Terminal deoxynucleotidyl transferase (TdT), cytochemistry, and membrane receptors in adult acute leukemia.

Terminal deoxynucleotidyl transferase activity, immunologic membrane markers, and cytochemical reactivity were examined in blasts of 80 adults with acute leukemia. The study was interinstitutional and prospective so that some assessment could be made of the usefulness and practicality of these tests in the classification of adult acute leukemias. Initial classification as to the type of acute leukemia was based primarily on cytochemistry and only secondarily on the morphology of the abnormal cells. Terminal transferase was uniformly elevated in eight of eight patients with null and T cell lymphoblastic leukemia and two of two patients with null cell lymphoma leukemia, whereas it was elevated in only 3 of 27 specimens defined cytochemically as acute myeloblastic leukemia. Terminal transferase activities were low in 24 of 27 patients with acute myelomonocytic, acute monocytic, and lymphoma leukemia of B or T cell type. Blasts from 17 of 80 patients did not show distinctive patterns of cytochemical staining, and these patients were classified as having acute undifferentiated leukemia. When these 17 coded specimens were submitted to a panel of four hematologists and classified by each as lymphoid or nonlymphoid based on morphology, there was disagreement in 9 of the 17. In this situation the usefulness of additional methods of cellular classification such as terminal transferase and membrane markers became manifest.