CTLA4 and melanoma: Here, we found that Activin-A indirectly inhibits CTL proliferation and accumulation in BRAF wild-type and oncogenic mutant preclinical melanoma models and that its expression correlates with anti-PD1 therapy resistance in human melanoma and impairs the response to combined anti-PD1/anti-CTLA4 therapy in gain-of-function and loss-of-function settings.