High Terminal Deoxynucleotidyl Transferase Activity in Acute Myelogenous Leukemia1

Although leukocytes from all 13 acute lymphoblastic ieu kemia patients examined had high terminal deoxynucleoti dyl transferase (terminal transferase) activity (20 to 100 units/mg of cellular DNA, where 1 unit equals 1 nmole of nucleotide polymenized 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 myeIocytic leukemia, diagnosed on the basis of clinical features and the morphology, cytochemistry, and cytoge netics of the leukemic cells, had terminal transferase activ ity (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 lympho blasts and, secondarily, the derivation of acute lymphoblas tic leukemia cells in all cases from thymocytes. Perhaps malignant transformation in a pleunipotent stem cell with derepression of the genome for terminal transferase could account for high terminal transferase activity observed in certain leukemic cells.