GPC1 and cancer: Although both HM2 and D4 CAR T cells exhibited similar killing ability, D4 CAR T cells triggered 2- to 7-fold more secretion of cytokines including IFN-γ, IL-2, and TNF-α than HM2 CAR T cells after exposure to GPC1-positive cancer cells (Fig. 2c and Supplementary Fig. 5g).