DNA prime and peptide boost immunization elicits robust neoantigen-specific CD8 + T cell responses and therapeutic protection in mouse tumor models

Therapeutic immunization against tumor neoantigens has the potential to induce potent and highly selective CD8+ T-cell-mediated antitumor immunity. Consequently, immunization strategies that generate robust neoantigen-specific T-cell responses are needed. Here, we tested homologous and heterologous DNA- and peptide-based immunization strategies using a neoantigen model. We observed that priming with DNA followed by peptide boost immunization elicited the strongest CD8+ T-cell responses, which exhibited effector and memory precursor phenotypes and led to the formation of circulating and skin-resident memory T cells. In prophylactic settings, this immunization regimen delayed the growth of B16F10 melanoma and rejected EL4 lymphoma cells expressing a self-antigen. In a therapeutic setting, a DNA prime-peptide boost eliminated EL4 tumors expressing the neo-epitope model in most mice. Consistently, DNA prime-peptide boost targeting two bona fide neoepitopes of MC38 tumor model elicited neoepitope-specific CD8+ T-cell responses and a marked therapeutic effect, which may be enhanced by combining with anti-PD-1 antibody. These results highlight the potential of DNA prime-peptide boost as a promising strategy for therapeutic neoantigen immunization that elicits strong CD8+ T-cell responses and potent antitumor effects.