PDCD1 and cancer: The PD-1 molecule has been recognized as a hallmark of T-cell exhaustion, and PD-1-expressing antigen-specific T cells are dysfunctional in cytokine production and proliferation on antigen restimulation in a variety of viral infections.5 Anti-PD-1 antibody therapies are being developed to enhance T-cell responses in patients with cancers or chronic viral infections, such as HIV and hepatitis C.6 Although the role of PD-1 in adaptive immunity has been well characterized,7, 8 its function in innate immunity has seldom been investigated.