In tumours that are abundant in tumour-infiltrating FoxP3high, CD45RA−, CD4+ T cells [effector Treg (eTreg) cells], PD-1 blockade may actually facilitate the proliferation of these highly suppressive PD-1+ eTreg cells, resulting in further inhibition of pre-existing antitumor immunity80. Here, CD4 is linked to neoplasm.