Inhibition of MBTPS1 reprograms cold into inflamed tumors and potentiates anti-PD-1 immunotherapy

Despite notable advancements in cancer immunotherapy, the overall response rate among cancer patients remains low. Therefore, exploring strategies combining immunotherapy with adjuvant approaches to augment adaptive immune responses, such as by boosting the infiltration of T lymphocytes, is an attractive strategy. To pinpoint key regulators of tumor immunity, we developed a focused single guide RNA (sgRNA) library targeting membrane and secreted protein genes. Utilizing this library, we conducted an in vivo clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 screen in colorectal cancer mice model. We revealed that the loss of MBTPS1 in tumor cells enhanced anti-tumor immunity and synergized with anti-PD-1 therapy. Mechanistic studies uncovered that tumor cell-intrinsic MBTPS1 could compete with USP13 for binding with STAT1, thereby disrupting the USP13-dependent deubiquitination and stabilization of STAT1. MBTPS1 deficiency induced CXCR3+ CD8+ T cells infiltration in the tumor microenvironment by upregulating mRNA levels of Cxcl9, Cxcl10 and Cxcl11 transcribed by STAT1. Our study revealed that targeting MBTPS1 in cancer cells could turn cold tumors into inflamed ones, thereby enhancing the efficacy of anti-PD-1 blockade.