Finally, complete remission induced in an infant with MLL-rearranged ALL treated with a CD19 CAR containing a 41BB costimulatory domain with CAR persistence showed initial clearance of blasts with a relapse at day 30 with leukaemia that lost of B-cell markers, retained CD34 and HLA-DR, and gained of CD11b and CD33 expression (patient ALL_H0140, Fig. 1g,h). Here, CD34 is linked to leukemia.