{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"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."}]},{"type":"paragraph","children":[{"type":"text","value":"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."}]}]}