Terminal deoxyribonucleotidyltransferase (TdT) catalyses the condensation of deoxyribonucleotide triphosphates onto the 3' hydroxyl ends of DNA strands and adds N-regions to gene segment junctions during V (D) J recombination. Terminal deoxyribonucleotidyltransferase is expressed in immature, pre-B, pre-T lymphoid cells, and acute lymphoblastic leukemia/lymphoma cells[1].