Abstract 1575: The landscape of tumor intrinsic immune regulators revealed by genome-wide CRISPR immune screen integrated with comprehensive clinical data analysis

Abstract Despite approval of immunotherapy for a wide range of cancers, the majority of patients fail to respond to immunotherapy or relapse following initial response which may be attributed to immunosuppression co-opted by tumor cells. However, it is challenging to utilize conventional methods to systematically evaluate the potential of tumor intrinsic factors to act as immune regulators in cancer patients. In this study, we designed an unbiased integrative strategy to leverage the complementary strength of in vitro functional genomic screens and multi-omics clinical data to assess the role of individual tumor-intrinsic factors in regulating T cell tumor infiltration and T cell-mediated tumor killing, the two most important rate-limiting steps of cancer immunotherapy. Initially, a genome-wide CRISPR-Cas9 screening system using paired murine tumors and tumor-reactive T cells was employed to globally screen tumor intrinsic factors modulating the tumor sensitivity to T cell-mediated killing. Then, findings from the screening were integrated with the bioinformatics analysis of clinical datasets to further evaluate the role of each tumor intrinsic factor in governing antitumor immunity. The integrative analysis not only successfully identified several novel tumor intrinsic factors as effectors of immune resistance, but also demonstrated the distinct roles of these factors in controlling immune cell trafficking and tumor sensitivity to T cell-mediated killing. Among these factors, candidates controlling both rate-limiting steps were termed as "Dual immune resistance regulators" and the remaining factors whose expression were not associated with tumor immune infiltration were termed as "Cytotoxicity resistance regulators". By selecting PRMT1 and RIPK1 as representatives of the two groups respectively, we confirmed that genetically depletion of PRMT1 and RIPK1 sensitized tumors to T-cell mediated killing via two independent experimental approaches. Furthermore, inhibiting Prmt1 or Ripk1 tumors sensitizes tumors to cancer immunotherapy, such as anti-PD-1/anti-OX40 treatments (Tumor size (mm2) on day 21 after tumor inoculation: for anti-PD-1 treatment, Ctrl 84.05±23.10, PRMT1 KO 7.30±7.81, RIPK1 KO 2.03±4.96; similar results were also observed from anti-OX40 treatment) and extended the survival of tumor-bearing mice. Moreover, by using a RIPK1-specific inhibitor, GSK2982772, we demonstrated that targeting cytotoxicity resistance regulators could also enhance the antitumor activity of T cell-based cancer immunotherapy, despite limited impact on T cell tumor infiltration. Collectively, our data not only demonstrate the distinct immunoregulatory roles and therapeutic potentials of PRMT1 and RIPK1 in T cell-mediated antitumor activity, but also provides a rich resource of novel targets for rational immuno-oncology combinations. Citation Format: Jiakai Hou, Yunfei Wang, Leilei Shi, Yuan Chen, Chunyu Xu, Arash Saeedi, Ke Pan, Ritu Bohat, Nicholas A. Egan, Jodi A. McKenzie, Rina M. Mbofung, Leila J. Williams, Zhenghuang Yang, Ming Sun, Xiaofang Liang, Jordi Rodon Ahnert, Navin Varadarajan, Cassian Yee, Yiwen Chen, Patrick Hwu, Weiyi Peng. The landscape of tumor intrinsic immune regulators revealed by genome-wide CRISPR immune screen integrated with comprehensive clinical data analysis [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 1575.