| Abstract: | Although leukocytes from all 13 acute lymphoblastic leukemia patients examined had high terminal deoxynucleotidyl transferase (terminal transferase) activity (20 to 100 units/mg of cellular DNA, where 1 unit equals 1 nmole of nucleotide polymerized in 1 hr) and those from 21 acute myelocytic leukemia patients had low terminal transferase activity (0.2 to 2 units/mg of cellular DNA), the bone marrow and peripheral blood leukocytes from 2 patients with acute myelocytic leukemia, diagnosed on the basis of clinical features and the morphology, cytochemistry, and cytogenetics of the leukemic cells, had terminal transferase activity (39 to 52 units/mg of cellular DNA) equivalent to that found in leukemic lymphoblasts. These results bring under question the specificity of high terminal transferase activity outside of the thymus as a marker for leukemic lymphoblasts and, secondarily, the derivation of acute lymphoblastic leukemia cells in all cases from thymocytes. Perhaps malignant transformation in a pleuripotent stem cell with derepression of the genome for terminal transferase could account for high terminal transferase activity observed in certain leukemic cells. |
