Recurrent RNA-lipoplex vaccination is required to sustain functional tumor-infiltrating neoantigen-specific CD8 T cells and therapeutic efficacy

Cancer vaccines induce durable, polyepitopic T cell responses, and show promising clinical benefit in adjuvant settings, yet they are largely ineffective in advanced disease. Using a clinically relevant RNA-lipoplex vaccine, we investigated the efficacy constraints in a preclinical model. Vaccination remodeled the tumor microenvironment (TME), increasing T cell infiltration and promoting a proinflammatory myeloid compartment. This was associated with complete regression of smaller, immature tumors, but only delayed growth of larger, established tumors. While vaccine-induced T cells were long-lived and functional in peripheral tissues, intratumoral T cells declined rapidly in abundance, diversity, and function, reverting to a prevaccine-like state. scRNA-seq suggested that this was driven by a pro-apoptotic program, with surviving T cells showing signatures of cellular stress and impaired activation. Importantly, recurrent vaccination replenished functional T cells in the TME and enhanced efficacy. These findings highlight the importance of optimizing vaccine schedules and tailoring therapeutic strategies to tumor stage.