TGF-β antagonizes IFN-γ-mediated adaptive immune evasion via activation of the AKT-Smad3-SHP1 axis in lung adenocarcinoma

IFN-γ-mediated signaling in tumor cells can induce immunosuppressive responses and cause tumor resistance to immunotherapy. Blocking TGF-β promotes T lymphocyte infiltration and turns immunologically cold tumors into hot tumors, thereby improving the efficacy of immunotherapy. Several studies have shown that TGF-β inhibits IFN-γ signaling in immune cells. We thus sought to determine whether TGF-β affects IFN-γ signaling in tumor cells and plays a role in the development of acquired resistance to immunotherapy. TGF-β stimulation of tumor cells increased SHP1 Phosphatase activity in an AKT-Smad3-dependent manner, decreased IFN-γ-mediated tyrosine phosphorylation of JAK1/2 and STAT1, and suppressed the expression of STAT1-dependent immune evasion-related molecules, e.g., PD-L1, IDO1, HVEM, and Gal-9. In a lung Cancer mouse model, dual blockade of TGF-β and PD-L1 led to superior antitumor activity and prolonged survival compared to anti-PD-L1 therapy alone. However, prolonged combined treatment resulted in tumor resistance to immunotherapy and increased expression of PD-L1, IDO1, HVEM, and Gal-9. Interestingly, after initial anti-PD-L1 monotherapy, dual TGF-β and PD-L1 blockade promoted both immune evasion gene expression and tumor growth compared to that in tumors treated with continuous PD-L1 monotherapy. Alternatively, treatment with JAK1/2 inhibitor following initial anti-PD-L1 therapy effectively suppressed tumor growth and downregulated immune evasion gene expression in tumors, indicating the involvement of IFN-γ signaling in immunotherapy resistance development. These results demonstrate an unappreciated effect of TGF-β on the development of IFN-γ-mediated tumor resistance to immunotherapy.