Therefore, it is possible to assume, at least theoretically, that, in the absence of genetic mechanisms leading to a total loss of the CD 19 antigen, a simple down-modulation that reduces the number of CD 19 molecules on the membrane surface could lead to the escape from the leukemia of the CAR CD19–4-1BBζ employed in tisagenlecleucel. The gene discussed is CD19; the disease is leukemia.