CD4 and neoplasm: CD4+ T cells play a substantial role in supporting CD8+ T cell function and have been used by many investigators in adoptive therapy.41 However, the CD8+ subsets in our AFP-TCR-T system are the main effectors that can kill the tumor cells instead of the CD4+ TCR-T subset.42 The potential defect in CD4+ TCR-T does not impair the effector function of CD8+ TCR-T subsets against tumors in our study.