Terminal transferase in leukemias by flow cytometry.

Area of Science:

• Hematology
• Immunology
• Cell Biology

Background:

• Terminal transferase (TdT) is a key enzyme in lymphoid development.
• TdT expression is a marker for certain types of leukemia, particularly acute lymphoblastic leukemia (ALL).
• Accurate measurement of TdT is crucial for leukemia diagnosis and monitoring.

Purpose of the Study:

• To develop and validate a flow cytometry procedure for quantifying TdT in leukemic cells.
• To compare the flow cytometry method with existing slide-based immunofluorescence and immunoperoxidase tests.
• To assess the utility of TdT measurement in diagnosing and monitoring various leukemias.

Main Methods:

• Indirect immunofluorescence staining for TdT on leukemic cells.
• Flow cytometric analysis to quantify TdT-positive cells.
• Comparison with slide-based immunofluorescence and immunoperoxidase assays.
• Co-expression analysis of TdT with HLA-DR and CALLA antigens.

Main Results:

• The flow cytometry method demonstrated high sensitivity and specificity for TdT detection.
• TdT was present in approximately 80% of cells from patients with ALL, T-lymphoblastic leukemia, and CML in lymphoid blast crisis.
• Less than 3% of cells were TdT-positive in nonlymphocytic leukemias and normal donors.
• TdT-positive cells in ALL frequently co-expressed HLA-DR (11/12) and CALLA (8/12) antigens.

Conclusions:

• Flow cytometry provides a reliable and efficient method for measuring TdT in leukemic cells.
• This technique enhances the diagnostic capabilities for ALL, including the detection of minimal residual disease.
• TdT expression, along with other markers like HLA-DR and CALLA, aids in characterizing leukemic cell populations.