While CD19-positive relapses (70-80% of patients) are produced by mechanisms inherent to CAR T cells, which are unable to expand or persist in the circulation, CD19-negative relapses (20-30% of patients) are produced by evasion mechanisms inherent to leukemia and occur in the presence of perfectly functioning CART cells from which it manages to escape (23). Here, CD19 is linked to leukemia.