Precursor Cell Marker : TdT, in Visit Clinic

TdT (terminal deoxynucleotidyl transferase) is a nuclear enzyme expressed in immature lymphoid precursors and serves as a marker of lymphoid immaturity. It is routinely used to identify precursor B‑cell and T‑cell acute lymphoblastic leukemia/lymphoma, distinguishing these from mature B‑cell neoplasms. TdT is generally absent in mature lymphocytes and most myeloid leukemias.

TdT is expressed mainly in immature lymphoid cells—precursor B and T lymphoblasts in bone marrow and thymus. It is a nuclear marker of early B‑ and T‑cell development and is typically positive in acute lymphoblastic leukemia/lymphoblastic lymphoma. Mature B cells, plasma cells, and most myeloid and non‑lymphoid cells are TdT‑negative. Occasional rare tumors may show variable TdT expression.

Terminal deoxynucleotidyl transferase (TdT) is a specialized DNA polymerase in immature lymphoid cells that inserts non-templated nucleotides at V(D)J junctions during B- and T-cell development, increasing antigen receptor diversity and adaptive immunity. Clinically, TdT expression is used as an immunophenotypic marker of lymphoblasts—especially in acute lymphoblastic leukemia—to aid diagnosis, prognosis, and treatment planning.

TdT stands for terminal deoxynucleotidyl transferase, a specialized DNA polymerase that adds deoxynucleotides to the 3′ ends of DNA strands without a template. It is predominantly expressed in immature lymphoid cells (precursors in bone marrow and thymus) and is used as an immunohistochemical marker in diagnosing acute lymphoblastic leukemia and lymphoblastic lymphoma.

Terminal deoxynucleotidyl transferase (TdT) is expressed in early lymphoid precursors—pro‑ and pre‑B and pre‑T lymphoblasts in bone marrow and thymus—during V(D)J recombination. It is present in immature lymphocytes but absent in mature B or T cells and plasma cells. TdT is commonly detected in acute lymphoblastic leukemia blasts, reflecting arrested early lymphoid differentiation.

TdT (terminal deoxynucleotidyl transferase) is an enzyme marker, not a disease. Its presence in bone marrow or blood cells indicates immature lymphoid cells and is commonly seen in acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma. TdT is detected by immunohistochemistry or flow cytometry; findings are interpreted with cell morphology, immunophenotype, and genetic tests to confirm diagnosis and guide treatment.