The over-expression of CD39 but not PD-1 on CD4+ T cells in NILs suggested that CD39 or PD-1 alone might not contribute to tumor-specific immune suppression, and that co-expression of CD39 with PD-1 in TILs indicated a T-cell dysfunction mechanism used by tumor cells to evade host immune response. This evidence concerns the gene PDCD1 and neoplasm.