Tumor suppressor p53 deficiency increases tumor immunogenicity through promoting IL33-mediated anti-tumor immune responses

Recent studies have shown that p53 contributes to poor survival during immune checkpoint blockade (ICB) therapy. Lung cancer patients with p53 mutations have significantly improved response rates to PD-1 ICB therapy. While previous studies have shown that tumor-derived IL-33 is required for the anti-tumor immune response and efficacy of ICB therapies, the relationship between p53 and IL-33 during ICB therapy is unknown. In this study, we characterized the role of the p53/IL-33 axis in regulating the tumor microenvironment (TME) in response to ICB therapy. CRISPR-Cas9-mediated deletion of Trp53 in tumor cells combined with PD-1 ICB therapy synergistically inhibited tumor growth in a murine MC38 colon adenocarcinoma model. We observed increased CD4+ and CD8+ T cell infiltration, as well as reduced Treg infiltration. IL-33 was upregulated and its expression increased with time and response to treatment. Simultaneous deletion of Il33 in the MC38 tumor cells reversed the efficacy of PD-1 ICB therapy. ST2 -/- (IL-33 receptor) mice with Trp53-deficient MC38 tumors also showed no response to PD-1 ICB. Our findings depict a novel mechanism by which the loss of p53 in tumors treated with ICB therapy induces upregulation of tumoral IL-33 and host ST2 signaling. p53 mutations may be a double-edged sword for cancer, i.e. loss of the tumor suppressor initially facilitates tumorigenesis, but also leads to upregulation of danger signals in the tumor. These danger signals, such as IL-33, mediate the anti-tumor effect of ICB.