[Bi-phenotypic leukemia and hybrid leukemia]

Phenotypes of leukemic cells can be determined through dual staining with pairs of FITC-labeled and PE-labeled monoclonal antibodies using a laser flow cytometer. Hybrid acute leukemia (HAL) was diagnosed when leukemic cells expressed 2 or more lymphoid markers and at least one myeloid maker simultaneously. Based on this criteria, forty out of 111 cases with untreated acute leukemia were diagnosed as HAL, 16 of 41 (39%) patients with acute lymphoblastic leukemia and 15 of 70 (21%) patients with acute non-lymphocytic leukemia were diagnosed as having HAL. We classified these HAL cells into 4 types by the following items. Type I; leukemic cells expressed only CD33 and 2 or more B-cell antigens, type II; only CD33 and 2 or more T-cell antigens, type III; CD13 and/or CD33 and 2 or more B-cell antigens, and type IV; CD13 and/or CD33 and 2 or more T-cell antigens. There were 7 type I cases and 16 type III cases. The leukemic cells of these two types were thought to be ALL cells expressing one or several myeloid lineage-associated antigens. There were 4 type II cases and 10 type IV cases. Type II and IV were regarded as lymphoid-lineage associated antigens positive AMLs. At least in adults, the expression of myeloid-associated antigens of ALL cells seems to identify a high risk group of ALL patients with a poorer response to standard ALL therapy.