Recent advances in the generation of bispecific antibodies for tumor immunotherapy

Bispecific antibodies are currently in clinical and preclinical development for the treatment of various cancers. Designed to direct and enhance the body's immune response to specific tumors, bispecific antibodies consist of a targeting domain (typically an antibody fragment that binds to a tumor antigen) linked to a triggering arm that is specific for a cell-surface molecule capable of mediating a phagocytic or lytic response by macrophages, natural killer cells, T-cells, or other effector cells. Recent animal studies have confirmed the therapeutic potential of bispecific antibodies; however, results from clinical trials so far have been less promising and have revealed clear limitations of these molecules, such as immunogenicity and severe side effects caused by mass release of inflammatory cytokines. A second generation of bispecific molecules, bispecific single-chain antibodies and hetero-oligomeric-engineered antibodies, has now been produced by using DNA recombinant technology; these may theoretically improve tumor targeting and minimize side effects, eventually replacing the full-length bispecific antibodies. Over the next few years, several recombinant bispecific antibodies are expected to enter clinical trials and ultimately emerge as new pharmaceutical products. This review briefly summarizes major trends in the development of bispecific antibodies for tumor therapy, and describes a rationale for the generation of novel recombinant molecules.