Pharmacologicalinhibitors of cyclin dependent kinases 4 and 6 (CDK4/6) are an approvedtreatment forhormone receptor-positive breast cancer and are currently under evaluation across hundreds of clinical trials for other cancertypes. The clinical success of these inhibitorsis largely attributedto well-defined tumor-intrinsic cytostatic mechanisms, while their emerging role as immunomodulatory agents is lessunderstood. Usingintegrated epigenomic, transcriptomic and proteomicanalyses, we demonstrateda novel action of CDK4/6inhibitorsin promoting the phenotypic and functional acquisition of immunological T cell memory.Short-term priming with a CDK4/6inhibitorpromoted long-termendogenousanti-tumor T cell immunityin mice, enhanced the persistence and therapeutic efficacy of chimeric antigen receptor (CAR)-T cells, and induced an RB-dependent T cell phenotype supportive offavorable responses to immune checkpoint blockade in melanoma patients.Together, thesemechanistic insights significantlybroaden the prospective utility of CDK4/6 inhibitors as clinical tools to boostanti-tumorT cell immunity.