MUTATIONAL STATUS OF REARRANGED IMMUNOGLOBULIN HEAVY CHAINVARIABLE GENES IN PATIENTS WITH CHRONIC LYMPHOCYTIC LEUKAEMIA

Abstract

BACKGROUND Mutational status of rearranged immunoglobulin heavy chain variable genes (IGHV)in leukaemia cells of patients with chronic lymphocytic leukaemia (B-CLL) is importantindependent prognostic factor. The outcome of patients with leukaemia cells that use anunmutated IGHV gene is inferior to those patients with leukaemia cells that use a mutatedIGHV gene. Unmutated VH genes can be observed in about half of all B-CLL cases. In addition, the VH3-21 gene usage is an unfavourable prognostic marker independent of theIGHV mutational status. The aims of the study were to determine the mutational statusand IGHV gene usage in our cohort of patients with B-CLL and compare the results to thosepublished in the literature. METHODS 49 B-CLL patients (19 female, 30 male), median age 63 (range from 37 to 88 years) invarious Binet stages (39 Binet A, 6 Binet B, 4 Binet C) were included in the study. All thepatients were untreated at the time of blood collection. Leukaemia cells were isolated fromvenous blood samples of patients by the Ficoll density gradient centrifugation. Total cellular RNA was isolated from leukaemia cells and used to the prepare cDNA by reverse transcription. After heteroduplex analysis, clonal PCR products were identified with polyacrylamide gel electrophoresis. The PCR products were sequenced and mutational status wasdetermined by comparing the sequence of the IGHV region of the patient sample to themost homologous germ line V sequence. Sequence that was homologous more than 98 %with their corresponding germ line sequence was considered unmutated. RESULTS Unmutated and mutated IGHV mutational status in our cohort of patients with B-CLL wasfound in 44.9 % and 55.1 %, respectively.At the IGH subgroup level, the most frequently used subgroup was IGHV3 (34.9 %),followed by IGHV1 and IGHV4, found in 28.5 % and 26.5 %, respectively. Subgroup IGHV2was found out in 2 patients (4.1 %). The other subgroups, IGHV2, IGHV5 and IGHV6, weredetermined in one patient each. At the specific gene level, the most frequently used geneIGHV was IGHV1-69, found out in 18.4 %. Genes V4-34 and V4-39 were determined in8.2 %, followed by genes V3-07, V3-11 and V3-23 identified in 6,2 % each. The others wereidentified at the lower frequency.In patients with unmutated IGHV genes, the most frequently observed gene was V1-69(32.5 %). The most frequently used gene in mutated rearrangements was IGHV4-34(14.8 %). The gene V3-21 was not found out in our cohort of patients and results bearsimilarity to the Mediterranean-based study (3 %). CONCLUSIONS In the study performed, we have found out that the portion of unmutated IGHV genes ofthe clonal B lymphocytes was in agreement with the available data from the literature andwas approximately 50 %. The gene usage and somatic mutations frequency were similarto those published in the literature. In the future, the population based investigations ofIGHV gene use in large series of CLL patients may reveal the true frequencies of differentIGHV genes in Slovenian region. Furthermore, the geographic comparison and more definitive conclusions could be made based on it