A subpopulation of exhausted T cells that expressed the transcription factor Tcf7 (protein is Tcf1) and intermediate levels of PD-1 proliferate and differentiate into effector T cells following PD-1 blockade during chronic viral infection and melanoma, as opposed to PD1highTcf1- terminally exhausted T cells which fail to proliferate following ICB (74–77). The gene discussed is TCF7; the disease is melanoma.