Rgs16 promotes antitumor CD8 ⁺ T cell exhaustion

Abstract

T cells become functionally exhausted in tumors, limiting T cell-based immunotherapies. Although several transcription factors regulating the exhausted T (T_ex) cell differentiation are known, comparatively little is known about the regulators of T_ex cell survival. Here, we reported that the regulator of G protein signaling 16 (Rgs-16) suppressed T_ex cell survival in tumors. By performing lineage tracing using reporter mice in which mCherry marked Rgs16-expressing cells, we identified that Rgs16⁺CD8⁺ tumor-infiltrating lymphocytes (TILs) were terminally differentiated, expressed low levels of T cell factor 1 (Tcf1), and underwent apoptosis as early as 6 days after the onset of Rgs16 expression. <i>Rgs16</i> deficiency inhibited CD8⁺ T cell apoptosis and promoted antitumor effector functions of CD8⁺ T cells. Furthermore, <i>Rgs16</i> deficiency synergized with programmed cell death protein 1 (PD-1) blockade to enhance antitumor CD8⁺ T cell responses. Proteomics revealed that Rgs16 interacted with the scaffold protein IQGAP1, suppressed the recruitment of Ras and B-Raf, and inhibited Erk1 activation. <i>Rgs16</i> deficiency enhanced antitumor CD8⁺ TIL survival in an Erk1-dependent manner. Loss of function of Erk1 decreased antitumor functions of <i>Rgs16</i>-deficient CD8⁺ T cells. <i>RGS16</i> mRNA expression levels in CD8⁺ TILs of patients with melanoma negatively correlated with genes associated with T cell stemness, such as <i>SELL</i>, <i>TCF7</i>, and <i>IL7R</i>, and predicted low responses to PD-1 blockade. This study uncovers Rgs16 as an inhibitor of T_ex cell survival in tumors and has implications for improving T cell-based immunotherapies.