The complex cross-talk occurring among cells in the tumor microenvironment influences the anti-cancer immune response. Here we employed an RNAi screen of a murine cancer cell line syngeneic to C57Bl/6 mice to parse out the ability of the immune system to identify and eliminate malignant cells. To identify rate-limiting immune modulators, the EO771 mammary cancer cell line was transduced with a barcoded genome-wide shRNA library and engrafted in immune-competent as well as immune-deficient mice. Analysis of tumors grown in the presence of a functional adaptive immune system compared to those grown in immune-deficient mice, revealed cancer cell autonomous genes that modulate immune recognition. Pathway analysis identified enrichment of shRNAs targeting previously identified immune regulators including the TGF-BR pathway and MHC class I antigen processing. Among the candidates, we selected CD47, Tex9, Yif1a, EMP2, Pex14, and Sgpl1 for validation based on consistency between independent screens and known association with immune regulation. The roles of CD47, Tex9, Pex14, and Sgpl1 were validated for T cell-dependent recognition and elimination of EO771 tumors. CD47, a known inhibitor of target cell phagocytosis by macrophages, also regulated the adaptive immune response in this novel system. Two previously understudied molecules, Pex14 and Sgpl1, have immune inhibitory functions, as their respective knockdown suppressed EO771 tumor growth and increased survival in immunocompetent mice. Tex9 serves as a potential tumor antigen or immune stimulant, as reduction of expression enhances tumor growth when EO771 tumors are grown in immunocompetent mice. Therefore, this functional in vivo screening approach enabled the discovery of CD47, Pex14, Sgpl1, and Tex9 as novel tumor-based modulators of anti-tumor adaptive immunity. To the best of our knowledge, we are the first to report the successful utilization of an in vivo functional genomics approach to identify novel tumor cell-based mediators of immune regulation.
Note:This abstract was not presented at the conference.
Citation Format: Casey W. Shuptrine, Elana J. Fertig, Marsha Salcie-Gautreaux, Louis M. Weiner. An in vivo functional genomics screen identifies molecular determinants of adaptive immune rejection. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A142.
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