Our data suggest that blocking only the TGF-β1 produced on Treg surfaces with anti-GARP:TGF- β1 mAbs is sufficient to increase the anti-tumor activity of PD-1/PD-L1 targeting, while exerting less undesired effects on the tumor microenvironment than that induced by broad blockade of all TGF-β activity. The gene discussed is TGFB1; the disease is neoplasm.