PDCD1 and neoplasm: Interestingly, within the small number of CD8+ T cells from primary tumors that fell into cluster L0, treatment with anti-PD-1 antibody induced high expression of Tox (Supplementary Fig. 6b and Supplementary Data 4), a critical regulator of tumor-specific T cell differentiation that promotes T cell commitment to an exhausted and dysfunctional phenotype52–54.