GPC2 and neuroblastoma: The dynamics of CARCD28ζ engagement to mLRs at a modest antigen density could explain their higher antigen sensitivity when compared to CAR4-1BBζ, akin to the reports on the molecular sensitivity of ROR1-CARCD28ζ, cells in response to antigen dose titration (51) and functional sensitivity of CD19-CARCD28ζ T cells in ALL and GPC2-CARCD28ζ T cells in neuroblastoma (20, 23).