We first evaluated the phenotype and function of PD-1+Tim-3hi CD8+ T cells isolated from metastatic melanoma (MM), which produced fewer cytokines (TNF and IL-2) upon stimulation with phorbol myristate acetate (PMA)/ionomycin ex vivo (Supplemental Figure 1, A and B; supplemental material available online with this article; https://doi.org/10.1172/JCI152864DS1) and spontaneously exhibited higher degranulating capability (CD107a, perforin) and upregulated PS (annexin V staining) as compared with PD-1+Tim-3– CD8+ TILs (Figure 1, A and B, and Supplemental Figure 1C). Here, PRF1 is linked to metastatic melanoma.