TdT

Terminal Deoxynucleotidyl Transferase (also known as TdT and terminal transferase) is a specialized DNA polymerase expressed in immature, pre-B, pre-T lymphoid cells and acute Lymphoblastic Leukemia/ Lymphoma cells. TdT catalyzes the addition of nucleotides to the 3’ terminus of a DNA molecule. Unlike most DNA polymerases, it does not require a template. The preferred substrate of this enzyme is a protruding 3’ overhang, but it can also add nucleotides to blunt or recessed 3’ ends.

TdT is normally found in cortical thymocytes and primitive lymphocytes. TdT antibody detects its antigen found in the nucleus of normal hematopoietic cells, normal cortical thymocytes and in the cytoplasm of megakaryocytes of the bone marrow. TdT expression is seen in over 90% of Acute Lymphocytic Leukemia cases with the exception of pre-B-Cell ALL, and normal mature T- or B-lymphocytes. TdT is positive for approximately one third of all cases of Chronic Myeloid Leukemia, making it a good indicator of better response to chemotherapy.

Anti-TdT is a purified immunoglobulin fraction of rabbit antiserum that is filter sterilized and diluted in buffer pH 7.5, containing BSA and sodium azide as a preservative.

1. Elias JM , TdT. A Practical Approach to Diagnosis, ASCP Press, Chicago. 1990;312-316
2. Arber DA, et al. Am J Clin Pathol. 1996;Oct;106(4):462-8
3. Orazi A, et al. Mod Pathol. 1994;Jun;7(5):582-6
4. Suzumiya J, et al. J Pathol. 1997;May;182(1):86-91
5. Mathewson RC, et al. Pediatr Pathol Lab Med. 1997;Nov-Dec;17(6):835-44

1. Cut and mount 3-4 micron formalin-fixed paraffin-embedded tissues on positive charged slides.
2. Air dry for 2 hours at 58° C.
3. Deparaffinize, dehydrate and rehydrate tissues.
4. Subject tissues to heat epitope retrieval using a suitable retrieval solution such as ImmunoDNA Retriever with Citrate (BSB 0020-BSB 0023) or EDTA (BSB 0030-BSB 0033).
5. Any of three heating methods may be used:
   • Electric Pressure Cooker
     Place standoff rack at base of pressure cooker. Add 1-2 inches of distilled water to the pressure cooker and turn heat to high, and incubate for 15 minutes. Open and immediately transfer slides to room temperature.
   • Water Bath Method
     Place tissues/slides in a pre-warmed staining dish or coplin jar containing the ImmunoDNA Retriever with Citrate or EDTA in a water bath set at 95°-99° C. Incubate for 30-60 minutes.
   • Conventional Steamer Method
     Place tissues/slides in a pre-warmed staining dish or coplin jar containing the ImmunoDNA Retriever with Citrate or EDTA in a Steamer, cover and steam for 30-60 minutes.
6. After heat treatment, transfer slides in ImmunoDNA Retriever with Citrate or EDTA to room temperature and let stand for 15-20 minutes.
7. Wash slides with IHC wash buffer or DI water.
8. Continue IHC staining protocol.