[Current state and key challenges of immune and cell therapy for multiple myeloma in Japan]

Treatment of relapsed or refractory multiple myeloma (MM) has advanced substantially with the introduction of chimeric antigen receptor T-cell (CAR-T) therapy and bispecific antibody therapy targeting B-cell maturation antigen (BCMA). CAR-T therapy induces high complete response rates and deep minimal residual disease negativity after a single infusion. In a subset of patients, remission persists beyond completion of therapy, making treatment-free intervals an achievable therapeutic objective in MM. In contrast, BCMA-directed bispecific antibody therapy can be administered without manufacturing delay and provides rapid and durable responses. It also reduces the cumulative treatment burden by enabling outpatient management and extended dosing intervals. Despite these advances, clinically relevant challenges remain. Sustained T-cell activation may result in hypogammaglobulinemia and increased susceptibility to infections, while antigen loss and T-cell exhaustion represent key mechanisms of relapse. Careful monitoring of immune reconstitution and appropriate infection prophylaxis are therefore essential components of MM management. Future therapeutic strategies should emphasize optimal treatment sequencing, evaluation of fixed-duration approaches, and development of multi-antigen targeting platforms to overcome resistance. Achieving durable remission while preserving functional capacity and improving quality of life has become an important goal in the treatment of MM.