Antibody molecules having specificity for human OX40

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,
• 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 (VL1comprises 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.