Abstract

 Background and Objectives

 Diversity of heavy chain immunoglobulin (IgH) and T-cell receptor (TCR) molecules occures during B- and T-lymphocyte differentiation through the rearrangement of variable (V), diversity (D), junction (J) and constant (C) gene segments. Lymphoid leukemia cells are similar to normal precursors and have rearranged IgH, Igκ and TCR (cross-lineage rearrangement) genes which can be used as a marker of clonality and evaluation of minimal residual disease (MRD). The purpose of this study is to evaluate the pattern of TCR- δ/γ gene rearrangements using polymerase chain reaction (PCR) in B-precursor acute lymphoblastic leukemia (ALL) in Iranian children.

  Materials and Methods

 In our prospective study, bone marrow aspirates of 183 children with early diagnosis of acute leukemia were collected at admission before any chemotherapy. After reviewing cytomorphology and immunophenotyping, only 140 subjects with diagnosis of B-precursor ALLs were selected for study. Sixteen were excluded from our study due to various reasons including cellular degeneration. Mononuclear cells including leukemic blasts were isolated by density gradient. After DNA extraction, hyper-variable regions TCR- δ (Vδ2-Dδ3 and Dδ2-Dδ3) and TCR- γ(V γ V γ I and V γ II) were amplified by consensus primers using PCR. PCR products were analyzed after heteroduplex analysis and polyacrylamide gel electrophoresis (silver stain). The DNA sequences were compared and aligned to the homologous sequences of Gene Bank for confirmation. T-test, Mann whitney, Fisher exact test and Chi-square were used for data analysis.

 Results

 Clonal rearrangement of TCR-γ (Vγ) and VγI/II were present in 79.3% and 64.9% of patients respectively and only 5% of cases showed biclonal pattern. The VγII rearrangement was the most common (46.8%) type in TCR-γ. 47 (45.2%) and 11 (16.6%) of patients had Vδ2- Dδ3 and Dδ2–Dδ3 partial gene rearrangements, respectively. Biclonal/oligoclonal patterns were present respectively in 27.7% and 4.3% of cases with Vδ2-Dδ3 rearrangement. Only one patient had biclonal Dδ2 Dδ3 rearrangement.

 Conclusions

 Clonal rearrangement of TCR-δ (Vδ2-Dδ3 and Dδ2-Dδ3) genes had similar pattern to other populations. Frequency of TCR- γ (V γ I and V γ II) rearrangements were slightly higher than previous reports. and in contrary to others except Brazilian report the V γ II rearrangement was the most common type. We found no significant correlation between presence of different types of rearrangements and quantitative variables and the only significat point was the reduction of Vδ2Dδ3 with increase in age . According to preliminary results, these clonal markers can be used in diagnosis and follow up of MRD.

 Key words: Gene rearrangement, Clonality, Minimal Residual Disease (MRD)