nature). The domains are in the order (a)-(b)-(c), running either from C-terminus to N-terminus or from N-terminus to C-terminus. It is more usual to have the transmembrane domain at or near the C-terminus of the protein. 
     Inclusion of a transmembrane domain in the polypeptide allows a plurality of oligomerisation domains to associate in order to present the polypeptide in oligomeric form on the surface of a membrane. As well as associating via their oligomerisation domains, polypeptides may also associate via interaction of their transmembrane domains within a lipid bilayer, thereby maintaining oligomeric structure. The inclusion of transmembrane sequences can also help in the correct folding of some antigens. The multimers of reference 2 are designed to avoid the presence of transmembrane sequences. 
     The invention provides a polypeptide comprising: (a) an antigenic domain; and (b) an oligomerisation domain from an adhesin, wherein domains (a) and (b) are not all found together in the same polypeptide in nature. The domains are in the order (a)-(b), running either from C-terminus to N-terminus or from N-terminus to C-terminus. The polypeptide will generally include sequences in addition to (a) and (b). For surface display of antigenic polypeptides, for instance, the invention will generally involve the use of a transmembrane domain in addition to an oligomerisation domain, as described above. The adhesin is preferably a bacterial adhesin, more preferably an ‘Oca’ adhesin, and most preferably the NadA adhesin from  Neisseria meningitidis.    
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the structure of a SARS coronavirus E2 monomer. 
         FIG. 2  illustrates the domains within meningococcal NadA protein {4}. 
         FIG. 3  illustrates the domains within HIV gp120 Env protein. 
         FIG. 4  illustrates domains within NadA. 
         FIG. 5  shows hybrid proteins comprising regions from both Env and from NadA. 
         FIG. 6  shows the make-up of gp120-NadA (824aa) and gp140-NadA (741aa) constructs. 
         FIG. 7  shows western blots of  E. coli  expressing gp120-NadA and gp140-NadA. 
         FIG. 8  shows SDS-PAGE of  E. coli  expressing gp120-NadA and gp140-NadA. 
         FIGS. 9-11  show FACS analysis of  E. coli  expressing gp120-NadA or gp140-NadA. 
         FIG. 12  shows dose-dependent CD4 binding by  E. coli  expressing gp140-NadA. 
         FIGS. 13-14  show number of  E. coli  expressing gp140-NadA that bind to CD4. 
         FIG. 15  shows FACS analysis of CD4 binding by  E. coli  expressing gp140-NadA, with or without pre-incubation with pure gp140. 
         FIGS. 16 and 17  show HPLC analysis of CD4/Env complexes. 
         FIG. 18  shows anti-gp140ΔV2 antibody titres as determined by ELISA. The dotted horizontal line shows the pre-bleed titre. Arrows on the X-axis show when priming doses were administered, and the “B” shows the booster dose. The four data lines are, from top to bottom: the negative control (−); OMV-gp140-NadA (▪); OMV-gp120-NadA &amp; gp140 (▴); and the gp140 positive control (•). 
     
    
    
     DESCRIPTION OF THE SEQUENCE LISTING 
     
       
         
           
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Description 
               
               
                   
               
             
            
               
                  1 
                 E2 spike protein from SARS coronavirus. 
               
               
                   
                 Leader peptide &amp; membrane anchor shown. 
               
               
                  2 
                 Globular head domain from SEQ ID NO: 1 
               
               
                 3-9 
                 NadA-gp120 hybrids 
               
               
                 10 
                 gp140ΔV2 sequence, expressed off NadA leader peptide 
               
               
                 11 
                 Leader peptide from meningococcal NadA (29 aa) 
               
               
                 12 
                 gp120 sequence (475 aa) 
               
               
                 13 
                 NadA stalk (263 aa) 
               
               
                 14 
                 Dipeptide linker Gly-Ser (2 aa) 
               
               
                 15 
                 NadA anchor (55 aa) 
               
               
                 16 
                 gp120ΔV2 (448 aa) 
               
               
                 17 
                 Gp4 (171 aa) 
               
               
                 18 
                 Dipeptide linker Lys-Leu (2 aa) 
               
               
                 19 
                 Extended NadA anchor (74 aa) 
               
               
                 20 
                 Extended NadA anchor (108 aa) 
               
               
                 21 
                 Protein 287 from  Neisseria meningitidis   
               
               
                 22 
                 Protein 936 from  Neisseria meningitidis   
               
               
                 23-25 
                 Protein 741 from  Neisseria meningitidis  (three alleles) 
               
               
                 26 
                 Protein 953 from  Neisseria meningitidis   
               
               
                 27 
                 Gly-rich linker 
               
               
                 28 
                 NadA 
               
               
                 29 
                 HadA 
               
               
                 30 
                 YadA 
               
               
                 31 
                 UspA2 
               
               
                 32-33 
                 gp120-NadA hybrids 
               
               
                 34-35 
                 gp140-NadA hybrids 
               
               
                 36 
                 gp120 
               
               
                 37-38 
                 Thrombin sequences 
               
               
                 39 
                 gp140 
               
               
                 40 
                 Extended NadA anchor 
               
               
                 41 
                 SEQ ID NO: 13 + SEQ ID NO: 15 
               
               
                 42-58 
                 Adhesins from reference 71 
               
               
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention expresses an antigen of interest in the form of a polypeptide comprising an antigenic domain from the antigen and a heterologous oligomerisation domain. Oligomerisation domains in individual monomeric polypeptides can associate and result in formation of an oligomer in which multiple copies of the antigenic domain of interest are displayed in proximity to each other. 
     The invention relies in part on the principle that natural proteins can be divided into autonomously folding domains, and that these domains can be separated and recombined without loss of their essential function {5, 6}. Thus the oligomerisation domain, the antigenic domain and any other optional domains (e.g. transmembrane domains, signal sequences, etc.) can be selected according to their function and then combined without loss of that function. 
     Oligomerisation Domains 
     An oligomerisation domain is a sequence of amino acids within a polypeptide of the invention which forms a structure that can interact with oligomerisation domains (whether the same or different) in other polypeptides (whether the same or different) such that the polypeptides associate non-covalently to form oligomers. 
     Naturally-occurring protein oligomers (both hetero-oligomers and homo-oligomers) associate in a variety of different ways e.g. by association of β-sheets in different monomers, by association of α-helices in different monomers, by association of hydrophobic surface patches, etc. 
     A common structural motif involved in protein oligomerisation is the coiled-coil domain. The coiled α-helix structural motif can itself form coils, and two, three, four or five α-helices can wrap around each other to form a left-handed super-helix known as the “coiled coil” {7-13}. The simplicity of the coiled-coil domain has made it a popular choice for designing chimeric proteins with defined oligomerisation states {10}. 
     In a coiled-coil structure the α-helices interact through hydrophobic residues that form an apolar stripe along one side of each helix, and there may also be stabilising electrostatic interactions between side chains on either side of this stripe. Within the abcdefg heptad repeat of an α-helix, the apolar stripe is defined by hydrophobic side chains at residues a and d, with any electrostatic interactions being primarily at residues e and g. Position a is most frequently Leu, Ile or Ala and position d is usually Leu or Ala. Residues e and g are often Glu or Gln, with Arg and Lys also prominent at position g. Charged residues are common at positions b, c and f as these residues are in contact with solvent. There are exceptions to this general heptad pattern, however, and Pro residues are sometimes found within the heptad. Such exceptions usually have functional significance. 
     Hundreds of coiled-coil domain sequences are known in the art, and any suitable sequence can be used as an oligomerisation motif with the invention, provided that it retains the ability to oligomerise with other coiled-coil domains and that it does not destroy the function of the other domains within the polypeptide. It is preferred to use a coiled-coil domain which is found extracellularly {14} and which naturally acts as an oligomerisation domain. As an alternative to using a natural coiled-coil domain, artificial coiled-coil domains can be used {15, 16}. Domain (b) may include a leucine zipper sequence or an alanine zipper sequence {17}. 
     The coiled-coil domain used in the polypeptide of the invention is preferably one which forms a trimer, such that the polypeptide of the invention can also assemble into a trimer. 
     Preferred coiled-coil domains are those taken from bacterial transmembrane proteins. A preferred subset of transmembrane proteins is the adhesins (i.e. cell-surface proteins that mediate adhesion to other cells or to surfaces), and particularly non-fimbrial adhesins (e.g. in the oligomerisation coiled-coil adhesins, or ‘Oca’, family). Specific transmembrane sequences for use with the invention are those from  Yersinia enterocolitica  adhesin YadA {69; e.g. SEQ ID NO: 30 herein, or other polymorphic forms in the sequence databases},  Neisseria meningitidis  adhesin NadA {4; e.g. SEQ ID NO: 28 herein, or other polymorphic forms e.g. see reference 18 }, Moraxella catarrhalis  surface protein UspA2 {19, 70; e.g. SEQ ID NO: 31 herein, or other polymorphic forms in the sequence databases} and other adhesins, such as the HadA adhesin from  Haemophilus influenzae  biogroup  aegyptius { 71; SEQ ID NO: 29 herein} and the other adhesins disclosed as SEQ ID NOS: 42 to 58. Thus domain (b) in the polypeptide of the invention may comprise a fragment of one of amino acid sequences SEQ ID NO S : 28 to 31 or 42 to 58 herein, or may comprise a fragment of an amino acid sequence having at least m % identity to one or more of SEQ ID NO S : 28-31 or 42-58, where m is 50 or more (e.g. 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99; 99.5 or more). The fragment may be at least n consecutive amino acids of one or more of SEQ ID NO S : 28-31 or 42-58, wherein n is 7 or more (e.g. 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 or more). These polypeptides include variants (e.g. allelic variants, homologs, orthologs, paralogs, mutants, etc.) of SEQ ID NO S : 28-31 or 42-58. It is preferred to use adhesins from within SEQ ID NOS 28-31 and 42-58 where the boundary between the head region and the coiled-coil regions is known. 
     Within the amino acid sequence of a polypeptide having a coiled-coil region, the heptad-repeat nature of the α-helices means that the boundary of the coiled-coil domain can be determined with some precision, but the precise residue where a coiled-coil arrangement can be said to end may not be known with absolute accuracy. This lack of absolute precision is not a problem for practising the invention, however, as routine testing can reveal whether the coiled-coil requires any particular amino acid residue for which there might be doubt. Even so, the invention does not require the boundaries to be known with absolute precision, as the only basic requirement for the invention is that the coiled-coil domain should function in a way which allows the polypeptide to oligomerise with other coiled-coil domains without destroying the function of the other domains within the polypeptide. Within NadA, the boundaries of the coiled-coil domain are given in reference 4. 
     Another class of oligomerisation domain which can be used with the invention is found in the left-handed triple helix known as the collagen helix {20}. These triple helix-forming sequences involve a basic tripeptide repeat sequence of  1 Gly- 2 Xaa- 3 Xaa, where  2 Xaa is often Pro, and  3 Xaa is often 4-hydroxyproline. Although this motif is known as the “collagen” helix, it is found in many proteins beyond just collagen. The oligomerisation domain may thus be a sequence comprising multiple repeats of the sequence motif  1 Gly- 2 Xaa- 3 Xaa, which motif folds to form a helical structure which can oligomerise with corresponding helical structures in other polypeptide chains. 
     Collagen also provides another class of oligomerisation domain. Reference 21 describes a motif found in the non-collagenous domain 1 (NC1) of type X collagen, and this motif can be used for trimer and higher order multimer formation without a triple helix. This trimeric association is highly thermostable without intermolecular disulfide bonds. The oligomerisation domain may thus comprise a NC1 sequence. 
     Oligomerisation domains used with the invention can generally maintain an oligomeric structure without the need for the formation of inter-monomer disulfide bridges, but oligomers containing disulfide-linked monomers are not excluded from the invention. 
     The Antigenic Domain 
     An antigenic domain is a sequence of amino acids within a polypeptide of the invention which forms a structure that can bind to an antibody. The antigenic domain is arranged such that it does not prevent the oligomerisation activity of an associated oligomerisation domain. 
     The antigenic domain of the polypeptide can be derived from any suitable polypeptide antigen. The invention can be used to prepare oligomeric forms of polypeptides that are not naturally oligomeric, or to recombinantly express polypeptides in a form that mimics their natural oligomeric assembly. The invention can be used to present surface oligomers of polypeptides that are naturally displayed on a cell surface, or can be used to present non-surface polypeptides in a surface context. The invention can be used to display polypeptides from bacteria, plants, animals, as well as from viruses. 
     The invention is particularly suitable for use with surface antigens and/or antigens which naturally form oligomers. Bacterial and viral antigens are preferred sources of antigenic domains. 
     A preferred group of antigens is viral surface glycoproteins, and in particular those from enveloped viruses. The surface proteins of enveloped viruses include a transmembrane domain and an extraviral domain (ectodomain), with the major antigenic determinants located in the extraviral portion. As mentioned above, it is known to separate the extraviral domain from the transmembrane domain {1} to give a soluble form of the membrane antigen. According to the present invention the extraviral domain can be separated from the transmembrane domain and recombined with heterologous amino acid domains. Preferred antigenic domains for use with the invention are thus extraviral domains of surface proteins from enveloped viruses. 
     Particular viral proteins of interest include:
         The envelope glycoproteins of retroviridae. Retroviridae include lentiviruses and spumaviruses. Viruses of interest include HTLV-I, HTLV-II, feline immunodeficiency virus (FIV), human immunodeficiency virus (HIV), simian immunodeficiency virus (SIV), chimpanzee foamy virus and human spumavirus. The Env glycoprotein of HIV has a trimeric coiled-coil fusion region {22} and is of particular interest.   The envelope glycoproteins of paramyxoviridae, such as the F proteins. Paramyxoviridae include (a) the Paramyxovirinae, which includes Paramyxoviruses, Rubulaviruses and Morbilliviruses and (b) the Pneumovirinae, which includes the Pneumoviruses. Viruses of interest include parainfluenza virus (PIV), human paramyxovirus, Rinderpest virus, Peste Des Petit Ruminant virus, Measles virus, Mumps virus, respiratory syncytial virus (RSV), Nipah Virus, Hendra Virus, Equine Morbillivirus (EMV), Lyssavirus and Menangle virus. The F glycoproteins of paramyxovirus {23}, measles virus {24} and RSV {25, 26, 27} have trimeric coiled-coil fusion regions and are of particular interest.   The envelope glycoproteins of filoviridae. Filoviridae include the Marburg and Ebola viruses. The Gp protein of Ebola virus forms coiled-coil trimers {28} and is of particular interest.   The envelope glycoproteins of orthomyxoviridae. Orthomyxoviridae include influenza virus and thogoto viruses. The hemagglutinin (HA) protein is the fusion protein of influenza virus, and forms a trimer {29} with a coiled-coil stem {30}. HA is of particular interest.   The spike glycoproteins of coronaviridae. Coronaviridae include coronaviruses and toroviruses. Viruses of interest include the human coronaviruses, Avian infectious bronchitis virus, Feline infectious peritonitis virus, Murine hepatitis virus, Porcine epidemic diarrhea virus, Porcine hemagglutinating encephalomyelitis virus, Porcine transmissible gastroenteritis virus, and Berne virus. The spike (E2) protein of human SARS coronavirus is a class I viral fusion protein {31} which is believed to form trimers, may be of interest.   The envelope glycoproteins of rhabdoviridae. Rhabdoviridae include Rhabdoviruses, Vesiculoviruses, Lyssaviruses, Ephemeroviruses, Cytorhabdoviruses and Nucleorhabdoviruses. Viruses of interest include vesicular stomatitis virus, rabies virus, mokola virus, bovine ephemeral fever virus. The G proteins of rabies virus {32, 33}, lyssavirus {34} and mokola virus {34} form trimers on the viral surface and are of particular interest.   The envelope glycoproteins of togaviridae. Togaviridae include Alphaviruses and Rubiviruses. Viruses of interest include Sindbis virus, Eastern and Western encephalitis viruses, Semliki Forest virus, rubella virus, Aura virus, Babanki virus, Barmah Forest virus avis-A, bebaru virus, Buggy Creek virus, chikungunya virus, Everglades virus, Fort Morgan virus, getah virus, Highlands J virus, Kyzylagach virus, Mayaro virus, Middelburg virus, Mucambo virus, Ndumu virus, Ockelbo virus, o&#39;nyong-nyong virus, Pixuna virus, Ross River virus, Sagiyama virus, Una virus, Venezuelan equine encephalitis virus, and Whataroa virus. The E1 spike protein of Semliki Forest virus forms trimeric coiled-coil structures {35} and is responsible for fusion, and is thus of particular interest.   The envelope (‘E’) glycoproteins of flaviviridae {36}. Flaviviridae include Flaviviruses, Pestiviruses and Hepaciviruses. Viruses of interest include dengue virus, hepatitis C virus, yellow fever virus, japanese encephalitis virus, west nile virus, St. Louis encephalitis virus, bovine diarrhea virus and tick-borne encephalitis (TBE) virus. The E proteins of west nile virus {37}, dengue virus {38}, yellow fever virus {38} and TBE virus {39} form trimeric structures on the viral surface and are of particular interest.   The envelope glycoproteins of bunyaviridae. Bunyaviridae include Bunyaviruses, Nairoviruses, Phleboviruses, Hantaviruses, and Tospoviruses. Viruses of interest include bunyavirus, Bunyamwera virus, california encephalitis virus, La Cross virus, Hantaan virus, Sin Nombre virus, Crimean-congo hemorrhagic fever virus, Sandfly fever Sicilian virus and Rift valley fever virus. The nucleocapsid proteins of hantaviruses form trimeric coiled coils {40} and is of particular interest.   The envelope glycoproteins of arenaviridae. Arenaviridae include lymphocytic choriomeningitis virus, ippy virus and lassa virus.       

     These proteins may be used in any known forms e.g. in native form, mutant form, truncated form, deleted form, etc. For example, various forms of HIV Env protein are known, including modified and domain-deleted proteins, and all of these various forms can be used with the invention. 
     Where a viral protein is naturally presented in a cleaved form (e.g. gp160 in HIV, cleaved to gp120/gp41; Spike protein in coronaviruses, cleaved to S1/S2; etc.), the invention preferably uses the N-terminus cleavage product, or the extracellular region, as the antigenic domain. 
     Within the group of viral surface proteins, a preferred sub-group is antigens which naturally form oligomers on the viral surface. Particularly preferred antigens are the viral fusion proteins (or spike proteins), which must usually be in oligomeric form in order to be fusogenically active {41}. The invention provides a way of presenting the antigenic portions of these proteins in a native oligomeric form. Preferred antigenic domains for use with the invention are thus the globular head domains of viral fusion proteins from enveloped viruses. 
     Viral fusion proteins are usually described in terms of a stalk domain and a globular head domain. The extraviral head domain contains the antigenic determinants, and the transmembrane stalk domain both anchors the protein to the virion envelope and mediates the native trimeric assembly via its coiled-coil motifs. In the native virion the stalk and head domains may be non-covalently or covalently associated. They may be formed by proteolytic cleavage of a precursor polypeptide, with the cleavage products remaining associated on the virion&#39;s surface. 
     The E2 spike protein of SARS coronavirus is a viral fusion polypeptide, and its S1 globular head domain can be used as an antigenic domain. Several genome sequences for the E2 protein are available, and SEQ ID NO: 1 herein is a preferred sequence. The globular head within SEQ ID NO: 1 is around residues 14 to 662 (SEQ ID NO: 2). Thus domain (a) in the polypeptide of the invention may comprise amino acid sequence SEQ ID NO:2 herein, or may comprise an amino acid sequence: (i) having at least m % identity to SEQ ID NO:2, where m is 50 or more (e.g. 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5 or more); and/or (ii) which is a fragment of at least n consecutive amino acids of SEQ ID NO:2, wherein n is 7 or more (e.g. 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 or more). These polypeptides include variants (e.g. allelic variants, homologs, orthologs, paralogs, mutants, etc.) of SEQ ID NO:2. Preferred fragments of (ii) comprise an epitope from SEQ ID NO:2, preferably a B-cell epitope. B-cell epitopes can be identified empirically or can be predicted algorithmically. Other preferred fragments of (ii) lack one or more amino acids (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25 or more) from the C-terminus and/or one or more amino acids (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 45 or more) from the N-terminus of the relevant amino acid sequence from SEQ ID NO:2. 
     Within the amino acid sequence of a viral fusion polypeptide, the boundary of the globular head domain may not be known with absolute accuracy, but this is not a problem for practising the invention. The globular sequence can initially be identified approximately and then, if necessary, its boundaries can be determined by testing the antigenicity of the first approximation with and without neighbouring amino acid residues. Even so, the invention does not require the boundaries to be known with absolute precision, as the only basic requirement for the invention is that the sequence should function in a way which retains the relevant antigenic determinants of the viral protein without destroying the function of the other domains within the polypeptide. The inclusion of extraneous non-globular-head amino acids does not generally detract from this basic function. 
     Another preferred group of antigens is bacterial surface proteins. Specific bacteria whose surface proteins may be manipulated for oligomeric expression according to the invention are:  Neisseria meningitidis , particularly serogroup B;  Neisseria gonorrhoeae; Streptococcus pneumoniae; Streptococcus pyogenes; Streptococcus agalactiae; Staphylococcus aureus; Haemophilus influenzae , including type b and non-typeable strains;  Moraxella catarrhalis; Helicobacter pylori; Chlamydia trachomatis; Chlamydia pneumoniae; Corynebacterium diphtheriae; Clostridium tetani; Bordetella pertussis ; etc. The invention will generally use the extracellular antigenic region of a bacterial surface protein, with any bacterial transmembrane sequence being omitted. The transmembrane sequence of a bacterial surface protein can readily be identified (if present) based on pattern recognition, sequence analysis and homology. 
     Domain (a) in the polypeptide of the invention may comprise any of the following specific amino acid sequences, or may comprise an amino acid sequence: (i) having at least m % identity to one or more of the following amino acid sequences, where m is 50 or more (e.g. 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5 or more); and/or (ii) which is a fragment of at least n consecutive amino acids of the following amino acid sequences, wherein n is 7 or more (e.g. 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 or more):
         Where the antigenic domain is derived from a  N. meningitidis  antigen, domain (a) may be based on an amino acid sequence selected from SEQ ID NO S : 21 to 26.   Where the antigenic domain is derived from a  S. pneumoniae  antigen, domain (a) may be based on an amino acid sequence selected from PhtA, PhtD, PhtB, PhtE, SpsA, LytB, LytC, LytA, Sp125, Sp101, Sp128, Sp130 and Sp133, as disclosed in reference 42.   Where the antigenic domain is derived from a  S. pyogenes  or  S. agalactiae  antigen, domain (a) may be based on an amino acid sequence selected from the streptococcal amino acid sequences disclosed in reference 43.   Where the antigenic domain is derived from a  S. aureus  antigen, domain (a) may be based on an amino acid sequence selected from even-numbered SEQ ID NO S : 2 to 5642 in ref. 44.   Where the antigenic domain is derived from a  H. influenzae  antigen, domain (a) may be based on an amino acid sequence selected from SEQ ID NOS: 2 to 5080 in reference 45.   Where the antigenic domain is derived from a  M. catarrhalis  antigen, domain (a) may be based on an amino acid sequence selected from the antigens disclosed in references 46 to 58.   These polypeptides include variants (e.g. allelic variants, homologs, orthologs, paralogs, mutants, etc.). Preferred fragments of (ii) comprise an epitope from said amino acid sequences, preferably a B-cell epitope. B-cell epitopes can be identified empirically or can be predicted algorithmically. Other preferred fragments of (ii) lack one or more amino acids (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25 or more) from the C-terminus and/or one or more amino acids (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 45 or more) from the N-terminus of the amino acid sequences.       

     Within the amino acid sequence of a bacterial surface polypeptide, the boundary between an extracellular antigenic domain and a transmembrane domain may not be known with absolute accuracy, but this is not a problem for practising the invention. The antigenic sequence can initially be identified approximately and then, if necessary, its boundaries can be determined by testing the antigenicity of the first approximation with and without neighbouring amino acid residues. Even so, the invention does not require the boundaries to be known with absolute precision, as the only basic requirement for the invention is that the sequence should function in a way which retains the relevant antigenic determinants of the bacterial protein without destroying the function of the other domains within the polypeptide. 
     The Transmembrane Domain 
     Polypeptides of the invention will typically include a transmembrane domain that enables the polypeptide to be located within a lipid bilayer. Thousands of transmembrane sequences are available for use with the invention. In general terms, the transmembrane domain of one protein can be taken as a complete unit and substituted for the transmembrane domain of another protein, without disrupting the protein&#39;s membrane localisation. 
     When in situ within a lipid bilayer, the amino acid chain of the transmembrane domain will pass through the lipid bilayer at least once, but can pass through several times (single-pass or multi-pass). If it passes through the bilayer an odd number of times then the start of the transmembrane domain will be on the opposite side of the bilayer from the end of the transmembrane domain (and of the antigenic domain); if it passes through an even number of times then the start and end will be on the same side. 
     Transmembrane domains typically comprise α-helical sequences, although membrane-spanning β-stranded sequences are also known, as are α-helical sequences that include short pore-forming helices buried in the membrane. 
     One class of transmembrane domain which can be used with the invention is found in the seven-transmembrane-helix receptors (7-TMR family). As the name suggests, the transmembrane domain from these proteins crosses the lipid bilayer seven times. A comprehensive database of sequences of the human 7-TMR family is found in references 59 &amp; 60. 
     More generally, the freely-available TMbase database {61, 62} includes details of transmembrane proteins and their helical membrane-spanning domains. In contrast, DB-NTMR {63} is a database of the non-transmembrane sequences of transmembrane proteins. TMPDB {64, 65} is a database of experimentally-characterised transmembrane topologies that have been determined by X-ray crystallography, NMR, gene-fusion technique, substituted cysteine accessibility method, N-linked glycosylation experiment and other biochemical methods. 
     Further transmembrane domains can be identified by subjecting amino acid sequences to the many transmembrane prediction algorithms that are available e.g. HMMTOP, TMHMM, TMPred, PHDhtm, DAS, TMFinder, SOSUI, TMAP, MEMSAT and TOPPred2 {66, 67}. 
     Within the amino acid sequence of a transmembrane protein, the boundary of the transmembrane domain may not be known with absolute accuracy (e.g. it may be unclear whether a particular amino acid residue should be classified as part of a transmembrane domain or as part of a cytoplasmic or extracellular domain), but this is not a problem for practising the invention. The transmembrane sequence can initially be identified approximately and then, if necessary, its boundaries can be determined by testing the sequence and truncated forms as fusions. Even so, the invention does not require the boundaries to be known with absolute precision, as the only basic requirement for the invention is that the sequence should function in a way which allows the polypeptide to be localised within a lipid bilayer without destroying the function of the other domains within the polypeptide. The inclusion of extraneous non-transmembrane amino acids on either or both sides of the membrane generally does not detract from this basic function of the transmembrane sequence. 
     Transmembrane domains can be taken from eukaryotic or prokaryotic polypeptides (e.g. from plants, animals, mammals, yeasts, Gram-negative bacteria, Gram-positive bacteria, viruses, etc.) or, alternatively, artificial transmembrane domains {e.g. 68} can be used. 
     Preferred transmembrane domains are those taken from bacterial transmembrane proteins. A preferred subset of transmembrane proteins is the adhesins. Specific transmembrane sequences for use with the invention are those from  Yersinia enterocolitica  adhesin YadA {69 }, Neisseria meningitidis  adhesin NadA {4 }, Moraxella catarrhalis  surface protein UspA2 {70} and other adhesins {71}, such as the transmembrane domains of SEQ ID NOS: 42-58. Thus domain (c) in the polypeptide of the invention may comprise one of NadA amino acid sequences SEQ ID NO S : 15, 19, 20 or 40 herein, or may comprise an amino acid sequence: (i) having at least m % identity to one or more of SEQ ID NO S : 15, 19, 20 or 40, where m is 50 or more (e.g. 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5 or more); and/or (ii) which is a fragment of at least n consecutive amino acids of one or more of SEQ ID NO S : 15, 19, 20 or 40 wherein n is 7 or more (e.g. 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 or more). These polypeptides include variants (e.g. allelic variants, homologs, orthologs, paralogs, mutants, etc.) of SEQ ID NO S : 15, 19, 20 &amp; 40. Preferred fragments of (ii) comprise an epitope from one or more of SEQ ID NO S : 15, 19, 20 &amp; 40, preferably a B-cell epitope. B-cell epitopes can be identified empirically or can be predicted algorithmically. Other preferred fragments of (ii) lack one or more amino acids (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25 or more) from the C-terminus and/or one or more amino acids (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 45 or more) from the N-terminus of the relevant amino acid sequence from SEQ ID NO S : 15, 19, 20 &amp; 40. 
     Other preferred transmembrane domains are those taken from the same protein as the antigenic domain. Thus domains (a) and (c) may be from the same protein, but with the oligomerisation domain being from a different protein. For example, if the antigenic domain is from the envelope protein of a virus (e.g. HIV) then the transmembrane domain may also be from that envelope protein. 
     Preferred Combinations of Domains (a), (b) and (c) 
     For domains (a), (b) and (c), it is preferred that at least one has a eukaryotic origin and at least one has a prokaryotic origin. Alternatively, at least one of (a), (b) and (c) may be an artificial domain that is not found in nature. A virus is considered to be a prokaryote or eukaryote based on its natural host e.g. HIV is a eukaryote, whereas a bacteriophage is a prokaryote. 
     The invention is particularly suitable for bacterial presentation of eukaryotic antigens. It is thus preferred that domain (c) is from a prokaryote, such as a bacterium, and that domain (a) is from a eukaryote, and more particularly from a eukaryotic virus. Domain (b) may be from a prokaryote or a eukaryote, but it is preferred to use a prokaryotic sequence. 
     In preferred embodiments, domains (b) and (c) are from the same prokaryotic protein. The domains are then certain to be compatible with each other and without the need for confirmation. Bacterial surface proteins are a preferred source for domains (b) and (c), with bacterial adhesins being useful. YadA, NadA, UspA2 the adhesins of reference 71 are suitable sources. The NadA adhesin is most preferred, and so domains (b) and (c) may together have an amino acid sequence such as SEQ ID NO: 41. 
     A particularly preferred polypeptide of the invention comprises: (a) an antigenic domain from the viral fusion protein of an enveloped eukaryotic virus; (b) a coiled-coil domain from a bacterial adhesin; and (c) a transmembrane domain from the same bacterial adhesin as (b). Examples of such proteins, having domains (b) and (c) from  N. meningitidis  NadA and domain (a) from HIV, are SEQ ID NOS: 3, 4, 5, 6, 32 and 33. 
     Further Sequences 
     As well as having domains (a), (b) and, optionally, (c), polypeptides of the invention may include further sequences. 
     Polypeptides may include a N-terminus leader or signal peptide to direct protein trafficking. These will be present in the nascent translated polypeptide, but will typically not be present in the mature form of the polypeptide e.g. when it is in situ within a lipid bilayer. Where a protein is to be displayed on the cell surface then a leader peptide that directs proteins to the membrane in the expression host is preferred. For expression in  E. coli  then the leader peptide of NadA can be conveniently used, but many other suitable leader peptides are available to the skilled person. 
     Polypeptides will typically include a cytoplasmic sequence which extends inwards from domain (c). This cytoplasmic sequence will typically be located at the C-terminus of domain (c), and at the C-terminus of the complete polypeptide. Suitable cytoplasmic tails are available from transmembrane proteins. For convenience, it is normal to use the cytoplasmic tail which is found in nature with domain (c), although modifications of the native tail sequence may, of course, be made. Thus the cytoplasmic sequence may comprise an amino acid sequence: (i) having at least m % identity to the natural cytoplasmic tail, where m is 50 or more (e.g. 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5 or more); and/or (ii) which is a fragment of at least n consecutive amino acids of the cytoplasmic tail, wherein n is 7 or more (e.g. 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 or more). Tails may influence protein trafficking. 
     Polypeptides may include amino acid sequences between these various domains. These can be artificial sequences (e.g. to assist in DNA manipulation or cloning, such as restriction sites) or can be taken from the same polypeptides as domains (a) to (c) e.g. the sequence already between a transmembrane domain and a coiled-coil sequence may be used. A useful artificial linker sequence is GSGGGG (SEQ ID NO:27), with the Gly-Ser dipeptide being formed from a BamHI restriction site, thus aiding cloning and manipulation, and the (Gly) 4  tetrapeptide being a typical poly-glycine linker for flexibility. 
     In general, therefore, polypeptides of the invention have the formula NH 2 -A-B-C-D-E-F-G-H-COOH where: -A- is an optional leader sequence; -B- is an optional linker sequence; -C- is an antigenic sequence; -D- is an optional linker sequence; -E- is a coiled-coil sequence; -F- is an optional linker sequence; -G- is a transmembrane sequence; and -H- is an optional cytoplasmic tail. 
     Sequences -A-, -B-, -D-, -F- and -H- will typically be short (e.g. 40 or fewer amino acids i.e. 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1). Short peptide can facilitate cloning or purification (e.g. histidine tags i.e. His h  where h=3, 4, 5, 6, 7, 8, 9, 10 or more). 
     Polypeptides may include one or more protease recognition sequences, thereby allowing release of desired parts of the polypeptide (e.g. the extracellular portion) after it has been expressed e.g. such that a protein can be expressed conveniently on the cell surface, but then may be released for further use. A protease recognition sequence may be introduced at various positions e.g. between domains (e.g. together with a linker), or may be inserted within domains. A protease recognition sequence may be positioned between the coiled-coil domain and the antigenic domain, such that the protease releases the antigenic domain and disrupts oligomerisation, or it may be between the transmembrane domain and the coiled-coil domain, such that the protease releases the polypeptide in oligomeric form. Having the cleavage site within the coiled-coil domain will have various effects on oligomerisation depending on the site&#39;s position. Thus one or more of sequences -D-, -E- and/or -F- in the above formula may include a protease recognition site. It is preferred to include the site in sequence -F-. 
     The thrombin recognition sequence is LVPR/GS (SEQ ID NO: 38), and this can be inserted on its own or together with a linker (e.g. SEQ ID NO: 37). Other proteases and their recognition sequences are well known in the art. 
     Preparation of Nucleic Acid Vectors for Polypeptide Expression 
     Polypeptides of the invention can be prepared by various means (e.g. recombinant expression, purification from cell culture, chemical synthesis, etc.) and in various forms (e.g. native, with fusion partners, non-glycosylated, lipidated, etc.). They are preferably prepared in substantially pure form (i.e. substantially free from other bacterial or host cell proteins). 
     Use of a recombinant host is a preferred route for polypeptide expression according to the invention. The host will include a nucleic acid sequence encoding a polypeptide of the invention. Such nucleic acid sequences can be prepared by fusing, in frame, sequences encoding the separate domains of the protein. For example, nucleic acid fragments encoding an antigenic domain and an oligomerisation domain may be prepared by chemical synthesis, by amplification, or by digestion. After any necessary treatment to make the fragments compatible (e.g. blunt-ending, etc.) the fragments can be ligated such that their coding sequences are in-frame, to give a coding sequence for the polypeptide as a whole. The coding sequence can be placed into an expression vector downstream of a promoter and used for expression purposes. 
     Oligomers 
     Within the polypeptides of the invention, the coiled-coil domains confer the ability to assemble into oligomers e.g. dimers, trimers, tetramers or pentamers. 
     Thus the invention provides an oligomeric protein, comprising oligomerised polypeptides of the invention. The monomeric units of the oligomer may be the same or different e.g. for a dimeric protein, the invention provides both heterodimers and homodimers. 
     Hetero-oligomers can arise in several ways. For example: monomers may have the same transmembrane and coiled-coil domains, but different antigenic domains; monomers may have the same coiled-coil and antigenic domains, but different transmembrane domains; monomers may have the same transmembrane and antigenic domains, but different coiled-coil domains; monomers may share only one domain in common; etc. Formation of hetero-oligomeric coiled-coils is known {16}. 
     Preferred oligomers of the invention are trimers. 
     Hosts 
     The invention offers the convenience of expressing a eukaryotic polypeptide in a prokaryotic host, without losing the oligomeric assembly of the native eukaryotic polypeptide. The antigenic domain of the polypeptide will be extracellular when expressed. Thus the invention provides a host cell, wherein the host cell expresses a polypeptide of the invention. The polypeptide is preferably expressed on the surface of the host cell. 
     It is thus preferred to express the polypeptides of the invention in a prokaryotic host, such as a bacterium.  Escherichia coli  is a convenient host. Other suitable hosts include  Bacillus subtilis, Vibrio cholerae, Salmonella typhi, Salmonella typhimurium, Neisseria lactamica, Neisseria cinerea, Mycobacteria  (e.g.  M. tuberculosis ),  Shigella  spp.,  Yersinia enterocolitica, Listeria monocytogenes , yeasts, etc. These hosts may be manipulated to incorporate eukaryotic glycosylation pathways. In many cases, however, the lack of endogenous glycosylation pathways in bacterial hosts is an advantage, as glycosylation can mask immunogenically-important T- and B-cell epitopes. 
     Immunogens 
     The invention concerns expression of antigenic polypeptides. These are suitable for immunisation purposes, and the immunogen can take various forms. 
     For example, complete polypeptides may be purified for used as immunogens, either in monomeric or, preferably, in oligomeric form. Where a polypeptide includes a protease cleavage site, the polypeptides may be treated with protease and then the cleaved extracellular portions may be used as immunogens. Where a polypeptide is expressed in a cell, the cell itself may be used as an immunogen, with its surface exposed polypeptide giving immunogenic activity. As an alternative, outer membrane vesicles, or blebs, containing exposed polypeptides, may be used as immunogens. 
     Immunisation with cell membranes (either intact cells (‘bacterial vector vaccines’), which may be live or killed, or membrane preparations derived from the cells) including the polypeptides of the invention is a preferred route. Host cells which contain nucleic acid of the invention and which express polypeptide of the invention may be used as delivery vehicles e.g. commensal bacteria {72}. This is particularly useful for delivery to mucosal surfaces, including oral administration, particularly if an intact cell&#39;s natural trophisms are exploited for in vivo delivery. Preferred bacterial hosts are genetically defined, attenuated and/or well-tolerated by a recipient animal or human. Preferred hosts for immunisation in this way include live oral  Salmonella  vector vaccines,  Yersinia enterocolitica, Shigella  spp.,  Vibrio cholerae, Mycobacterium  strain BCG and  Listeria monocytogenes.    
     Nucleic Acids 
     The invention also provides nucleic acid encoding the polypeptides of the invention. Furthermore, the invention provides nucleic acid which can hybridise to this nucleic acid, preferably under “high stringency” conditions (e.g. 65° C. in a 0.1×SSC, 0.5% SDS solution). 
     Nucleic acid according to the invention can be prepared in many ways (e.g. by chemical synthesis, from genomic or cDNA libraries, from the organism itself, etc.) and can take various forms (e.g. single stranded, double stranded, vectors, probes, etc.). They are preferably prepared in substantially pure form (i.e. substantially free from other bacterial or host cell nucleic acids). 
     The term “nucleic acid” includes DNA and RNA, and also their analogues, such as those containing modified backbones (e.g. phosphorothioates, etc.), and also peptide nucleic acids (PNA), etc. The invention includes nucleic acid comprising sequences complementary to those described above (e.g. for antisense or probing purposes). 
     Immunogenic Compositions and Medicaments 
     The invention provides a composition comprising a polypeptide and/or a nucleic acid of the invention. Compositions of the invention are preferably immunogenic compositions, and are more preferably vaccine compositions. Vaccines according to the invention may either be prophylactic (i.e. to prevent infection) or therapeutic (i.e. to treat infection), but will typically be prophylactic. 
     The pH of the composition is preferably between 6 and 8, preferably about 7. The pH may be maintained by the use of a buffer. The composition may be sterile and/or pyrogen-free. The composition may be isotonic with respect to humans. 
     The invention also provides a composition of the invention for use as a medicament. The medicament is preferably able to raise an immune response in a mammal (i.e. it is an immunogenic composition) and is more preferably a vaccine. 
     The invention also provides the use of one or more (e.g. 2, 3, 4, 5, 6) of the polypeptides of the invention in the manufacture of a medicament for raising an immune response in a mammal. The medicament is preferably a vaccine. 
     The invention also provides a method for raising an immune response in a mammal comprising the step of administering an effective amount of a composition of the invention. The immune response is preferably protective and preferably involves antibodies and/or cell-mediated immunity. The method may raise a booster response. 
     The mammal is preferably a human. Where the vaccine is for prophylactic use, the human is preferably a child (e.g. a toddler or infant) or a teenager; where the vaccine is for therapeutic use, the human is preferably a teenager or an adult. A vaccine intended for children may also be administered to adults e.g. to assess safety, dosage, immunogenicity, etc. 
     One way of checking efficacy of therapeutic treatment involves monitoring infections after administration of the composition of the invention. One way of checking efficacy of prophylactic treatment involves monitoring immune responses against the polypeptides after administration of the composition. 
     Compositions of the invention will generally be administered directly to a patient. Direct delivery may be accomplished by parenteral injection (e.g. subcutaneously, intraperitoneally, intravenously, intramuscularly, or to the interstitial space of a tissue), or by rectal, oral (e.g. tablet, spray), vaginal, topical, transdermal {e.g. see ref. 73} or transcutaneous {e.g. see refs. 74 &amp; 75}, intranasal {e.g. see ref. 76}, ocular, aural, pulmonary or other mucosal administration. 
     The invention may be used to elicit systemic and/or mucosal immunity. 
     Dosage treatment can be a single dose schedule or a multiple dose schedule. Multiple doses may be used in a primary immunisation schedule and/or in a booster immunisation schedule. In a multiple dose schedule the various doses may be given by the same or different routes e.g. a parenteral prime and mucosal boost, a mucosal prime and parenteral boost, etc. 
     Infections affect various areas of the body and so the compositions of the invention may be prepared in various forms. For example, the compositions may be prepared as injectables, either as liquid solutions or suspensions. Solid forms suitable for solution in, or suspension in, liquid vehicles prior to injection can also be prepared (e.g. a lyophilised composition). The composition may be prepared for topical administration e.g. as an ointment, cream or powder. The composition may be prepared for oral administration e.g. as a tablet or capsule, as a spray, or as a syrup (optionally flavoured). The composition may be prepared for pulmonary administration e.g. as an inhaler, using a fine powder or a spray. The composition may be prepared as a suppository or pessary. The composition may be prepared for nasal, aural or ocular administration e.g. as drops. The composition may be in kit form, designed such that a combined composition is reconstituted just prior to administration to a patient. Such kits may comprise one or more antigens in liquid form and one or more lyophilised antigens. 
     Immunogenic compositions used as vaccines comprise an immunologically effective amount of antigen(s), as well as any other components, as needed. By ‘immunologically effective amount’, it is meant that the administration of that amount to an individual, either in a single dose or as part of a series, is effective for treatment or prevention. This amount varies depending upon the health and physical condition of the individual to be treated, age, the taxonomic group of individual to be treated (e.g. non-human primate, primate, etc.), the capacity of the individual&#39;s immune system to synthesise antibodies, the degree of protection desired, the formulation of the vaccine, the treating doctor&#39;s assessment of the medical situation, and other relevant factors. It is expected that the amount will fall in a relatively broad range that can be determined through routine trials. 
     Further Components of the Composition 
     The composition of the invention will typically, in addition to the components mentioned above, comprise one or more ‘pharmaceutically acceptable carriers’, which include any carrier that does not itself induce the production of antibodies harmful to the individual receiving the composition. Suitable carriers are typically large, slowly metabolised macromolecules such as proteins, polysaccharides, polylactic acids, polyglycolic acids, polymeric amino acids, amino acid copolymers, and lipid aggregates (such as oil droplets or liposomes). Such carriers are well known to those of ordinary skill in the art. The vaccines may also contain diluents, such as water, saline, glycerol, etc. Additionally, auxiliary substances, such as wetting or emulsifying agents, pH buffering substances, and the like, may be present. A thorough discussion of pharmaceutically acceptable excipients is available in reference 77. 
     Compositions of the invention may be administered in conjunction with immunoregulatory agents. In particular, compositions will usually include one or more adjuvants. Such adjuvants include, but are not limited to: 
     A. Mineral-Containing Compositions 
     Mineral containing compositions suitable for use as adjuvants in the invention include mineral salts, such as aluminium salts and calcium salts. The invention includes mineral salts such as hydroxides (e.g. oxyhydroxides), phosphates (e.g. hydroxyphosphates, orthophosphates), sulphates, etc. {e.g. see chapters 8 &amp; 9 of ref. 78}, or mixtures of different mineral compounds, with the compounds taking any suitable form (e.g. gel, crystalline, amorphous, etc.), and with adsorption being preferred. The mineral containing compositions may also be formulated as a particle of metal salt {79}. 
     B. Oil Emulsions 
     Oil emulsion compositions suitable for use as adjuvants in the invention include squalene-water emulsions, such as MF59 {Chapter 10 of ref. 78; see also ref. 80} (5% Squalene, 0.5% Tween 80, and 0.5% Span 85, formulated into submicron particles using a microfluidizer). Complete Freund&#39;s adjuvant (CFA) and incomplete Freund&#39;s adjuvant (IFA) may also be used. 
     C. Saponin Formulations {Chapter 22 of Ref 78} 
     Saponin formulations may also be used as adjuvants in the invention. Saponins are a heterologous group of sterol glycosides and triterpenoid glycosides that are found in the bark, leaves, stems, roots and even flowers of a wide range of plant species. Saponin from the bark of the  Quillaia saponaria  Molina tree have been widely studied as adjuvants. Saponin can also be commercially obtained from  Smilax ornata  (sarsaprilla),  Gypsophilla paniculata  (brides veil), and  Saponaria officianalis  (soap root). Saponin adjuvant formulations include purified formulations, such as QS21, as well as lipid formulations, such as ISCOMs. QS21 is marketed as Stimulon™. 
     Saponin compositions have been purified using HPLC and RP-HPLC. Specific purified fractions using these techniques have been identified, including QS7, QS17, QS18, QS21, QH-A, QH-B and QH-C. Preferably, the saponin is QS21. A method of production of QS21 is disclosed in ref. 81. Saponin formulations may also comprise a sterol, such as cholesterol {82}. 
     Combinations of saponins and cholesterols can be used to form unique particles called immunostimulating complexs (ISCOMs) {chapter 23 of ref. 78}. ISCOMs typically also include a phospholipid such as phosphatidylethanolamine or phosphatidylcholine. Any known saponin can be used in ISCOMs. Preferably, the ISCOM includes one or more of QuilA, QHA and QHC. ISCOMs are further described in refs. 82-84. Optionally, the ISCOMS may be devoid of additional detergent {85}. 
     A review of the development of saponin based adjuvants can be found in refs. 86 &amp; 87. 
     D. Virosomes and Virus-Like Particles 
     Virosomes and virus-like particles (VLPS) can also be used as adjuvants in the invention. These structures generally contain one or more proteins from a virus optionally combined or formulated with a phospholipid. They are generally non-pathogenic, non-replicating and generally do not contain any of the native viral genome. The viral proteins may be recombinantly produced or isolated from whole viruses. These viral proteins suitable for use in virosomes or VLPs include proteins derived from influenza virus (such as HA or NA), Hepatitis B virus (such as core or capsid proteins), Hepatitis E virus, measles virus, Sindbis virus, Rotavirus, Foot-and-Mouth Disease virus, Retrovirus, Norwalk virus, human Papilloma virus, HIV, RNA-phages, Qβ-phage (such as coat proteins), GA-phage, fr-phage, AP205 phage, and Ty (such as retrotransposon Ty protein p1). VLPs are discussed further in refs. 88-93. Virosomes are discussed further in, for example, ref. 94 
     E. Bacterial or Microbial Derivatives 
     Adjuvants suitable for use in the invention include bacterial or microbial derivatives such as non-toxic derivatives of enterobacterial lipopolysaccharide (LPS), Lipid A derivatives, immunostimulatory oligonucleotides and ADP-ribosylating toxins and detoxified derivatives thereof. 
     Non-toxic derivatives of LPS include monophosphoryl lipid A (MPL) and 3-O-deacylated MPL (3dMPL). 3dMPL is a mixture of 3 de-O-acylated monophosphoryl lipid A with 4, 5 or 6 acylated chains. A preferred “small particle” form of 3 De-O-acylated monophosphoryl lipid A is disclosed in ref. 95. Such “small particles” of 3dMPL are small enough to be sterile filtered through a 0.22 μm membrane {95}. Other non-toxic LPS derivatives include monophosphoryl lipid A mimics, such as aminoalkyl glucosaminide phosphate derivatives e.g. RC-529 {96, 97}. 
     Lipid A derivatives include derivatives of lipid A from  Escherichia coli  such as OM-174. OM-174 is described for example in refs. 98 &amp; 99. 
     Immunostimulatory oligonucleotides suitable for use as adjuvants in the invention include nucleotide sequences containing a CpG motif (a dinucleotide sequence containing an unmethylated cytosine linked by a phosphate bond to a guanosine). Double-stranded RNAs and oligonucleotides containing palindromic or poly(dG) sequences have also been shown to be immunostimulatory. 
     The CpG&#39;s can include nucleotide modifications/analogs such as phosphorothioate modifications and can be double-stranded or single-stranded. References 100, 101 and 102 disclose possible analog substitutions e.g. replacement of guanosine with 2′-deoxy-7-deazaguanosine. The adjuvant effect of CpG oligonucleotides is further discussed in refs. 103-108. 
     The CpG sequence may be directed to TLR9, such as the motif GTCGTT or TTCGTT {109}. The CpG sequence may be specific for inducing a Th1 immune response, such as a CpG-A ODN, or it may be more specific for inducing a B cell response, such a CpG-B ODN. CpG-A and CpG-B ODNs are discussed in refs. 110-112. Preferably, the CpG is a CpG-A ODN. 
     Preferably, the CpG oligonucleotide is constructed so that the 5′ end is accessible for receptor recognition. Optionally, two CpG oligonucleotide sequences may be attached at their 3′ ends to form “immunomers”. See, for example, refs. 109 &amp; 113-115. 
     Bacterial ADP-ribosylating toxins and detoxified derivatives thereof may be used as adjuvants in the invention. Preferably, the protein is derived from  E. coli  ( E. coli  heat labile enterotoxin “LT”), cholera (“CT”), or pertussis (“PT”). The use of detoxified ADP-ribosylating toxins as mucosal adjuvants is described in ref. 116 and as parenteral adjuvants in ref. 117. The toxin or toxoid is preferably in the form of a holotoxin, comprising both A and B subunits. Preferably, the A subunit contains a detoxifying mutation; preferably the B subunit is not mutated. Preferably, the adjuvant is a detoxified LT mutant such as LT-K63, LT-R72, and LT-G192. The use of ADP-ribosylating toxins and detoxified derivaties thereof, particularly LT-K63 and LT-R72, as adjuvants can be found in refs. 118-125. Numerical reference for amino acid substitutions is preferably based on the alignments of the A and B subunits of ADP-ribosylating toxins set forth in ref. 126, specifically incorporated herein by reference in its entirety. 
     F. Human Immunomodulators 
     Human immunomodulators suitable for use as adjuvants in the invention include cytokines, such as interleukins (e.g. IL-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-12 {127}, etc.) {128}, interferons (e.g. interferon-γ), macrophage colony stimulating factor, and tumor necrosis factor. 
     G. Bioadhesives and Mucoadhesives 
     Bioadhesives and mucoadhesives may also be used as adjuvants in the invention. Suitable bioadhesives include esterified hyaluronic acid microspheres {129} or mucoadhesives such as cross-linked derivatives of poly(acrylic acid), polyvinyl alcohol, polyvinyl pyrollidone, polysaccharides and carboxymethylcellulose. Chitosan and derivatives thereof may also be used as adjuvants in the invention {130}. 
     H. Microparticles 
     Microparticles may also be used as adjuvants in the invention. Microparticles (i.e. a particle of ˜100 nm to ˜150 μm in diameter, more preferably ˜200 nm to ˜30 μm in diameter, and most preferably ˜500 nm to ˜10 μm in diameter) formed from materials that are biodegradable and non-toxic (e.g. a poly(α-hydroxy acid), a polyhydroxybutyric acid, a polyorthoester, a polyanhydride, a polycaprolactone, etc.), with poly(lactide-co-glycolide) are preferred, optionally treated to have a negatively-charged surface (e.g. with SDS) or a positively-charged surface (e.g. with a cationic detergent, such as CTAB). 
     I. Liposomes (Chapters 13 &amp; 14 of Ref 78) 
     Examples of liposome formulations suitable for use as adjuvants are described in refs. 131-133. 
     J. Polyoxyethylene Ether and Polyoxyethylene Ester Formulations 
     Adjuvants suitable for use in the invention include polyoxyethylene ethers and polyoxyethylene esters {134}. Such formulations further include polyoxyethylene sorbitan ester surfactants in combination with an octoxynol {135} as well as polyoxyethylene alkyl ethers or ester surfactants in combination with at least one additional non-ionic surfactant such as an octoxynol {136}. Preferred polyoxyethylene ethers are selected from the following group: polyoxyethylene-9-lauryl ether (laureth 9), polyoxyethylene-9-steoryl ether, polyoxytheylene-8-steoryl ether, polyoxyethylene-4-lauryl ether, polyoxyethylene-35-lauryl ether, and polyoxyethylene-23-lauryl ether. 
     K. Polyphosphazene (PCPP) 
     PCPP formulations are described, for example, in refs. 137 and 138. 
     L. Muramyl Peptides 
     Examples of muramyl peptides suitable for use as adjuvants in the invention include N-acetyl-muramyl-L-threonyl-D-isoglutamine (thr-MDP), N-acetyl-normuramyl- L -alanyl- D -isoglutamine (nor-MDP), and N-acetylmuramyl- L -alanyl- D -isoglutaminyl- L -alanine-2-(1′-2′-dipalmitoyl-sn-glycero-3-hydroxyphosphoryloxy)-ethylamine MTP-PE). 
     M. Imidazoquinolone Compounds. 
     Examples of imidazoquinolone compounds suitable for use adjuvants in the invention include Imiquamod and its homologues (e,g. “Resiquimod 3M”), described further in refs. 139 and 140. 
     The invention may also comprise combinations of aspects of one or more of the adjuvants identified above. For example, the following adjuvant compositions may be used in the invention: (1) a saponin and an oil-in-water emulsion {141}; (2) a saponin (e.g. QS21)+a non-toxic LPS derivative (e.g. 3dMPL) {142}; (3) a saponin (e.g. QS21)+a non-toxic LPS derivative (e.g. 3dMPL)+a cholesterol; (4) a saponin (e.g. QS21)+3dMPL+IL-12 (optionally+a sterol) {143}; (5) combinations of 3dMPL with, for example, QS21 and/or oil-in-water emulsions {144}; (6) SAF, containing 10% squalane, 0.4% Tween 80™, 5% pluronic-block polymer L121, and thr-MDP, either microfluidized into a submicron emulsion or vortexed to generate a larger particle size emulsion. (7) Ribi™ adjuvant system (RAS), (Ribi Immunochem) containing 2% squalene, 0.2% Tween 80, and one or more bacterial cell wall components from the group consisting of monophosphorylipid A (MPL), trehalose dimycolate (TDM), and cell wall skeleton (CWS), preferably MPL+CWS (Detox™); and (8) one or more mineral salts (such as an aluminum salt)+a non-toxic derivative of LPS (such as 3dMPL). 
     Other substances that act as immunostimulating agents are disclosed in chapter 7 of ref. 78. 
     Further Antigens 
     As well as containing polypeptides of the invention, the compositions of the invention may also include one or more further antigens. Further antigens for inclusion may be, for example:
         antigens from  Helicobacter pylori  such as CagA {145 to 148}, VacA {149, 150}, NAP {151, 152, 153}, HopX {e.g. 154}, HopY {e.g. 154} and/or urease.   a protein antigen from  N. meningitidis  serogroup B, such as those in refs. 155 to 161.   an outer-membrane vesicle (OMV) preparation from  N. meningitidis  serogroup B, such as those disclosed in refs. 162 to 165, etc.   a saccharide antigen from  N. meningitidis  serogroup C, such as the oligosaccharide disclosed in ref. 166 from serogroup C {see also ref. 167}.   a saccharide antigen from  Streptococcus pneumoniae  {e.g. 168, 169, 170}.   an antigen from hepatitis A virus, such as inactivated virus {e.g. 171, 172}.   an antigen from hepatitis B virus, such as the surface and/or core antigens {e.g. 172, 173}.   an antigen from hepatitis C virus {e.g. 174}.   a diphtheria antigen, such as a diphtheria toxoid {e.g. chapter 3 of ref. 175} e.g. the CRM 197  mutant {e.g. 176}.   a tetanus antigen, such as a tetanus toxoid {e.g. chapter 4 of ref. 175}.   an antigen from  Bordetella pertussis , such as pertussis holotoxin (PT) and filamentous haemagglutinin (FHA) from  B. pertussis , optionally also in combination with pertactin and/or agglutinogens 2 and 3 {e.g. refs. 177 &amp; 178}.   a cellular pertussis antigen.   a saccharide antigen from  Haemophilus influenzae  B {e.g. 167}.   an antigen from  N. gonorrhoeae  {e.g. 155, 156, 157}.   an antigen from  Chlamydia pneumoniae  {e.g. 179, 180, 181, 182, 183, 184, 185}.   an antigen from  Chlamydia trachomatis  {e.g. 186}.   an antigen from  Porphyromonas gingivalis  {e.g. 187}.   polio antigen(s) {e.g. 188, 189} such as IPV or OPV.   rabies antigen(s) {e.g. 190} such as lyophilised inactivated virus {e.g. 191, RabAvert™}.   measles, mumps and/or rubella antigens {e.g. chapters 9, 10 &amp; 11 of ref. 175}.   antigen(s) from influenza virus {e.g. chapter 19 of ref. 175}, such as the haemagglutinin and/or neuraminidase surface proteins   antigen(s) from a paarmyxovirus such as respiratory syncytial virus (RSV {192, 193}) and/or parainfluenza virus (PIV3 {194}).   an antigen from  Moraxella catarrhalis  {e.g. 195}.   an antigen from  Streptococcus agalactiae  (group B  streptococcus ) {e.g. 196, 197}.   an antigen from  Streptococcus pyogenes  (group A  streptococcus ) {e.g. 197, 198, 199}.   an antigen from  Staphylococcus aureus  {e.g. 200}.   an antigen from  Bacillus anthracis  {e.g. 201, 202, 203}.   an antigen from a virus in the flaviviridae family (genus flavivirus), such as from yellow fever virus, Japanese encephalitis virus, four serotypes of Dengue viruses, tick-borne encephalitis virus, West Nile virus.   a pestivirus antigen, such as from classical porcine fever virus, bovine viral diarrhoea virus, and/or border disease virus.   a parvovirus antigen e.g. from parvovirus B19.   a prion protein (e.g. the CJD prion protein)   an amyloid protein, such as a beta peptide {204}   a cancer antigen, such as those listed in Table 1 of ref. 205 or in tables 3 &amp; 4 of ref. 206.
 
The composition may comprise one or more of these further antigens. It is preferred that combinations of antigens should be based on shared characteristics e.g. antigens associated with respiratory diseases, antigens associated with enteric diseases, antigens associated with sexually-transmitted diseases, etc.
       

     Where a saccharide or carbohydrate antigen is used, it is preferably conjugated to a carrier protein in order to enhance immunogenicity {e.g. refs. 207 to 216}. Preferred carrier proteins are bacterial toxins or toxoids, such as diphtheria or tetanus toxoids. The CRM 197  diphtheria toxoid is particularly preferred {217}. Other carrier polypeptides include the  N. meningitidis  outer membrane protein {218}, synthetic peptides {219, 220}, heat shock proteins {221, 222}, pertussis proteins {223, 224}, protein D from  H. influenzae { 225}, cytokines {226}, lymphokines {226}, hormones {226}, growth factors {226}, toxin A or B from  C. difficile { 227}, iron-uptake proteins {228}, etc. Different saccharides can be conjugated to the same or different type of carrier protein. Any suitable conjugation reaction can be used, with any suitable linker where necessary. 
     As an alternative to using protein antigens in the composition of the invention, nucleic acid encoding the antigen may be used {e.g. refs. 229 to 237}. Protein components of the compositions of the invention may thus be replaced by nucleic acid (preferably DNA e.g. in the form of a plasmid) that encodes the protein. 
     Processes 
     The invention also provides a process for producing a polypeptide of the invention, comprising the step of culturing a host cell transformed with nucleic acid of the invention under conditions which induce polypeptide expression. 
     The invention provides a process for producing a polypeptide of the invention, comprising the step of synthesising at least part of the polypeptide by chemical means. 
     The invention provides a process for producing nucleic acid of the invention, comprising the step of amplifying nucleic acid using a primer-based amplification method (e.g. PCR). 
     The invention provides a process for producing nucleic acid of the invention, comprising the step of synthesising at least part of the nucleic acid by chemical means. 
     General 
     The term “comprising” encompasses “including” as well as “consisting of” e.g. a composition “comprising” X may consist exclusively of X or may include something additional e.g. X+Y. 
     The term “about” in relation to a numerical value x means, for example, x±10%. 
     The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention. 
     References to a percentage sequence identity between two amino acid sequences means that, when aligned, that percentage of amino acids are the same in comparing the two sequences. This alignment and the percent homology or sequence identity can be determined using software programs known in the art, for example those described in section 7.7.18 of reference 238. A preferred alignment is determined by the Smith-Waterman homology search algorithm using an affine gap search with a gap open penalty of 12 and a gap extension penalty of 2, BLOSUM matrix of 62. The Smith-Waterman homology search algorithm is disclosed in reference 239. 
     In certain embodiments, the invention does not encompass a polypeptide in which: (a) the oligomerisation domain is the NadA adhesin from  N. meningitidis , or a fragment thereof; and (b) the antigenic domain is the SARS coronavirus S1 protein, or a fragment thereof. Similarly, in certain embodiments the invention does not encompass nucleic acid encoding such a polypeptide. These polypeptides and nucleic acids are disclosed in reference 240 and are thus disclaimed from certain embodiments of the present invention. 
     MODES FOR CARRYING OUT THE INVENTION 
     Identification of Bacterial Adhesins 
     Virulence-associated antigens involved in adhesion have been identified in several bacteria {71}, and the stalk domains of these antigens can be used with heterologous antigenic sequences according to the invention. 
     Antigens have been identified in:  Haemophilus influenzae  biogroup  aegyptius  (‘HadA’, SEQ ID NO: 29);  Escherichia coli  K1 (SEQ ID NOS: 42 &amp; 43) and also in EHEC strain EDL933;  Actinobacillus actinomycetemcomitans  (SEQ ID NO: 44);  Haemophilus somnus  (SEQ ID NO: 45);  Haemophilus ducreyi  (SEQ ID NO: 46); EPEC  E. coli  strain E2348/69 (SEQ ID NOS: 47 &amp; 48); EAEC  E. coli  strain O42 (SEQ ID NOS: 49 &amp; 50); uropathogenic  E. coli  (SEQ ID NO: 51);  Shigella flexneri  (SEQ ID NO: 52);  Brucella melitensis  (SEQ ID NO: 53);  Brucella suis  (SEQ ID NO: 54);  Ralstonia solanacearum  (SEQ ID NO: 55);  Sinorhizobium meliloti  (SEQ ID NO: 56);  Bradorhizobium japonicum  (SEQ ID NO: 57); and  Burkholderia fungorum  (SEQ ID NO: 58). 
     The positions of these features in SEQ ID NO S : 29 &amp; 42-58 are as follows: 
                                                     SEQ                   Coiled-           ID   Organism   Length   Leader   Head   coil   Anchor                                                            29     H. aegyptius     256   1-26   27-55     56-184   185-256       42   EHEC   338   1-23   24-207   208-266   267-338                                     43       1588   1-53   54-1515 *   1516-1588                                         44     A. actino -   295   1-25   26-150   151-222   223-295             mycetem -             comitans         45     H. somnus     452   1-26   27-158   159-378   379-452                                     46     H. ducreyi     273   1-21   22-198 *    199-273                                         47   EPEC   338   1-24   25-209   210-266   267-338                                 48       577   1-504 *   505-577                                         49   EAEC   717   1-23   24-109   110-645   646-717                                     50       1743   1-53   54-1670 *   1671-1743       51   UPEC   1778   1-53   54-1705 *   1706-1778                                 52     S. flexneri     990   1-917 *   918-990                                         53     B. melitensis     227   1-27   28-122   123-154   155-227       54     B. suis     311   1-27   28-206   207-238   239-311                                     55     R. solana -   1309   1-230*   231-708   1239-1309             cearum                                   56     S. meliloti     1291    1-1219 *   1220-1291                                     57     B. japonicum     372   1-72   73-300 *    301-372       58     B. fungorum     3399   1-57   58-3328 *   3329-3399               * The boundary between domains is less distinct for some of these adhesins            
SARS Coronavirus Spike Protein
 
     The E2 spike protein of the SARS coronavirus has been reported. An amino acid sequence of this protein is given herein as SEQ ID NO:1. A secondary structure prediction is given below, where C represents a coil, H represents a helix and E represents an extended sequence: 
                          10        20         30       40        50        60        70                    |         |         |         |         |         |         |         MFIFLLFLTLTSGSDLDRCTTFDDVQAPNYTQHTSSMRGVYYPDEIFRSDTLYLTQDLFLPFYSNVTGFH         CeEEEEEEccCCCccceeeeCCCCCCCCCCCCCceEEEEEeCCcEEEEEEEEceEEEEEEeceEEcCeEe                 TINHTFGNPVIPFKDGIYFAATEKSNVVRGWVFGSTMNNKSQSVIIINNSTNVVIRACNFELCDNPFFAV         ceeeeCCCceeeEeCCccecCCCCCCceEEEEEEEEccCCCcEEEEEeCCCEEEEEEEEEeccCCCCCCC                 SKPMGTQTHTMIFDNAFNCTFEYISDAFSLDVSEKSGNFKHLREFVFKNKDGFLYVYKGYQPIDVVRDLP         CCCCCCeEEEEEEEcCCCCcEEEEEeeeEEEcCCCCCChhHHheEEEEeCCCEEEEEEcCCCCCCcCCCC                 SGFNTLKPIFKLPLGINITNFRAILTAFSPAQDIWGTSAAAYFVGYLKPTTFMLKYDENGTITDAVDCSQ         CCCccccccceEEEeeeeceeeeEEEeccCcCCCcCCccchHHhhhccceEEEEEcCCCCEEEEeccCCC                 NPLAELKCSVKSFEIDKGIYQTSNFRVVPSGDVVRFPNITNLCPFGEVFNATKFPSVYAWERKKISNCVA         CCCceEEeCceEeeeCCcEEEeCCeEEEeCCEEEEEeCCCCCCCccceecCCCCCCccHHHhHHHhhcch                 DYSVLYNSTFFSTFKCYGVSATKLNDLCFSNVYADSFVVKGDDVRQIAPGQTGVIADYNYKLPDDFMGCV         hHHHHHHhhceEEeeeeceeececcccceeeEeEeeEEEcCCCeeecccCCCceEeecccceCCccceEE                 LAWNTRNIDATSTGNYNYKYRYLRHGKLRPFERDISNVPFSPDGKPCTPPALNCYWPLNDYGFYTTTGIG         EEEeCCCCCCcCCCCCCCCceccccCccCCccCCCCCCCCCCCCCCCCCCCCCCCCCCCCCceeccCCcc                 YQPYRVVVLSFELLNAPATVCGPKLSTDLIKNQCVNFNFNGLTGTGVLTPSSKRFQPFQQFGRDVSDFTD         eeEEEEEEEEEeCCCCCcccCCCCcCCceEEeeeeEEEEeeccceeeeHHHHHHHhhHHHhheccCCCcc                 SVRDPKTSEILDISPCSFGGVSVITPGTNASSEVAVLYQDVNCTDVSTAIHADQLTPAWRIYSTGNNVFQ         cccccCCCcEEEEEEccCceEEEEEeCCCCCCCceEEeeecceEEEeCCCCcccCCCCccccCCCCcHHH                 TQAGCLIGAEHVDTSYECDIPIGAGICASYHTVSLLRSTSQKSIVAYTMSLGADSSIAYSNNTIAIPTNF         hhccceeeccCCCCCCCCCccCCCcceeEEeecceeeeeecCeEEEEEecCCCCCcccCCCCeEEeeCcc                 SISITTEVMPVSMAKTSVDCNMYICGDSTECANLLLQYGSFCTQLNRALSGIAAEQDRNTREVFAQVKQM         EcccceEEEEEeCCceeecccccccCChHHHHHHHHHHhHHHHHHHHHHHHHHHHhhchHHHHHHHHHhC                 YKTPTLKYFGGFNFSQILPDPLKPTKRSFIEDLLFNKVTLADAGFMKQYGECLGDINARDLICAQKFNGL         CeeeEEecCCceecccCCCCCCCcCChHHHHHHHhccceeeeccceccccccCCCcccccEEEEEEcCCc                 TVLPPLLTDDMIAAYTAALVSGTATAGWTFGAGAALQIPFAMQMAYRFNGIGVTQNVLYENQKQIANQFN         EeccCCCCcHHHHHHHHHHHhhhcCCCchhHhhHHHhccceeEeEhhhcCCcchhhHHHHHHHHHHHHHH                 KAISQIQESLTTTSTALGKLQDVVNQNAQALNTLVKQLSSNFGAISSVLNDILSRLDKVEAEVQIDRLIT         HHHHHHHHhhHhHHHHHHHHHHHHHHHHHHHHHHHHHHHhcchHHHHHHHHHHHHHHHHHHHHHHHHHHH                 GRLQSLQTYVTQQLIRAAEIRASANLAATKMSECVLGQSKRVDFCGKGYHLMSFPQAAPHGVVFLHVTYV         HHHHHHHHHHHHHHhHHHHHHHHHHHHHHHHHHHHHhcccceccccchhHhheeeccCCCcEEEEEEEEE                 PSQERNFTTAPAICHEGKAYFPREGVFVFNGTSWFITQRNFFSPQIITTDNTFVSGNCDVVIGIINNTVY         ECceeeeeccCCeeeeeeeecccCcEEEecCCEEEEcCCCccCCCcccCCCEEEEEEEEEEEeCCceecC                 DPLQPELDSFKEELDKYFKNHTSPDVDFGDISGINASVVNIQKEIDRLNEVAKNLNESLIDLQELGKYEQ         cCCCCCCcHHHHHHHHHHHhCCCCCCCCCcCcceeEeeeccHHHHHHHHHHHHHHhcchhhHHhCCcEEE                 YIKWPWYVWLGFIAGLIAIVMVTILLCCMTSCCSCLKGACSCGSCCKFDEDDSEPVLKGVKLHYT         EecchHHHHHHHHHHHHhheeEEEEEEEeCCCCcceecCCCCCCCcccCCCCCCeEEcccEEEcC            
HIV Envelope Protein
 
     The HIV envelope glycoprotein is expressed as gp160 from the HIV genome, and is cleaved post-translationally to give gp120 and gp41, which remain associated. The gp120 protein is the extracellular domain of the envelope, and the gp41 protein is the transmembrane protein of the envelope. The associated proteins form trimers on the virion surface, but recombinantly-expressed gp120 is monomeric. To increase the immunogenicity of the envelope protein, it has been expressed in  E. coli  as a non-glycosylated trimer by using the NadA oligomerisation structures. 
     The sequence of the Envelope protein up to but not including its transmembrane sequence (optionally with deletion of the 30aa hypervariable V2 region, which is aa 133-162 of SEQ ID NO: 12, replaced by Gly-Ala-Gly, to give gp140ΔV2 {241}) was used as an antigenic domain in combination with the anchor region of  N. meningitidis  NadA protein, joined by the stalk of either NadA or of gp160 (i.e. gp41). Seven different forms of this hybrid sequence were constructed, with a NadA leader peptide (SEQ ID NO: 11). The seven sequences are given as SEQ ID NO S  3 to 9, and are described in more detail in the following table: 
     
       
         
           
               
               
               
             
               
                   
               
               
                 SEQ ID 
                 Length 
                 Description of polypeptide 
               
               
                 NO: 
                 (aa) 
                 (constituent SEQ ID NO s , N-terminus to C-terminus) 
               
               
                   
               
             
            
               
                 3 
                 824 
                 11 - 12 - 14 - 13 - 15 
               
               
                 4 
                 769 
                 11 - 12 - 14 - 13 
               
               
                 5 
                 797 
                 11 - 16 - 14 - 13 - 15 
               
               
                 6 
                 742 
                 11 - 16 - 14 - 13 
               
               
                 7 
                 705 
                 11 - 16 - 17 - 18 - 15 
               
               
                 8 
                 724 
                 11 - 16 - 17 - 18 - 19 
               
               
                 9 
                 758 
                 11 - 16 - 17 - 18 - 20 
               
               
                   
               
            
           
         
       
     
     Thus all of SEQ ID NO S  3-9 include a leader peptide derived from NadA (SEQ ID NO: 11), an antigenic Envelope domain (SEQ ID NO: 12 or 16) and a coiled-coil region (either from the HIV envelope (SEQ ID NO: 17) or from NadA (SEQ ID NO: 13), with a dipeptide linker (SEQ ID NO: 14 or 18) between viral and bacterial sequences. SEQ ID NO S  3, 5, 7, 8 and 9 also include transmembrane anchor sequences (SEQ ID NO S  15, 19 &amp; 20) derived from NadA. 
     A 648 aa eighth sequence (SEQ ID NO: 10, composed of SEQ ID NO S  11-16-17 from N-terminus to C-terminus i.e. the same as SEQ ID NO S  7-9, but without the C-terminus anchor portions from NadA) was also constructed. These constructs are shown in  FIGS. 3-5 . 
     In further experiments, polypeptides were constructed by replacing (a) the head of NadA with the gp120 subunit (‘gp120-NadA’) or (b) the head and stalk of NadA with the entire gp140 (‘gp140-NadA’). These constructs are shown in  FIG. 6  (SEQ ID NOS: 32-35): 
     
       
         
           
               
               
               
             
               
                   
               
               
                 SEQ ID 
                   
                   
               
               
                 NO: 
                 Length 
                 Description of polypeptide 
               
               
                   
               
             
            
               
                 32 
                 824 
                 aa 1-29: leader of NadA (SEQ ID NO: 11) 
               
               
                   
                   
                 aa 30-504: gp120 (SEQ ID NO: 36) 
               
               
                   
                   
                 aa 505-506: Gly-Ser dipeptide (SEQ ID NO: 14) 
               
               
                   
                   
                 aa 507-824: NadA stalk &amp; anchor 
               
               
                   
                   
                 (SEQ ID NO: 13 + SEQ ID NO: 15) 
               
               
                 33 
                 837 
                 aa 1-29: leader of NadA (SEQ ID NO: 11) 
               
               
                   
                   
                 aa 30-504: gp120 (SEQ ID NO: 36) 
               
               
                   
                   
                 aa 505-506: Gly-Ser dipeptide (SEQ ID NO: 14) 
               
               
                   
                   
                 aa 507-734 &amp; 748-837: NadA stalk &amp; anchor 
               
               
                   
                   
                 (SEQ ID NOs: 13 + 15) 
               
               
                   
                   
                 aa 735-747: thrombin cleavage sequence 
               
               
                   
                   
                 (SEQ ID NO: 37) 
               
               
                 34 
                 741 
                 aa 1-29: leader of NadA (SEQ ID NO: 11) 
               
               
                   
                   
                 aa 30-665: gp140 (mut3-5) (SEQ ID NO: 39) 
               
               
                   
                   
                 aa 666-667: Lys-Leu dipeptide (SEQ ID NO: 18) 
               
               
                   
                   
                 aa 668-741: NadA anchor (SEQ ID NO: 19) 
               
               
                 35 
                 768 
                 aa 1-29: leader of NadA (SEQ ID NO: 11) 
               
               
                   
                   
                 aa 30-665: gp140 (mut3-5) (SEQ ID NO: 39) 
               
               
                   
                   
                 aa 666-678: thrombin cleavage sequence 
               
               
                   
                   
                 (SEQ ID NO: 37) 
               
               
                   
                   
                 aa 679-768: NadA anchor (SEQ ID NO: 40) 
               
               
                   
               
            
           
         
       
     
     The gp120-NadA and gp140-NadA polypeptides were expressed in  E. coli  BL21(DE3) using the pET system. Expression and localisation in  E. coli  were assayed by SDS-PAGE and western blot analysis on total cell lysate and on outer membrane vesicles. As shown in  FIG. 7 , a western blot of total cell lysate using anti-NadA antibody reveals expression of the protein in monomeric and oligomeric forms. Moreover, the proteins are also seen in SDS-PAGE of outer membrane vesicles, showing that the proteins are efficiently transported to the  E. coli  surface ( FIG. 8 ). The gp140-NadA protein was also seen in the culture supernatant. 
     To confirm cell-surface exposure of the proteins, the  E. coli  were analysed by FACS on whole cell bacteria. Antibodies against NadA (polyclonal) and against the C4 conserved epitope of gp120 (monoclonal) were used for the gp120-NadA protein and, as shown in  FIG. 9 , surface expression was confirmed. Antibodies against NadA (polyclonal) and against a gp41 epitope (monoclonal 2F5) were used for the gp140-NadA protein, and surface expression was confirmed ( FIG. 10 ). 
     To investigate folding, the CD4 affinity of the proteins was measured. The  E. coli  were incubated with soluble CD4 for 1 hour at 37° C., and binding was detected by FACS using a monoclonal anti-CD4 antibody.  FIGS. 13 and 14  show the percentage of gp140-NadA  E. coli  that are able to bind to CD4. As shown in  FIG. 11 ,  E. coli  expressing either of the proteins was able to bind to CD4. Dose-dependent binding was also seen, as shown in  FIG. 12  for gp140-NadA. Moreover, pre-incubation of the CD4 with glycosylated gp140 inhibits the binding ( FIG. 15 ). 
     Confirmation of the interaction between CD4 and gp140-NadA was obtained using a HPLC-based receptor binding assay with fluorescent-labelled CD4 (CD4-FITC). A positive control experiment ( FIG. 16 ) showed that CD4-FITC alone has a retention time of 8.3 minutes, which is reduced to 7.0 minutes in the presence of purified glycosylated HIV gp120. As shown in  FIG. 17 , incubation of the CD4 with the culture supernatant of gp140-NadA ( FIG. 8 , right-hand column) resulted in the retention time of CD4 being reduced to 5.2 minutes, indicating formation of a complex between gp140-NadA and CD4. 
     To confirm that the Env domains maintain immunogenic properties, outer membrane preparations enriched with the recombinant Env-NadA proteins were used to immunize animals using a prime-boost strategy. Two or three rabbits per group were primed on days 0, 21, 35 and 49 with outer membrane vesicle preparations from  E. coli /gp120-NadA,  E. coli /gp140-NadA and  E. coli /pET (negative control), using an aluminium hydroxide adjuvant. Glycosylated gp140 (purified from human cells) was used as positive control in combination with a MF59 adjuvant. 
     The group immunised with gp120-NadA was boosted at day 49 with complete glycosylated Env ectodomain (gp140ΔV2) to select antibodies that can bind to the native viral spike. Sera were analyzed at day 35 (post-two), 49 (post-three) and 64 (bleed out) by ELISA and neutralization assay. 
     Results showed that immunization with OMV gp120-NadA induced antibodies able to recognise the glycosylated gp140ΔV2 in ELISA ( FIG. 18 ). These sera were tested for their ability to neutralize HIV-1 isolates. Titres at which the serum dilution reduced relative luminescence units by 50% compared to virus control wells were as follows: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Sera post-three 
                 Sera bleed out 
               
               
                 Antigen 
                 (day 49) 
                 (day 64) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 #7 
                 — 
                 1:34  
               
               
                 OMV/gp120-NadA 
                 #8 
                 1:80  
                 1:950 
               
               
                   
                 #9 
                 — 
                 1:185 
               
               
                 Gp140deltaV2 
                 #17  
                 1:2154 
                 nd 
               
               
                   
                 #18  
                 1:3590 
                 nd 
               
               
                   
               
            
           
         
       
     
     The sera against gp120-NadA OMV were able to neutralize homologous HIV-1 isolate SF162 at considerable dilution. In contrast, immunization with OMV gp140-NadA produced lower antibody titers, and these antibodies were not neutralizing antibodies against the homologous strain. 
     Thus the use of oligomerisation and transmembrane domains from NadA permits cell surface expression of the HIV envelope protein in  E. coli  in non-glycosylated CD4-binding oligomeric form. 
     It will be understood that the invention has been described by way of example only and modifications may be made whilst remaining within the scope and spirit of the invention. 
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