CD19 and precursor B-cell acute lymphoblastic leukemia: Studies on the genome of CD19 in pediatric patients with relapsed B-ALL after CAR-T identified multiple somatic mutations enabling skipping or alternative splicing of exon 2, leading to retention or alternate folding of the membranous fraction, thus indicating loss of the CD19 epitope required for CAR-T cells to trigger targeted cell death [19,20,21,22].