Recent studies suggest p53 contributes to poor survival in the context of immune checkpoint blockade (ICB). Mutations to p53 significantly improve the response rate to PD-1 ICB in lung cancer patients. Tumor-derived IL-33 is required for the anti-tumor immune response and efficacy of ICB. However, the relationship between p53 and IL-33 during ICB is unknown. In this study, we characterize the role of the p53/IL-33 axis in regulating the response of the tumor microenvironment to ICB. We use CRISPR-Cas9 to delete Trp53 from murine MC38 colon adenocarcinoma. Deletion of Trp53 and PD-1 ICB synergistically inhibits tumor growth. Il33 is upregulated in the Trp53-deficient and treated tumor cells, and its expression increases with time and response to treatment. Cd4+ and Cd8+ T cell infiltration increases adjacent to IL-33 expressing tumor cells, while Treg infiltration is decreased. Simultaneous deletion of Il33 in MC38 tumors reverses the efficacy PD-1 ICB. Trp53-deficient MC38 in ST2-/- (IL-33 receptor) mice also show no response to PD-1 ICB. Our findings depict a novel mechanism by which the loss of p53 in tumors treated with ICB unleashes the expression of tumoral IL-33 and induces downstream signaling. p53 mutations may be a double-edged sword for cancer, i.e. the loss of the tumor suppressor initially facilitates tumorigenesis, but eventual buildup of mutations and activation of damage pathways, such as NF-kB, leads to upregulation of danger signals in the tumor. These danger signals, such as IL-33, mediate the anti-tumor effect of ICB.

Citation Format: David Shihong Gao, Yang Li, Jason Shoush, Runzi Sun, Binfeng Lu. Loss of p53 sensitizes tumor cells to immune checkpoint blockade therapy via upregulation of IL-33 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1326.