Contributions
Abstract: PB1852
Type: Publication Only
Background
The IGHV (immunoglobulin heavy-chain variable region) gene mutational status is considered as an important prognostic factor in chronic lymphocytic leukemia (CLL), readily identifiable at diagnosis and independent of clinical stage or other prognostic factors. In addition, about 30% of CLL patients carry quasi-identical B-cell receptor (BCR) immunoglobulins that can be assigned to distinct stereotyped subsets. At present, information about IGHV repertoire and stereotyped BCRs (BCRSs) in CLL patients from South America is scarce.
Aims
In the current study, we have evaluated IGHV mutational status, gene usage and BCRSs in CLL patients from a multicenter study developed in the context of the Latin American Group of CLL.
Methods
Our cohort included 707 unselected CLL patients from Argentina (253), Brazil (276), Uruguay (99) and Venezuela (79) (413 males; mean age: 66.6 years, range: 27-105 years; Rai clinical stages: 0: 35.8%, I-II: 41.9%, III-IV: 22.3%). The study was approved by the local Ethics Committees of each Institution. All individuals provided their informed consent. PCR was performed on cDNA or gDNA using VH framework region 1 consensus family specific (VH1-VH6) or leader primers and antisense primers JH or Cµ. PCR products were analyzed on an automated DNA sequence analyzer. Sequence data were evaluated using IgBLAST and IMGT/V-Quest databases. IGHV sequences with ≥98% homology with respect to the germline counterpart were considered as unmutated. Stereotyped rearrangements and clusters were assigned by means of pair-wise alignment with known stereotyped sequences available from different public databases and using the new bioinformatics approach to identify major clusters.
Results
Our cohort showed over-representation of mutated cases, except for Brazilian patients. Concerning IGHV family usage, VH3>VH4>VH1 distribution was found in Argentina, while VH3>VH1>VH4 was present in the other countries. The most frequently used IGHV genes were IGHV1-69 (12.3%), IGHV3-23 (8.2%) and IGHV4-34 (9.5%). IGHV3-21 was present in 10% of Venezuelan patients but showed lower frequencies in Uruguayan (2%) and Brazilian (2.1%) cohorts and intermediate frequency in the Argentinean series (6.5%). BCRSs were present in 15.2% of total cases, 73.9% belonged to major clusters; three novel potential subsets were detected. As a whole, our cohort showed the following frequencies: cluster #1 (11; 1.53%), cluster #2 (9; 1.26%), cluster #4 (16; 2.23%) and cluster #8 (5; 0.70%). Argentinean series exhibited similar frequencies of clusters #1 (2.00%) and #2 (3.13%) than series previously reported. These clusters were under-represented or absent in the other studied countries, meanwhile cluster #4 was over-represented in South American cohort, particularly in Uruguay, followed by Argentina and Venezuela On the contrary, Venezuelan CLL patients showed very low percentages of major clusters (5.1%). A graphic showing cluster frequencies among different countries is shown in Figure 1. Interestingly, the analysis of the distribution between stereotyped and heterogeneous (not stereotyped) receptors showed that IGHV3-21 gene was always included in the heterogeneous group in Brazilian and Venezuelan cohorts.
Conclusion
Our results showed interesting differences compared to those from other geographical regions, highlighting the need for further research to understand the role of genetic background and environmental factors operating in CLL pathogenesis in the different geographical regions.
Session topic: 5. Chronic lymphocytic leukemia and related disorders – Biology & Translational Research
Keyword(s): B cell subsets, Chronic Lymphocytic Leukemia, Immunoglobulin gene, Somatic hypermutation
Abstract: PB1852
Type: Publication Only
Background
The IGHV (immunoglobulin heavy-chain variable region) gene mutational status is considered as an important prognostic factor in chronic lymphocytic leukemia (CLL), readily identifiable at diagnosis and independent of clinical stage or other prognostic factors. In addition, about 30% of CLL patients carry quasi-identical B-cell receptor (BCR) immunoglobulins that can be assigned to distinct stereotyped subsets. At present, information about IGHV repertoire and stereotyped BCRs (BCRSs) in CLL patients from South America is scarce.
Aims
In the current study, we have evaluated IGHV mutational status, gene usage and BCRSs in CLL patients from a multicenter study developed in the context of the Latin American Group of CLL.
Methods
Our cohort included 707 unselected CLL patients from Argentina (253), Brazil (276), Uruguay (99) and Venezuela (79) (413 males; mean age: 66.6 years, range: 27-105 years; Rai clinical stages: 0: 35.8%, I-II: 41.9%, III-IV: 22.3%). The study was approved by the local Ethics Committees of each Institution. All individuals provided their informed consent. PCR was performed on cDNA or gDNA using VH framework region 1 consensus family specific (VH1-VH6) or leader primers and antisense primers JH or Cµ. PCR products were analyzed on an automated DNA sequence analyzer. Sequence data were evaluated using IgBLAST and IMGT/V-Quest databases. IGHV sequences with ≥98% homology with respect to the germline counterpart were considered as unmutated. Stereotyped rearrangements and clusters were assigned by means of pair-wise alignment with known stereotyped sequences available from different public databases and using the new bioinformatics approach to identify major clusters.
Results
Our cohort showed over-representation of mutated cases, except for Brazilian patients. Concerning IGHV family usage, VH3>VH4>VH1 distribution was found in Argentina, while VH3>VH1>VH4 was present in the other countries. The most frequently used IGHV genes were IGHV1-69 (12.3%), IGHV3-23 (8.2%) and IGHV4-34 (9.5%). IGHV3-21 was present in 10% of Venezuelan patients but showed lower frequencies in Uruguayan (2%) and Brazilian (2.1%) cohorts and intermediate frequency in the Argentinean series (6.5%). BCRSs were present in 15.2% of total cases, 73.9% belonged to major clusters; three novel potential subsets were detected. As a whole, our cohort showed the following frequencies: cluster #1 (11; 1.53%), cluster #2 (9; 1.26%), cluster #4 (16; 2.23%) and cluster #8 (5; 0.70%). Argentinean series exhibited similar frequencies of clusters #1 (2.00%) and #2 (3.13%) than series previously reported. These clusters were under-represented or absent in the other studied countries, meanwhile cluster #4 was over-represented in South American cohort, particularly in Uruguay, followed by Argentina and Venezuela On the contrary, Venezuelan CLL patients showed very low percentages of major clusters (5.1%). A graphic showing cluster frequencies among different countries is shown in Figure 1. Interestingly, the analysis of the distribution between stereotyped and heterogeneous (not stereotyped) receptors showed that IGHV3-21 gene was always included in the heterogeneous group in Brazilian and Venezuelan cohorts.
Conclusion
Our results showed interesting differences compared to those from other geographical regions, highlighting the need for further research to understand the role of genetic background and environmental factors operating in CLL pathogenesis in the different geographical regions.
Session topic: 5. Chronic lymphocytic leukemia and related disorders – Biology & Translational Research
Keyword(s): B cell subsets, Chronic Lymphocytic Leukemia, Immunoglobulin gene, Somatic hypermutation