PRF1 and neoplasm: These second-generation CAR-T cells with CD28 co-stimulatory molecules differentiate into effector memory T cells, and those containing 4-1BB domains differentiate into central memory T cells, both of which were able to proliferate more effectively and enhance expansion after tumor-antigen exposure [49,50,112,113,114] and produce an increased level of cytokines such as perforin or granzyme B, leading to higher anti-tumor activity in preclinical models.