Interestingly, 35 of 36 primary B-ALL also exhibited an additional band, which nucleotide sequencing (n = 11) revealed as a novel APRIL isoform, APRIL-δ (reported to GenBank as accession number DQ149579) that results from an alternative-splicing event where exon 2 is missing, thus lacking the furin convertase motif RKRR [32] (Figure 2B; Figure S1). This evidence concerns the gene TNFSF13 and precursor B-cell acute lymphoblastic leukemia.