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Abstract 998: Searching for genetic alterations that drive the capability of evading tumor immunosurveillance in lung cancer

Background The capability of tumors to avoid immune surveillance has emerged as therapeutically approachable, especially through the blockade of immune checkpoints (ICB) such as PD-L1/PD-1. We previously reported that B2M inactivating mutations in lung cancer (LC) impair immunorecognition through the disruption of the MHC-I complex. On the other hand, the refractoriness to IFNγ has also emerged as a mechanism that promotes tumor9s immunoescape. Our purpose is to identify novel gene alterations that contribute to immunoescape in LC. Methods A panel of 44 NSCLC cell lines (35 commercially available and 9 ex vivo, derived from LC patients with metastatic pleural effusions, PE) were tested for response to IFNγ. Whole exome sequencing and RNA-sequencing was performed in the PE or gathered from public databases (Sanger and Cancer Cell Line Encyclopaedia) in the commercially available LC cells. The response to IFNγ was evaluated by determining the activation of various downstream targets, including an increase in the expression of CD274 (PD-L1) or IRF1 among others, using WB or RT-qPCR. We evaluated other parameters, such as the levels and location of the HLA-1/B2M proteins (HLA-I complex) by immunofluorescence, in selected LC cell lines. Results We could distinguish three different categories in the response to IFNγ; good responders, 75% (readily increase the levels of all downstream targets); non responders, 9% (did not increase the levels of any of the targets tested) or partial responders, 16% (were able to up-regulate all the targets tested but CD274/PD-L1, upon IFNγ exposure). By immunofluorescence, we observed that none of the non responders were able to increase HLA-1/B2M proteins in the cell surface, after IFNγ exposure. We identified biallelic inactivating alterations at JAK2 in three non responders (intragenic homozygous deletion, p.R426X and p.S507X in the NCI-H2126, NCI-H1993 and NCI-H1573, respectively). These mutations were concurrent with genetic alterations of main oncodrivers in LC. In the remaining non responder (PE-1), we identified a truncating mutation in a candidate gene. We overexpressed the wild type version of this gene and the response to IFNγ was restored. A mutational screening of this gene and immunostaining information for the encoded protein is currently ongoing in a cohort of 100 primary LC samples. Conclusions Alterations in molecules that are related with immunorecognition (B2M and HLA-I) are associated to immunotolerance, in LC. Here, we report that genetic alterations in factors that mediate the response to IFNγ are also involved in mediating immunotolerance in LC. Functional characterization of alterations in these genes is crucial to understand the mechanisms that contribute to tumor9s immunoescape. Loss of function mutations in our candidate genes are likely to facilitate tumor growth by enabling immune tolerance and may affect the response to ICB. Citation Format: Juan Jose Alburquerque-Bejar, Maria Saigi, Eva Pros, Octavio Romero, Montse Sanchez-Cespedes. Searching for genetic alterations that drive the capability of evading tumor immunosurveillance in lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 998.