As cancers are antigenic, numerous efforts have been devoted to harnessing the exquisite specificity of the immune system to destruct tumors over the past two decades. In this study, we have employed a practical approach called in situ vaccination without the need to previously identify and isolate antigen targets. Intratumoral injection of a TLR7 ligand R837 and an agonistic anti-OX40 antibody showed impressive synergistic anti-tumor effects. R837 upregulated the expression of OX40 on CD4+ T cells in the treated tumor. Then, anti-OX40 antibody triggered systemic tumor-specific T cell responses, with one-fold increase of effector memory T cells properties and stronger toxicity of lymphocytes in spleen. Remarkably, both the injected tumor and the noninjected tumor in the distant lesion of the mice were eliminated after vaccination. IL-1α is a pro-inflammatory cytokine, however IL-10 is an important anti-inflammatory cytokine that plays a central role as a negative immune regulator. In the tumor microenvironment, we found that the level of IL-1α increased and IL-10 decreased after vaccination. From RNA-seq analysis, many immune-related pathways in the tumor microenvironment were activated after vaccination, such as TNF signaling pathway, NOD-like receptor signaling pathway, C-type lectin receptor signaling pathway, Toll-like receptor signaling pathway and so on. This in situ vaccine based on two low doses of immunoomdulators caused little harm to normal organs and provided long-term protection against the same syngeneic tumor rechallenge. It could be applied to various types of late stage solid tumors and worthy of further clinical research.

Citation Format: Yanhong Chu, Qin Liu, Baorui Liu. Tumor eradicated by an effective in situ vaccine based on a TLR agonist and an agonistic anti-OX40 antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1718.