Preparation and biomedical applications of bispecific antibodies.

Bispecific antibodies are immunoglobulin molecules with two different antigen binding sites. They can be prepared either by chemical crosslinking of immunoglobulins with different antigen specificities or by reassortment of the polypeptide chains from two different immunoglobulins to produce hybrid molecules with dual specificity. None of the earlier methods for the preparation of bispecific antibodies assure molecular homogeneity without difficult purification procedures; recently, however, a facile and efficient method was developed which can yield pure bispecific antibodies from monoclonal antibody fragments. This new method avoids some of the problems encountered earlier by using arsenite as a dithiol complexing agent to prevent intramolecular disulfide formation and 5,5'-dithiobis (2-nitrobenzoic acid) as a thiol activating agent to effect the directed recombination of two different antibody half-molecules. Bispecific monoclonal antibodies thus obtained are useful heterobifunctional reagents on account of their ability to bind two different antigens in a uniquely defined spatial relationship. They have potential applications as agents for enzyme immobilization, in the assembly of enzyme electrodes and multienzyme complexes, as reagents for two-site and homogeneous immunoassays, as electron microscopy markers for subcellular structures, and as targeting agents for cytotoxic drugs. In many of these applications, bispecific monoclonal antibodies have fundamental advantages over the heterogeneous mixtures containing hybrid antibodies that were available in the past.