Title of Invention: ANTIBODY MOLECULES HAVING SPECIFICITY FOR HUMAN OX40 Abstract: The invention relates to antibody molecules having specificity for antigenic determinants of human OX40, therapeutic uses of the antibody molecules and methods for producing said antibody molecules. Detailed Description: CROSS REFERENCE TO RELATED APPLICATIONS The present application claims priority under 35 U.S.C. §119(e) to Provisional Application Ser. No. 61/558,545, filed Nov. 11, 2011, which is incorporated herein by reference in its entirety. The present invention relates to antibody molecules having specificity for antigenic determinants of OX40 and compositions comprising the same. The present invention also relates to the therapeutic uses of the antibody molecules, compositions and methods for producing said antibody molecules. OX40 (also known as CD134, TNFRSF4, ACT35 or TXGP1L) is a member of the TNF receptor superfamily, which includes 4-1BB, CD27, CD30 and CD40. The extracellular ligand binding domain of OX40 is composed of 3 full cysteine-rich domains (CRDs) and a partial, fourth C-terminal CRD (Bodmer et al., 2002, Trends Biochem Sci, 27, 19-26). The ligand for OX40 is OX40L and 3 copies of OX40 bind to the trimeric ligand to form the OX40-OX40L complex (Compaan and Hymowitz, 2006, Structure, 14, 1321-1330). OX40 is a membrane-bound receptor; however a soluble isoform has also been detected (Taylor and Schwarz, 2001, J. Immunol. Methods, 255, 67-72). The functional significance of the soluble form is presently unknown. OX40 is not expressed on resting T cells, but is transiently expressed on activated T cells after ligation of the T cell receptor (TCR). The ligand for OX40, OX40L, is a member of the TNF family and is expressed on activated antigen presenting cells (APC), including B cells, macrophages, endothelial cells and dendritic cells (DC). OX40 is a major costimulatory receptor with sequential engagement of CD28 and OX40 being required for optimal T cell proliferation and survival. Ligation of OX40 on activated T cells leads to enhanced cytokine production and proliferation of both CD4+ and CD8+ T cells (Gramaglia et al., 2000, J. Immunol, 165, 3043-3050, Bansal-Pakala et al., 2004, J. Immunol, 172, 4821-425) and can contribute to both ongoing Th1 and Th2 responses (Gramaglia et al., 1998, J. Immuno., 161, 6510-6517, Arestides et al., 2002, Eur. J. Immunol. 32, 2874-2880). OX40 costimulation prolongs T cell survival beyond the initial effector phase of the immune response and increases the number of memory T cells through inhibition of effector T cell death. When immune activation is excessive or uncontrolled, pathological allergy, asthma, inflammation, autoimmune and other related diseases may occur. Because OX40 functions to enhance immune responses, it may exacerbate autoimmune and inflammatory diseases. The role of OX40/OX40L interactions in models of disease has been demonstrated in OX40 knockout mice. In experimental allergic encephalomyelitis (EAE), a model of multiple sclerosis, less severe clinical signs of disease and reduced inflammatory infiltrate within the CNS was noted in OX40 knockout mice (Carboni et al., 2003, J. Neuroimmunology, 145, 1-11). Also OX40 knockout mice primed and challenged with ovalbumin exhibit diminished lung inflammation (80-90% reduction in eosinophilia), reduced mucus production, and significantly attenuated airway hyper-reactivity (Jember et al., 2001, J. Exp. Med., 193, 387-392). Monoclonal antibodies to murine OX40 ligand have shown beneficial effects in the collagen-induced arthritis model of rheumatoid arthritis (Yoshioka et al., 2000, Eur. J. Immunol., 30, 2815-2823), EAE (Nohara et al., 2001, J. Immunol., 166, 2108-2115), non-obese diabetic (NOD) mice (Pakala et al., 2004, Eur. J. Immunol., 34, 3039-3046), colitis in T cell restored mice (Malmstrom et al., 2001, J. Immunol., 166, 6972-6981, Totsuka et al., 2003, Am. J. Physiol. Gastrointest. Liver Physiol., 284, G595-G603) and models of lung inflammation (Salek-Ardakani et al., 2003, J. Exp. Med., 198, 315-324, Hoshino et al., 2003, Eur. J. Immunol, 33, 861-869). An antibody to human OX40L has been profiled in a model of lung inflammation in rhesus monkeys and resulted in reduced levels of IL-5, IL-13 and effector memory T cells in bronchiolar lavage fluid after allergen challenge (Seshasayee et al., 2007, J. Clin. Invest, 117, 3868-3878). An increase in the expression of OX40 has been noted in several autoimmune and inflammatory diseases. This includes an increase in OX40 expression on T cells isolated from the synovial fluid of rheumatoid arthritis patients (Brugnoni D et al., 1998, Br. J. Rheum., 37, 584-585; Yoshioka et al., 2000, Eur. J. Immunol., 30, 2815-2823; Giacomelli R et al., 2001, Clin. Exp. Rheumatol., 19, 317-320). Similarly an increase in OX40 expression has been noted in gastrointestinal tissue from patients with ulcerative colitis and Crohn's disease (Souza et al., 1999, Gut, 45, 856-863; Stuber et al., 2000, Eur. J. Clin. Invest., 30, 594-599) and in active lesions of patients with multiple sclerosis (Carboni et al., 2003, J. Neuroimmunology, 145, 1-11). OX40L can also be detected on human airway smooth muscle (ASM) and asthma patients ASM cells show greater inflammatory responses to OX40L ligation than healthy donors, indicating a role for the OX40/OX40L pathway in asthma (Burgess et al., 2004, J. Allergy Clin Immunol., 113, 683-689; Burgess et al., 2005, J. Allergy Clin Immunol., 115, 302-308). It has also been reported that CD4+ T cells isolated from the peripheral blood of systemic lupus erythematosus (SLE) patients express elevated levels of OX40 which is associated with disease activity (Patschan et al., 2006, Clin. Exp. Immunol., 145, 235-242). Given the role of OX40 in allergy, asthma and diseases associated with autoimmunity and inflammation, one approach to therapy in these diseases is to block OX40-OX40L signalling through the use of anti-OX40L antibodies or antagonistic anti-OX40 antibodies Anti-OX40L antibodies have been described, see for example WO2006/029879. Numerous agonistic anti-OX40 antibodies have been described but very few antagonistic anti-OX40 antibodies are known. A rabbit polyclonal anti-mouse OX40 antibody was produced by Stuber et al., 1996, J. Exp. Med, 183, 979-989 which blocks the interaction between OX40 and OX40L. Mouse monoclonal antibodies, 131 and 315 which bind human OX40 were generated by Imura et al., 1996, J. Exp. Med, 2185-2195. Fully human antagonistic antibodies have been described in WO2007/062245, the highest affinity of these antibodies had an affinity for cell surface expressed OX40 (activated T cells) of 11 nM. Humanised antagonistic antibodies have been described in WO2008/106116 and the antibody with the best affinity for OX40 had an affinity of 0.94 nM. Other anti-OX40 antibodies have been described, including murine L106 (U.S. Pat. No. 6,277,962) and murine ACT35, commercially available from eBioscience. We have previously described high affinity antagonistic anti-OX40 antibodies in International Patent application number WO2010/096418. We have also previously described in International Patent application number WO2010/035012, a novel multi-specific antibody fusion molecule, hereinafter referred to as a Fab-dsFv and illustrated herein in FIG. 1. The same application provides useful anti-albumin binding variable regions which may be used to extend the half-life of the molecule. In the present invention these albumin binding variable regions have been improved and combined in the Fab-dsFv format with the anti-OX40 antibodies described in WO2010/096418. The new bispecific molecule of the present invention has improved efficacy in a number of in vitro and in vivo assays described herein when compared to the Fab′-PEG molecule previously described in WO2010/096418. Accordingly, the present invention provides a bispecific antibody fusion protein which binds both human OX40 and human serum albumin which is suitable for use in the treatment or prophylaxis of pathological disorders mediated by OX40 or associated with an increased level of OX40. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a bispecific antibody fusion of the present invention (Fab-dsFv format) FIG. 2: A) Light chain V region of antibody A26 (SEQ ID NO:7) B) Heavy chain V region of antibody A26 (SEQ ID NO:8) C) CDRH1 (SEQ ID NO:1), CDRH2 (SEQ ID NO:2), CDRH3 (SEQ ID NO:3), CDRL1 (SEQ ID NO:4), CDRL2 (SEQ ID NO:5) and CDRL3 (SEQ ID NO:6) of antibody A26. D) Light chain of antibody A26 Fab component (SEQ ID NO:9) E) Heavy chain of antibody A26 Fab component (SEQ ID NO:10) FIG. 3 A) Heavy chain of anti-albumin Fv component 645gH5 (SEQ ID NO:11) B) Light chain of anti-albumin Fv component 645gL4 (SEQ ID NO:12) C) Linker 1 (SEQ ID NO:13) D) Linker 2 (SEQ ID NO:14) E) Fab-dsFv heavy chain (SEQ ID NO:15) F) Fab-dsFv light chain (SEQ ID NO:16) FIG. 4 A) 645g1 heavy chain variable domain (SEQ ID NO:17) B) 645g1 light chain variable domain (SEQ ID NO:18) C) A26 Fab-dsFv 645gH1 (SEQ ID NO:19) D) A26 Fab-dsFv 645gL1 (SEQ ID NO:20) FIG. 5 A) DNA encoding heavy chain of the Fab-dsFv including OmpA leader (SEQ ID NO:21) B) DNA encoding heavy chain of the Fab-dsFv without OmpA leader (SEQ ID NO:22) FIG. 6 A) DNA encoding light chain of the Fab-dsFv including OmpA leader (SEQ ID NO:23) B) DNA encoding light chain of the Fab-dsFv without OmpA leader (SEQ ID NO:24) FIG. 7 A) DNA encoding heavy chain of the Fab-dsFv including B72.3 leader (SEQ ID NO:25) B) DNA encoding heavy chain of the Fab-dsFv without B72.3 leader (SEQ ID NO:26) FIG. 8 A) DNA encoding light chain of the Fab-dsFv including B72.3 leader (SEQ ID NO:27) B) DNA encoding light chain of the Fab-dsFv without B72.3 leader (SEQ ID NO:28) FIG. 9A shows binding of AlexaFluor 488 labelled A26 Fab-dsFv to activated human CD4+OX40+ T cells FIG. 9B shows binding for A26 Fab′, A26 Fab-Fv and A26 Fab′-PEG in the presence of 5% HSA on activated human CD4+, OX40+ T cells. FIG. 10A shows the effect of A26 Fab-dsFv on cytokine production from PBMC exposed to Dermatophagoides pteronyssinus allergic extract FIG. 10B shows the ability of A26 Fab-dsFv to inhibit CD4+ and CD8+ T cell proliferation in a Hu-NSG mouse model FIG. 11A shows inhibition of OX40L binding to human activated CD4+ OX40+ T cells by A26 Fab-dsFv FIG. 11B shows inhibition of OX40L binding to human activated CD4+ OX40+ T cells by A26 Fab′, A26 Fab-dsFv, A26 Fab′-PEG and two controls. FIG. 12A shows A26 Fab-Fv inhibits a human mixed lymphocyte reaction (MLR) FIG. 12B shows A26 Fab-Fv inhibits IFN-gamma production during a human MLR FIG. 13 shows A26 Fab-Fv reduces the percentage of activated (CD25+) CD4+ T cells after secondary antigen re-stimulation with Dermatophagoides pteronyssinus allergenic extract FIG. 14A shows A26 Fab-Fv administered prior to cell transfer dose dependently inhibits CD4+ T cell proliferation in the blood in the Hu-NSG model. FIG. 14B shows A26 Fab-Fv administered prior to cell transfer dose dependently inhibits CD8+ T cell proliferation in the blood in the Hu-NSG model. FIG. 14C shows A26 Fab-Fv administered prior to cell transfer dose dependently inhibits CD4+ T cell proliferation in the spleen in the Hu-NSG model. FIG. 14D shows A26 Fab-Fv administered prior to cell transfer dose dependently inhibits CD8+ T cell proliferation in the spleen in the Hu-NSG model. Humanised CA044—00026 anti-OX40 antibody, is referred to herein as A26. The antibody fusion molecule of the present invention, referred to herein as a Fab-dsFv, is illustrated in FIG. 1. In the present invention the Fab portion (comprising the first heavy and light chain variable regions and the constant domains) binds human OX40 and the dsFv portion (comprising the second heavy and light chain variable regions, linked by a disulphide bond) binds human serum albumin. In particular, the Fab portion comprises the CDRs derived from an antagonistic anti-OX40 antibody and the Fv portion comprises the heavy and light chain variable regions of a humanised anti-albumin antibody, and these albumin binding variable regions are linked by a disulphide bond. Accordingly, the present invention provides a bispecific antibody fusion protein which binds human OX40 and human serum albumin comprising: a heavy chain comprising, in sequence from the N-terminal, a first heavy chain variable domain (VH1), a CH1 domain and a second heavy chain variable domain (VH2), a light chain comprising, in sequence from the N-terminal, a first light chain variable domain (VL1), a CL domain and a second light chain variable domain (VL2), wherein said heavy and light chains are aligned such that VH1 and VL1 form a first antigen binding site and VH2 and VL2 form a second antigen binding site, wherein the antigen bound by the first antigen binding site is human OX40 and the antigen bound by the second antigen binding site is human serum albumin, in particular wherein the first variable domain of the heavy chain (VH1) comprises the sequence given in SEQ ID NO:1 for CDR-H1, the sequence given in SEQ ID NO:2 for CDR-H2 and the sequence given in SEQ ID NO:3 for CDR-H3 and the first variable domain of the light chain (VL1) comprises the sequence given in SEQ ID NO:4 for CDR-L1, the sequence given in SEQ ID NO:5 for CDR-L2 and the sequence given in SEQ ID NO:6 for CDR-L3, wherein the second heavy chain variable domain (VH2) has the sequence given in SEQ ID NO:11 and the second light chain variable domain (VL2) has the sequence given in SEQ ID NO: 12 and the second heavy chain variable domain (VH2) and second light chain variable domain (VL2) are linked by a disulphide bond. The residues in antibody variable domains are conventionally numbered according to a system devised by Kabat et al. This system is set forth in Kabat et al., 1987, in Sequences of Proteins of Immunological Interest, US Department of Health and Human Services, NIH, USA (hereafter “Kabat et al. (supra)”). This numbering system is used in the present specification except where otherwise indicated. The Kabat residue designations do not always correspond directly with the linear numbering of the amino acid residues. The actual linear amino acid sequence may contain fewer or additional amino acids than in the strict Kabat numbering corresponding to a shortening of, or insertion into, a structural component, whether framework or complementarity determining region (CDR), of the basic variable domain structure. The correct Kabat numbering of residues may be determined for a given antibody by alignment of residues of homology in the sequence of the antibody with a “standard” Kabat numbered sequence. The CDRs of the heavy chain variable domain are located at residues 31-35 (CDR-H1), residues 50-65 (CDR-H2) and residues 95-102 (CDR-H3) according to the Kabat numbering system. However, according to Chothia (Chothia, C. and Lesk, A. M. J. Mol. Biol., 196, 901-917 (1987)), the loop equivalent to CDR-H1 extends from residue 26 to residue 32. Thus unless indicated otherwise ‘CDR-H1’ as employed herein is intended to refer to residues 26 to 35, as described by a combination of the Kabat numbering system and Chothia's topological loop definition. The CDRs of the light chain variable domain are located at residues 24-34 (CDR-L1), residues 50-56 (CDR-L2) and residues 89-97 (CDR-L3) according to the Kabat numbering system. The bispecific fusion protein of the present invention comprises a Fab fragment of the anti-OX40 antagonistic antibody previously described in WO2010/096418. As used herein, the term ‘antagonistic’ describes an antibody fusion protein that is capable of inhibiting and/or neutralising the biological signalling activity of OX40, for example by blocking binding or substantially reducing binding of OX40 to OX40 ligand and thus inhibiting the activation of OX40. Screening for antibodies to identify those that bind OX40 can be performed using assays to measure binding to human OX40 and/or assays to measure the ability to block the binding of OX40 to its ligand, OX40L. An example of a binding assay is an ELISA, in particular, using a fusion protein of human OX40 and human Fc, which is immobilized on plates, and employing a conjungated secondary antibody to detect anti-OX40 antibody bound to the fusion protein. An example of a blocking assay is a flow cytometry based assay measuring the blocking of OX40 ligand fusion protein binding to OX40 on human CD4 cells. A fluorescently labelled secondary antibody is used to detect the amount of OX40 ligand fusion protein binding to the cell. This assay is looking for a reduction in signal as the antibody in the supernatant blocks the binding of ligand fusion protein to OX40. A further example of a blocking assay is an assay where the blocking of costimulation of naive human T cells mediated by OX40 ligand fusion protein coated to a plate is measured by measuring tritiated thymidine incorporation. In the present invention, the variable regions are humanised. Humanised antibodies (which include CDR-grafted antibodies) are antibody molecules having one or more complementarity determining regions (CDRs) from a non-human species and a framework region from a human immunoglobulin molecule (see, e.g. U.S. Pat. No. 5,585,089; WO91/09967). It will be appreciated that it may only be necessary to transfer the specificity determining residues of the CDRs rather than the entire CDR (see for example, Kashmiri et al., 2005, Methods, 36, 25-34). Humanised antibodies may optionally further comprise one or more framework residues derived from the non-human species from which the CDRs were derived. In the present invention the CDRs of VH1 and VL1 are derived from the antibody known as A26, described in WO2010/096418. Accordingly, in the bispecific antibody fusion protein of the present invention, the first variable domain of the heavy chain (VHI) comprises the sequence given in SEQ ID NO:1 for CDR-H1, the sequence given in SEQ ID NO:2 or SEQ ID NO:23 for CDR-H2 and the sequence given in SEQ ID NO:3 for CDR-H3 and the first variable domain of the light chain (VL1) comprises the sequence given in SEQ ID NO:4 or SEQ ID NO:24 for CDR-L1, the sequence given in SEQ ID NO:5 for CDR-L2 and the sequence given in SEQ ID NO:6 for CDR-L3. It will be appreciated that one or more amino acid substitutions, additions and/or deletions may be made to the CDRs provided by the present invention without significantly altering the ability of the antibody to bind to OX40 and to neutralise OX40 activity. The effect of any amino acid substitutions, additions and/or deletions can be readily tested by one skilled in the art, for example by using the methods described in WO2010/096418, to determine OX40 binding and inhibition of the OX40/OX40L interaction. Accordingly, the present invention provides a bispecific antibody having specificity for human OX40 comprising CDRH-1 (SEQ ID NO:1), CDRH-2 (SEQ ID NO:2), CDRH-3 (SEQ ID NO:3), CDRL-1 (SEQ ID NO:4), CDRL-2 (SEQ ID NO:5) and CDRL-3 (SEQ ID NO:6) as shown in FIG. 2C, for example in which one or more amino acids, for example 1 or 2 amino acids, in one or more of the CDRs has been substituted with another amino acid, such as a similar amino acid as defined herein below. In one embodiment, a bispecific antibody fusion protein of the present invention comprises a heavy chain, wherein the first variable domain of the heavy chain comprises three CDRs wherein the sequence of CDRH-1 has at least 90% identity or similarity to the sequence given in SEQ ID NO:1, CDRH-2 has at least 90% identity or similarity to the sequence given in SEQ ID NO:2 and/or CDRH-3 has at least 90% identity or similarity to the sequence given in SEQ ID NO:3. In another embodiment, a bispecific antibody fusion protein of the present invention comprises a heavy chain, wherein the variable domain of the heavy chain comprises three CDRs wherein the sequence of CDRH-1 has at least 95% or 98% identity or similarity to the sequence given in SEQ ID NO:1, CDRH-2 has at least 95% or 98% identity or similarity to the sequence given in SEQ ID NO:2 and/or CDRH-3 has at least 95% or 98% identity or similarity to the sequence given in SEQ ID NO:3. “Identity”, as used herein, indicates that at any particular position in the aligned sequences, the amino acid residue is identical between the sequences. “Similarity”, as used herein, indicates that, at any particular position in the aligned sequences, the amino acid residue is of a similar type between the sequences. For example, leucine may be substituted for isoleucine or valine. Other amino acids which can often be substituted for one another include but are not limited to: phenylalanine, tyrosine and tryptophan (amino acids having aromatic side chains); lysine, arginine and histidine (amino acids having basic side chains); aspartate and glutamate (amino acids having acidic side chains); asparagine and glutamine (amino acids having amide side chains); and cysteine and methionine (amino acids having sulphur-containing side chains). Degrees of identity and similarity can be readily calculated (Computational Molecular Biology, Lesk, A. M., ed., Oxford University Press, New York, 1988; Biocomputing. Informatics and Genome Projects, Smith, D. W., ed., Academic Press, New York, 1993; Computer Analysis of Sequence Data, Part 1, Griffin, A. M., and Griffin, H. G., eds., Humana Press, New Jersey, 1994; Sequence Analysis in Molecular Biology, von Heinje, G., Academic Press, 1987, Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M Stockton Press, New York, 1991, the BLAST™ software available from NCBI (Altschul, S. F. et al., 1990, J. Mol. Biol. 215:403-410; Gish, W. & States, D. J. 1993, Nature Genet. 3:266-272. Madden, T. L. et al., 1996, Meth. Enzymol. 266:131-141; Altschul, S. F. et al., 1997, Nucleic Acids Res. 25:3389-3402; Zhang, J. & Madden, T. L. 1997, Genome Res. 7:649-656,). In another embodiment, a bispecific antibody fusion protein of the present invention comprises a light chain, wherein the first variable domain of the light chain comprises three CDRs wherein the sequence of CDRL-1 has at least 90% identity or similarity to the sequence given in SEQ ID NO:4, CDRL-2 has at least 90% identity or similarity to the sequence given in SEQ ID NO:5 and/or CDRL-3 has at least 90% identity or similarity to the sequence given in SEQ ID NO:6. In another embodiment, a bispecific antibody fusion protein of the present invention comprises a light chain, wherein the first variable domain of the light chain comprises three CDRs wherein the sequence of CDRL-1 has at least 95% or 98% identity or similarity to the sequence given in SEQ ID NO:4, CDRL-2 has at least 95% or 98% identity or similarity to the sequence given in SEQ ID NO:5 and/or CDRL-3 has at least 95% or 98% identity or similarity to the sequence given in SEQ ID NO:6. In one embodiment the Fab portion of the bispecific antibody fusion protein provided by the present invention is a humanised or CDR-grafted antibody molecule comprising one or more of the CDRs provided in SEQ ID NOs:1, 2, 3, 4, 5 and/or 6 (FIG. 2C or variants thereof. As used herein, the term ‘CDR-grafted antibody molecule’ refers to an antibody molecule wherein the heavy and/or light chain contains one or more CDRs (including, if desired, one or more modified CDRs) from a donor antibody (e.g. a murine monoclonal antibody) grafted into a heavy and/or light chain variable region framework of an acceptor antibody (e.g. a human antibody). For a review, see Vaughan et al, Nature Biotechnology, 16, 535-539, 1998. In one embodiment rather than the entire CDR being transferred, only one or more of the specificity determining residues from any one of the CDRs described herein above are transferred to the human antibody framework (see for example, Kashmiri et al., 2005, Methods, 36, 25-34). In one embodiment only the specificity determining residues from one or more of the CDRs described herein above are transferred to the human antibody framework. In another embodiment only the specificity determining residues from each of the CDRs described herein above are transferred to the human antibody framework. When the CDRs or specificity determining residues are grafted, any appropriate acceptor variable region framework sequence may be used having regard to the class/type of the donor antibody from which the CDRs are derived, including mouse, primate and human framework regions. Suitably, the CDR-grafted antibody according to the present invention has a variable domain comprising human acceptor framework regions as well as one or more of the CDRs or specificity determining residues described above. Thus, provided in one embodiment is a neutralising CDR-grafted antibody wherein the variable domain comprises human acceptor framework regions and non-human donor CDRs. Examples of human frameworks which can be used in the present invention are KOL, NEWM, REI, EU, TUR, TEI, LAY and POM (Kabat et al., supra). For example, KOL and NEWM can be used for the heavy chain, REI can be used for the light chain and EU, LAY and POM can be used for both the heavy chain and the light chain. Alternatively, human germline sequences may be used; these are available at: http://vbase.mrc-cpe.cam.ac.uk/ In a CDR-grafted antibody of the present invention, the acceptor heavy and light chains do not necessarily need to be derived from the same antibody and may, if desired, comprise composite chains having framework regions derived from different chains. A suitable framework region for the first heavy chain variable domain (VH1) of the present invention is derived from the human sub-group VH3 sequence 1-3 3-07 together with JH4. A suitable framework region for the light chain for the first light chain variable domain (VL1) is derived from the human germline sub-group VK1 sequence 2-1 1-02 together with JK4. Also, in a CDR-grafted antibody variable region of the present invention, the framework regions need not have exactly the same sequence as those of the acceptor antibody. For instance, unusual residues may be changed to more frequently-occurring residues for that acceptor chain class or type. Alternatively, selected residues in the acceptor framework regions may be changed so that they correspond to the residue found at the same position in the donor antibody (see Reichmann et al., 1998, Nature, 332, 323-324). Such changes should be kept to the minimum necessary to recover the affinity of the donor antibody. A protocol for selecting residues in the acceptor framework regions which may need to be changed is set forth in WO 91/09967. Suitably, in the first heavy chain variable region (VH1) of the present invention, if the acceptor heavy chain has the human VH3 sequence 1-3 3-07 together with JH4, then the acceptor framework regions of the heavy chain comprise, in addition to one or more donor CDRs, a donor residue at at least one of positions 37, 73, 78 or 94 (according to Kabat et al., (supra)). Accordingly, provided is a bispecific antibody fusion protein, wherein at least the residues at positions 37, 73, 78 and 94 of the first variable domain of the heavy chain are donor residues. Suitably, in the first light chain variable region (VL1) of the present invention, if the acceptor light chain has the human sub-group VK1 sequence 2-1 1-02 together with JK4, then the acceptor framework regions of the light chain comprise, in addition to one or more donor CDRs, a donor residue at at least one of positions 64 or 71. Accordingly, provided is a bispecific antibody fusion protein wherein at least the residues at positions 64 and 71 of the first variable domain of the light chain are donor residues. Donor residues are residues from the donor antibody, i.e. the antibody from which the CDRs were originally derived. In one embodiment, a bispecific antibody fusion protein of the present invention comprises a heavy chain, wherein the first variable domain of the heavy chain (VH1) comprises the sequence given in FIG. 2B SEQ ID NO:8. It will be appreciated that one or more amino acid, for example 1 or 2 amino acid, substitutions, additions and/or deletions may be made to the first heavy and light chain variable domains, provided by the present invention, without significantly altering the ability of the antibody fusion protein to bind to OX40 and to neutralise OX40 activity. The effect of any amino acid substitutions, additions and/or deletions can be readily tested by one skilled in the art, for example by using the methods described in WO2010/096418, to determine OX40 binding and ligand blocking. In one embodiment, a bispecific antibody fusion protein of the present invention comprises a heavy chain, wherein the first variable domain of the heavy chain comprises a sequence having at least 60% identity or similarity to the sequence given in FIG. 2B SEQ ID NO:8. In one embodiment, an antibody fusion protein of the present invention comprises a heavy chain (VH1), wherein the first variable domain of the heavy chain comprises a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:8. In one embodiment, a bispecific antibody fusion protein of the present invention comprises a light chain, wherein the first variable domain of the light chain (VL1) comprises the sequence given in FIG. 2A SEQ ID NO:7. In another embodiment, a bispecific antibody fusion protein of the present invention comprises a light chain, wherein the first variable domain of the light chain comprises a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:7. In one embodiment the antibody fusion protein of the present invention comprises a light chain, wherein the first variable domain of the light chain comprises a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO: 7. In one embodiment a bispecific antibody fusion protein of the present invention comprises a heavy chain, wherein the first variable domain of the heavy chain (VH1) comprises the sequence given in SEQ ID NO:8 and a light chain, wherein the first variable domain of the light chain (VL1) comprises the sequence given in SEQ ID NO:7. In another embodiment of the invention, the antibody fusion protein comprises a heavy chain and a light chain, wherein the first variable domain of the heavy chain comprises a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:8 and the first variable domain of the light chain comprises a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:7. Suitably, the antibody fusion protein comprises a heavy chain, wherein the first variable domain of the heavy chain comprises a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:8 and a light chain, wherein the first variable domain of the light chain comprises a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:7. In the bispecific antibody fusion protein of the present invention the heavy chain comprises a CH1 domain and light chain comprises a CL domain, either kappa or lambda. In one embodiment a bispecific antibody fusion protein of the present invention comprises a heavy chain, wherein the heavy chain comprises the sequence given in SEQ ID NO:10 and a light chain, wherein the light chain comprises the sequence given in SEQ ID NO:9. It will be appreciated that one or more amino acid, for example 1 or 2 amino acid, substitutions, additions and/or deletions may be made to the antibody variable and/or constant domains provided by the present invention without significantly altering the ability of the antibody to bind to OX40 and to neutralise OX40 activity. The effect of any amino acid substitutions, additions and/or deletions can be readily tested by one skilled in the art, for example by using the methods described in WO2010096418, to determine OX40 binding and blocking of the OX40/OX40L interaction. In one embodiment of the invention, the antibody fusion protein comprises a heavy chain, wherein the VH1 and CH1 domains of heavy chain comprise a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:10. Suitably, the antibody fusion comprises a heavy chain, wherein the VH1 and CH1 domains of the heavy chain comprise a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:10. In one embodiment a bispecific antibody fusion molecule according to the present invention comprises a light chain comprising the sequence given in FIG. 2D, SEQ ID NO:9. In one embodiment of the invention, the antibody fusion protein comprises a light chain, wherein the VL1 and the CH1 domains of the light chain comprise a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:9. For example, the antibody fusion protein comprises a light chain, wherein the VL1 and CL domains of the light chain comprise a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:9. The second antigen bound by the bispecific antibody fusion protein of the present invention is human serum albumin. This is bound by the Fv portion of the Fab-dsFv which is made up of the second heavy and light chain variable domains, VH2 and VL2. In the present invention, VH2 and VL2 are derived from one of the antibodies described in WO2010/035012 and represent an improved, more human graft of that antibody. In one embodiment the second heavy chain variable domain (VH2) has the sequence given in FIG. 3A SEQ ID NO:11. In one embodiment the second light chain variable domain (VL2) has the sequence given in FIG. 3B SEQ ID NO:12. Accordingly, the present invention provides a bispecific antibody fusion protein which binds human OX40 and human serum albumin comprising: a heavy chain comprising, in sequence from the N-terminal, a first heavy chain variable domain (VH1), a CH1 domain and a second heavy chain variable domain (VH2), a light chain comprising, in sequence from the N-terminal, a first light chain variable domain (VL1), a CL domain and a second light chain variable domain (VL2), wherein said heavy and light chains are aligned such that VH1 and VIA form a first antigen binding site and VH2 and VL2 form a second antigen binding site, wherein the antigen bound by the first antigen binding site is human OX40 and the antigen bound by the second antigen binding site is human serum albumin, wherein the first variable domain of the heavy chain (VH1) comprises the sequence given in SEQ ID NO:1 for CDR-H1, the sequence given in SEQ ID NO:2 for CDR-H2 and the sequence given in SEQ ID NO:3 for CDR-H3 and the first variable domain of the light chain (VL1) comprises the sequence given in SEQ ID NO:4 for CDR-L1, the sequence given in SEQ ID NO:5 for CDR-L2 and the sequence given in SEQ ID NO:6 for CDR-L3, wherein the second heavy chain variable domain (VH2) has the sequence given in SEQ ID NO:11 and the second light chain variable domain (VL2) has the sequence given in SEQ ID NO: 12 and the second heavy chain variable domain (VH2) and second light chain variable domain (VL2) are linked by a disulphide bond. Preferably the CH1 domain and the second heavy chain variable domain (VH2) are connected via a linker and the CL domain and the second light chain variable domain (VL2) are connected via linker. Any suitable peptide linker sequence may be used and these may be the same in each chain or different. Suitable linkers have previously been described in WO2010/035012 and are incorporated herein by reference. Examples of suitable linkers are shown in FIGS. 3C and 3D. In one embodiment the linker between the CH1 domain and the second heavy chain variable domain (VH2) comprises or consists of the sequence given in FIG. 3C SEQ ID NO:13. In one embodiment the linker between the CH1 domain and the second heavy chain variable domain (VH2) comprises or consists of the sequence given in FIG. 3C SEQ ID NO:14. In one embodiment the linker between the CL domain and the second light chain variable domain (VL2) comprises or consists of the sequence given in FIG. 203D SEQ ID NO:14. In one embodiment the linker in the light chain is a 15 amino acid sequence, in particular GGGGSGGGGSGGGGS (SEQ ID NO: 29). In one embodiment the linker in the heavy chain is a 16 amino acid sequence, in particular SGGGGSGGGGTGGGGS (SEQ ID NO: 30). In one embodiment the present invention provides a bispecific antibody fusion protein in which the heavy chain comprises or consists of the sequence given in FIG. 3E (SEQ ID NO:15) and the light chain comprises or consists of the sequence given in FIG. 3F (SEQ ID NO:16). In one embodiment of the invention, the bispecific antibody fusion protein comprises a heavy chain and a light chain, wherein the heavy chain comprises a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:15 and the light chain comprises a sequence having at least 60% identity or similarity to the sequence given in SEQ ID NO:16. Generally, the antibody fusion comprises a heavy chain, wherein the heavy chain comprises a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:15 and a light chain, wherein the light chain comprises a sequence having at least 70%, 80%, 90%, 95% or 98% identity or similarity to the sequence given in SEQ ID NO:16. The antibody fusion molecules of the present invention suitably have a high binding affinity, in particular picomolar affinity for human OX40 and nanomolar affinity for human serum albumin. Affinity may be measured using any suitable method known in the art, including Surface Plasmon Resonance e.g. BIAcore™, as described for OX40 in WO2010096418 and serum albumin in WO2010/035012, using isolated natural or recombinant OX40 or serum albumin or a suitable fusion protein/polypeptide. In one example affinity is measured using recombinant human OX40 extracellular domain as described in WO2010/096418. In one example the recombinant human OX40 extracellular domain used is a dimer, for example an Fc fusion dimer. Suitably the antibody fusion molecules of the present invention have a binding affinity for isolated human OX40 of about 200 pM or less. In one embodiment the antibody molecule of the present invention has a binding affinity of about 100 pM or less. In one embodiment the antibody molecule of the present invention has a binding affinity of about 50 pM or less. In one embodiment the antibody fusion molecule of the present invention has a binding affinity of about 40 pM or less. The antibody fusion molecules of the present invention suitably have a high binding affinity for human OX40 expressed on the surface of activated T cells, for example nanomolar or picomolar affinity. Affinity may be measured using any suitable method known in the art, including the method as described in WO2010096418 using activated CD4+ OX40+ human T cells. In particular the antibody fusion molecules of the present invention have a binding affinity for cell surface expressed human OX40 of about 2 nM or better. In one example the antibody molecules of the present invention have a binding affinity for cell surface expressed human OX40 of about 1 nM or better. In another example the antibody molecules of the present invention have a binding affinity for cell surface expressed human OX40 of about 0.5 nM or better. In another example the antibody molecules of the present invention have a binding affinity for cell surface expressed human OX40 of about 0.2 nM or better. Suitably the antibody fusion molecules of the present invention have a binding affinity for isolated human serum albumin about 50 nM or less. Suitably the antibody fusion molecules of the present invention have a binding affinity for isolated human serum albumin of about 20 nM or less. In one embodiment the antibody molecule of the present invention has a binding affinity of about 10 nM or less. In one embodiment the antibody molecule of the present invention has a binding affinity of about 5 nM or less. In one embodiment the antibody fusion molecule of the present invention has a binding affinity of about 2 nM or less. The antibody fusion molecules of the present invention can bind human serum albumin and cynomologous, mouse and rat serum albumin. In one embodiment the antibody fusion protein of the present invention bind cynomologus serum albumin with an affinity of 5 nM or less. In one embodiment the antibody fusion protein of the present invention binds mouse serum albumin with an affinity of 5 nM or less. The antibody fusion molecules of the present invention are able to bind human OX40 and human serum albumin simultaneously. Advantageously, the fusion molecules of the present invention have a high affinity for OX40 and also have a adequate half-life in vivo to be therapeutically useful, for example the half-life is in the range 5-15 days, such as 7-11 days. It will be appreciated that the affinity of antibody fusion protein provided by the present invention for human OX40 and/or human serum albumin may be altered using any suitable method known in the art. The present invention therefore also relates to variants of the antibody molecules of the present invention, which have an improved affinity for OX40 or human serum albumin. Such variants can be obtained by a number of affinity maturation protocols including mutating the CDRs (Yang et al., J. Mol. Biol., 254, 392-403, 1995), chain shuffling (Marks et al., Bio/Technology, 10, 779-783, 1992), use of mutator strains of E. coli (Low et al., J. Mol. Biol., 250, 359-368, 1996), DNA shuffling (Patten et al., Curr. Opin. Biotechnol., 8, 724-733, 1997), phage display (Thompson et al., J. Mol. Biol., 256, 77-88, 1996) and sexual PCR (Crameri et al., Nature, 391, 288-291, 1998). Vaughan et al. (supra) discusses these methods of affinity maturation. In one embodiment the bispecific antibody fusion molecules of the present invention block the interaction between OX40 and OX40L. Numerous assays suitable for determining the ability of an antibody to block this interaction are described in WO2010/096418. In one embodiment the present invention provides an antibody fusion protein having specificity for human OX40 which is capable of inhibiting the binding of human OX40L (tested at a final concentration of 2 μg/ml) to activated human CD4+OX40+ T cells by 50% at a concentration of less than 0.5 nM. In one embodiment the human OX40L used in the assay is natural human OX40. In one embodiment the human OX40 used in the assay is recombinant human OX40. If desired an antibody for use in the present invention may be conjugated to one or more effector molecule(s). It will be appreciated that the effector molecule may comprise a single effector molecule or two or more such molecules so linked as to form a single moiety that can be attached to the antibodies of the present invention. Where it is desired to obtain an antibody fragment linked to an effector molecule, this may be prepared by standard chemical or recombinant DNA procedures in which the antibody fragment is linked either directly or via a coupling agent to the effector molecule. Techniques for conjugating such effector molecules to antibodies are well known in the art (see, Hellstrom et al., Controlled Drug Delivery, 2nd Ed., Robinson et al., eds., 1987, pp. 623-53; Thorpe et al., 1982, Immunol. Rev., 62:119-58 and Dubowchik et al., 1999, Pharmacology and Therapeutics, 83, 67-123). Particular chemical procedures include, for example, those described in WO 93/06231, WO 92/22583, WO 89/00195, WO 89/01476 and WO 03/031581. Alternatively, where the effector molecule is a protein or polypeptide the linkage may be achieved using recombinant DNA procedures, for example as described in WO 86/01533 and EP0392745. The term effector molecule as used herein includes, for example, antineoplastic agents, drugs, toxins, biologically active proteins, for example enzymes, other antibody or antibody fragments, synthetic or naturally occurring polymers, nucleic acids and fragments thereof e.g. DNA, RNA and fragments thereof, radionuclides, particularly radioiodide, radioisotopes, chelated metals, nanoparticles and reporter groups such as fluorescent compounds or compounds which may be detected by NMR or ESR spectroscopy. Examples of effector molecules may include cytotoxins or cytotoxic agents including any agent that is detrimental to (e.g. kills) cells. Examples include combrestatins, dolastatins, epothilones, staurosporin, maytansinoids, spongistatins, rhizoxin, halichondrins, roridins, hemiasterlins, taxol, cytochalasin B, gramicidin D, ethidium bromide, emetine, mitomycin, etoposide, tenoposide, vincristine, vinblastine, colchicin, doxorubicin, daunorubicin, dihydroxy anthracin dione, mitoxantrone, mithramycin, actinomycin D, 1-dehydrotestosterone, glucocorticoids, procaine, tetracaine, lidocaine, propranolol, and puromycin and analogs or homologs thereof. Effector molecules also include, but are not limited to, antimetabolites (e.g. methotrexate, 6-mercaptopurine, 6-thioguanine, cytarabine, 5-fluorouracil decarbazine), alkylating agents (e.g. mechlorethamine, thioepa chlorambucil, melphalan, carmustine (BSNU) and lomustine (CCNU), cyclothosphamide, busulfan, dibromomannitol, streptozotocin, mitomycin C, and cis-dichlorodiamine platinum (II) (DDP) cisplatin), anthracyclines (e.g. daunorubicin (formerly daunomycin) and doxorubicin), antibiotics (e.g. dactinomycin (formerly actinomycin), bleomycin, mithramycin, anthramycin (AMC), calicheamicins or duocarmycins), and anti-mitotic agents (e.g. vincristine and vinblastine). Other effector molecules may include chelated radionuclides such as 111In and 90Y, Lu177, Bismuth213, Californium252, Iridium192 and Tungsten188/Rhenium188; or drugs such as but not limited to, alkylphosphocholines, topoisomerase I inhibitors, taxoids and suramin. Other effector molecules include proteins, peptides and enzymes. Enzymes of interest include, but are not limited to, proteolytic enzymes, hydrolases, lyases, isomerases, transferases. Proteins, polypeptides and peptides of interest include, but are not limited to, immunoglobulins, toxins such as abrin, ricin A, pseudomonas exotoxin, or diphtheria toxin, a protein such as insulin, tumour necrosis factor, α-interferon, β-interferon, nerve growth factor, platelet derived growth factor or tissue plasminogen activator, a thrombotic agent or an anti-angiogenic agent, e.g. angiostatin or endostatin, or, a biological response modifier such as a lymphokine, interleukin-1 (IL-1), interleukin-2 (IL-2), granulocyte macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), nerve growth factor (NGF) or other growth factor and immunoglobulins. Other effector molecules may include detectable substances useful for example in diagnosis. Examples of detectable substances include various enzymes, prosthetic groups, fluorescent materials, luminescent materials, bioluminescent materials, radioactive nuclides, positron emitting metals (for use in positron emission tomography), and nonradioactive paramagnetic metal ions. See generally U.S. Pat. No. 4,741,900 for metal ions which can be conjugated to antibodies for use as diagnostics. Suitable enzymes include horseradish peroxidase, alkaline phosphatase, beta-galactosidase, or acetylcholinesterase; suitable prosthetic groups include streptavidin, avidin and biotin; suitable fluorescent materials include umbelliferone, fluorescein, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride and phycoerythrin; suitable luminescent materials include luminol; suitable bioluminescent materials include luciferase, luciferin, and aequorin; and suitable radioactive nuclides include 125I, 131I, 111In and 99Tc. Where the effector molecule is a polymer it may, in general, be a synthetic or a naturally occurring polymer, for example an optionally substituted straight or branched chain polyalkylene, polyalkenylene or polyoxyalkylene polymer or a branched or unbranched polysaccharide, e.g. a homo- or hetero-polysaccharide. Specific optional substituents which may be present on the above-mentioned synthetic polymers include one or more hydroxy, methyl or methoxy groups. Specific examples of synthetic polymers include optionally substituted straight or branched chain poly(ethyleneglycol), poly(propyleneglycol) poly(vinylalcohol) or derivatives thereof, especially optionally substituted poly(ethyleneglycol) such as methoxypoly(ethyleneglycol) or derivatives thereof. Specific naturally occurring polymers include lactose, amylose, dextran, glycogen or derivatives thereof. “Derivatives” as used herein is intended to include reactive derivatives, for example thiol-selective reactive groups such as maleimides and the like. The reactive group may be linked directly or through a linker segment to the polymer. It will be appreciated that the residue of such a group will in some instances form part of the product as the linking group between the antibody fragment and the polymer. The size of the polymer may be varied as desired, but will generally be in an average molecular weight range from 500Da to 50000Da, for example from 5000 to 40000Da such as from 20000 to 40000Da. In one example suitable effector molecules may be attached through any available amino acid side-chain or terminal amino acid functional group located in the antibody fusion protein, for example any free amino, imino, thiol, hydroxyl or carboxyl group. Such amino acids may occur naturally in the antibody fragment or may be engineered into the fragment using recombinant DNA methods (see for example U.S. Pat. No. 5,219,996; U.S. Pat. No. 5,667,425; WO98/25971). The present invention also provides an isolated DNA sequence encoding the heavy and/or light chain(s) of an antibody molecule of the present invention. Suitably, the DNA sequence encodes the heavy or the light chain of an antibody molecule of the present invention. The DNA sequence of the present invention may comprise synthetic DNA, for instance produced by chemical processing, cDNA, genomic DNA or any combination thereof. DNA sequences which encode an antibody molecule of the present invention can be obtained by methods well known to those skilled in the art. For example, DNA sequences coding for part or all of the antibody heavy and light chains may be synthesised as desired from the determined DNA sequences or on the basis of the corresponding amino acid sequences. DNA coding for acceptor framework sequences is widely available to those skilled in the art and can be readily synthesised on the basis of their known amino acid sequences. Standard techniques of molecular biology may be used to prepare DNA sequences coding for the antibody molecule of the present invention. Desired DNA sequences may be synthesised completely or in part using oligonucleotide synthesis techniques. Site-directed mutagenesis and polymerase chain reaction (PCR) techniques may be used as appropriate. Examples of suitable sequences are provided in FIG. 5A SEQ ID NO:21; FIG. 5B SEQ ID NO:22; FIG. 6A SEQ ID NO:23; FIG. 6B SEQ ID NO:24. Nucleotides 1-63 in SEQ ID NO 21 and 1-63 in SEQ ID NO:23 encode the signal peptide sequence OmpA which is cleaved to give an antagonistic antibody fusion molecule of the present invention.
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