Among them, IL-2, IL-7, IL-15 and IL-21 have been widely utilized for the CAR-T cell preparation, because these cytokines play pivotal roles in fueling T cells to thrive, combat tumors and drive long-lived memory against tumor metastasis or relapse (Hashimoto et al., 2019; Shourian et al., 2019; Dwyer et al., 2019). The gene discussed is IL21; the disease is neoplasm.