(PA-041) Enhanced Persistence and Antitumor Activity of IL-15–Armored Anti-BCMA CAR NK Cells in Myeloma Mouse Model.

Chimeric Antigen Receptor (CAR) Natural Killer (NK) cell therapy has emerged as a promising approach in cancer immunotherapy. However, its clinical efficacy remains constrained by challenges such as inefficient gene transfer, suboptimal in vitro expansion, and limited proliferation and persistence in vivo. Interleukin-15 (IL-15) is known to enhance NK cell proliferation and cytotoxicity. In this study, we investigated the persistence and therapeutic efficacy of genetically engineered NK cells transduced with a lentiviral vector encoding an anti-B-cell maturation antigen (BCMA) CAR construct incorporating IL-15.

Methods:   

CAR NK cell cytotoxicity was evaluated using CD107a degranulation and lactate dehydrogenase (LDH) release assays. Long-term cytotoxic effects were assessed by monitoring target cell confluence over time in co-culture systems. IL-15 concentrations in the culture supernatant were quantified via ELISA. The in vivo antitumor efficacy of IL-15–expressing BCMA CAR NK cells was assessed in an MM.1s-Fluc xenograft mouse model.

Results:   

Anti-BCMA–IL-15 CAR NK cells were successfully generated, demonstrating a purity of 96.9%, fold expansion ranging from 53.99 to 67.20, and a transduction efficiency of 21.6%. In short-term (4-hour) cytotoxicity assays, IL-15–armored CAR NK cells displayed comparable cytotoxicity to BCMA CAR NK cells lacking IL-15. However, in long-term co-culture experiments, IL-15–armored CAR NK cells maintained superior and sustained cytotoxic activity across multiple BCMA-positive myeloma cell lines. Culture supernatants from the BCMA–IL-15 group exhibited elevated IL-15 levels (10.58–11.02 pg/mL) relative to BCMA-only and mock-transduced controls (1.51–1.96 pg/mL). The vector copy number per cell ranged from 2.15 to 2.50. In vivo, BCMA–IL-15 CAR NK cells exhibited the most potent and durable antitumor activity, as evidenced by significantly reduced bioluminescence signals in MM.1s-Fluc xenograft mice. While both BCMA and IL-15 CAR NK cells initially suppressed tumor growth, only the BCMA–IL-15 CAR NK group sustained tumor control up to day 44. This group also demonstrated the longest survival and no significant weight loss, indicating effective and well-tolerated therapy.

Conclusions:   

In conclusion, IL-15–armored anti-BCMA CAR NK cells show enhanced long-term persistence and cytotoxicity in myeloma mouse model. These findings support the potential of IL-15–armored CAR NK cells as a promising therapeutic candidate for the treatment of multiple myeloma.