State of the Art of CAR-NK Cell Therapy in Multiple Myeloma: A Comprehensive Review of Cell Sources and Target Antigens

Multiple myeloma (MM) is a clonal malignancy of plasma cells that remains largely incurable despite major advances in proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies. Chimeric antigen receptor (CAR)-engineered immune cells have transformed the therapeutic landscape, but CAR-T cell therapy faces challenges such as severe cytokine release syndrome (CRS), neurotoxicity, limited persistence, and logistical complexity. In recent years, natural killer (NK) cells have emerged as a promising platform for next-generation cellular immunotherapy, offering innate antitumor activity, a reduced risk of graft-versus-host disease (GvHD), and the feasibility of "off-the-shelf" allogeneic production. This review summarizes current advances in CAR-NK cell therapy for MM, focusing on two major aspects: the diversity of cell sources-including NK-92, peripheral (PB) and cord blood (CB), and induced pluripotent stem cell (iPSC)-derived NK cells-and the expanding repertoire of target antigens such as BCMA (B-cell maturation antigen), NKG2D, CD38, CD70, SLAMF7, CD138, and GPRC5D. We highlight preclinical and early clinical studies demonstrating potent cytotoxicity, favorable safety profiles, and innovative multi-targeting strategies designed to overcome antigen escape and enhance persistence. Emerging clinical data suggest that CAR-NK cell therapy may combine the specificity of CAR recognition with the inherent safety and versatility of NK biology, offering a potential paradigm shift in the treatment of relapsed or refractory MM. Further clinical validation will determine whether CAR-NK cell therapy can achieve durable remission and complement or surpass current CAR-T modalities.