Method of monomerisation of recombinant antibody molecules

1. A method of increasing the percentage of Fab-dsFv monomer in a composition of recombinantly expressed antibody molecules characterised in that Fab-dsFv comprises at least one Fv comprising one VII and one VL and having specificity for an antigen of interest wherein said VII and VL are connected directly or indirectly via one or more linkers and are stabilised by a disulfide bond therebetween, said method comprising

a conversion step comprising treating the composition with a denaturant selected from urea, guanidine hydrochloride, or a combination thereof, wherein the urea is at a concentration of 1M to 5M and/or guanidine hydrochloride is at a concentration of 1M to 2M, wherein the conversion step is

performed in the presence of a reducing agent or after treatment with a reducing agent, wherein the reducing agent is 2-mercaptoethylamine at a concentration of 10 to 150 millimolar.

2. The method according to claim 1 , wherein the 2-mercaptoethylamine is at a concentration of 50 to 150 millimolar.

3. The method according to claim 2 , wherein the 2-mercaptoethylamine is at a concentration of 95 to 135 millimolar.

4. The method according to claim 1 , wherein the urea is at a concentration of 3M to 5M.

5. The method according to claim 4 , wherein the urea is at a concentration of 4.5M to 4.9M.

6. The method according to claim 1 , wherein the conversion step is carried out for a period of 2 to 70 hours.

7. The method according to claim 1 , wherein the method is performed at room temperature.

8. The method according to claim 1 , wherein the Fab-dsFv is at a concentration in the range 0.5 g/L to 5 g/L.

9. The method according to claim 1 , wherein the conversion step is performed in the presence of concomitant stirring.

10. The method according to claim 9 , wherein the stirring is at a stirring rate between 100 and 1200 rpm.

11. The method according to claim 1 , comprising a further step of downstream processing.

12. The method according to claim 11 , wherein downstream processing comprises chromatography.

13. The method according to claim 1 , wherein the antibody is 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 (V H 1), a C H 1 domain and a second heavy chain variable domain (V H 2),

a light chain comprising, in sequence from the N-terminal, a first light chain variable domain (V L 1), a C L domain and a second light chain variable domain (V L 2),

wherein said heavy and light chains are aligned such that V H 1 and V L 1 form a first antigen binding site and V H 2 and V L 2 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 heavy chain variable domain (V H 1) 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 light chain variable domain (V L 1) 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 (V H 2) has the sequence given in SEQ ID NO:11 and the second light chain variable domain (V L 2) has the sequence given in SEQ ID NO: 12 and

the second heavy chain variable domain (V H 2) and second light chain variable domain (V L 2) are linked by a disulfide bond.

14. The method according to claim 1 , wherein the composition of recombinantly expressed antibody molecules is a clarified supernatant.

15. The method according to claim 1 , wherein, prior to the conversion step, the method further comprises a step of protein A chromatography to remove impurities from the composition.