CD4 and neoplasm: Moreover, levels of CD4+PD-1+ T cells were correlated with levels of FoxP3+ Tregs, Helios+ T cells, FoxP3+Helios+ Tregs, FoxP3+Helios− Tregs, and FoxP3−Helios+ T cells in normal tissues, indicating that PD-1 expression is not induced solely by tumor cells.