Selective inhibition of TGF-ß1 produced by GARP-expressing Tregs overcomes resistance to PD-1/PD-L1 blockade in cancer.

TGF-ß1, ß2 and ß3 bind a common receptor to exert vastly diverse effects in cancer, supporting either tumor progression by favoring metastases and inhibiting anti-tumor immunity, or tumor suppression by inhibiting malignant cell proliferation. Global TGF-ß inhibition thus bears the risk of undesired tumor-promoting effects. We show that selective blockade of TGF-ß1 production by Tregs with antibodies against GARP:TGF-ß1 complexes induces regressions of mouse tumors otherwise resistant to anti-PD-1 immunotherapy. Effects of combined GARP:TGF-ß1/PD-1 blockade are immune-mediated, do not require FcγR-dependent functions and increase effector functions of anti-tumor CD8+ T cells without augmenting immune cell infiltration or depleting Tregs within tumors. We find GARP-expressing Tregs and evidence that they produce TGF-ß1 in one third of human melanoma metastases. Our results suggest that anti-GARP:TGF-ß1 mAbs, by selectively blocking a single TGF-ß isoform emanating from a restricted cellular source exerting tumor-promoting activity, may overcome resistance to PD-1/PD-L1 blockade in patients with cancer.