PDCD1 and neoplasm: Additionally, IL-6 and IFN-γ are considered to be the prominent stimulators that contribute to the expression of PD-1 and PD-L1 in the tumor microenvironment (34, 35); however, we were unable to detect any significant correlations between IL-6 or IFN-γ and PD-1+ T cells, which would thus tend to indicate that inflammatory cytokines are not associated with the abnormally high percentages of PD-1+ T cells.