The mechanism is still unknown, but recent studies on a large cohort of adult patients with relapsed ALL and treated with CD19-CAR T cells, have related a significant correlation between neurotoxicity and high tumor burden, and specifically, that concerns our review, the correlation between neurotoxicity and a high level of CAR T cells and early increase in serum cytokines [61]. Here, CD19 is linked to acute lymphoblastic leukemia.