CD28 and neoplasm: The CD28-CD3ζ-CAR-T cells induced infiltration of Treg cells into tumors more effectively than CD3ζ -CAR-T cells, and deletion of lck binding region inside CD28 endodomain linked to IL-2 production reversed the induction of Treg’s tumor infiltration, and increased the anti-tumor activity of CAR-T cells [36].