Terminal deoxyribonucleotidyl transferase in human leukemia

Summary Thymic specific deoxyribonucleotidyl transferase (terminal transferase) was identified and partially purified from peripheral blood leukocytes of a patient with chronic myeloblastic leukemia (CML). The enzyme polymerizes deoxyribonucleoside triphosphates in the presence of an oligodeoxynucleotide alone as initiator, independent of template and the incorporation of one radiolabeled deoxyribonucleotide is inhibited by the presence of other unlabeled deoxynucleotides. The purified enzyme prefers oligo(dA) among various primers tested and favors Mn ++ for activity. This finding and the previous report in human acute lymphocytic leukemic cells (4) suggest that some human leukemias may be thymic cell derived. Alternatively, the results may be explained by the presence of thymic gland derived cells among the leukemic cells or if in certain leukemias which may have nothing to do with thymus cells, terminal transferase activity is increased.