In a cohort of patients with advanced, unresectable stage III/IV melanoma treated with anti-PD-1-based therapy, densities of specificCD8 + cell phenotypes, including a high density of early effector T cells characterized by CD8 + FoxP3 + PD-1low/mid expression, showed strong predictive value for response, whereas a CD163 + PD-L1 − myeloid phenotype was associated with non-response. The gene discussed is FOXP3; the disease is melanoma.