Antibodies targeting immune checkpoints are emerging as potent and viable cancer therapies, but not all patients respond to these as single agents. Concurrently targeting additional immunosuppressive pathways is a promising approach to enhance immune checkpoint blockade, and bifunctional molecules designed to target two pathways simultaneously may provide a strategic advantage over the combination of two single agents. M7824 (MSB0011359C) is a bifunctional fusion protein composed of a monoclonal antibody against programmed death ligand 1 (PD-L1) fused to the extracellular domain of human transforming growth factor-β (TGF-β) receptor II, which functions as a "trap" for all three TGF-β isoforms. We demonstrate that M7824 efficiently, specifically, and simultaneously binds PD-L1 and TGF-β. In syngeneic mouse models, M7824 suppressed tumor growth and metastasis more effectively than treatment with either an anti-PD-L1 antibody or TGF-β trap alone; furthermore, M7824 extended survival and conferred long-term protective antitumor immunity. Mechanistically, the dual anti-immunosuppressive function of M7824 resulted in activation of both the innate and adaptive immune systems, which contributed to M7824's antitumor activity. Finally, M7824 was an effective combination partner for radiotherapy or chemotherapy in mouse models. Collectively, our preclinical data demonstrate that simultaneous blockade of the PD-L1 and TGF-β pathways by M7824 elicits potent and superior antitumor activity relative to monotherapies.

Summary The BRAFV600E mutation, which approaches 50% in human melanomas, constitutively activates pERK and contributes to disease progression. The BRAFV600E inhibitor, Vemurafenib (PLX4032), shows promising clinical responses, but resistance to PLX4032 usually develops within a year. Transgenic mouse models allow the study of BRafV600E melanoma in vivo, however in vitro models are necessary to better understand the molecular mechanism underlying disease progression and resistance. We established melanoma cell lines (D4M cells) from the conditional mouse model of metastatic melanoma: Tyr::CreER;BrafCA;Ptenlox/lox, which recapitulates human disease. Cultured D4M cells express high constitutive pERK. PLX4032 abrogates ERK phosphorylation, inhibits D4M proliferation, and increases expression of the melanoma associated antigen, pmel, in vitro, consistent with human BRAFV600E melanoma cell lines. D4M cells are transplantable in either immune-compromised or syngeneic B6 mice. Thus, D4M cell lines allow correlation of in vitro studies on molecular mechanisms of melanoma with in vivo investigations on pathology and immunology.

Highlights d BA synergizes with RT to overcome tumor immune evasion via TME reprogramming d Reconstitution of tumor immunosurveillance by BART induces abscopal effects d In fibrotic lungs, PD-L1 + endothelial cells and M2-like lipofibroblasts express TGF-b d BA attenuates lung fibrosis by neutralizing TGF-b in the relevant PD-L1 + compartments