This phase I, open-label, non-randomized trial of combination therapy with an anti–PD-1 (nivolumab) and GPS, a novel WT1-targeting non–HLA-restricted heteroclitic tetravalent peptide vaccine, administered as maintenance therapy in patients with WT1-positive ovarian cancer in second or third remission met its predetermined endpoint of safety and tolerability. This evidence concerns the gene PDCD1 and ovarian cancer.