In patients with metastatic melanoma, remarkably promising clinical efficacy has been shown from first-line treatment with a vaccine based on peptides derived from indoleamine 2,3-dioxygenase (IDO) and programmed cell death ligand (PD-L) 1 in combination with anti-programmed cell death protein 1 (PD-1) antibodies. The gene discussed is PDCD1; the disease is metastatic melanoma.