Bispecifics, trispecifics, and other novel immune treatments in myeloma

Despite recent advances in treatment, relapses in multiple myeloma (MM) are inevitable. Off-the-shelf immunotherapeutics represent a promising avenue for research, with various classes of agents under development and several demonstrating deep and durable responses in patients who have exhausted all available therapies. Antibody-drug conjugates (ADCs) seek to improve on naked monoclonal antibodies by delivering a cytotoxic payload directly to tumor cells while largely limiting systemic effects. Belantamab mafodotin, a B-cell maturation antigen (BCMA)-targeted ADC, has shown response rates >30% in a phase 2 trial of highly refractory patients and is being investigated in a variety of settings and combinations. Several other ADCs are in earlier stages of development that target cell surface antigens that are internalized, including BCMA, CD38, CD46, CD56, CD74, and CD138. Bispecifics are designed to bring cytotoxic immune effector cells into proximity with tumor cells, and several agents have shown high response rates in early trials. Current targets include BCMA, CD38, GPRC5d, and FCRH5, and all of these seek to engage T cells through CD3. Bispecifics targeting natural killer (NK) cells through CD16 are still in preclinical development. Trispecific antibodies may represent an advance over bispecifics by providing a T-cell costimulatory signal such as CD28, or alternatively, dual MM antigens to increase specificity of NK or T-cell targeting. This is an area of active preclinical research at this time. Lastly, designed ankyrin repeat proteins, which are small antibody-mimetic proteins with high target-binding affinity, have the potential to block multiple pathways at once and provide stimulatory signals to the immune system.