Terminal transferase in leukemias by flow cytometry.

The object of this study was to develop a flow-cytometric procedure for measuring terminal transferase (TdT) in leukemic cells by indirect immunofluorescence. We demonstrated the presence of TdT in an average of approximately 80% of the cells from 12 patients with ALL, one with CML in lymphoid blast crisis, and one with T-lymphoblastic leukemia. These results compared favorably to a separate slide test for TdT using an immunofluorescent or immunoperoxidase method. In the 21 patients with nonlymphocytic leukemias and in six normal donors we studied, less than a mean of 3% of the cells were TdT+. In 11 of 12 patients with ALL, the TdT+ cells also carried the HLA-DR antigen and in 8 of 12 cases of ALL the TdT+ cells also expressed the CALLA antigen. We concluded that the flow-cytometric method facilitates the measurement of TdT and may significantly increase the ability to diagnose residual and recurrent ALL leukemias.