INHBA/Activin A promotes tumor growth and induces resistance to anti-PD-L1 therapy by suppressing IFN-γ signaling

Inhibin beta A (INHBA) and its homodimer activin A have pleiotropic effects on modulation of immune responses and tumor progression, respectively, but it remains uncertain whether tumors may release activin A to regulate anti-tumor immunity. As evidenced by our RNA-Seq and in vitro results, the interferon-γ (IFN-γ) signaling pathway was significantly down-regulated by tumor intrinsic activin A. Tumor INHBA deficiency led to lower expression of PD-L1 induced by IFN-γ, resulting in poor responsiveness to anti-PD-L1 therapy. On the other hand, decreased secretion of IFN-γ-stimulated chemokines, including C-X-C motif chemokine 9 (CXCL9) and 10 (CXCL10), impaired the infiltration of effector T cells into the tumor microenvironment. Furthermore, the activin A-specific antibody garetosmab improved anti-tumor immunity and its combination with the anti-PD-L1 antibody atezolizumab showed a superior therapeutic effect to monotherapy. Our findings reveal that INHBA/activin A is involved in anti-tumor immunity by inhibiting the IFN-γ signaling pathway and considered to be a potential target to overcome anti-PD-L1 resistance in clinical cancer treatment.