In baseline or post-treatment tumor biopsies and peripheral blood mononuclear cells (PBMCs) from metastatic melanoma patients, numbers of PD-1 + CD38hi CD8 + T cells correlated with the anti-PD-1 therapeutic response, High numbers of dysfunctional CD8 + T-cells in the tumors and PBMCs served as a predictor of failure of anti-PD-1 therapy. The gene discussed is CD8A; the disease is neoplasm.