PDCD1 and viral infectious disease: To understand whether the TSCM-CTL cells are likely the close parallels to the most recently described TCF1+PD1+TOX+ stem-like precursors of exhausted T cells and the correlates of protection described in mouse models of both chronic and acute viral infection, we examined the expression of thymocyte selection–associated high-mobility group box (TOX) and programmed cell death 1 (PD1) in TSCM-CTL cells (43, 44).