ICOS and cancer: The activation of the ICOS pathway plays a key role in activating the expansion of Treg and the release of IL-10 by secretion from memory CD4+ T cells, both of which create an immunosuppressive environment for cancer growth (Akbari et al., 2002; Faget et al., 2013; Gobert et al., 2009; Sharma et al., 1999).