Enumeration of terminal deoxynucleotidyl transferase positive cells in leukemia/lymphoma by flow cytometry

The method to fix single cells in suspension and its application for the detection of TdT-positive cells by flow cytometry are described. In comparison to formalin-methanol fixation, formalin-acetone fixation resulted more formation of aggregated cells which caused non-specific staining. In our assay system 80% cells in human thymus were TdT-positive. Levels of TdT in normal human peripheral blood was 0.5 +/- 0.6% (means +/- 1 S.D., n = 50). A total of 104 patients with leukemia/lymphoma was examined for TdT. TdT-positive cells were detected in ALL (87.5% cases), AML (57.1% cases), CML-BC (58.3% cases) and ML (17.6% cases). Mean channel of fluorescence intensity of the TdT-staining in AML was significantly reduced in comparison with that in ALL. When antigen density of TdT was very low, fluorescence microscopy gave false negative results and flow cytometry could detect this dim fluorescence.