Activin-A can attenuate NK cell proliferation and cytotoxicity directly, although modestly.26 35 In addition, NK cells are likely depleted due to impaired accumulation of CTLs.36 37 Indeed, several lines of evidence suggest that immune evasion induced by Activin-A requires reprogramming of the TME, which in turn primarily inhibits the recruitment and activity of CTLs: First, the tumor growth advantage mediated by Activin-A was lost in Rag1-/- hosts that specifically lack adaptive immunity. This evidence concerns the gene RAG1 and neoplasm.