MUTATIONAL STATUS of REARRANGED IMMUNOGLOBULIN HEAVY CHAIN VARIABLE Genes in a COHORT of SLOVENIAN PATIENTS with CHRONIC LYMPHOCYTIC LEUKAEMIA.

The aims of the study were to determine the mutational status and IGHV gene usage in our cohort of patients with B-CLL and compare the results to those published in the literature.

57 B-CLL patients (22 female, 35 male), median age 65 (range from 37 to 88 years) in various Binet stages (47 Binet A, 6 Binet B, 4 Binet C) were included in the study. All the patients were untreated at the time of blood collection. Leukaemia cells were isolated from venous blood samples of patients by 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 was determined by comparing the sequence of the IGHV region of the patient sample to the most homologous germ line V sequence. Sequence that was homologous more than 98 % with their corresponding germ line sequence was considered unmutated.

Unmutated and mutated IGHV mutational status in our cohort of patients with B-CLL was found in 42 % (N=24) and 58 % (N=33), respectively.

At the IGH subgroup level, the most frequently used subgroup was IGHV3 (38,55 %), followed by IGHV1 and IGHV4, found in 28,10 % and 22,85 %, respectively. Subgroups IGHV2 and IGHV5 were found out in 2 patients each (3,5 %). The other subgroups, IGHV6 and IGHV2, were determined in one patient each. At the specific gene level, the most frequently used gene IGHV was IGHV1-69, found out in 15,85 %. Genes V4-34, V4-39 in V3-23 were determined in 7,05 %, followed by genes V3-07, V3-11, V3-15, V3-30 and V3-48 identified in 5,25 % each. The others were identified at the lower frequency.

In patients with unmutated IGHV genes, the most frequently observed gene was V1-69 (33,3 %). The most frequently used gene in mutated rearrangements was IGHV4-34 (12,13 %). The gene V3-21 was not found out in our cohort of patients.

In the study performed, we have found out that the portion of unmutated IGHV genes of the clonal B lymphocytes, the gene usage and somatic mutations frequency were similar to those published in the literature. Interestingly, the gene V3-21 was not found out in our cohort of patients, the results that is similar to the Mediterranean-based study. In the future, the geographic comparison and more definitive conclusions could be made on the population based investigations of IGHV gene use in large series of CLL patients in Slovenian region.

No relevant conflicts of interest to declare.