Intrinsic RIG-I restrains STAT5 activation to modulate antitumor activity of CD8(+) T cells

Antitumor activity of CD8(+) T cells is potentially restrained by a variety of negative regulatory pathways that are triggered in the tumor microenvironment, yet, the exact mechanisms remain incompletely defined. Here, we report that intrinsic RIG-I in CD8(+) T cells represents such a factor, as evidenced by observations that the tumor-restricting effect of endogenous or adoptively transferred CD8(+) T cells was enhanced by intrinsic Rig-I deficiency or inhibition, with the increased accumulation, survival, and cytotoxicity of tumor-infiltrating CD8(+) T cells. Mechanistically, T cell activation–induced RIG-I upregulation restrained STAT5 activation via competitive sequestering of HSP90. In accordance with this, the frequency of RIG-I(+) tumor-infiltrating CD8(+) T cells in human colon cancer positively correlated with attenuated survival and effector signatures of CD8(+) T cells as well as poor prognosis. Collectively, these results implicate RIG-I as a potentially druggable factor for improving CD8(+) T cell–based tumor immunotherapy.