Molecular diagnosis of clonality in B-precursor acute lymphoblastic leukemia of children using immunoglobulin heavy and

Enormous diversities of heavy chain immunoglobulin (IgH) & IgK molecules are generated during B- and T-lymphocyte differentiation through the rearrangement of gene segments. Additionally, random insertion and deletion of nucleotides between gene segments make unique sequences which are cell or clone specific. IgH and IgK gene rearrangements are the most and relatively common reported rearrangements in B-precursor acute lymphoblastic leukemia, respectively. The purpose of this study is to evaluate the pattern of IgH and IgK gene rearrangements using polymerase chain reaction (PCR) in BP-ALL in Iranian children. For this prospective study, bone marrow aspirates of 183 patients with the diagnosis of acute leukemia were collected at admission before any chemotherapy. Having reviewed cytomorphology (L1:44%, L2:41%) and immunophenotyping, only 140 cases with the diagnosis of B-precursor ALL were selected. Mononuclear cells including leukemic blasts were isolated by density gradient. Having DNA extracted, hyper-variable regions of IgH and IgK 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 sequences homologous for IgH and IgK published by Gene Bank. IgH gene rearrangements were found in 114 (90.4%) of patients using consensus primers for CDR-III and CDR-I regions (monoclonal 57.8% biclonal 34.9% oligoclonal 5.5%). Four of nine patients with T-ALL had clonal rearrangements of IgH. Clonal pattern of Igκ-Kde were present in 59 (67%) of cases (biclonal 10%). VKI (25%) and VKШ (22.7%) were the most common type of rearrangements. Clonal rearrangement pattern of IgH gene was similar to other populations. Using FRI and FRIII primers in multiplex PCR increased the rate of detection and reducing turnaround time. IgK was slightly more frequent than previous reports while VKI (25%) was the most common type.