Bispecific antibodies appear to have immense potential as therapeutic agents, for the recruitment of antibody effector functions and cytotoxic T-cell responses. However, difficulties in the production of bispecific have limited their clinical application.
Diabodies are a new class of small bivalent and bispecific antibody fragments that can be expressed in bacteria (E.coli) and yeast (Pichia pastoris) in functional form and with high yields (up to 1g/l).
Holliger et al.(1993) Proc. Natl. Acad. Sci., 90, 6444.
Diabodies comprise a heavy (VH) chain variable domain connected to a light chain variable domain (VL) on the same polypeptide chain (VH-VL) connected by a peptide linker that is too short to allow pairing between the two domains on the same chain. This forces paring with the complementary domains of another chain and promotes the assembly of a dimeric molecule with two functional antigen binding sites.
To construct bispecific diabodies the V-domains of antibody A and antibody B are fused to create the two chains VHA-VLB, VHB-VLA. Each chain is inactive in binding to antigen, but recreates the functional antigen binding sites of antibodies A and B on pairing with the other chain.