IL-12 augments adoptive cell therapy by reshaping CD8+ T dynamics and broadening antitumor immunity.

Adoptive cell therapy (ACT) against solid tumors is constrained by tumor heterogeneity, immunosuppressive microenvironments, and insufficient T cell potency and persistence. Although IL-12 has long been recognized as a potent enhancer of T-cell immunity, its clinical application has been hindered by systemic toxicity and the lack of a strategy to harness its benefits without chronic exposure. Here, we show that ex vivo IL-12 preconditioning programs tumor-specific T cells with increased antigen sensitivity, yielding superior antitumor activity compared with IL-7/IL-15. Systemic delivery of Pro-IL-12 further rejuvenates exhausted CD8+ tumor-infiltrating lymphocytes (TILs) by restoring IL-2 hypersensitivity, sustaining persistence, and strengthening effector machinery. When combined with ACT, a single dose of Pro-IL-12 reinstated IFN-γ production in exhausted TILs and doubled intratumoral T-cell accumulation via upregulation of IL-2Rα and increased IL-2 sensitivity. Pro-IL-12 markedly improved therapeutic outcomes, inducing durable complete tumor regression, promoting antigen spreading, and establishing long-term immune memory that prevented relapse from antigen-loss tumor. Across multiple xenograft models, including pancreatic cancer, lymphoma and triple negative breast cancer, distinct human CAR-T products paired with Pro-IL-12 enhanced tumor eradication without cytokine release syndrome. Together, these findings establish precision delivery of IL-12 as a translatable strategy that harnesses known IL-12 biology to achieve robust antitumor efficacy without systemic toxicity.