DNTT and leukemia: V(D)J recombination creates diversity of antigen receptors in immune system.12 TdT is responsible for inserting nucleotides to the junctions of gene segment during V (D) J recombination.13-15 TdT gene is present in pre-B and pre-T cells and increases in some human leukemia’s.9,16 For this reason, TdT is an effective biochemical marker for classifying leukemia’s.17