A retinoic acid-rich tumor microenvironment provides clonal survival cues for tumor-specific CD8⁺ T cells

While vitamin A has been implicated in host resistance to infectious disease, little is known about the role of vitamin A and its active metabolite, retinoic acid (RA) in host defenses against cancer. Here, we show that local RA production within the tumor microenvironment (TME) is increased up to 5-fold as compared with naïve surrounding tissue, with a commensurate increase in RA signaling to regionally infiltrating tumor-reactive T cells. Conditional disruption of RA signaling in CD8⁺ T cells using a dominant negative retinoic acid receptor a (dnRARa) established that RA signaling is required for tumor-specific CD8⁺ T-cell expansion/accumulation and protective antitumor immunity. In vivo analysis of antigen-specific CD8⁺ T-cell responses revealed that early T-cell expansion was RA-independent; however, late T-cell expansion and clonal accumulation was suppressed strongly in the absence of RA signaling. Our findings indicate that RA function is essential for the survival of tumor-reactive CD8⁺ T cells within the TME.