ViCloD, an interactive web tool for visualizing B cell repertoires and analyzing intraclonal diversities: application to human B-cell tumors.

High throughput sequencing of adaptive immune receptor repertoire (AIRR-seq) has provided numerous human immunoglobulin (IG) sequences allowing specific B cell receptor (BCR) studies such as the antigen-driven evolution of antibodies (soluble forms of the membrane-bound IG part of the BCR). AIRR-seq data allows researchers to examine intraclonal differences caused primarily by somatic hypermutations in IG genes and affinity maturation. Exploring this essential adaptive immunity process could help elucidate the generation of antibodies with high affinity or broadly neutralizing activities. Retracing their evolutionary history could also clarify how vaccines or pathogen exposition drive the humoral immune response, and unravel the clonal architecture of B cell tumors. Computational methods are necessary for large-scale analysis of AIRR-seq properties. However, there is no efficient and interactive tool for analyzing intraclonal diversity, permitting users to explore adaptive immune receptor repertoires in biological and clinical applications. Here we present ViCloD, a web server for large-scale visual analysis of repertoire clonality and intraclonal diversity. ViCloD uses preprocessed data in the format defined by the Adaptive Immune Receptor Repertoire (AIRR) Community. Then, it performs clonal grouping and evolutionary analyses, producing a collection of useful plots for clonal lineage inspection. The web server presents diverse functionalities, including repertoire navigation, clonal abundance analysis, and intraclonal evolutionary tree reconstruction. Users can download the analyzed data in different table formats and save the generated plots as images. ViCloD is a simple, versatile, and user-friendly tool that can help researchers and clinicians to analyze B cell intraclonal diversity. Moreover, its pipeline is optimized to process hundreds of thousands of sequences within a few minutes, allowing an efficient investigation of large and complex repertoires.

A multi-objective based clustering for inferring BCR clonal lineages from high-throughput B cell repertoire data.

The adaptive B cell response is driven by the expansion, somatic hypermutation, and selection of B cell clonal lineages. A high number of clonal lineages in a B cell population indicates a highly diverse repertoire, while clonal size distribution and sequence diversity reflect antigen selective pressure. Identifying clonal lineages is fundamental to many repertoire studies, including repertoire comparisons, clonal tracking, and statistical analysis. Several methods have been developed to group sequences from high-throughput B cell repertoire data. Current methods use clustering algorithms to group clonally-related sequences based on their similarities or distances. Such approaches create groups by optimizing a single objective that typically minimizes intra-clonal distances. However, optimizing several objective functions can be advantageous and boost the algorithm convergence rate. Here we propose MobiLLe, a new method based on multi-objective clustering. Our approach requires V(D)J annotations to obtain the initial groups and iteratively applies two objective functions that optimize cohesion and separation within clonal lineages simultaneously. We show that our method greatly improves clonal lineage grouping on simulated benchmarks with varied mutation rates compared to other tools. When applied to experimental repertoires generated from high-throughput sequencing, its clustering results are comparable to the most performing tools and can reproduce the results of previous publications. The method based on multi-objective clustering can accurately identify clonally-related antibody sequences and presents the lowest running time among state-of-art tools. All these features constitute an attractive option for repertoire analysis, particularly in the clinical context. MobiLLe can potentially help unravel the mechanisms involved in developing and evolving B cell malignancies.

Evidence of somatic hypermutation in the antigen binding sites of patients with CLL harboring IGHV genes with 100% germline identity.

Classification of patients with chronic lymphocytic leukemia (CLL) based on the somatic hypermutation (SHM) status of the clonotypic immunoglobulin heavy variable (IGHV) gene has established predictive and prognostic relevance. The SHM status is assessed based on the number of mutations within the IG heavy variable domain sequence, albeit only over the rearranged IGHV gene excluding the variable heavy complementarity determining region 3 (VH CDR3). This may lead to an underestimation of the actual impact of SHM, in fact overlooking the most critical region for antigen-antibody interactions, i.e. the VH CDR3. Here we investigated whether SHM may be present within the VH CDR3 of cases bearing 'truly unmutated' IGHV genes (i.e. 100% germline identity across VH FR1-VH FR3) employing Next Generation Sequencing. We studied 16 patients bearing a 'truly unmutated' CLL clone assigned to stereotyped subsets #1 (n=12) and #6 (n=4). We report the existence of SHM within the germline-encoded 3'IGHV, IGHD, 5'IGHJ regions of the VH CDR3 in both the main IGHV-IGHD-IGHJ gene clonotype and its variants. Recurrent somatic mutations were identified between different patients of the same subset, supporting the notion that they represent true mutational events rather than technical artefacts; moreover, they were located adjacent to/within AID hotspots, pointing to SHM as the underlying mechanism. In conclusion, we provide immunogenetic evidence for intra-VH CDR3 variations, attributed to SHM, in CLL patients carrying 'truly unmutated' IGHV genes. Although the clinical implications of this observation remain to be defined, our findings offer a new perspective into the immunobiology of CLL, alluding to the operation of VH CDR3-restricted SHM in U-CLL.

Immunoglobulin gene analysis in chronic lymphocytic leukemia in the era of next generation sequencing.

Twenty years after landmark publications, there is a consensus that the somatic hypermutation (SHM) status of the clonotypic immunoglobulin heavy variable (IGHV) gene is an important cornerstone for accurate risk stratification and therapeutic decision-making in patients with chronic lymphocytic leukemia (CLL). The IGHV SHM status has traditionally been determined by conventional Sanger sequencing. However, NGS has heralded a new era in medical diagnostics and immunogenetic analysis is following this trend. There is indeed a growing demand for shifting practice and using NGS for IGHV gene SHM assessment, although it is debatable whether it is always justifiable, at least taking into account financial considerations for laboratories with limited resources. Nevertheless, as this analysis impacts on treatment decisions, standardization of both technical aspects, and data interpretation becomes essential. Also, the need for establishing new recommendations and providing dedicated education and training on NGS-based immunogenetics is greater than ever before. Here we address potential and challenges of NGS-based immunogenetics in CLL. We are convinced that this perspective helps the hematological community to better understand the pros and cons of this new technological development for CLL patient management.

The helicases DinG, Rep and UvrD cooperate to promote replication across transcription units in vivo.

How living cells deal with head-on collisions of the replication and transcription complexes has been debated for a long time. Even in the widely studied model bacteria Escherichia coli, the enzymes that take care of such collisions are still unknown. We report here that in vivo, the DinG, Rep and UvrD helicases are essential for efficient replication across highly transcribed regions. We show that when rRNA operons (rrn) are inverted to face replication, the viability of the dinG mutant is affected and over-expression of RNase H rescues the growth defect, showing that DinG acts in vivo to remove R-loops. In addition, DinG, Rep and UvrD exert a common function, which requires the presence of two of these three helicases. After replication blockage by an inverted rrn, Rep in conjunction with DinG or UvrD removes RNA polymerase, a task that is fulfilled in its absence by the SOS-induced DinG and UvrD helicases. Finally, Rep and UvrD also act at inverted sequences other than rrn, and promote replication through highly transcribed regions in wild-type E. coli.