EXPRESSION OF MYELOPEROXIDASE MESSENGER-RNA BY LEUKEMIC-CELLS FROM CHILDHOOD ACUTE LYMPHOBLASTIC-LEUKEMIA

The frequency of acute lymphoblastic leukemia (ALL) expressing the mye loperoxidase (MPO) gene and other myeloid-associated characteristics w as determined in 26 (20 B-lineage, six T-lineage) children at diagnosi s. All cases were diagnosed as ALL by standard morphological and cytoc hemical criteria. In the 26 cases, leukemic blast cells from four B-li neage and two T-lineage ALL patients were simultaneously expressing my eloid-associated antigens. By Northern blot analysis, MPO mRNA was det ected in leukemic cells from five out of six cases expressing both lym phoid and myeloid antigens, and from four out of 16 B-lineage and one out of four T-lineage ALL without myeloid antigens. There was no detec table MPO protein or enzymatic activity in the leukemic cells of these cases as examined by immunocytochemistry and cytochemistry. MPO mRNA expression in ALL cells was significantly associated with age <1 year: leukemic blast cells from all five infant ALL patients expressed MPO mRNA, compared to five out of 21 ALL patients > 1 year of age whose le ukemic cells were MPO mRNA(+) (p < 0.01). These results suggest that M PO gene transcription in the absence of translation may characterize a recently described subset of pediatric ALL patients who also express myeloid markers, and may serve as a useful marker for this entity.