Tumor-priming CD8⁺ natural killer T-like cells as an efficient novel cell therapy for relapsed/refractory multiple myeloma

Background: Relapsed and refractory multiple myeloma (RRMM) remains a major clinical challenge, as most patients eventually relapse following standard treatments and are left with limited therapeutic options. Although b-cell maturation antigen (BCMA) CAR-T cell therapy has recently shown remarkable efficacy in select patients, broader implementation is hindered by its reliance on autologous cells, prolonged manufacturing timelines, high costs, and severe immune-related toxicities. These challenges have prompted an urgent demand for safer, more accessible, and rapidly applicable immunotherapeutic alternatives. Methods: CBMC (cord blood mononuclear cells) were cultured with irradiated BMMC (bone marrow mononuclear cells) from RRMM patients in the presence of defined cytokines, aiming to develop a new therapeutic immune cell product for RRMM. Their phenotypic and functional characteristics, including non-MHC-restricted and MHC-restricted cytotoxicity mechanisms, were analyzed using surface marker profiling, cytokine secretion assays, in vitro cytotoxicity assays, functional and blocking assays. Antitumor activity was evaluated in xenograft mouse models using MM.1 S and RPMI-8226 cells. Results: We successfully generated CD8⁺ NKT-like cells through tumor priming, which exhibited potent cytotoxicity and elevated cytokine production against multiple myeloma cell lines and primary RRMM samples. Mechanistically, tumor-priming CD8⁺ NKT-like cells (TPNC) cytotoxicity was mediated by both non-MHC–restricted pathways involving LFA-1 and DNAM-1, and MHC-restricted, TCR-mediated recognition. TPNC efficiently formed immune synapses, rapidly polarized cytotoxic granules, and engaged in serial killing. In xenograft models, TPNC significantly suppressed tumor progression, prolonged survival, and persisted in circulation without observable toxicity. Based on these findings, we extended the tumor-priming strategy to acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), successfully generating TPNC with robust cytotoxic activity. In ALL samples, TPNC exhibited cytotoxicity comparable to anti-CD19 CAR-NK cells. Conclusions: TPNC represents a novel cytotoxic lymphocyte product generated through tumor-driven priming. Their dual recognition capacity, functional versatility, and favorable safety profile highlight their potential as a scalable and personalized immunotherapy platform for hematologic malignancies.