ICOS and leukemia: Then, we found that compared with CAR19/20-1 or CAR19/20-2 with commonly used CD8 or CD28 transmembrane domain and CD137/CD3z or CD28/CD3z intracellular domain, CAR19/20-3 with ICOS incorporation in transmembrane and intracellular domains significantly enhanced the activity of human T cells in killing leukemia cells.