PDCD1 and cancer: In addition to CD8+Foxp3+Tregs, other CD8+Foxp3−T cells, such as CD8+CD103+ cells, CD8+CD39+CD103+ cells, CD8+CD28− cells, and CD8+CD122+CD49d+ cells expressing PD-1 and IL-10, behave as immunoregulatory/immunosuppressive T cells in different inflammatory conditions, such as aging, CVIs, cancers, GVHD, and AIDs [266,278,279,280,281,282].