TGF-beta regulates the stem-like state of PD-1(+) TCF-1(+) virus-specific CD8 T cells during chronic infection

Recent studies have defined a novel population of PD-1(+) TCF-1(+) stem-like CD8 T cells in chronic infections and cancer. These quiescent cells reside in lymphoid tissues, are critical for maintaining the CD8 T cell response under conditions of persistent antigen, and provide the proliferative burst after PD-1 blockade. Here we examined the role of TGF-beta in regulating the differentiation of virus-specific CD8 T cells during chronic LCMV infection of mice. We found that TGF-beta signaling was not essential for the generation of the stem-like CD8 T cells but was critical for maintaining the stem-like state and quiescence of these cells. TGF-beta regulated the unique transcriptional program of the stem-like subset, including upregulation of inhibitory receptors specifically expressed on these cells. TGF-beta also promoted the terminal differentiation of exhausted CD8 T cells by suppressing the effector-associated program. Together, the absence of TGF-beta signaling resulted in significantly increased accumulation of effector-like CD8 T cells. These findings have implications for immunotherapies in general and especially for T cell therapy against chronic infections and cancer. This study demonstrates the role of TGF-beta on virus-specific CD8 T cell differentiation during chronic LCMV infection. TGF-beta maintains the stem-like state of TCF-1(+) CD8 T cells and promotes terminal differentiation of exhausted cells by suppressing effector- and proliferation-associated programs.