Abstract
The leukemic cells from two children with a TdT+, CALLA-, Ia+ acute lymphoblastic leukemia (null ALL) showed myeloid or myelo-monocytic characteristics by phenotyping studies using monoclonal antibodies.
Patient 1 was a 7-month-old boy presented with WBC of 397,200/mm3 with 98% of lymphoid blasts (L1 by FAB classification) which showed a chromosome abnormality of t (4; 11). Leukemic cells were positive for BA-1, BA-2, B7/21, PI 153·3 and TdT, while they were negative for J5, B1, MCS-1, MCS-2 and Mo2. Although they remained negative for MCS-1 or MCS-2 following 3 days culture with 20 ng/ml of 12-O-tetradecanoylphorbol-13-acetate (TPA), a definitively positive expression of MCS-1 was observed in the blasts when the disease relapsed after 4 months of complete remission.
Patient 2 was a 5 and 4/12-year-old girl presented with WBC of 266,700/mm3 containing 92% blasts of lymphoblastoid appearance (L2 by FAB classification). Her bone marrow cells possessed Ph1 chromosome. The leukemic cells from this patient were positive for antigens recognized by BA-1, BA-2, B7/21, PI153·3 and TdT. However, they were negative for J5, B1, MCS-1, MCS-2 and Mo2. Following 3 days culture with 20 ng/ml of TPA, leukemic cells became positive for MCS-2 with increasing of the fluorescence intensity.
The study showed that the leukemic cells of null ALL may have the potential of differentiation into myeloid or myelo-monocytic cells. Such information should be taken into consideration when plans of chemotherapy are made for null ALL patients.
