pattern of cross lineage T-cell receptor delta/gamma gene rearrangements in B-precursor acute lympho-blastic leukemia of Iranian children using polymerase chain reaction

ABSTRACT

Diversity in 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, IgK 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- delta/gamma gene rearrangements using Polymerase Chain Reaction [PCR] in B-precursor acute lymphoblastic leukemia [ALL] in Iranian children. 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-delta [V delta2-D delta3 and D delta2-D delta3] and TCR-gamma [V gamma; V gamma I and V gamma 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 then 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. Clonal rearrangement of TCR-gamma [V gamma] and V gamma l/Il were present in 79.3% and 64.9% of patients respectively and only 5% of cases showed biclonal pattern. The V gamma ll rearrangement was the most common [46.8%] type in TCR-gamma. 47 [45.2%] and 11 [16.6%] of patients had V delta2- D delta3 and D delta2-D delta3 partial gene rearrangements, respectively. Biclonal/oligoclonal patterns were present respectively in 27.7% and 4.3% of cases with Vdelta2-D delta3 rearrangement. Only one patient had biclonal D delta2 D delta3 rearrangement. Clonal rearrangement of TCR-delta [Vdelta2-Ddelta3 and D delta2-D delta3] genes had a pattern similar to other populations. Frequency of TCR- gamma [V gamma I and V gamma II] rearrangements was slightly higher than previous reports, and in contrary to others except for Brazilian report the V gamma II rearrangement was the most common type. We found no significant correlation between presence of different types of rearrangements and quantitative variables. The only significant point was the reduction of Vdelta2Ddelta3 with increase in age. According to preliminary results, these clonal markers can be used in diagnosis and follow up of MRD