Likewise, 10,000 CAR T cells eradicated most CD19+ leukemia blasts (initial response) but spared CD19− ones which thus expanded unrestrainedly, reminiscent of clinical relapse cases driven by pre-existing CD19− populations (surface antigen loss) and selective pressure from CAR T cell (Extended Data Fig. 9a,b). The gene discussed is CD19; the disease is leukemia.