Exhaustion or dysfunction of T cells occurs in tumor microenvironments and during chronic viral infection, which show high expression of inhibitory molecules such as PD-1, Tim-3, and interleukin (IL)-10 and low production of proinflammatory cytokines including IFN-γ, TNF-α, and granzyme B, which lead to tumor progression or unsuccessful viral eradication21,22. The gene discussed is PDCD1; the disease is neoplasm.