Ambra1 modulates the tumor immune microenvironment and response to PD-1 blockade in melanoma

BackgroundLoss of Ambra1 (autophagy and beclin 1 regulator 1), a\r\nmultifunctional scaffold protein, promotes the formation of nevi and\r\ncontributes to several phases of melanoma development. The suppressive\r\nfunctions of Ambra1 in melanoma are mediated by negative regulation of\r\ncell proliferation and invasion; however, evidence suggests that loss of\r\nAmbra1 may also affect the melanoma microenvironment. Here, we\r\ninvestigate the possible impact of Ambra1 on antitumor immunity and\r\nresponse to immunotherapy.MethodsThis study was performed using an\r\nAmbra1-depleted Braf(V600E)/Pten(-/)(-) genetically engineered mouse\r\n(GEM) model of melanoma, as well as GEM-derived allografts of\r\nBraf(V600E)/Pten(-/)(-) and Braf(V600E)/Pten(-/)(-)/Cdkn2a(-/)(-) tumors\r\nwith Ambra1 knockdown. The effects of Ambra1 loss on the tumor immune\r\nmicroenvironment (TIME) were analyzed using NanoString technology,\r\nmultiplex immunohistochemistry, and flow cytometry. Transcriptome and\r\nCIBERSORT digital cytometry analyses of murine melanoma samples and\r\nhuman melanoma patients (The Cancer Genome Atlas) were applied to\r\ndetermine the immune cell populations in null or low-expressing AMBRA1\r\nmelanoma. The contribution of Ambra1 on T-cell migration was evaluated\r\nusing a cytokine array and flow cytometry. Tumor growth kinetics and\r\noverall survival analysis in Braf(V600E)/Pten(-/)(-)/Cdkn2a(-/)(-) mice\r\nwith Ambra1 knockdown were evaluated prior to and after administration\r\nof a programmed cell death protein-1 (PD-1) inhibitor.ResultsLoss of\r\nAmbra1 was associated with altered expression of a wide range of\r\ncytokines and chemokines as well as decreased infiltration of tumors by\r\nregulatory T cells, a subpopulation of T cells with potent\r\nimmune-suppressive properties. These changes in TIME composition were\r\nassociated with the autophagic function of Ambra1. In the\r\nBraf(V600E)/Pten(-/)(-)/Cdkn2a(-/)(-) model inherently resistant to\r\nimmune checkpoint blockade, knockdown of Ambra1 led to accelerated tumor\r\ngrowth and reduced overall survival, but at the same time conferred\r\nsensitivity to anti-PD-1 treatment.ConclusionsThis study shows that loss\r\nof Ambra1 affects the TIME and the antitumor immune response in\r\nmelanoma, highlighting new functions of Ambra1 in the regulation of\r\nmelanoma biology.