A membrane-bound IL-2 promotes CAR-NK cell proliferation, anti-apoptosis and anti-tumor activity.

Chimeric antigen receptor (CAR)-engineered natural killer (NK) cells hold promise for off-the-shelf cancer immunotherapy, yet their clinical application is hindered by poor persistence due to cytokine dependency and systemic toxicity from exogenous cytokine support. Here, we developed membrane-bound cytokine (mbCytokine) modules to enable autonomous survival signaling in CAR-NK cells. By fusing IL-2, IL-15, or the potent mimic Neo-2/15 to their cognate receptor α-chains (IL-2Rα or IL-15Rα), we generated self-sustaining CAR-NK92 cells that bypass reliance on external cytokines. Among these constructs, membrane-bound IL-2 (mbIL2) demonstrated superior efficacy, driving robust proliferation and resistance to apoptosis under serum-free conditions. Notably, mbIL2-armored CAR-NK cells exhibited enhanced cytotoxicity against MICA/B-expressing tumor cells. Mechanistically, mbIL2 mitigated activation-induced apoptosis and suppressed exhaustion during tumor engagement, thereby sustaining NK cell viability. These findings establish mbIL2 as a critical enhancer of CAR-NK cell persistence and antitumor function, offering a clinically translatable strategy to overcome the limitations of cytokine-dependent therapies.