In patients with metastatic melanoma who respond to anti-PD-1 therapy, the proliferation of intra-tumour CD8+ T cells is directly correlated with the clinical response, making tumour-infiltrating lymphocytes (TILs) a treatment of interest in combination with a PD-1 inhibitor, which is the undisputed gold standard in the management of metastatic melanoma. The gene discussed is PDCD1; the disease is neoplasm.