Abstract 2764: Mechanisms of genomic-microenvironmental interactions in uveal melanoma

Uveal melanoma (UM) is the most common primary eye cancer and has a high rate of metastasis with liver tropism. UM can be stratified according to metastatic risk into low risk Class 1 and high risk Class 2 tumor. Biallelic mutational inactivation of the tumor suppressor BAP1 is the quintessential molecular feature of Class 2 UM, but the mechanism by which loss of BAP1 leads to metastasis is poorly understood. We recently showed using single-cell RNA sequencing that the tumor microenvironment of primary and metastatic Class 2 UM is characterized by large numbers of inhibitory T cells and macrophages. Taken together, these findings led us to hypothesize that loss of BAP1 triggers changes in tumor-immune cell interactions that lead to an immunosuppressive microenvironment. To test this hypothesis, we performed RNA-seq and proteomic mass spectrometry in uveal melanocytes and UM cells engineered to lack BAP1 expression. These experiments identified a small cassette of immune modulatory genes that are up-regulated at the mRNA and protein levels following BAP1 loss. These proteins are known to drive monocytes towards type 2 macrophage polarization, which secrete cytokines that can inhibit T cell activation. Our findings suggest that altered interaction between UM cells and monocytes may be key to the emergence of metastatic competence in UM, and we are exploring this possibility with function experiments that may open the door to targeted therapy to subvert this process. Citation Format: Christopher J. Kaler, James J. Dollar, Stefan Kurtenbach, Jeffim N. Kuznetsov, Michael A. Durante, J. William Harbour. Mechanisms of genomic-microenvironmental interactions in uveal melanoma [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 2764.