ENPP3 and chronic myelogenous leukemia, BCR-ABL1 positive: The most specific cell surface antigen for basophils is the ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3) also known as CD203c.43, 44 This antigen is expressed on mature basophils as well as on immature basophil progenitor cells at various stages, including most immature, agranular CD34+ basophil progenitor cells.43, 44 CML basophils also display CD203c (Figure 1).