Unravelling enhancement of antibody fragment stability - Role of format structure and cysteine modification

Antibody-based diagnostics and therapeutics have huge commercial value. However, applications of antibodies are often limited by instability, particularly for recombinant antibody formats. This paper describes the conversion of a single-chain variable fragment (scFv) antibody to a single-chain antibody fragment (scAb) with notably improved stability characteristics. This scAb retains antigen-binding activity (i) at high temperature (up to 60 °C), (ii) in guanidine hydrochloride (GdnHCl, up to 1 M), and (iii) when stored at 37 °C for 6 months. However, limited improvement was observed when the original scFv was converted to a larger fragment antigen-binding (Fab) format. Certain Cys-to-Ala mutations in the third complementarity determining region of the antibody heavy chain (CDR H3) also led to stability improvements. Our findings indicate that the stability of an antibody derivative depends on its format and on the positions of cysteines in the CDRs.