Obese melanoma mice secrete leptin, and leptin activates the p-STAT3 pathway in peripheral blood CD8+ T cells through leptin receptor to bind to the PD-1 gene promoter region, up-regulating the transcription and expression of PD-1, thus inducing T cells of obese mice in a state of depletion with high expression of PD-1. The gene discussed is CD8A; the disease is melanoma.