CAR-T cell immunotherapy hasn’t been terribly successful in solid tumors owing to poor migration and infiltration of CAR-T cells into tumors. In addition to in vitro assays (performed outside a living organism), Yi tested the capacity of human T9 CAR-T cells to repress solid tumor growth in murine tumor models. Tumor-bearing mice treated with T9 CAR-T cells showed greater T9 CAR-T cell infiltration into tumor sites, greater survival, and reduced tumor growth compared with T1 CAR-T treated mice. Thus, T9 CAR-T cells show considerable therapeutic efficacy and potential for solid human tumors. According to Yi, “Our findings highlight a promising clinical potential of human IL-9 secreting T cells for CAR-T cell immunotherapy for human cancers that are attributed to their central memory phenotype and are less exhausted, hyperproliferative and long-lived in vivo. The unique features of T9 CAR-T cells endow them with greater potential for clinical immunotherapy, which can lead to increased frequency of complete remission, high survival rates, and decreased number of patient relapse after treatment.” Treatment outcomes in solid and liquid tumor patients can be significantly enhanced by harnessing the hyperproliferative capacity and robust antitumor potency of human T9 CAR-T cells. Engineering T cells with a CAR is justifiable and human T9 CAR-T cell therapy is likely to lead to better long-term remission among cancer patients.