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Post-Transformation IGHV-IGHD-IGHJ Mutations in Chronic Lymphocytic Leukemia B Cells: Implications for Mutational Mechanisms and Impact on Clinical Course.

ABSTRACT: Analyses of IGHV gene mutations in chronic lymphocytic leukemia (CLL) have had a major impact on the prognostication and treatment of this disease. A hallmark of IGHV-mutation status is that it very rarely changes clonally over time. Nevertheless, targeted and deep DNA sequencing of IGHV-IGHD-IGHJ regions has revealed intraclonal heterogeneity. We used a DNA sequencing approach that achieves considerable depth and minimizes artefacts and amplification bias to identify IGHV-IGHD-IGHJ subclones in patients with prolonged temporal follow-up. Our findings extend previous studies, revealing intraclonal IGHV-IGHD-IGHJ diversification in almost all CLL clones. Also, they indicate that some subclones with additional IGHV-IGHD-IGHJ mutations can become a large fraction of the leukemic burden, reaching numerical criteria for monoclonal B-cell lymphocytosis. Notably, the occurrence and complexity of post-transformation IGHV-IGHD-IGHJ heterogeneity and the expansion of diversified subclones are similar among U-CLL and M-CLL patients. The molecular characteristics of the mutations present in the parental, clinically dominant CLL clone (CDC) differed from those developing post-transformation (post-CDC). Post-CDC mutations exhibit significantly lower fractions of mutations bearing signatures of activation induced deaminase (AID) and of error-prone repair by Polη, and most of the mutations were not ascribable to those enzymes. Additionally, post-CDC mutations displayed a lower percentage of nucleotide transitions compared with transversions that was also not like the action of AID. Finally, the post-CDC mutations led to significantly lower ratios of replacement to silent mutations in VH CDRs and higher ratios in VH FRs, distributions different from mutations found in normal B-cell subsets undergoing an AID-mediated process. Based on these findings, we propose that post-transformation mutations in CLL cells either reflect a dysfunctional standard somatic mutational process or point to the action of another mutational process not previously associated with IG V gene loci. If the former option is the case, post-CDC mutations could lead to a lesser dependence on antigen dependent BCR signaling and potentially a greater influence of off-target, non-IG genomic mutations. Alternatively, the latter activity could add a new stimulatory survival/growth advantage mediated by the BCR through structurally altered FRs, such as that occurring by superantigen binding and stimulation.

SUBMITTER: Bagnara D

PROVIDER: S-EPMC8186829 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundIGHV mutation status is a crucial prognostic biomarker for CLL. In the present study, we investigated the transcriptomic signatures associating with IGHV mutation status and CLL prognosis.MethodsThe co-expression modules and hub genes correlating with IGHV status, were identified using the GSE28654, by 'WGCNA' package and R software (version 4.0.2). The over-representation analysis was performed to reveal enriched cell pathways for genes of correlating modules. Then 9 external cohorts were used to validate the correlation of hub genes expression with IGHV status or clinical features (treatment response, transformation to Richter syndrome, etc.). Moreover, to elucidate the significance of hub genes on disease course and prognosis of CLL patients, the Kaplan-Meier analysis for the OS and TTFT of were performed between subgroups dichotomized by the median expression value of individual hub genes.Results2 co-expression modules and 9 hub genes ((FCRL1/FCRL2/HELQ/EGR3LPL/LDOC1/ZNF667/SOWAHC/SEPTIN10) correlating with IGHV status were identified by WGCNA, and validated by external datasets. The modules were found to be enriched in NF-kappaB, HIF-1 and other important pathways, involving cell proliferation and apoptosis. The expression of hub genes was revealed to be significantly different, not only between CLL and normal B cell, but also between various types of lymphoid neoplasms. HELQ expression was found to be related with response of immunochemotherapy treatment significantly (p?=?0.0413), while HELQ and ZNF667 were expressed differently between stable CLL and Richter syndrome patients (p?<?0.0001 and p?=?0.0278, respectively). By survival analysis of subgroups, EGR3 expression was indicated to be significantly associated with TTFT by 2 independent cohorts (GSE39671, p?=?0.0311; GSE22762, p?=?0.0135). While the expression of HELQ and EGR3 was found to be associated with OS (p?=?0.0291 and 0.0114 respectively).The Kras, Hedgehog and IL6-JAK-STAT3 pathways were found to be associating with the expression of hub genes, resulting from GSEA.ConclusionsThe expression of HELQ and EGR3 were correlated with IGHV mutation status in CLL patients. Additionally, the expression of HELQ/EGR3 were prognostic markers for CLL associating with targetable cell signaling pathways.

Project description:BackgroundPrognostic index for survival estimation by clinical-demographic variables were previously proposed in chronic lymphocytic leukemia (CLL) patients. Our objective was to test in a large retrospective cohort of CLL patients the prognostic power of biological and clinical-demographic variable in a comprehensive multivariate model. A new prognostic index was proposed.MethodsOverall survival and time to treatment in 620 untreated CLL patients were analyzed retrospectively to evaluate the multivariate independence and predictive power of mutational status of immunoglobulin heavy chain variable gene segments (IGHV), high-risk chromosomal aberration such as 17p or 11q deletions, CD38 and ZAP-70 expression, age, gender, Binet stage, ?2-microglobulin levels, absolute lymphocyte count and number of lymph node regions.ResultsIGHV mutational status and 17p deletion were the sole biological variables with independent prognostic relevance in a multivariate model for overall survival, which included easily measurable clinical parameters (Binet staging, ?2-microglobulin levels) and demographics (age and gender). Analysis of time to treatment in Binet A patients below 70 years of age showed that IGHV was the most important predictor. A novel 6-variable clinical-biological prognostic index was developed and internally validated, which assigned 3 points for Binet C stage, 2 points/each for Binet B stage and for age > 65 years, 1 point/each for male gender, high ?2-microglobulin levels, presence of an unmutated IGHV gene status or 17p deletion. Patients were classified at low-risk (score = 0-1; 21%), intermediate-risk (score 2-5; 63% of cases), high-risk (score 6-9; 16% of cases). Projected 5-year overall survival was 98%, 90% and 58% in low-, intermediate- and high-risk groups, respectively. A nomogram for individual patient survival estimation was also proposed.ConclusionsData indicate that IGHV mutational status and 17p deletion may be integrated with clinical-demographic variables in new prognostic tools to estimate overall survival.

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Post-Transformation IGHV-IGHD-IGHJ Mutations in Chronic Lymphocytic Leukemia B Cells: Implications for Mutational Mechanisms and Impact on Clinical Course.

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