Abstract:
A polynucleotide, comprising a contiguous nucleotide sequence coding for a human antibody with factor VIII specificity, or complementary to a nucleotide sequence coding for a human antibody for factor VIII specificity, or capable of selectively hybridizing under stringent conditions to such nucleotide sequence. Such polynucleotide may be used as a probe or primer for detection of factor VIII inhibitors, or be used for producing a recombinant polypeptide. A polypeptide, comprising a contiguous amino acid sequence corresponding to or mimicking a fragment or derivative of a human antibody with factor VIII specificity capable of specific binding to factor VIII. An antibody, comprising a recombinant human antibody with factor VIII specificity or an anti-idiotypic antibody directed against a human antibody with factor VIII specificity. Pharmaceutical compositions which contain such polypeptide or antibody.

Description:
FIELD OF THE INVENTION  
     This invention is in the fields of diagnosis and medical treatment. More particularly, the invention provides means and methods for diagnosing the presence of inhibitory antibodies directed against factor VIII in the blood of human individuals, and provides means, pharmaceutical compositions and methods for treating human individuals in which such inhibitory antibodies occur. 
     BACKGROUND OF THE INVENTION  
     Haemophilia A is an X-linked bleeding disorder which is characterized by the functional absence of blood coagulation factor VIII. Depending on the residual factor VIII activity in the plasma of the patient, haemophilia A can be classified as severe (factor VIII&lt;1%), moderate (factor VIII 1-5%) or mild (&gt;5%). Bleeding episodes in patients with haemophilia A can be effectively controlled by intravenous administration of purified factor VIII concentrates. These factor VIII-concentrates may be derived from pools of human plasma. Alternatively, recombinant factor VIII produced by geneticaly engineered eukaryotic cells may be used as a starting material for the preparation of factor VIII concentrates. 
     A serious complication of current haemophilia A treatment constitutes the development of neutralizing antibodies directed against factor VIII. These antibodies, commonly termed factor VIII inhibitors, arise in approximately 25% of the patients with severe haemophilia A, usually after 5-20 exposure-days (Ehrenforth et al. 1992, Lancet 339: 594-598). In patients with moderate and mild haemophilia A, anti-factor VIII antibodies occur less frequently and this is most likely due to induction of tolerance by endogenous factor VIII present in the plasma of this group of patients (McMillan et al. 1988, Blood 71: 344-348). Antibodies to factor VIII may develop with low frequency in healthy individuals. 
     Diagnosis of factor VIII inhibitors is commonly performed using the so-called Bethesda assay (Kasper et al. 1975, Thromb. Diath. Haemorrh. 34: 869-872). In this assay equal amounts of normal plasma and dilutions of inhibitor plasma are incubated for two hours at 37° C. Next, residual factor VIII activity is determined and compared to control incubation in which normal plasma is incubated with 0.1 M imidazole for 2 hours at 37° C. The amount of inhibitor is expressed in Bethesda units; one Bethesda unit corresponds to the amount of inhibitor that is capable of reducing the activity of factor VIII in normal plasma by 50%. A recent study has proposed several adaptations to the original assay system which serve to improve the stability of factor VIII during the assay (Verbruggen et al. 1995, Thromb. Haemostas. 73: 247-251). This so-called “Nijmegen modification” of the Bethesda assay is particularly useful for the detection of low titre factor VIII inhibitors. It should be noted that the Bethesda assay does not provide information on the epitopes of factor VIII inhibitory antibodies. 
     The occurrence of factor VIII-inhibiting antibodies renders factor VIII replacement therapy inadequate. Several treatment options are available to the clinician. Low titre inhibitors (up to 5-10 BU/ml) are usually treated with infusion of high doses of factor VIII. A subset of factor VIII inhibitors does not cross react with porcine factor VIII. Porcine factor VIII has been used for management of patients with an inhibitor. Administration of porcine factor VIII may present with side effects. After multiple treatment 30-50% of the patients develop antibodies that neutralize the activity of the administered porcine factor VIII. 
     An alternative treatment of patients with factor VIII inhibitor constitutes the use of factor VIII bypassing agents. Activated prothrombin concentrate complexes (APCC) have been used to bypass the activity of factor VIII. APCC has been used successfully to control bleeding episodes in a large number of patients with an inhibitor. However, treatment is not effective in all cases and an anamnestic rise in the titre of the inhibitor following administration of APCC (most likely due to trace amounts of factor VIII in the preparation) has been reported in a number of patients. In the last 5 years recombinant factor VIIa has become available as a new factor VIII bypassing agent for the treatment of patients with an inhibitor (Lusher et al. 1996. Haemostasis 26 (suppl. 1): 124-130). Recombinant factor VIIa has been successfully used to control the bleeding episodes in patients with an inhibitor. Treatment by this agent is however limited by the short half-life of this compound in the circulation which requires multiple infusions at relatively short time intervals. APC-resistant factor V has recently been suggested as an alternative means to bypass the biological activity of factor VIII inhibitors (WO 95/29259). The agents described above do not act directly on factor VIII inhibitors but merely serve to bypass factor VIII by infusion of large amounts of clotting factor concentrates with increased procoagulant activity. 
     Other methods of inhibitor neutralization have been proposed but their effectiveness has not been convincingly shown. Immunoglobulin preparations derived from plasma of healthy donors has been proposed as an active suppressor of factor VIII inhibitors (Sultan et al. 1984, Lancet 333, 765–768). Despite success in patients with acquired haemophilia A and high titre inhibitors, immunoglobulin preparations are not applied universally for treatment of patients with an inhibitor. The beneficial effects of immunoglobulin preparations in these patients have been attributed to the presence of anti-idiotypic antibodies that neutralize the activity of factor VIII inhibitors. Indeed in some patients the decline in the level of factor VIII inhibitors coincided with the appearance of anti-idiotypic antibodies (Sultan et al. 1987, Proc. Natl. Acad. Sci. USA 84: 828-831). Control of factor VIII inhibitors by anti-idiotypic antibodies in both haemophilia A patients and healthy individuals has been strongly advocated by some investigators (Gilles et al. 1996, J. Clin. Inv. 97: 1382-1388). The same group has proposed that infusion of antigen-antibody complexes in patients with inhibitors may accelerate a decline in anti-factor VIII antibodies in patients with an inhibitor (U.S. Pat. No. 5, 543,145). It has been proposed that this decline is mediated by an increase in the number of anti-idiotypic antibodies which are induced by the infused antigen-antibody complexes. The factor VIII specific antibody used in this treatment protocol is derived from plasma of patients with an inhibitor. Obviously, this presents a heterogeneous mixture of antibodies and no details with respect to the epitope specificity of these antibodies are available. Also the primary structure of the antibodies in these antigen-antibody preparations has not been disclosed. 
     SUMMARY OF THE INVENTION  
     This invention relates to methods for diagnosis and treatment using inhibitory antibodies directed against factor VIII. Methods are disclosed that show how to arrive at nucleotide and amino acid sequences that encode factor VIII specific antibodies. This invention discloses diagnostic tests that allow for detection of nucleotide and amino acid sequences that encode factor VIII specific antibodies within a heterogeneous mixture of antibody-encoding nucleotide or amino acid sequences. This invention further discloses how to use recombinant antibody fragments which bind specifically to factor VIII as novel therapeutic agents for the treatment of patients with factor VIII inhibitors. 
     The invention provides a polynucleotide in substantially isolated form, comprising a contiguous nucleotide sequence (a) coding for a human antibody with factor VIII specificity, or (b) complementary to a nucleotide sequence coding for a human antibody with factor VIII specificity, or (c) capable of selectively hybridizing under stringent conditions to nucleotide sequence (a) or (b). 
     Preferably, the contiguous nucleotide sequence is at least 8, preferably at least 10 nucleotides. 
     In a preferred embodiment, the invention provides a probe or primer which comprises a polynucleotide as defined herein, optionally further comprising a detectable label, such as a radioactive atom or group, an enzyme, a fluorescent or luminescent group, a dye or biotin. 
     The invention also provides an assay kit for detecting nucleic acid coding for a human antibody with factor VIII specificity, comprising a probe or primer as defined herein in a suitable container. 
     Furthermore, the invention provides a nucleic acid amplification and detection kit for detecting nucleic acid coding for a human antibody with factor VIII specificity, comprising a pair of primers as defined herein capable of priming the synthesis of cDNA, and optionally further comprising a probe as defined herein capable of selectively hybridizing to (the complement of) a region of the nucleic acid to be detected between and not including the sequences from which the primers are derived. 
     The invention provides a method for assaying a sample for the presence or absence of nucleic acid coding for a human antibody with factor VIII specificity, comprising contacting the sample with a probe as defined herein under conditions that allow the selective hybridization of said probe to the (complement of the) nucleic acid to be detected in the sample, and determined whether polynucleotide duplexes comprising said probe are formed. 
     The invention also provides a method for assaying a sample for the presence or absence of nucleic acid coding for a human antibody with factor VIII specificity, comprising subjecting nucleic acid present in the sample to a nucleic acid amplification process using a pair of primers as defined herein capable of priming the synthesis of cDNA, contacting the nucleic acid resulting from the amplification process with a probe as defined herein under conditions that allow the selective hybridization of said probe to the (complement of the) nucleic acid to be detected in the sample, and determining whether polynucleotide duplexes comprising said probe are formed. 
     Furthermore, the invention provides a method of producing a recombinant polypeptide, comprising providing a polynucleotide coding for said polypeptide, preparing a recombinant vector containing said polynucleotide operably linked to a control sequence capable of providing for the expression of the polynucleotide by a host cell, transforming a host cell with said recombinant vector, growing said host cell under conditions that provide for the expression of the polynucleotide and optionally isolating the thus produced polypeptide, wherein said polynucleotide codes for a human antibody with factor VIII specificity, or a fragment or derivative thereof capable of specific binding to factor VIII. 
     According to another aspect, the invention provides a polypeptide in substantially isolated form, comprising a contiguous amino acid sequence corresponding to or mimicking a fragment or derivative of a human antibody with factor VIII specificity capable of specific binding to factor VIII. In a preferred embodiment of the invention, the contiguous amino acid sequence is capable of reducing the activity of factor VIII inhibiting antibodies. 
     Preferably, the fragment is (part of) a variable region of the heavy chain or light chain of said antibody, and the derivative is preferably a single chain Fv fragment of said antibody. 
     The invention furthermore provides an antibody in substantially isolated form, comprising a recombinant human antibody with factor VIII specificity. 
     The invention furthermore provides a pharmaceutical composition for the treatment of factor VIII inhibition in a human individual, comprising a polypeptide as defined herein or an antibody as defined herein, together with a pharmaceutically acceptable carrier. Optionally, the composition further contains factor VIII, or a substitute of factor VIII. 
     The invention also provides a method of treatment of factor VIII inhibition in a human individual comprising administering (an effective amount to reduce or prevent said factor VIII inhibition of) a polypeptide as defined herein or an antibody as defined herein, optionally together with factor VIII or a substitute of factor VIII. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the light chain specificity of 12 clones obtained after 4 rounds of panning of the IgG4-specific library described in Example 2. Phage expressing recombinant antibodies were incubated on microtiter wells which contained factor VIII light chain (black bars; ′80K). To correct for background binding phage were also incubated on microtiter wells that did not contain factor VIII light chain (grey bars; +80K). On the Y-axis the OD(450-540 nm) is depicted. Two clones (c) express antibody fragments that do not bind specifically to the factor VIII light chain. 
         FIG. 2  shows the light chain specificity of 12 clones randomly chosen after the first round of panning of the IgG4-specific library described in Example 2. Clones 7, 8 and 10 express antibody fragments with factor VIII light chain specificity. The other clones do not specifically bind to the factor VIII light chain. Only background binding of the phage to the microtiter wells is observed (grey bars). Two clones (c) express antibody fragments that do not bind specifically to the factor VIII light chain. 
         FIG. 3  shows the nucleotide sequence of clone EL14 (SEQ. ID. NO: 19) and clone IT2 (SEQ. ID. NO: 21). The nucleotide sequence of both clones is aligned with the nucleotide sequence of the germline sequences DP-10 (SEQ. ID. NO: 20) (for EL14) and DP-14 (SEQ. ID. NO: 22) (for IT2). The different regions of the variable part of the heavy chain are indicated in the following order: framework  1 , CDR 1 , framework  2 , CDR 2 , framework  3 , CDR 3  and framework  4 . Homology of clones EL14 and IT2 with the germline sequences DP-10 and DP-14 is indicated by horizontal bars (−). Differences are indicated by the nucleotides that occur in the germline sequences DP-10 and DP-14. Note that both CDR 3  and framework  4  are not derived from the germline sequences DP-10 and DP-14. Consequently, no homology is given for this part of the nucleotide sequence. 
         FIG. 4A  gives the amino acid sequence (VHEL-14 (SEQ. ID. NO. 23) and VHIT-2 (SEQ. ID. NO: 25)) derived of the nucleotide sequence of clone EL14 (SEQ. ID NO: 19) and IT2 (SEQ. ID. NO: 21). Deviations in the amino acid sequence of the germline segments DP-10 (SEQ. ID. NO: 24) and DP-14 (SEQ. ID. NO: 26) are indicated in the lower lines. Framework is abbreviated as “FR”. 
         FIG. 4B  compares the amino acid sequence of three related clones that are derived from the germline segment DP-14 (SEQ. ID. NO: 26). The amino acid sequences of clone IT2 (SEQ. ID. NO: 25), clone EL5 (SEQ. ID. NO: 27) and clone EL25 (SEQ. ID. NO: 28) are compared to that of the germline segment DP-14 (SEQ. ID. NO: 26). Deviations in amino acid sequence are indicated for each clone. Note that some amino acid substitutions are shared by the three different clones. 
         FIG. 4C  compares the amino acid sequences of the third variable loop (CDR3) of the heavy chain of clone EL14 (SEQ. ID. NO: 29) and IT2 (SEQ. ID. NO: 30). Homologous amino acid residues are indicated by vertical lines. Dots denote amino acids related in charge or hydrophobicity. 
         FIG. 5  shows the specificity of binding of scFv-EL14 and scFv-IT2 to the factor VIII light chain as assessed by the murine monoclonal antibodies CLB-CAg A and CLB-CAg 117. ScFv-EL14 binds specifically to the factor VIII light chain when peroxidase labelled CLB-CAg A (80K/Apo) is used as an indicator antibody (hatched bars). Also scFv-IT2 binds to the factor VIII light chain under these conditions (hatched bars). In contrast, when peroxidase labelled CLB-CAg 117 (80K/117po) is used as indicator antibody binding of scFv-EL14 and scFv-IT2 is strongly reduced (black bars). No binding is observed in the absence of factor VIII light chain (−/117po; −/Apo). Clone O4 does not bind to factor VIII under these experimental conditions. These experiments show that the epitope of scFv-EL14 and scFv-IT2 overlaps with that of CLB-CAg 117. On the y-axis the absorbance OD (450-540 nm) is given. On the x-axis scFv-EL14, scFv-IT2 and scFv-O4 are given. 
         FIG. 6  shows the binding of different dilutions of purified scFv-EL14 (open circles), scFv-IT2 (closed circles) and scFv-O4 (negative control). On the x-axis the different concentrations of protein tested are indicated (μg/ml), on the y-axis the absorbance OD(450-540 nm) is given. Clone scFv-O4 does not bind to the factor VIII light chain at the protein concentration tested in this experiment. Both scFv-IT2 and scFv-EL14 bind to the factor VIII light chain. ScFv-EL14 binds with a higher affinity to the factor VIII light chain when compared scFv-IT2. 
         FIG. 7A  shows the neutralization of the inhibitory activity of the murine monoclonal antibody CLB-CAg 117 by scFv-EL14. Antibody CLB-CAg 117 was diluted till a value of 2 Bu/ml which corresponds with a residual factor VIII activity of about 25%. Increasing amounts of scFv-EL14 were capable of neutralizing the inhibitory activity of CLB-CAg 117 (closed circles). A concentration of 0.75 μg/ml suffices to restore factor VIII activity to its original level. ScFv-EL14 did not affect the inhibitory activity of the murine monoclonal antibody CLB-CAg A (open circles). On the y-axis residual factor VIII activity is depicted. On the x-axis the amount of scFc added is given in μg/ml. 
         FIG. 7B  shows the neutralization of the inhibitory activity of CLB-CAg 117 by scFv-IT2 (closed circles). A concentration of 65 μg/ml is needed to restore factor VIII activity to its original level. ScFv-IT2 did not affect the inhibitory activity of CLB-CAg A (open bars). On the y-axis residual factor VIII activity is depicted. On the x-axis the amount of scFv added is given in μg/ml. 
         FIG. 8A  shows the epitope specificity of 15 clones obtained after four rounds of panning of the IgG4-specific library described in example 8. Panning was performed using factor VIII immoblized on immunotubes. Phage expressing recombinant antibodies were incubated on microtiter wells which contained factor VIII light chain (black bars) or A3-C1-domain (hatched bars). To correct for background binding, phage were also incubated on microtiter wells that did not contain factor VIII light chain or A3-C1 domain (white bars). On the y-axis the OD (450-540 nm) is depicted. 
         FIG. 8B  shows the epitope specificity of 15 clones obtained after four rounds of panning the IgG4 specific library described in example 8. Panning was performed using factor VIII light chain that had been immoblized in microtiter wells employing CLB-CAg 117. Phage expressing recombinant antibodies were incubated on microtiter wells which contained factor VIII light chain (black bars) or A3-C1-domain (hatched bars). To correct for background binding, phage were also incubated on microtiter wells that did not contain factor VIII light chain or A3-C1 domain (white bars). On the y-axis the OD (450-540 nm) is depicted. 
         FIG. 9A  shows the deduced amino acid sequence of recombinant antibody fragments specific for the A3-C1 domain. The amino acid sequence of germline variable heavy chain gene segments DP-15 (SEQ. ID. NO: 31), DP31 (SEQ. ID. NO: 33), DP49 (SEQ. ID. NO: 35) and DP77 (SEQ. ID. NO: 37) is given. Deviations in amino acid sequence from these germline gene segments are indicated for clone B38 (SEQ. ID. NO: 32), B18 (SEQ. ID. NO: 34), B35 (SEQ. ID. NO: 36) and B04 (SEQ. ID. NO: 38). Also the amino acid of the CDR3 and FR4 of the A3-C1 specific recombinant antibodies encoded by clone B38, B18, B35 and B04 is given. 
         FIG. 9B  gives the nucleotide (SEQ. ID. NO: 39), complementary strand (SEQ. ID. NO: 41), and amino acid (SEQ. ID. NO: 40) sequence of the variable heavy chain domain of clone B38. 
         FIG. 9C  gives the nucleotide (SEQ. ID. NO: 42), complementary strand (SEQ. ID. NO: 43), and amino acid (SEQ. ID. NO: 34) sequence of the variable heavy chain domain of clone B18. 
         FIG. 9D  gives the nucleotide (SEQ. ID. NO: 44), complementary strand (SEQ. ID. NO: 45), and amino acid (SEQ. ID. NO: 36) sequence of the variable heavy chain domain of clone B35. 
         FIG. 9E  gives the nucleotide (SEQ. ID. NO: 46), complementary strand (SEQ. ID. NO: 48), and amino acid (SEQ. ID. NO: 47) sequence of the variable heavy chain domain of clone B04. 
         FIG. 10A  shows the epitope specificity of 20 clones obtained after four rounds of panning of the IgG4-specific library described in Example 9. Panning was performed using factor VIII heavy chain (90K+) that had been immobilized in microtiter wells employing CLB-CAg 9. Phage expressing recombinant antibodies were incubated on microtiter wells which contained factor VIII heavy chain that was immobilized using the anti-heavy chain monoclonal antibody ESH5 (black bars). To correct for background binding, phage were also incubated on microtiter wells did not contain factor VIII heavy chain (white bars). On the y-axis the OD (450-540 nm) is depicted. 
         FIG. 10B  shows the epitope specificity of 20 clones obtained after four rounds of panning of the IgG4-specific library described in Example 9. Panning was performed using factor VIII heavy chain (90K+) that had been immobilized in immunotubes. Phage expressing recombinant antibodies were incubated on microtiter wells which contained factor VIII heavy chain that was immobilized using the anti-heavy chain monoclonal antibody ESH5 (black bars). To correct for background binding, phage were also incubated on microtiter wells that did not contain factor VIII heavy chain (white bars). On the y-axis the OD (450-540 nm) is depicted. 
         FIG. 11A  shows the deduced amino acid sequence (SEQ. ID. NOS: 49 and 51) of recombinant antibody fragments specific for the factor VIII heavy chain. The amino acid sequence of germ line variable heavy chain gene segments DP10 (SEQ. ID. NO: 24) and DP47 (SEQ. ID. NO: 50) is given. Deviations in amino acid sequence from these germline gene segments are indicated for two clones that encode recombinant antibodies that bind to the factor VIII heavy chain. Also the amino acid of the CDR3 and FR4 of the factor VIII heavy chain specific recombinant antibodies encoded by the two clones is given. 
         FIGS. 11B  and C give the nucleotide (SEQ. ID. NOS: 52 and 54), complementary strand (SEQ. ID. NOS: 53 and 55) and amino acid (SEQ. ID. NOS: 49 and 51) sequence of the variable heavy chain domain of two clones that encode recombinant antibodies that bind specifically to the factor VIII heavy chain. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     A number of investigators have addressed the epitope-specificity and mode of action of factor VIII inhibitory antibodies. Molecular cloning of the factor VIII cDNA revealed that factor VIII consists of a series of repeated domains which appear in the order A1-A2-B-A3-C1-C2. In plasma, factor VIII circulates as a heterodimer which consists of a heavy chain of variable length (90-220 kDa) and a light chain of 80 kDa. The factor VIII light chain consists of the domains A3-C1-C2 while the factor VIII heavy chain comprises the domains A1-A2-B. Heterogeneity of the factor VIII heavy chain is caused by limited proteolysis within the B-domain which contains several sites that are sensitive towards proteolytic cleavage. In plasma, factor VIII circulates in complex with von Willebrand factor, a large multimeric protein involved in the initial steps of platelet adhesion to a damaged vessel wall. Binding to von Willebrand factor protects factor VIII from proteolytic degradation. The physiological importance of this interaction is underscored by the low levels of factor VIII in plasma of patients that lack von Willebrand factor. Factor VIII is a precursor molecule which upon activation functions as a cofactor for factor IXa in the phospholipid and Ca 2+ -dependent conversion of factor X to factor Xa. Activation of factor VIII involves proteolytic cleavages in both the heavy and light chain of factor VIII. Thrombin is considered to be the physiological activator of factor VIII and cleaves at Arg 372 , Arg 740  and Arg 1689  of factor VIII. Thrombin activated factor VIII thus consists of a hetero-trimer of the separate A1 and A2-domains and the cleaved factor VIII light chain (A3-C1-C2). Cleavage at Arg 1689  of the factor VIII light chain results in removal of amino-acid sequence Glu 1649 -Arg 1689  which is essential for binding of factor VIII to von Willebrand factor. Sofar, three major binding sites for factor VIII inhibitors have been characterized (Scandella et al. 1994, Blood 86: 1811-1819; Healey et al. 1995, J. Biol. Chem. 270: 14505-14509; Fijnvandraat et al. 1998, Blood 91: 2347-2352). 
     Amino acid residues Val 2248 -Ser 2312  in the C2-domain constitute a binding site for factor VIII inhibitors. The large size of this epitope suggests that a number of antibodies which bind to different amino acid regions in this area occur in plasma of patients with inhibitors of C2-specificity. The mechanisms of action of anti-C2 antibodies has been explored in considerable detail. Most of these antibodies interfere with binding of factor VIII to phospholipids. Furthermore, some of the antibodies with C2-specificity also inhibit the interaction of factor VIII with its carrier von Willebrand factor. A new mechanism for inhibition of factor VIII by a human alloantibody has been described recently (Saenko et al. 1996, J. Biol. Chem. 271: 27424-27431). A human alloantibody that binds only to the amino-terminal portion (Val 2248 -Gly 2285 ) of the C2-epitope has been shown to inhibit the thrombin induced release of factor VIII from von Willebrand factor. 
     Amino acid residues Arg 484 -Ile 508  in the A2-domain of factor VIII constitute a major epitope for factor VIII inhibitors. Studies on the mechanism of inhibition of anti-A2 antibodies have shown that anti-A2 antibodies interfere with conversion of factor X to Xa by the lipid bound factor VIIIa-factor IXa-complex (Lollar et al., 1995). The anti-A2-antibodies do not interfere with binding of factor X to the factor VIIIa-factor IXa complex but simply limit the conversion of factor X. 
     A third major epitope of factor VIII inhibitors has been found in the A3-domain of factor VIII. Binding of inhibitory antibodies was dependent on the presence of amino acids Gln 1178 -Met 1823 . Previous studies have shown that this site constitute a binding site for factor IXa and indeed antibodies binding to this site interfered with complex assembly of factor VIIIa and factor IXa (Fijnvandraat et al. 1998. Blood 91: 2347-2352). In a number of patients with an inhibitor, inhibitory antibodies directed against other epitopes have been observed. An early study has shown that inhibitory antibodies may recognize amino acid region Met 336 -Arg 372  of factor VIII (Ware et al. 1998. Proc. Natl. Acad. Sci USA 85: 3165-3169). The mechanism of inhibition has not yet been explored but recently a binding site for factor X has been proposed in this part of the factor VIII molecule (Lapan, K. A. and Fay, P. J. 1997. J. Biol. Chem. 272: 2082-2088). 
     The restricted epitope specificity of factor VIII inhibitors suggests that a limited number of dominant B-cell epitopes is involved in the immune response to factor VIII. Apparently, human anti-factor VIII antibodies synthesized by B-cell clones from a variety of patients are surprisingly similar with respect to epitope specificity. This suggests that the primary amino acid and nucleotide sequence of antibodies with factor VIII specificity is similar at the molecular level. Based on this it is desirable to define the presence and epitope specificity of anti-factor VIII antibodies by simply addressing the presence of nucleotide sequences that correspond to antibodies with factor VIII inhibiting capacity. Sofar, the primary sequences of anti-factor VIII antibodies have been poorly defined. Davies and co-workers have suggested an association between factor VIII inhibitors and use of VH gene segment DP73 (Davies et al. 1997. Thromb. Haemostas. supplement: 2352A). The nucleotide and primary amino acid sequence of these antibodies has not been disclosed and details with respect to the epitope specificity of these antibodies are lacking. Clearly, there is a need to define the primary amino acid and nucleotide sequence of factor VIII antibodies in more detail. Such sequence information can be used to design diagnostic tests which can be used to monitor the occurrence of B-cell clones that produce factor VIII inhibitors in patients with haemophilia A. These diagnostic tests can be extremely sensitive and give information on the epitope specificity of factor VIII inhibitors. 
     Studies directed at defining the epitope specificity and mode of action of these antibodies are limited by the heterogeneity of these antibodies in the plasma of these patients. Clearly, more stringent diagnostic criteria would be required to define the properties of factor VIII inhibitors in more detail. 
     A sudden increase in the frequency of inhibitor development in a group of previously treated patients has been associated with a particular pasteurized factor VIII concentrate manufactured in the Netherlands (Roosendaal et al. 1993. Blood 81: 2180-2186). These factor VIII inhibitors are directed against the factor VIII light chain and epitope mapping revealed that the majority of inhibitors reacted with epitopes in the A3-C1 and the C2-domain of factor VIII (Sawamoto et al. 1998. Thromb. Haemostas. 79: 62-68). Recently, a second pasteurized factor VIII concentrate has been implicated in the development of inhibitors in a group of previously treated patients. Also in this case the inhibitory antibodies were predominantly of factor VIII light chain specificity (Peerlinck et al. 1997. Thromb. Haemostas. 77: 80-86). It has been suggested that inhibitor development in these patients is due to small alterations in the factor VIII molecule which have been induced by the manufacturing process. This may indicate that the antibodies that developed in these patients have different properties compared to the factor VIII inhibitory antibodies that develop in other patients. Clearly, knowledge of nucleotide and amino acid sequence of factor VIII specific antibodies could provide additional information on the etiology of factor VIII inhibitor which is desirable for the characterization of the antibody response in patients who have received these factor VIII concentrates. 
     Until now, the primary nucleotide and amino acid sequence of anti-factor VIII antibodies has not been disclosed. This invention describes the nucleotide sequences that encode human antibodies with factor VIII-specificity. Based on the primary sequence of these antibodies, oligonucleotide primers are designed that allow for detection of B-cells that produce antibodies with affinity for factor VIII. Detection of factor VIII specific B-cells may be accomplished using both mRNA, cDNA or DNA which are derived from lymphocytes of patients. Genomic DNA, RNA and cDNA are prepared from lymphocytes by methods that are generally known in the art. Some methods for the detection of factor VIII specific B-cell clones are listed below. Other methods for the detection of nucleotide sequences of factor VIII specific antibodies, disclosed in this invention, are considered to fall within the scope of this invention. Selective amplification of heavy chain variable sequences (VH-genes) can be used to detect nucleotide sequences that encode antibodies that are part of the human antibody repertoire that can bind specifically to factor VIII. The variable part of the human heavy chain is assembled from the variable heavy chain regions (VH), the diversity regions (D) and the joining regions (J). Fusion of these three different gene segments is not a precise event and this so-called “junctional diversity”, together with the process of nucleotide addition and deletion, results in the generation of the hypervariable complementary determining region 3 CDR3. The human light chain is assembled in a similar manner but lacks diversity region D. Additional sequence diversity of both heavy and light chain sequences is generated by somatic hypermutation and together with the mechanisms outlined above this ultimately results in the generation of high affinity antibodies. Knowledge on the nucleotide sequences that encode factor VIII-specific antibody allows for the detection of this specific antibody in the repertoire of patients who are at risk of developing factor VIII-specific antibodies (such as haemophilia A patients who are treated with factor VIII or patients with acquired haemophilia). Amplification may be performed with a combination of oligonucleotide primers directed against constant regions or variable regions of heavy and light chain of factor VIII-specific antibodies. Detection of factor VIII specific antibodies may be performed using one oligonucleotide primer derived from the variable parts of the nucleotide sequences encoding factor VIII antibodies and one oligonucleotide primer that is derived from the constant regions of factor VIII specific antibodies. Detection may also be performed using two oligonucleotide primers specific for variable parts of the nucleotide sequence that encodes an antibody that binds to factor VIII. The methods described herein also include the amplification of immunoglobulin genes using oligonucleotide primers that are directed against the constant regions of the immunoglobulin genes. Subsequent detection of nucleotide sequences of factor VIII specific antibodies can be performed using selective hybridization with (radiolabelled) oligonucleotide primers that are directed against the variable parts of the nucleotide sequence encoding factor VIII specific antibodies. From the above it follows that oligonucleotide primers are preferentially but not exclusively directed towards the constant and variable regions of factor VIII specific antibodies. In example 5, methods are disclosed that can be used to detect the presence of factor VIII specific antibodies in a mixture of nucleotide sequences. Combination of oligonucleotide primers derived from the nucleotide sequence of factor VIII specific antibodies can be used to directly assess the presence of factor VIII specific antibodies in the antibody-repertoire of patients. Alternatively, analysis by methods that include but are not limited to sequencing analysis, re-amplification of obtained fragments with more specific oligonucleotide primers, digestion with restriction enzymes and selective hybridization may be utilized to address the presence of factor VIII antibodies. Quantification of the amount of nucleotide sequences encoding factor VIII antibodies may be obtained by various methods that are generally known in the art and include but are not limited to the following. The amount of radioactivity incorporated into a PCR-fragment that encodes part of a factor VIII specific antibody can be determined. Furthermore, radioactively labelled oligonucleotide probes can be used to estimate the amount of a nucleotide sequence encoding a factor VIII specific antibody in a mixture of DNA fragments that code for part of a patients antibody repertoire. Quantitative PCR-amplification can be performed using for example dye-modified oligonucleotide primers which allow for direct monitoring of the amount of PCR-product generated during amplification. 
     Other methods that selectively detect and quantify specific nucleotide sequences that encode factor VIII specific antibodies may be devised by an average expert in the art. These methods are considered to fall within the scope of the present invention. 
     Examples 1-10 provide details on the identification and detection of nucleotide sequences that encode factor VIII specific antibodies in haemophilia patients. These examples teach how to arrive at the nucleotide sequence of factor VIII inhibitors and provide information on how to use this information for the detection of factor VIII specific antibodies. 
     This invention discloses the nucleotide and primary amino acid sequences of factor VIII specific antibodies. Factor VIII inhibitors are commonly directed against three major epitopes on factor VIII within the A2-A3 and C2-domain of factor VIII. In Example 4 the nucleotide and amino acid sequence of anti-C2 antibodies is disclosed. In examples 8 and 9, the nucleotide and amino acid sequence of anti-A2 and anti-A3-C1 antibodies is disclosed. This invention teaches how to arrive at the nucleotide and amino acid sequence of factor VIII specific antibodies and the methods disclosed in this invention can be used to derive the nucleotide and amino acid sequence of anti-factor VIII antibodies with specificity for other domains of factor VIII which are a target for factor VIII inhibitors. Anti-factor VIII antibodies encoded by the nucleotide sequences disclosed here, can be used for the development of therapeutic agents that are capable of limiting the biological activity of factor VIII inhibitors. These therapeutic agents preferentially contain, but are not limited to:
         1. The antibody fragments (or agents based on the nucleotide or amino acid sequence) can be used for the generation of anti-idiotypic antibodies. Antibody fragments can be either administered together with factor VIII or administered alone. Also, peptides or related agents which are based on the primary amino acid sequence of the variable parts of factor VIII specific antibodies can be used to induce the formation of anti-idiotypic antibodies direct against factor VIII inhibitors. Anti-idiotypic antibodies can also be obtained by screening large (semi-synthetic) libraries that encode a wide variety of recombinant antibodies. The preparation of anti-idiotypic antibodies can also take place in animals that include but are not limited to mouse by injection of recombinant antibody disclosed in this invention. Anti-idiotypic antibodies can subsequently be obtained by methods that are known to those skilled in the art. An anti-idiotypic response to factor VIII specific antibodies may also be obtained by injection of DNA encoding part of the nucleotide sequences of factor VIII specific antibodies which can be obtained by the methods outlined in this invention. Immunization by injection of DNA is considered to be only modestly immunogenic and other agents are needed to obtain a sufficiently high immune response. Co-injection of plasmid DNA encoding IL-2, GM-CSF and tetanus toxoid has been used to enhance the immune response to injected DNA (Spellerberg et al. 1997. J. Immunol. 15:1885-1892). Similar methods can be applied to enhance the immune response towards DNA fragments encoding factor VIII specific antibodies.   2. The recombinant antibody fragments described in this invention can be used as a therapeutic for treatment of patients with an inhibitor. Examples 7 and 10 disclose that recombinant antibody fragments (termed scFv&#39;s) which bind specifically to the C2-domain, interfere with binding of inhibitory antibodies to factor VIII. These scFv&#39;s can be used for treatment of patients with inhibitory antibodies directed against the C2-domain. This invention discloses how to arrive at recombinant antibody fragments that bind specifically to the A2, A3-C1 and C2-domain of factor VIII. Using the methods outlined in this invention additional antibody fragments directed against these and other regions on factor VIII may be obtained. These regions include but are not limited to Arg 484 -Ile 508  in the A2-domain, Gln 1778 -Met 1823  in the A3-domain and Val 2248 -Ser 2312  in the C2-domain. Recombinant antibodies directed against multiple epitopes preferentially will be part of a pharmaceutical preparation since most patients have inhibitory antibodies directed against multiple epitopes on factor VIII. The inhibitor neutralizing activity of the recombinant antibody fragments described in this invention may be modified by the introduction of point mutations in the constant and variable parts of these fragments. Furthermore, the recombinant antibody fragments described in this invention may be cloned into vectors which allow for expression of these fragments for example as Fab-fragment. Other vectors for expression of antibodies and antibody fragments are available to an average expert in the field (see for example: “Antibody Engineering; A Practical Approach” edited by Mc Cafferty et al. 1996. Oxford University Press). Methods to increase the affinity of recombinant antibodies or antibody fragments are readily available and can be used to modulate the biological activities of the recombinant antibody fragments described in this invention. Peptides and peptide-related agents which have been designed based on the amino acid sequence of the recombinant antibodies described in this invention (for example peptides derived from the amino acid sequence of CDR3) can be used to interfere with the activity of factor VIII inhibitors.       

     In summary, this invention provides an improved method to define factor VIII inhibitory antibodies. The methods described result in definition of the nucleotide sequence of factor VIII inhibitors and teaches how to utilize this information for the development of improved methods for the detection of factor VIII inhibitors. This invention also discloses pharmaceutical preparations, derived from the nucleotide and/or primary amino acid sequence of factor VIII specific antibodies, that can be used in the treatment of haemophilia A patients with inhibitory antibodies directed against factor VIII. The dose of the therapeutic agents to be administered to a patient, obviously depends on the affinity of the therapeutic agent for factor VIII. The affinity of the recombinant antibody fragments described in this invention can vary considerably as is disclosed in Examples 6 and 7. The dose to be administered also depends on bodyweight of the patient, the titre of the factor VIII inhibitor and the biological activities of the different components of the therapeutic agent used. The dose to be administered can be estimated according to methods that are disclosed in Examples 7 and 10. These methods may be complemented with dose finding studies which involve administration of the therapeutic agents in animal models and healthy individuals. In general, the dose administered will vary between 10 μg-5 g/kg and more preferably between 100 μg-1 g/kg of bodyweight per day. 
     The therapeutic agent may be administered in combination with factor VIII (or a substitute of factor VIII). The dose of factor VIII administered together with the therapeutic agent may vary between 0.1 and 2000 Units per kg and more preferably between 1 and 200 Units per kg of body weight per day. 
     The words “substantially isolated form” as used herein are intended to refer to a form of the material which is different from any naturally occurring form of said material, i.e. different from the material in its natural environment. In particular, the words are intended to define relative freedom or absence of substances that naturally accompany the material. 
     EXAMPLE 1: Characterization of Anti-factor VIII Antibodies in Patient&#39;s Plasma 
     Anti-factor VIII antibodies present in the plasma of a patient with acquired haemophilia were characterized by immunoprecipitation and neutralization experiments. The construction of recombinant factor VIII fragments corresponding to the A2, A3-C1-C2 and C2-domain of factor VIII has been described perviously (Fijnvandraat et al. 1997. Blood 89: 4371-4377; Fijnvandraat et al. 1998. Blood 91: 2347-2352). These recombinant factor VIII fragments were metabolically labelled with [ 35 S]-methionine and subsequently used for the detection of anti-factor VIII antibodies by immunoprecipitation using methods that have been described previously (Fijnvandraat et al. 1998. Blood 91: 2347-2352). Reactivity with both metabolically labeled A2, A3-C1-C2 and C2 domain was observed (data not shown). This indicates that at least two classes of antibodies directed against factor VIII were present in the plasma of the patient. To determine the contribution of the different antibodies in the patient&#39;s plasma to the titre of the inhibitor as measured in the Bethesda assay we performed neutralization experiments. Increasing concentrations of recombinant factor VIII fragments were mixed with samples that contained factor VIII antibodies diluted until a final inhibitory capacity of 2 BU/ml. Addition of both recombinant factor VIII light chain (A3-C1-C2) and C2-domain resulted in a decrease in the inhibitory activity of 50 and 20%, respectively. Addition of the factor VIII heavy chain (domains A1-A2-B) resulted in 45% neutralization of the inhibitor in the plasma of the patient. Based on these data we conclude that inhibitory antibodies directed against the heavy chain contribute for 45% to the inhibitory capacity of the patient&#39;s anti-factor VIII antibodies whereas anti-A3-C1-C2 antibodies account for the other half of the inhibitory capacity. Our results provide evidence for the occurrence of at least three classes of inhibitory antibodies in the patient&#39;s plasma. Next, we determined the subclass of the anti-factor VIII antibodies using methods that have been outlined previously (Fijnvandraat et al. 1997. Blood 89: 4371-4377). The antibodies with A2-specificity consisted predominantly of subclass IgG4; in addition small amounts of subclass IgG2 were observed. The antibodies directed against the factor VIII light chain consisted exclusively of subclass IgG4. The methods outlined above provide a starting point for further characterization of human antibodies with specificity for factor VIII. Similar analyses can be performed on samples derived of other patients which are analyzed for the presence of factor VIII inhibitors. 
     EXAMPLE 2: Construction of an IgG4 Specific Library 
     Peripheral blood lymphocytes were isolated from a blood sample of a patient with acquired haemophilia. The titre of the inhibitor was 1250 BU/ml. RNA was isolated from the lymphocytes using RNAzol (WAK Chemie, Germany) according to the instructions of the manufacturer. RNA was transcribed into cDNA employing random hexamer primers (Gibco, Breda, The Netherlands). Since, most of the anti-factor VIII antibodies described in Example 1 were of subclass IgG4, DNA fragments corresponding to the heavy chain of immunoglobulins of subclass IgG4 were amplified using the following set of oligonucleotide primers: 
     
       
         
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
           
               
                 (SEQ. ID. NO:1) 
               
             
          
           
               
                 conIgG1-4 
                 5′ CTTGTCCACCTTGGTGTTGCTGGG 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:2) 
               
             
          
           
               
                 huIgG4 
                 5′ ACGTTGCAGGTGTAGGTCTTC 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:3) 
               
             
          
           
               
                 huVH1aback 
                 5′ CAGGTGCAGCTGGTGCAGTCTGG 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:4) 
               
             
          
           
               
                 huVH2aback 
                 5′ CAGGTCAACTTAAGGGAGTCTGG 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:5) 
               
             
          
           
               
                 huVH3aback 
                 5′ GAGGTGCAGCTGGTGGAGTCTGG 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:6) 
               
             
          
           
               
                 huVH4aback 
                 5′ GAGGTGCAGCTGTTGCAGTCGGG 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:7) 
               
             
          
           
               
                 huVH5aback 
                 5′ GAGGTACAGCTGCAGCAGTCTGC 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:8) 
               
             
          
           
               
                 huVH6aback 
                 5′ CAGGTACAGCTGCAGCAGTCAGG 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:9) 
               
             
          
           
               
                 huJH1-2forSal 
                 5′ GAGTCAT TCTCGT GTCGAC ACGGTGACCAGGGT- 
               
               
                   
                 GCC 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:10) 
               
             
          
           
               
                 huJH3forSal 
                 5′ GAGTCATTCTCGT GTCGAC ACGGTGACCATTGT- 
               
               
                   
                 CCC 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:11) 
               
             
          
           
               
                 huJH4-SforSal 
                 5′ GAGTCATTCTCGT GTCGAC ACGGTGACCAGGGT- 
               
               
                   
                 TCC 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:12) 
               
             
          
           
               
                 huJH6forSal 
                 5′ GAGTCATTCTCGT GTCGAC ACGGTGACCGTGGT- 
               
               
                   
                 CCC 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:13) 
               
             
          
           
               
                 huVH1backNco 
                 5′ AAT CCATGG CCCAGGTGCAGCTGGTGCA 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:14) 
               
             
          
           
               
                 huVH2backNco 
                 5′ AAT CCATGG CCCAGGTCAACTTAAGGGA 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:15) 
               
             
          
           
               
                 huVH3backNco 
                 5′ AAT CCATGG CCGAGGTGCAGCTGGTGGA 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:16) 
               
             
          
           
               
                 huVH4backNco 
                 5′ AAT CCATGG CCGAGGTGCAGCTGTTGCA 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:17) 
               
             
          
           
               
                 huVH5backNco 
                 5′ AAT CCATGG CCGAGGTACAGCTGCAGCA 3′ 
               
             
          
           
               
                 (SEQ. ID. NO:18) 
               
             
          
           
               
                 huVH6backNco 
                 5′ AAT CCATGG CCCAGGTACAGCTGCAGCA 3′ 
               
             
          
         
       
     
     Oligonucleotide primers huVHa(1-6)back and huJH(1-6)for Sal (SEQ. ID. NOS: 9-12) have been described previously (Marks et al. 1991. J. Mol. Biol. 222: 581-597). Oligonucleotide primers huVH(1-6)backNco (SEQ. ID. NOS: 13-18) have been adapted from oligonucleotide primers described in the same paper. The first series of amplification involved primers huVH(1-6)back in conjunction with primer conIgG1-4 (SEQ. ID. NO: 1). Six different DNA fragments of about 700 bp, each corresponding to an individual VH-gene family were obtained. The six different fragments were isolated and re-amplified with primers huVH(1-6)back and primer huIgG4 (SEQ. ID. NO: 2). Six products of approximately 660 bp were obtained. The 6 different 660 bp fragments which represented the IgG4 repertoire of the patient were re-amplified with primers huVH(1-6)backNco (SEQ. ID. NOS: 13-18) and huJH(1-6)forSal (SEQ. ID. NOS: 9-12) in order to prepare these fragments for cloning. The resulting 24 fragments were pooled according to VH-gene family and the six different fragments were digested with NcoI and SalI. The digested fragments were purified and dissolved in TE (10 mM Tris-HCl pH=8.0; 0.1 mM EDTA). The vector pHEN-1-VLrep has been described previously (Griffin, H. M. and Ouwehand, W. H. 1995. Blood 86, 4430-4436; Schier et al. 1996. J. Mol. Biol. 225: 28-43) and contains a light chain repertoire derived of two non-immunized donors. Insertion of a heavy chain repertoire in this vector has been shown to result in the production of antibody fragments that consist of the variable domains of both heavy and light chain. These antibody fragments have been termed single chain Fv (scFv) fragments (Hoogenboom, H. R. et al. 1991. Nucleic Acid Res. 19: 4133-4137). The vector pHEN-1-VLrep (kindly provided by Dr. W. H. Ouwehand, Department of Transfusion Medicine, University of Cambridge, UK) was digested with XhoI and NcoI and the six fragments corresponding to the IgG4-specific heavy chain repertoire of the patient with acquired haemophilia were inserted. The ligation mixtures were transformed to  E. coli  TG1 and a library of 1,500,000-2,500,000 independent clones was obtained. Colonies were scraped and resuspended in 2TY supplemented with 15% glycerol, 100 μg/ml ampicillin and 1% glucose. Similar to the methods outlined above libraries that represent the immunoglobulin repertoire of other patients may be assembled. 
     EXAMPLE 3: Selection of Factor VIII Specific Antibodies 
     Selection of clones that encoded antibody fragments (scFvs) with factor VIII specificity was performed as outlined below. Glycerol stocks were plated onto 2TY plates that contained ampicillin (100 μg/ml) and 1% glucose. Colonies were grown overnight and scraped the next day and dissolved in 2TY supplemented with 100 μg/ml ampicillin and 1% glucose. These cells were diluted in 2TY supplemented with ampicillin (100 μg/ml) and 1% glucose till a final optical density (OD) of 0.3 (measured at 600 nm). Cells were grown at 37° C. till an OD of 0.5. Subsequently, 1 ml of culture was diluted 10 times in 2TY with ampicillin (100 μg/ml) and 1% glucose. Next, 20 μl of helper phage was added (VCSM13; 1×10 11  pfu/ml) and the mixture was incubated for 45 minutes at 37° C. without shaking. Then, cells were incubated at 37° C. with shaking at 150 rpm for another 45 minutes. The cells were spun down at low speed and resuspended in 100 ml of 2TY supplemented with ampicillin (100 μg/ml), 0.1% glucose and 25 μg/ml kanamycin. The cells were incubated overnight at 30° C. The next day cells were spun down at 10000 rpm for 30 minutes. The supernatant was harvested and recombinant phage were allowed to precipitate for 2 hours at 4° C. after the addition of 1/5 volume of 20% PEG6000/2.5 M NaCl. The phages were spun down (30 minutes 10000 rpm) and resuspended in 5 ml of TBS (50 mM Tris-HCl pH 7.4, 150 mM NaCl). This preparation was spun down for 5 minutes at 14000 rpm and the supernatant was stored at 4° C. 
     Selection of factor VIII-binding phages was performed as outlined below. Microtiter wells were coated overnight at 4° C. with 5 μg/ml of the murine factor VIII light chain specific monoclonal antibody CLB-CAg 12 which was diluted in 50 mM NaHCO 3  (pH 9.5). The wells were blocked for 1 hour at 37° C. with TBS containing 3% HSA. Phage solution (1×10 12  pfu/ml) was diluted 1 to 1 in TBS supplemented with 6% HSA and 1% Tween-20 and incubated for 2 hours at room temperature with microtiter wells that contained immobilized CLB-CAg 12. The phage solution was removed and transferred to a second microtiter well (also coated with CLB-CAg 12) which had been preincubated with 1 μg/ml of factor VIII light chain. Phages were incubated with factor VIII light chain for 2 hours at room temperature. Wells were washed 20 times with TBS/0.1% Tween-20 and 20 times with TBS and bound phage was eluted with 100 mM triethylamine (pH 12). Eluted phage (volume 1 ml) was neutralized by the addition of 500 μl of 1 M Tris-HCl pH 7.4 and subsequently added to 5 ml of  E. coli  TG1 (OD 600=0.5). Cells were incubated for ½ hour at 37° C. (no shaking) and 10 minutes at 37° C. (shaken at 200 rpm). Cells were collected by centrifugation for 10 minutes at 4000 rpm for 7 minutes. Subsequently, infected TG1 cells were plated on 2TY agar plates supplemented with ampicillin (100 μg/ml) and 1.0% glucose. Cells were grown overnight at 30° C. Cells were scraped in 2TY supplemented with ampicillin (100 μg/ml), 1% glucose and 15% glycerol. Ampoules were stored at −70° C. 
     Alternatively, factor VIII light chain (5 μg/ml in 50 mM NaHCO 3  (pH 9.6)) was immobilized on immunotubes (Nunc, Life Technologies, Breda, The Netherlands). First, 1 ml of phage solution diluted in TBS supplemented with 3% HSA was incubated for 2 hours at room temperature in non-coated Immunotubes. Subsequently, 1 ml of phage solution was removed and incubated for 2 hours at room temperature in immunotubes coated with factor VIII light chain. Immunotubes were washed 20 times with TBS/0.1% Tween-20 and 20 times with TBS. Bound phage was eluted with 100 mM triethylamine (pH 12) and processed as outlined above. 
     The second round of panning was initiated by inoculating 50 μl of glycerol stock obtained after the first selection in 10 ml 2TY supplemented with ampicillin (100 μg/ml) and 1% glucose till a final OD600 of 0.3. Cells were grown till an OD600 of 0.5, diluted 1 to 10 in 2TY supplemented with ampicillin (100 μg/ml), kanamycin (25 μg/ml) and 1% glucose and subsequently infected with a 20 fold excess of VCSM13. Cells were grown overnight at 30° C. Supernatant containing the phage was harvested as described above and again screened for binding to immobilized factor VIII light chain. After found rounds of panning, 30 clones selected by ELISA and 30 clones that were obtained after panning with factor VIII light chain immobilized to immunotubes were grown and analyzed for binding to the factor VIII light chain. Colonies were picked and grown overnight in 2 ml 2TY supplemented with 100 μg/ml ampicillin and 1% glucose. The next day the cultures were diluted 200 times and grown till an OD600 of approximately 0.5. Cells were subsequently infected with VCSM13 for 45 minutes at 37° C. (no shaking) and 45 minutes at 37° C. (shaken at 200 rpm). Infected cultures were diluted 1 to 10 in 2TY supplemented with 100 μg/ml ampicillin, 0.1% glucose and 25 μg/ml kanamycin and cells were grown overnight at 30° C. Supernatant containing phage was collected after centrifugation and tested for binding to the factor VIII light chain as described below. The non-inhibiting murine monoclonal antibody CLB-CAg 12 directed against an epitope in the A3-C1 domain of factor VIII was immobilized on microtiter wells at a concentration of 5 μg/ml in 50 mM NaHCO 3  (pH 9.5). Wells were blocked for 1 hour in TBS supplemented with 3% HSA. Wells were incubated with factor VIII light chain at a concentration of 1 μg/ml in 50 mM Tris HCl (pH 7.4), 1 M NaCl, 2% HSA for 2 hours at 37° C. Fifty μl of phage solution and an equal volume of TBS supplemented with 1% Tween-20 and 6% HSA were added to wells containing factor VIII light chain. To monitor specific binding of the phages, wells that did not contain factor VIII light chain were incubated simultaneously with the same phage solution. Phage was incubated at room temperature for 2 hours and were shaken at regular intervals. Subsequently, wells were extensively washed 5 times with TBS supplemented with 0.1% Tween-20 and washed 5 times with TBS. The presence of bound phage was monitored by incubating with a peroxidase labelled polyclonal antibody directed against M13 (Pharmacia-LKB, Woerden, The Netherlands) in a dilution of 1 to 4000 in TBS supplemented with 1% HSA and 0.1% Tween-20. Plates were washed 5 times with TBS supplemented with 0.1% Tween-20 and 5 times with TBS. Binding of peroxidase-labelled anti-M13 antibody was quantified by incubation with 3-3′-5-5′ tetramethylbenzidine (TMB). Substrate conversion was arrested by the addition of 100 μl of 2N H 2 SO 4 . Part of the results of this analysis are given in  FIG. 1 . An example of 12 clones that show specific binding to the factor VIII light chain is given. Clearly, phage encoded by clone 1 to 12 display binding to the factor VIII light chain (black bars). Some background binding is visible which is not dependent on the presence of the factor VIII light chain (grey bars). The bars labelled with c represent two clones that express antibody fragments that do not bind specifically to the factor VIII light chain. These clones have been derived from the initial library and have not been selected on the factor VIII light chain. To ensure that during subsequent rounds of panning an increase in the amount of factor VIII specific recombinant antibody fragments was obtained, we screened 12 clones obtained after the first round of panning for binding to the factor VIII light chain ( FIG. 2 ). Only 3 out of 12 clones bind specifically to the factor VIII light chain. In 9 out of 12 clones binding of phage is not dependent on the presence of the factor VIII light chain. These results clearly indicate that during panning the amount of phages that express factor VIII-specific antibodies can be selectively enriched. In summary, we have outlined a specific protocol for the selection of factor VIII specific antibodies that correspond to the spectrum of anti-factor VIII antibodies present in the patient with acquired haemophilia. In the first two examples our analysis is limited to material derived of one single patient and only antibodies directed against the factor VIII light chain have been analyzed. Using the methods outlined in these two examples the repertoire of anti-factor VIII antibodies of other patients with an inhibitor can easily be obtained. Furthermore, anti-factor VIII antibodies directed against epitopes located outside the factor VIII light chain may be obtained by adapting the screening methods used in Example 1 and 2. Antibodies directed against the heavy chain can be selected by immobilizing factor VIII heavy chain employing monoclonal antibody CLB-CAg 9. In these two examples we have focused on the IgG4-repertoire of the patient. Similarly, other subclasses may be investigated using the appropriate primers. For example, subclass IgG1-4 can be detected by simply using primer conIgG1-4 (SEQ. ID. NO: 1) described in Example 1. Similarly, other primers specific for IgA, IgM, IgE and IgD may be utilized to assemble antibody-repertoires that include factor VIII-specific antibodies. 
     EXAMPLE 4: Sequence Characteristics of Recombinant Antibodies with Factor VIII Light Chain Specificity 
     In the previous examples methods to obtain recombinant antibodies with factor VIII specificity has been outlined. To obtain information on the properties of these antibodies we selected 30 clones that have been selected by immobilized factor VIII in immunotubes. Also 30 clones which were selected employing factor VIII light chain with monoclonal antibody CLB-CAg 12 were analyzed. Clones were grown as descried in Example 2 and plasmid DNA was isolated. The nucleotide sequence of the variable part of the heavy chain (VH domain) of 55 clones was determined using fluorescently labelled M13 reverse primer on an ABI-Prism 377 DNA sequencer. The sequences obtained were aligned with heavy chain sequences in the database “V BASE” of the MRC Centre of Protein Engineering (Cambridge, UK). The 55 clones analyzed were encoded by two different VH-gene segments DP-10 (SEQ. ID. NO: 20) and DP-14 (SEQ. ID. NO: 22) (Cook and Tomlinson, Immunology Today 16: 237-242). The 41 clones that were encoded by the germline sequence DP14 (SEQ. ID. NO: 22) consisted of three groups of recombinant antibodies that differed mainly in the nucleotide sequences of the constant regions of the VH gene. Thirty-three clones which were represented by clone IT2, 5 clones were represented by EL25 and 3 clones were represented by clone EL5 (Table I). Two clones that were encoded by DP10 (SEQ. ID. NO: 20) (EL14) (SEQ. ID. NO: 19) and DP14 (SEQ. ID. NO: 22) (IT2) (SEQ. ID. NO: 21) were selected for further analysis. The nucleotide and primary amino acid sequence of these clones is listed in  FIGS. 3 and 4 . The characteristics of the two sequences are given in Table I. Part of clone EL14 is most likely derived of the D-segment D6-13 and J-segment JH-3b. Somatic hypermutation has occurred during the immune response as evidenced by the large number of nucleotide changes compared to the germline sequences of the VH segments. The variable heavy chain part of clone IT2 (SEQ ID. NO: 21) contains 20 nucleotide substitutions when compared to the germ line segment DP-14 (SEQ. ID. NO: 22). These 20 nucleotide substitutions result in a total of 13 amino acid changes (Table I). The variable heavy chain part of clone EL14 (SEQ. ID. NO: 19) contains 18 nucleotide substitutions when compared to the germ line segment DP-10 (SEQ. ID. NO: 20). These 18 nucleotide substitutions result in 12 amino acid changes (Table I). Clone IT2 has in part been derived from gene segments D3-3 and JH6b. Remarkably, a stretch of G-residues is observed between the germ line sequences DP14 (SEQ. ID. NO: 22) and D3-3 for clone IT2 that encodes for a flexable arm of glycine residues. Inspection of the amino acid sequence of clone EL14 (SEQ. ID. NO: 23) and IT2 (SEQ. ID. NO: 25) reveals several interesting features. Both CDR3 regions contain several glycine residues at their amino-terminal part which is in both cases followed by a tyrosine and a glutamic acid (GG-YE). Furthermore, a proline, alanine and an aspartic acid appear to be conserved in the carboxyl-terminal part of the CRD3 (P---A-D). A common motif can be derived from the amino acid sequences of the CDR3 regions of clone EL14 (SEQ. ID. NO: 23) and IT2 (SEQ. ID. NO: 25) which is given in  FIG. 4B . These features may determine the specificity of these antibodies for the factor VIII light chain. In this example the nucleotide and primary amino acid sequence of two recombinant factor VIII antibodies has been disclosed. With methods similar to the ones described in this example recombinant antibodies that are directed against other regions on the factor VIII molecule may be analyzed. Common features of these antibodies can be identified as outlined in this example and therapeutic and diagnostic agents derived of these common features can be used for diagnosis and treatment of patients with factor VIII inhibitors. 
     EXAMPLE 5: Detection of Nucleotide Sequences of Factor VIII Specific Antibodies in Patient Samples 
     The nucleotide and amino acid sequences outlines in the previous example can be used to specifically detect factor VIII antibodies with C2-specificity in heterogeneous mixtures of antibodies. This can be accomplished by developing reagents, for example, antibodies that specifically recognize the anti-factor VIII antibodies described in this invention. Detection of factor VIII-specific antibodies can also be performed by analysis of the presence of specific nucleotide sequences that encode factor VIII specific antibodies. Methods to obtain nucleotide sequences that encode factor VIII specific antibodies are disclosed in this invention. In this example the detection of nucleotide sequences encoding one of the factor VIII specific antibodies described in the previous example (EL14) (SEQ. ID. NO: 19) is disclosed. Lymphocytes of the patient with acquired haemophilia described in the first example were obtained. RNA was isolated and cDNA was prepared. Subsequently, DNA fragments were amplified with oligonucleotide primers huVH(1-6)aback (SEQ. ID NOS: 3-8) and conIgG1-4 (SEQ. ID. NO: 1) (see Example 2). The six different 700 bp fragments obtained were isolated and used for a second PCR with oligonucleotide primer huVH(1-6)aback (SEQ. ID. NOS: 3-8) and huIgG4 (SEQ. ID. NO: 2). This resulted in a fragment of 660 bp which was cloned into the vector pGEM-T (Promega, Madison, Wis., USA). The presence of nucleotide sequences that corresponded to that of clone EL14 (SEQ. ID. NO: 19) was addressed by nucleotide sequencing. One out of sixty clones analyzed did contain nucleotide sequences that were identical to that obtained for clone EL14 (SEQ. ID. NO: 19). This analysis shows that, using the nucleotide sequences disclosed in this invention as a starting point, it is possible to monitor the presence of factor VIII specific antibodies in patient samples. In this example oligonucleotide primers are used which have also been employed for the construction of the IgG4 specific library. Other combinations of oligonucleotide primers that are based on the nucleotide sequences of clone EL14 (SEQ. ID. NO: 19) and IT2 (SEQ. ID. NO: 21) may be designed which may include but are not limited to oligonucleotide primers that are based upon the CDR3 region of these antibodies. In this example detection of factor VIII specific antibodies is performed using analysis of nucleotide sequences. Alternatively, detection of factor VIII specific sequences may also be performed employing selective hybridization using probes that are based on the nucleotide sequence of the factor VIII specific antibodies disclosed in this invention. Other means of detection of specific nucleotide sequences that are known to an average expert in the art also fall within the scope of this invention. The methods disclosed in this invention allow for the isolation of factor VIII antibodies and determination of their nucleotide and amino acid sequence. In this example we have outlined described methods that detect factor VIII specific antibodies present in the repertoire of a patient with a factor VIII inhibitor. In examples 8 and 9 the nucleotide sequence of antibody fragments that bind to the A2- and A3-C1 domain of factor VIII is given. Methods similar to the ones described in this example can be used to detect nucleotide sequences that encode factor VIII inhibitors with A2-, A3-C1- or with a different epitope-specificity. 
     EXAMPLE 6: Properties of Factor VIII-specific Antibodies scFv-IT2 and scFv-EL14 
     The biochemical properties of the factor VIII specific antibodies IT2 and EL14 were characterized as follows. First, the plasmids pHEN-1-VL-EL14 and pHEN-1-VL-IT2 were digested with NcoI and NotI and the recombinant antibody fragments were isolated and cloned into the vector pUC119-sfi/Not-His6 (kindly provided by Dr. W. H. Ouwehand, University of Cambridge, Division of Transfusion Medicine, Cambridge UK). Positive clones were identified and grown till OD600 of 0.8-1.0 in 2TY medium supplemented with 1% glucose and 100 μg/ml ampicillin. Subsequently, Isopropyl-β-D-thiogalactopyranoside (IPTG) till a final concentration of 1 mM was added and cells were grown for 3 hours at 30° C. Cells were harvested by centrifugation for 15 minutes at 4000 g at 4° C. The pellet was dissolved in 10 ml of 30 mM Tris-HCl (pH 8.0), 1 mM EDTA and 20% sucrose in order to release the content of the periplasma. The mixture was incubated at 4° C. for 20 minutes and subsequently cells were collected by centrifugation (15 min 10800 g at 4° C.). The supernatant which consists primarily of proteins present in periplasma was collected. The pellet was resuspended in 10 ml 5 mM MgSO 4  and incubated for 20 minutes at 4° C. Residual cell debris was collected by centrifugation for 15 minutes at 10800 G. The supernatant (designated osmotic shock fraction) was collected and added to the fraction containing periplasma-derived proteins. The pooled fractions were centrifuged for 20 minutes at 30000 g at 4° C. and the supernatant was collected. The supernatant was filtered over a 0.22 μm filter. A mixture of protease inhibitors was added (Complete™ Mini, Boehringer Mannheim, Germany) and the pooled fractions were dialysed overnight against a buffer containing 50 mM NaPi (pH 7.4), 20 mM imidazole and 500 mM NaCl. ScFv&#39;s were purified by nickel affinity resin Ni-NTA (QIAGEN, Germany) as follows: 1 ml of Ni-NTA matrix was equilibrated with 50 mM NaPi (pH 7.4), 250 mM imidazole, 500 mM NaCl and subsequently with 50 mM NaPi (pH 7.4), 20 mM imidazole, 500 mM NaCl. Dialysed supernatant containing factor VIII specific scFv&#39;s were then batch-wise incubated with Ni-NTA matrix for 3 hours at 4° C. The Ni-NTA was then transferred to a column and washed with 7 ml of 50 mM NaPi (pH 7.4), 20 mM imidazole, 500 mM NaCl and 7 ml of 50 mM NaPi (pH 7.4), 35 mM imidazole, 500 mM NaCl. ScFv&#39;s were eluted with 50 mM NaPi (pH 7.4), 250 mM imidazole, 500 mM NaCl and stored at 4° C. The purity of the different scFv preparations was addressed by SDS-PAGE followed by staining with Coomassie Brilliant Blue. All purified ScFv&#39;s appeared for at least 90% homogenous and migrated with an apparent molecular weight of 30 kDa. In the preparations obtained a small amount of a protein with a lower molecular weight was observed. The identity of this band was investigated by immunoblotting with monoclonal antibody 9E10. The epitope of this antibody is present at the carboxyl-terminus of the scFV&#39;s. Both the protein migrating at a molecular weight of 30 kDa and 15 kDa reacted with monoclonal antibody 9E10 on Western blot. This indicates that the 15 kDa fragment most likely corresponds to the light chain of the scFv&#39;s. Purified scFv&#39;s corresponding to clone IT2 and EL14 were purified as outline above. A scFv derived of clone O4, a clone present in the patient library that did not bind to the factor VIII light chain was included as a negative control. The binding of scFv-IT2 and scFv-EL14 to the factor VIII light chain was addressed employing the following ELISA. Monoclonal antibody 9E10 (5 μg/ml) dissolved in 50 mM NaHCO 3  pH 9.5 was immobilized on microtiter wells overnight at 4° C. Subsequently, purified scFv&#39;s diluted in 50 mM Tris-HCl (pH 7.4), 150 mM NaCl, 1% HSA and 0.2% Tween-20 were added and incubated for 2 hours at room temperature. The microtiter plates were washed 5 times with TBS, 0.1% Tween-20. Next, purified factor VIII light chain was added (5 μg/ml) together with peroxidase labelled monoclonal antibody CLB-CAg A (0.5 μg/ml). The mixture (diluted in TBS, 0.1% Tween-20) was incubated for 2 hours at room temperature. The microtiter wells were washed 5 times with Tris-buffered saline (TBS) supplemented with 0.1% Tween-20 and 5 times with TBS. The amount of bound peroxidase labelled monoclonal antibody CLB-CAg A was quantified by the substrate TMB. The results of this analysis are given in  FIG. 5 . Both scFv-EL14 and scFv-IT2 react with specifically with the factor VIII light chain while scFv-04 did not react with the factor VIII light chain. Next, we used the factor VIII inhibitory murine monoclonal antibody CLB-CAg 117 for the detection of bound factor VIII light chain. The ELISA was performed as outlined above. Instead of peroxidase labelled CLB-CAg A we used peroxidase labelled CLB-CAg 117 for the detection of immobilized factor VIII light chain. We did not observe binding of CLB-CAg 117 when factor VIII light chain is immobilized by scFv-EL14 and scFv-IT2 ( FIG. 5 ). These results show that the epitope of scFv-EL14 and scFv-IT2 overlaps with that of CLB-CAg 117. Previously, we have shown that the inhibitory antibody CLB-CAg 117 is directed against the C2-domain of factor VIII (Fijnvandraat et al. 1998. Blood 91: 2347-2352). Apparently, both scFv&#39;s bind to an epitope in the C2-domain of factor VIII which overlaps with that of the inhibitory murine monoclonal antibody CLB-CAg 117. 
     Next, different dilutions of scFv-EL14 and scFv-IT2 were tested for binding to immobilized factor VIII light chain as outlined above using CLB-CAg A as the detecting antibody ( FIG. 6 ). From this analysis it appeared that scFv-EL14 binds with a higher affinity to the factor VIII light chain than scFv-IT2. These results were complemented by immunoprecipitation experiments for scFv-EL14. Immunoprecipitation experiments employing a metabolically labelled fragment corresponding to the C2-domain was performed essentially as described previously (Fijnvandraat et al. 1998. Blood 91: 2347-2352). Monoclonal antibody 9E10 was covalently linked to CNBr-activated Sepharose 4B and this matrix was used to bind scFv-EL14. Specific binding of scFv-EL14 to metabolically labelled C2-domain was detected and this confirms the C2-specificity of this recombinant antibody fragment. In this example methods have been disclosed to characterize recombinant antibodies with specificity for the C2-domain. In examples 8 and 9, we describe the nucleotide and amino acid sequence of recombinant antibody fragments that bind specifically to the A2 (SEQ. ID NOS: 49 and 51-55) and A3-C1 (SEQ. ID. NOS: 34, 36 and 39-48) domain of factor VIII. The methods described in this example can easily be adapted by an average expert skilled in the art, which will allow for characterization of recombinant antibodies directed against the A2 (SEQ. ID. NOS: 49 and 51-55), A3-C1 (SEQ. ID. NOS: 34, 36 and 39-48) or another epitope on factor VIII. 
     EXAMPLE 7: Factor VIII Specific Recombinant Antibody Fragments scFv-IT2 and scFv-EL14 Neutralize the Activity of Factor VIII Inhibitors 
     In the previous example, we have shown the scFv-EL14 and scFv-IT2 bind to the factor VIII light chain and compete for binding with the murine inhibitory monoclonal antibody CLB-CAg 117. These observations suggest that the epitope of both scFv-EL14 and scFv-IT2 overlaps with that of CLB-CAg 117. It is expected that similar to CLB-CAg 117, scFv-EL14 and scFv-IT2 inhibit the biological activity of factor VIII. Increasing amounts of purified scFv&#39;s were tested for inhibition in the Bethesda assay. Surprisingly, addition of up to 170 μg/ml scFv did not result in factor VIII inhibition as measured in the Bethesda assay. In contrast, CLB-CAg 117 readily inhibited factor VIII when measured in the same assay. Apparently, binding of scFv-EL14 and scFv-IT2 to factor VIII does not interfere with the biological activity of factor VIII. This finding prompted us to investigate the capacity of both scFv-EL14 and scFv-IT2 to overcome inhibition by CLB-CAg 117. Monoclonal antibody CLB-CAg 117 was diluted till a final inhibitory activity of 2 BU/ml. This value corresponds with a residual factor VIII activity of 25% in the Bethesda assay. Subsequently, increasing concentrations of scFv-EL14 and scFv-IT2 were added. Surprisingly, both scFv-EL14 and scFv-IT2 could overcome the factor VIII inhibitory activity of CLB-CAg 117 ( FIG. 7 ). ScFv-14 (panel A) proved to be more efficient than scFv-IT2 (panel B) in neutralizing the inhibitory activity of CLB-CAg 117. Both scFv-EL14 and scFv-IT2 were unable to neutralize the inhibitory activity of monoclonal antibody CLB-CAg A, directed against amino acid residues Glu 1811 -Lys 1818  on the factor VIII light chain (Lenting et al. 1996. J. Biol. Chem. 271: 1935-1940). These results for the first time show that antibody fragments with factor VIII specificity can be used to interfere with the activity of factor VIII inhibitors. Administration of these antibody fragments will be beneficial for the treatment of patients with inhibitory antibodies directed against factor VIII. In this example the biological activity of antibody fragments with C2-specificity is disclosed. In examples 8 and 9, the nucleotide and amino acid sequence of recombinant antibody fragments that bind to the A2 (SEQ. ID. NOS: 49 and 51-55) and A3-C1 (SEQ. ID. NOS: 34, 36 and 39-48) domain of factor VIII is disclosed. The methods disclosed in this and the previous example can easily be adapted by an average expert skilled in the art to establish the capacity of recombinant antibody fragments directed against the A2 or A3-C1 domain to neutralize factor VIII inhibitors. Similar to outlined in this example recombinant antibody fragments that bind to other regions can be evaluated for their neutralizing capacity of factor VIII inhibitors. Similarly to what has been described in this example for scFv-EL14 and scFv-IT2, antibody fragments binding to A2, A3-C1 and other domains on factor VIII can be used for treatment of patients with factor VIII inhibitors. 
     EXAMPLE 8: Isolation and Characteristics of Anti-factor VIII Antibodies that  Specifically Bind to the A3-C1 Domain of Factor VIII 
     Previous studies have indicated that plasma of a substantial number of inhibitor patients contains anti-factor VIII antibodies that bind specifically to the A3-C1 domains of factor VIII (Fijnvandraat et al. 1998. Blood 91: 2347-2352: Zhong et al. 1998. Blood 92: 136-142). Here, we have employed phage display technology to isolate anti-factor VIII antibodies from the total immunoglobulin repertoire of a haemophilia A patient with an inhibitor. Previously, we have shown that in plasma of this patient anti-factor VIII antibodies directed against the factor VIII light chain are present. The majority of the anti-factor VIII antibodies in this patient is directed against the A3-C1 domain whereas a small portion of anti-factor VIII antibodies reacts with the C2-domain (Fijnvandraat et al. 1998. Blood 91: 2347-2352). The majority of anti-factor VIII antibodies were of subclass IgG4. An IgG4-specific library was constructed using peripheral blood lymphocytes of the patient as starting material. A library consisting of 1.9×10 6  independent clones was obtained using the methods outlined in Example 2. Selection of recombinant phage that bind specifically to factor VIII was performed essentially as outlined in Example 3. 
     Microtiter wells were coated overnight at 4° C. with 5 μg/ml of the murine factor VIII light chain specific monoclonal antibody CLB-CAg 117 which was diluted in 50 mM NaHCO 3  (pH 9.5). Monoclonal antibody CLB-CAg 117 is directed against the C2-domain of factor VIII. The use of CLB-CAg 117 in the selection-protocol may result in elimination of recombinant phages that express immunoglobulin fragments directed against the C2-domain of factor VIII. Recombinant phages expressing the IgG4 specific immunoglobulin repertoire were prepared as described in Example 3. Recombinant phages were initially incubated on microtiter wells that contained immobilized CLB-CAg 117 for 2 hours in TBS supplemented with 3% HSA and 0.5% Tween-20. The phage solution was removed and transferred to a second microtiter well (also coated with CLB-CAg 117) which had been preincubated with 1 μg/ml of factor VIII light chain. Phages were allowed to bind to the immobilized factor VIII light chain for 2 hours at room temperature. Wells were washed extensively as described in Example 3 and bound phage were eluted with 100 mM triethylamine (pH 12). The eluted phage were neutralized by the addition of 1 M Tris-HCl pH 7.4 and the resulting solution was used to infect  E. coli  TG1 cells as described in Example 3. 
     Alternatively, purified factor VIII (5 μg/ml in 50 mM NaHCO 3  (pH 9.6)) was immobilized on immunotubes (Nunc, Life Technologies, Breda, The Netherlands). Recombinant phages diluted in TBS supplemented with 3% HSA were first incubated for 2 hours at room temperature in non-coated immunotubes. Subsequently, 1 ml of phage solution was removed and incubated for 2 hours at room temperature in Immunotubes coated with factor VIII. Following extensive washing (20 times with TBS/0.1% Tween-20 and 20 times with TBS) bound phage were eluted with 100 mM triethylamine (pH 12) and processed as outlined above. 
     The second, third and fourth round of panning were performed using the selection protocol described above. After the fourth round of panning 15 individual clones were picked and recombinant phage were tested for binding to the factor VIII light chain and the A3-C1 domain. Factor VIII light chain was purified as described previously. A construct expressing recombinant A3-C1 domain was prepared essentially as described previously (Sawamoto et al. 1998. Thrombosis and Haemostasis vol. 78, 62-68) and expressed in CHO-cells. The non-inhibitory murine monoclonal antibody CLB-CAg 12 directed against an epitope in the A3-C1 domain of factor VIII was immobilized on microtiter wells at a concentration of 5 μg/ml in 50 mM NaHCO 3  (pH 9.5). Wells were blocked for 1 hour in TBS supplemented with 3% HSA. Subsequently, wells were incubated with factor VIII light chain (1 μg/ml) or recombinant A3-C1 domain (0.06 nM) in 50 mM Tris HCl (pH 7.4), 1 M NaCl, 2% HSA for 2 hours at 37° C. Fifty μl of phage solution and an equal volume of TBS supplemented with 1% Tween-20 and 6% HSA were added to wells containing immobilized factor VIII light chain or A3-C1 domain. To monitor specific binding of the phage, wells that did not contain factor VIII light chain or recombinant A3-C1 domain were incubated with simultaneously with the phage solution. Phage were incubated at room temperature for 2 hours and were shaken at regular intervals. Wells were washed extensively with TBS supplemented with 0.1% Tween-20. The presence of bound phage was monitored as described in Example 3. The results of the analysis are depicted in  FIG. 8 . In panel A, 15 clones selected in immunotubes that contain factor VIII are depicted. Of the 15 clones analyzed, 1 clone (clone 20) did not react with factor VIII light chain and recombinant A3-C1 domain suggesting that this clone does not encode an antibody fragment with specificity for the A3-C1 domain of factor VIII. Three clones (clone 17, 23 and 24) do react with the factor VIII light chain but fail to react with recombinant A3-C1 domain. Apparently, the epitope of these recombinant antibody fragments is localized in the C2-domain of factor VIII. The remaining 11 clones react both with the factor VIII light chain and the recombinant A3-C1 domain. In panel B, 15 clones selected in microtiter wells that contain CLB-CAg 117 and factor VIII light chain are depicted. Clones 31-45 all interact with the factor VIII light chain (black bars) and recombinant A3-C1 domain (hatched bars). This analysis shows that phage derived of clone 31-45 encode antibody fragments that bind specifically to the A3-C1 domain of factor VIII. 
     These results show that the protocol outlined above is suitable for the selection of recombinant antibody fragments that bind specifically to the A3-C1 domain of factor VIII. Using the methods disclosed in this example, it is feasible to isolate recombinant phage encoding antibody fragments specific for the A3-C1 domain from other patients with factor VIII inhibitors. 
     The nucleotide sequence of the variable heavy chain fragments of 26 clones that reacted specifically with recombinant A3-C1 domain was determined essentially as described in Example 4. The sequences obtained were aligned with heavy chain sequences in the database “V BASE” of the MRC Centre of Protein Engineering (Cambridge, UK). The 26 clones analyzed were encoded by four different VH-gene segments DP15 (SEQ. ID. NO: 31), DP31 (SEQ. ID. NO: 33) and DP49 (SEQ. ID. NO: 35) and DP77 (SEQ. ID. NO: 37). The amino acid sequence of the variable heavy chain fragments of clones B38 (SEQ. ID. NO: 32), B18 (SEQ. ID. NO: 34), B35 (SEQ. ID. NO: 36) and B04 (SEQ. ID. NO: 38) is listed in  FIG. 9A . The nucleotide sequence of these four clones is presented in  FIGS. 9B-E  (SEQ. ID. NOS: 39, 42, 44 and 46). 
     EXAMPLE 9: Isolation and Characteristics of Anti-factor VIII Antibodies that Bind to the A2-domain of Factor VIII 
     An immunodominant region which constitutes a binding site for factor VIII inhibitors has been localized to the A2-domain of factor VIII (Healey et al. 1995, J. Biol. Chem. 270: 14505-14509). We characterized the anti-factor VIII antibodies in plasma of a patient with mild haemophilia A and an inhibitor, essentially as outlined in example 1. Recombinant factor VIII fragments corresponding to the A2, A3-C1-C2 and C2-domain of factor VIII were metabolically labelled with [ 35 S]-methionine and used for the detection of anti-factor VIII antibodies in the patient&#39;s plasma. Reactivity with metabolically labelled A2-domain and A3-C1-C2 domain was observed whereas only weak reactivity with metabolically labelled C2-domain was observed (data not shown). To determine the inhibitory capacity of both the anti-A2 and anti-A3-C1-C2 antibodies we performed neutralization experiments. The factor VIII inhibitor was diluted until a final value of 2 BU/ml and subsequently increasing amounts of recombinant A2 or A3-C1-C2 were added. Addition of recombinant A2-domain resulted in almost complete neutralization of the factor VIII inhibitors present in patient&#39;s plasma. Addition of recombinant A3-C1-C2 only neutralized the factor VIII inhibitor to a limited extent (&lt;10%). These results show that the majority of factor VIII inhibitors are directed towards the A2-domain of factor VIII. We assessed the subclass of the anti-factor VIII antibodies by enzyme linked sorbent assay. Both anti-A2 and anti-A3-C1-C2 antibodies consisted predominantly of subclass IgG4. 
     Peripheral blood lymphocytes of the patient were used to construct an IgG4-specific library as outlined in example 2. A library consisting of 1.9×10 6  clones was obtained. Recombinant phage expressing the IgG4-specific immunoglobulin repertoire of the patient were prepared as described in Example 3. Selection of phages binding to the A2-domain of factor VIII was performed by one of the following methods:
         1. Purified factor VIII heavy chain (10 μg/ml) was immobilized on immunotubes (Nunc, Life Technologies, Breda, The Netherlands) in 50 mM NaHCO 3  (pH 9.5). Recombinant phages diluted in TBS supplemented with 3% HSA were first incubated for 2 hours at room temperature in non-coated immunotubes. Non-bound phage were transferred to an immunotube coated with factor VIII. Following extensive washing (20 times with TBS/0.1% Tween-20 and 20 times with TBS) bound phage was eluted with 100 mM triethylamine (pH 12). Eluted phage was neutralized by the addition of 1 M Tris-HCl pH 7.4 and used to infect  E. coli  TG1 cells as described in Example 3.   2. Alternatively, the murine monoclonal antibody CLB-CAg 9, directed against amino acid sequence 713-740 in the A2-domain of factor VIII was immobilized on microtiter wells at a concentration of 5 μg/ml in 50 mM NaHCO 3  (pH 9.6). Purified factor VIII heavy chain (1 μg/ml) was then added and allowed to bind to CLB-CAg 9. Recombinant phage diluted in TBS 3% HSA and 0.5% Tween 20 were first incubated in microtiter wells containing only immobilized CLB-CAg 9. After 2 hours non-bound phage were transferred to a microtiter well which contained immobilized factor VIII heavy chain. Phage were allowed to bind to the factor VIII heavy chain for 2 hours at room temperature. Wells were washed extensively (see above) and finally bound phage were eluted with 100 mM triethylamine (pH 12) and processed as outlined above.       

     After four rounds of selection individual clones were picked and binding of recombinant phage to factor VIII heavy chain was evaluated by an enzyme linked immuno sorbent assay. Monoclonal antibody ESH5 (American Diagnostica, Greenwich, Conn., USA) was immobilized onto microtiter wells at a concentration of 5 μg/ml in 50 mM NaHCO 3  (pH 9.6). Purified factor VIII heavy chain (1 μg/ml) was added and incubated for 2 hours at 37° C. Subsequently, recombinant phage, diluted 1 to 1 in 50 mM Tris-HCl pH 7.4, 1 M NaCl and 2% HSA, was added and incubated for 2 hours at room temperature. The amount of recombinant phage bound was determined was determined as described in Example 3. The results of the analysis is given in  FIG. 10 . Twenty clones which were selected in microtiter wells in which factor VIII heavy chain was immobilized by CLB-CAg 9 were analyzed. Eleven out of 20 clones bound specifically to the heavy chain of factor VIII ( FIG. 10A ). Clones that were selected by immobilized factor VIII heavy chain in immunotubes were also analyzed. Fifteen out of 20 clones bound specifically to the factor VIII heavy chain ( FIG. 10B ). These results show that the protocol outlined above permits the isolation of anti-factor VIII antibodies that are directed against the heavy chain (A1-A2) of factor VIII. Using the methods disclosed in this example it is feasible to isolate anti-factor VIII antibodies from the repertoire of additional patients with factor VIII inhibitors directed against the A2-domain. 
     The nucleotide sequence of the variable heavy chain fragments of 26 clones that reacted specifically with the factor VIII heavy chain were determined essentially as described in Example 4. The sequences obtained were aligned with heavy chain sequences in the database “V BASE” of the MRC Centre of Protein Engineering (Cambridge, UK). The 26 clones analyzed were encoded by two different VH-gene segments DP10 SEQ. ID. NO: 24) and DP47 (SEQ. ID. NO: 50) ( FIG. 11A ). The nucleotide sequence of the variable heavy chain of these clones is listed in  FIG. 11B  (SEQ. ID. NO: 52) and C (SEQ. ID. NO: 54). 
     EXAMPLE 10: Factor VIII Specific Recombinant Antibody Fragments can Neutralize the Activity of Factor VIII Inhibitors Present in Plasma of Patients with Haemophilia 
     In example 7, we have shown that scFv-EL14 and scFv-IT2 neutralize the inhibitory activity of the murine monoclonal antibody CLB-CAg 117. We tested whether scFv-EL14 can also neutralize factor VIII inhibitors present in plasma of haemophilia A patients. First, we tested plasma of the patient with acquired haemophilia from whom the recombinant antibody fragments were derived. As described in example 1, recombinant C2-domain was capable of neutralizing 20% of the factor VIII inhibitor in patient&#39;s plasma (Table III). The effect of scFv-EL14 was evaluated in a similar set-up. Plasma was diluted till a final value of 2 BU/ml and increasing amounts of scFv-EL14 were added. ScFv-EL14 could neutralize about 20% of the total activity of factor VIII inhibitor in patient&#39;s plasma. These results suggest that scFv directed against the C2-domain prevent binding of factor VIII inhibitory antibodies that bind to the C2-domain of factor VIII. 
     Next, we tested two plasma samples derived of patients with congenital haemophilia A and factor VIII inhibitors. The relative contribution of the C2-domain to the total amount of factor VIII inhibitor for both samples ranged between 40% and 90%. Neutralization experiments indicate that addition of increasing concentrations of scFv-EL14 results in significant reduction of the levels of factor VIII inhibitor in plasma of these two patients with congenital haemophilia A. These results confirm that scFv-EL14 alleviates binding of human factor VIII inhibitors to the C2-domain. Our findings show that scFv-EL14 shields antigenic sites that are present in the C2-domain of factor VIII. This property of scFv-EL14 can be utilized to prevent binding of factor VIII inhibitors to the C2-domain of administered factor VIII in haemophilia A patients with an inhibitor. It has been firmly established that factor VIII inhibitors often recognize multiple epitopes that have been localized to the A2-, A3- and C2 domain of factor VIII. In this example the neutralizing activity of the C2-domain specific scFv-EL14 on the biological activity of factor VIII inhibitors is described. 
     In examples 8 and 9 we have disclosed methods to obtain recombinant antibodies that specifically react with the A3-C1 domain and heavy chain (A1-A2) of factor VIII. In this example, we have shown that recombinant antibodies directed against the C2-domain of factor VIII can shield antigenic sites on factor VIII. Similarly, anti-A3-C1 antibodies and anti-A2-antibodies described in examples 8 and 9 can be tested for their ability to compete with factor VIII inhibitors for binding to factor VIII. The anti-A3-C1 and anti-A1-A2 antibodies disclosed in this invention may also be used for treatment of patients with inhibitors, which react with the A3-C1 and/or the A1-A2-domain. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
             
             
               
                 Nucleotide sequences of clones expressing recombinant antibodies with 
               
               
                 specificity for the factor VIII light chain. Based on the nucleotide 
               
               
                 sequence 55 of the 60 clones analyzed could be arranged as depicted be- 
               
               
                 low. In the first colunm clones with the same nucleotide sequence are ar- 
               
               
                 ranged in four groups. The number of clones corresponding to this group 
               
               
                 is given in brackets. Clone EL5 (SEQ. ID. NO:27), EL25 (SEQ. ID. NO: 
               
               
                 28) and IT2 (SEQ. ID. NO:25) are related as indicated in Figure 4B. 
               
               
                 In the second column the heavy chain family to which these clones belong 
               
               
                 is depicted. All clones analyzed belong to the VH1-family. In the third 
               
               
                 column the germline segment is depicted. Clone EL5 (SEQ. ID. NO:27), 
               
               
                 E125 (SEQ. ID. NO:28) and IT2 (SEQ. ID NOS:21, 25) belong to germ- 
               
               
                 line segment DP-14 (SEQ. ID. NOS:22, 26) while clone EL14 (SEQ. ID. 
               
               
                 NOS:19, 23) belongs to germline sequence DP-10 (SEQ. ID. NOS:20, 24). 
               
               
                 In the fourth column the number of mutations in the different clones 
               
               
                 is depicted. The first number corresponds to the number of nucleotide 
               
               
                 mutations while the second one corresponds to the number of amino acid 
               
               
                 changes. The sequences were compared with the nucleotide and amino 
               
               
                 acid sequences of the germline segments indicated in the Table. 
               
             
          
           
               
                 Clone 
                 VH family 
                 Germline segment 
                 Mutations 
               
               
                   
               
               
                 EL5 (3) 
                 VH1 
                 DP-14 
                 20/12 
               
               
                 EL14 (14) 
                 VH1 
                 DP-10 
                 18/12 
               
               
                 EL25 (5) 
                 VH1 
                 DP-14 
                 19/11 
               
               
                 IT2 (33) 
                 VH1 
                 DP-14 
                 20/13