PD-L1 expression and immune escape in melanoma resistance to MAPK inhibitors

Thirty-eight tumors from 17 patients treated with BRAF inhibitor (n=12) or combination BRAF/MEK inhibitors (n=5) with known PD-L1 expression were analyzed. RNA expression arrays were performed on all pre-treatment (PRE, n=17), early during treatment (EDT, n=8) and progression (PROG, n=13) biopsies. HLA-A/HLA-DPB1 expression was assessed by immunohistochemistry (IHC). Gene set enrichment analysis (GSEA) of PRE, EDT and PROG melanomas revealed that transcriptome signatures indicative of immune cell activation were strongly positively correlated with PD-L1 staining. In contrast, MAPK signaling and canonical Wnt/--catenin activity were negatively associated with PD-L1 melanoma expression. The expression of PD-L1 and immune activation signatures did not simply reflect the degree or type of immune cell infiltration, and was not sufficient for tumor response to MAPK inhibition.

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Kakavand H, Rawson RV, Pupo GM, Yang JYH, Menzies AM, Carlino MS, Kefford RF, Howle JR, Saw RPM, Thompson JF, Wilmott JS, Long GV, Scolyer RA, Rizos H