Terminal deoxyribonucleotidyl transferase in human leukemia.

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Terminal deoxyribonucleotidyl transferase (TdT) is primarily found in the thymus.
• TdT has been previously identified in leukemic cells of children with acute lymphoblastic leukemia.

Purpose of the Study:

• To investigate the presence and activity levels of terminal deoxyribonucleotidyl transferase in an adult patient with acute myelomonocytic leukemia.
• To compare TdT activity in this patient with normal thymus, normal bone marrow, and other types of leukemia.

Main Methods:

• Enzyme assays were performed on bone marrow and circulating leukocytes.
• Quantification of terminal transferase activity was measured in units per 10(8) cells.
• Biochemical characterization including reaction properties, sedimentation, and chromatography was conducted.

Main Results:

• Unusually high levels of terminal deoxyribonucleotidyl transferase activity were detected in the bone marrow (16 units/10(8) cells) and peripheral leukocytes (14 units/10(8) cells) of the adult patient with acute myelomonocytic leukemia.
• This activity level was comparable to that found in normal thymus.
• TdT levels in typical acute and chronic myelogenous leukemias were significantly lower (average 0.5 and 0.3 units/10(8) cells, respectively), and normal bone marrow showed minimal activity (approx. 0.07 units/10(8) cells).

Conclusions:

• Terminal deoxyribonucleotidyl transferase can be present at significant levels in adult acute myelomonocytic leukemia, which is atypical.
• The enzyme's characteristics in human samples are consistent with the homogeneous enzyme from calf thymus.
• This finding expands the understanding of TdT expression in hematological malignancies.