The CD19-negative relapse rate ranges from 18% to 25% for pediatric B-ALL and 7% to 9% for adult B-ALL patients [50] and between 20% and 50% for LBCL in different clinical trials/studies [47, 49] while the frequency of de facto BCMA loss in MM is largely unknown [51]. This evidence concerns the gene CD19 and precursor B-cell acute lymphoblastic leukemia.