The Repertoire of Heavy Chain Immunoglobulin Genes in B-Cell Chronic Lymphocytic Leukemia in Russia and Belarus

Mutation status of the heavy chain variable region genes is known as an important factor in long-term prognosis in B-cell chronic lymphocytic leukemia (B-CLL). A more detailed study of the gene sequences of immunoglobulin heavy chain (IgVH) led to the discovery of stereotyped antigen receptors (SAR) - receptors that have the same set of VH-, D- and JH- genes used. SARs have been found almost in a quarter of all B-CLL cases. Since this study there have been no data available concerning VH-gene usage and SARs in Russian and Belarusian B-CLL patients.

DNA or cDNA was amplified in 6 separated reactions using primers specific for VH-families, and a consensus JH primer [Campbell et al. 1992] or primer sets recommended by the BIOMED-2 [van Dongen et al. 2003]. PCR products were sequenced using family-specific primers and Big Dye Terminator v3.1 kit (Applied Biosystems). Sequences were analyzed with IgBlast (http://www.ncbi.nlm.nih.gov/igblast). 98% homology cutoff was used to discriminate between mutated and unmutated cases.

Total of 547 patients with B-CLL where analyzed; 192 patients with mutated IgVH-genes (35%) and 355 patients with unmutated ones (65%). We have identified 65 stereotyped receptors (SARs) in 198 of 491 Russian patients (40%). Twenty one SARs (confirmed) appeared in more than 3 patients (110 out of 198, 55%), 44 SARs (potential) found in 2 patients (88 out of 198 cases, 45%). The vast majority of confirmed SARs were found in the subgroup of patients without mutations in IgVH genes (95%). Among the potential SARs 15 pairs were from patients with and without mutations (34%), seven pairs from patients with mutations (16%) and 22 pairs from patients without IgVH mutations (50%). The most common SARs were: VH1–69/D3-3/JH6 (24 patients, 5%); VH1–69/D3–16/JH3 (8 patients); VH1–69/D2-2/JH6 (8 patients); VH1–69/D3–10/JH6 (6 patients). Among 56 Belarusian patients we have identified only 4 SARs, one confirmed SAR (4 cases) and 3 potential ones. Confirmed (VH1–69/D3-3/JH6) and one potential (VH1–69/D3–16/JH3) were also found in Russia while other two potential (VH1–69/D2–15/JH6 and VH2–5/D2-2/JH6) were not observed in Russia.

In Russia and Belarus, VH1–69 gene is found in 20% of all cases of B-CLL, and almost always (95%) in unmutated cases. This finding well correlates to the data obtained by [Kryachok et al. 2012] concerning high VH1–69 usage in Ukrainian patients. In other European countries, this gene is less common: about 14% of cases in Sweden, France and Spain, 11% in the UK and about 6–7% in Greece and Italy [Ghia et al. 2005; Tobin et al. 2004; Duke et al. 2003]. In all these countries, this gene is also prevalent in patients with unmutated VH-genes. Nordic countries are characterized by very frequent use of gene VH3–21 - 9%, while in Russia and the countries of central and southern Europe, it occurs at least 3 times less (about 3%), and was not found in Belarusian samples. This gene is also associated with poor prognosis of B-CLL, regardless of mutation status of IgVH genes. Interestingly, in Asia (China, Japan, Iraq) VH1–69 and VH3–21 genes are almost not observed [Nakamura et al. 1999; Farsangi et al. 2007; Lijuan Chen et al. 2008]. Narrowing of the repertoire of IgVH genes - specific feature of B-CLL indicatites that influence of antigen (at least in some cases) occurs during the development of the disease. Also, factors of genetic background as well as geographical environment could be important. It is possible that future treatment decisions will be based not only on the IgVH mutation status, but also on the characteristics of certain antigen receptor.

No relevant conflicts of interest to declare.