CD4 and neoplasm: Whether self-tolerance to K17 epitopes remains during PDAC tumor development is unknown, but anti-K17 Treg cells could play a role in dampening immune responses in the TME as well, as evidence suggest that during the formation of central tolerance, CD4+ T cells that react to self-derived epitopes are less likely to be deleted than CD8+ Tcells, and differentiate into Tregs [53].