Myeloid antigen expression on common acute lymphatic leukaemia blasts after culture

Blast cells from seven out of ten patients with common acute lymphoblastic leukaemia (cALL) developed the myeloid antigen MY7 (CD13) after culture, and one of these coexpressed the myeloid antigen MY9 (CD33). CD13 expression appeared to be independent of maturation since it could be induced more readily in cultures which did not contain the differentiation promoter 12-O-tetradecanoyl-phorbol 13 acetate (TPA). CD13 expression in culture was not seen on one null ALL, or 6 B-CLL investigated or on normal tonsillar B cells or PBMC under similar conditions. CD13 expression on cALL blasts probably represents evidence of abnormal gene expression in the leukaemic cells. However the absence of CD13 expression on the earlier B null ALL or the later B-CLL suggests we cannot exclude the possibility that CD13 expression is a feature of normal precursor B cells.