Sequential STING and CD40 agonism drives massive expansion of tumor-specific T cells in liposomal peptide vaccines.

The clinical use of cancer vaccines is hampered by the low magnitude of induced T-cell responses and the need for repetitive antigen stimulation. Here, we demonstrate that liposomal formulations with incorporated STING agonists are optimally suited to deliver peptide antigens to dendritic cells in vivo and to activate dendritic cells in secondary lymphoid organs. One week after liposomal priming, systemic administration of peptides and a costimulatory agonistic CD40 antibody enables ultrarapid expansion of T cells, resulting in massive expansion of tumor-specific T cells in the peripheral blood two weeks after priming. In the MC-38 colon cancer model, this synthetic prime-boost regimen induces rapid regression and cure of large established subcutaneous cancers via the use of a single tumor-specific neoantigen. These experiments demonstrate the feasibility of liposome-based heterologous vaccination regimens to increase the therapeutic efficacy of peptide vaccines in the context of immunogenic adjuvants and costimulatory booster immunizations. Our results provide a rationale for the further development of modern liposomal peptide vaccines for cancer therapy.