Detection of minimal residual disease in acute lymphoblastic leukemia by flow cytometry with monoclonal antibodies.

To detect more precisely the minimal residual disease in acute lymphoblastic leukemia (ALL), two-color flow cytometric analysis for the detection of cell-surface antigen (CD10; CALLA) and nuclear terminal deoxynucleotidyl transferase (TdT) was performed in the six patients with CALLA-positive ALL coexpressing TdT. In all patients, the leukemic blasts coexpressed Ia (HLA-DR), CD9, CD19, CD20, CD24, and CD10. Five of six patients achieved complete remission, but one has so far relapsed. No leukemic blasts (CD10+, TdT+) were detected at the time of complete remission. During maintenance chemotherapy, leukemic blasts coexpressed C10 and TdT were found 2.32% in the patient's peripheral blood by two-color analysis, whereas no obvious leukemic cells were recognized morphologically. The patient relapsed leukemia with the same phenotype 4 weeks after the examination. On the basis of our findings, we suggest that two-color flow cytometric analysis with the use of these antibodies is quite valuable to detect the minimal residual leukemic cells in a patient with ALL. The reduction of leukemic cells below the threshold of detection of methods currently available appears to be necessary to achieve a cure in ALL. Hence accurate diagnosis of ALLs with monoclonal antibodies (MAbs) should contribute substantially to the development of an effective form of therapy for their cure.