Analysis of bone marrow and peripheral blood samples from untreated children and adults with CD19-positive B-ALL and non-leukemia patients revealed that the total deletion (ex2-isoform) and partial deletion of exon 2 (ex2part-isoform) of CD19 in B cells are expressed in both subjects, suggesting that B-cells that cannot be recognized by CAR T-cell therapy for lacking the CD19 epitope might exist in leukemia patients before treatment, even in healthy people. This evidence concerns the gene CD19 and acute lymphoblastic leukemia.