Terminal deoxynucleotidyl transferase staining in acute leukemia and normal bone marrow in routinely processed paraffin sections.

Terminal deoxynucleotidyl transferase (TdT) is a nuclear protein widely used as a marker for the diagnosis and classification of acute leukemia. The usual methods for detecting TdT require smears, imprints, or cryostat sections of unfixed tissue. A polyclonal rabbit anti-TdT serum was used to immunostain 54 routinely processed bone marrow sections from patients with acute leukemic disorders, using a recently described antigen-unmasking technique based on microwave oven heating. The specificity of this method of TdT analysis was confirmed by comparing the results obtained with conventional TdT analysis by indirect immunofluorescence. Terminal deoxynucleotidyl transferase reactivity was also evaluated in 44 nonmalignant and normal bone marrow specimens. All cases that were TdT-positive by immunofluorescence (41 of 42 "pre-B" and T-cell acute lymphoblastic leukemia, 2 of 5 acute myeloid leukemia, and 1 of 5 chronic myeloid leukemia in blast crisis) were also positive in paraffin sections. The percentage fluorescence positivity correlated with the percentage of immunoperoxidase stained cells in 44 of 45 cases. The remaining nonneoplastic and normal bone marrow biopsy specimens were TdT-negative. These results show that TdT immunoperoxidase staining of conventionally processed bone marrow specimens can be readily achieved by the use of a simple antigen-unmasking technique and may provide useful diagnostic information particularly in cases in which fresh tissue samples are unavailable.