high cytotoxic potency is linked to CD8+ effector memory T (TEM) and CD45RA+ TEM (TEMRA) cells, and to CD4+ TEM and central memory T (TCM)-cells due to their large number of preformed perforin and granzyme B-filled vesicles and their great proliferative capacity. Another notable T-cell subset in the context of immunotherapy are CD4+ regulatory T (TREG) cells. Their presence in the tumor microenvironment is implicated in the suppression of naturally occurring anti-tumor T-cell responses