Maine et al. designed self-replicating RNA vaccines engineered to evade protein translation shutdown and encode multiple predicted tumor neoepitopes with or without cytokines. Vaccination of mice induced epitope-specific polyfunctional CD4+ and CD8+ T cell responses that were differentially impacted by the design of poly-epitopes and the prime/boost interval, and were enhanced by cytokines, which promoted epitope spreading. Therapeutic vaccination of a mouse tumor model induced specific antitumor activity associated with antigen responses and was enhanced by anti-PD-1. Immunization of rhesus macaques induced polyfunctional CD4+ and CD8+ T cell responses.
Contributed by Paula Hochman
ABSTRACT: Historically poor clinical results of tumor vaccines have been attributed to weakly immunogenic antigen targets, limited specificity, and vaccine platforms that fail to induce high-quality polyfunctional T cells, central to mediating cellular immunity. We show here that the combination of antigen selection, construct design, and a robust vaccine platform based on the Synthetically Modified Alpha Replicon RNA Technology (SMARRT), a self-replicating RNA, leads to control of tumor growth in mice. Therapeutic immunization with SMARRT replicon-based vaccines expressing tumor-specific neoantigens or tumor-associated antigen were able to generate polyfunctional CD4(+) and CD8(+) T cell responses in mice. Additionally, checkpoint inhibitors, or co-administration of cytokine also expressed from the SMARRT platform, synergized to enhance responses further. Lastly, SMARRT-based immunization of non-human primates was able to elicit high quality T cell responses, demonstrating translatability and clinical feasibility of synthetic replicon technology for therapeutic oncology vaccines.