Expression of immunoglobulin heavy chain variable gene (VH) in B-chronic lymphocytic leukemia (B-CLL) and B-prolymphocytic leukemia (B-PLL) cell lines. "Restricted" usage of VH3 family

VDJSeq-Solver: in silico V(D)J recombination detection tool

In this paper we present VDJSeq-Solver, a methodology and tool to identify clonal lymphocyte populations from paired-end RNA Sequencing reads derived from the sequencing of mRNA neoplastic cells. The tool detects the main clone that characterises the tissue of interest by recognizing the most abundant V(D)J rearrangement among the existing ones in the sample under study. The exact sequence of the clone identified is capable of accounting for the modifications introduced by the enzymatic processes. The proposed tool overcomes limitations of currently available lymphocyte rearrangements recognition methods, working on a single sequence at a time, that are not applicable to high-throughput sequencing data. In this work, VDJSeq-Solver has been applied to correctly detect the main clone and identify its sequence on five Mantle Cell Lymphoma samples; then the tool has been tested on twelve Diffuse Large B-Cell Lymphoma samples. In order to comply with the privacy, ethics and intellectual property policies of the University Hospital and the University of Verona, data is available upon request to supporto.utenti@ateneo.univr.it after signing a mandatory Materials Transfer Agreement. VDJSeq-Solver JAVA/Perl/Bash software implementation is free and available at http://eda.polito.it/VDJSeq-Solver/.

Microarray Gene Expression Profiling of B-Cell Chronic Lymphocytic Leukemia Subgroups Defined by Genomic Aberrations and VH Mutation Status

Purpose

Genomic aberrations and mutational status of the immunoglobulin variable heavy chain (VH) gene have been shown to be among the most important predictors for outcome in patients with B-cell chronic lymphocytic leukemia (B-CLL). In this study, we report on differential gene expression patterns that are characteristic for genetically defined B-CLL subtypes.

Materials and Methods

One hundred genetically well-characterized B-CLL samples, together with 11 healthy control samples, were analyzed using oligonucleotide arrays, which test for the expression of some 12,000 human genes.

Results

Aiming at microarray-based subclassification, class predictors were constructed using sets of differentially expressed genes, which yielded in zero or low misclassification rates. Furthermore, a significant number of the differentially expressed genes clustered in chromosomal regions affected by the respective genomic losses/gains. Deletions affecting chromosome bands 11q22-q23 and 17p13 led to a reduced expression of the corresponding genes, such as ATM and p53, while trisomy 12 resulted in the upregulation of genes mapping to chromosome arm 12q. Using an unsupervised analysis algorithm, expression profiling allowed partitioning into predominantly VH-mutated versus unmutated patient groups; however, association of the expression profile with the VH mutational status could only be detected in male patients.

Conclusion

The finding that the most significantly differentially expressed genes are located in the corresponding aberrant chromosomal regions indicates that a gene dosage effect may exert a pathogenic role in B-CLL. The significant difference in the partitioning of male and female B-CLL samples suggests that the genomic signature for the VH mutational status might be sex-related.

The natural history of a lymphoproliferative disorder in aged NZB mice

The molecular lesions of human familial and common B-CLL remain unknown. As an approach to this problem, aged NZB mice with a B cell lymphoproliferative disorder were chosen as a murine model. Three groups of NZB mice (2 months, 6 months and > 18 months) for a total of nineteen were studied. A complete autopsy including a CBC was performed on each mouse. Spleen cells were immunophenotyped and cell cycle analysis was performed. Spleen weight, peritoneal cell counts and absolute lymphocytes counts were all elevated in the oldest group. All mice showed evidence of extramedulary hematopoiesis and the older group showed lymphocytic infiltrates in the lacrymal glands, kidneys, liver and lungs. Two of the seven aged mice had a malignant lymphoma. One was a marginal zone lymphoma and the other a lymphocytic lymphoma. Splenic immunophenotyping showed a loss of T cells with an increase in B cells as the mice age. Cell cycle analysis revealed hyperdiploidy in all of the aged mice with a decrease in the percentage G0G1 cells. This disease appears to involve an absolute lymphocytosis of the peritoneum and the peripheral blood compartment. This is associated with splenic aneuploidy. The infiltration of the spleen by malignant cells of varying morphology is a late event. The aged NZB mouse continues to be a model for human B-CLL.

Optimal primer selection for clonality assessment by polymerase chain reaction analysis: I. Low grade B-cell lymphoproliferative disorders of nonfollicular center cell type

Recent polymerase chain reaction (PCR)-based studies focused on the detection of immunoglobulin heavy chain gene (IgH) rearrangements have suggested that clonal populations may be amplified more easily from certain categories of B-cell neoplasia than others and that primer makeup can be a critical factor in successful amplification. However, these particular reports contained relatively few low grade B-cell lymphoproliferative disorders of nonfollicular center cell type (LG-BLPD) and used only a limited panel of available primer sets for PCR amplification of monoclonal B-cell populations. To address this issue more extensively we evaluated 156 samples of LG-BLPD by the PCR to determine optimal primer selection in this setting. All cases were classified according to standard morphological and immunophenotypic criteria, with monoclonality documented by Ig light chain restriction analysis. The LG-BLPD included 33 cases of chronic lymphocytic leukemia (CLL), 57 cases of small lymphocytic lymphoma (SLL), 10 cases of atypical CLL, 32 cases of mantle cell lymphoma (MCL), 17 plasma cell neoplasms (PCNs), and seven cases of hairy cell leukemia (HCL). All primer sets included a 3' IgH joining region consensus primer, whereas the 5' IgH variable region (VH) primer was different in each set. The first-line panel included the following: Set 1, VH-framework III consensus primer, and Set 2, seven separate VH-framework I family-specific primers. A reserve panel of alternate VH consensus primers directed at framework II or III regions was used only when Set 1 showed no evidence of B-cell monoclonality.(ABSTRACT TRUNCATED AT 250 WORDS)

The pathogenesis of chronic lymphocytic leukemia: analysis of the antibody repertoire

CD5+ B cells predominate early in ontogeny and have been associated with autoantibody production. In chronic lymphocytic leukemia (CLL), B lymphocytes express CD5 and frequently produce autoantibodies using developmentally regulated variable (V)-gene segments. Does the self-reactivity observed in CLL reflect transformation of a 'fetal' lineage of cells, or could overexpansion of these B cells occur as a consequence of antigen stimulation? Harry Schroeder and Guillermo Dighiero have reviewed the literature describing antibody sequences in CLL and have compared them with the 'fetal' repertoire. This analysis indicates that CLL cells use a repertoire characteristic of mature cells, and suggests that antigen may play a role in the pathogenesis of this disease.

IgG+, CD5+ human chronic lymphocytic leukemia B cells. Production of IgG antibodies that exhibit diminished autoreactivity and IgG subclass skewing

Several questions exist regarding CD5+ B cells. These include the ability of these cells, as compared to CD5- B cells, to undergo an Ig isotype class switch, the subclasses utilized, and the effects that switching may have on antigen binding. To address these issues, ten patients with chronic lymphocytic leukemia (CLL) whose CD5+ leukemic B cell clones produced IgG were studied. Monoclonal IgG was collected from PMA-stimulated CLL cells and from heterohybridomas constructed with these cells, and then analyzed for IgG subclass utilization, autoreactivity, and DNA idiotype expression. The monoclonal B cells from 80% of the CLL patients produced IgG1 and those from 20% produced IgG3. None produced IgG2. In contrast to the known autoreactivity of IgM-producing CD5+ CLL cells (> 50% autoreactive), none of these IgG antibodies reacted significantly with the autoantigens tested. However, three did react significantly with autoantigen after artificially increasing antibody valency by crosslinking. Whereas five of the IgG molecules expressed a cross reactive idiotypic (CRI) marker characteristic of non-mutated kappa anti-DNA antibodies, three expressed a CRI displayed primarily on mutated IgG anti-DNA antibodies. Thus, some CD5+ human B cells can undergo an isotype class switch that for these CLL cells is biased against IgG2 and in favor of the IgG1 and IgG3. In their native state the IgG molecules secreted by these isotype-switched CD5+ cells have diminished autoreactivity, as compared to IgM-producing CLL cells. Since some of the IgG antibodies could be made auto- and poly-reactive by increasing antigen-binding valency, while others expressed idiotypic markers of mutated antibodies, certain of these CD5+ B cells probably utilize non-mutated Ig V genes coding for polyreactive antibodies, whereas others may use genes that have undergone somatic mutation and that code for more restricted specificities. Therefore, both valency and VH gene mutation may account for the diminished autoreactivity of these CD5+ B cell-derived IgG antibodies.

Normal B lymphocyte differentiation

Normal differentiation of B lineage cells has been the subject of intensive investigation over the past three decades. Current models of this process in humans are melded from the results of studies in a variety of organisms, including humans, mice and birds. Several recent developments have significantly reshaped and refined these models. The technique of homologous recombination in embryonic stem cells has allowed the production of mice with selectively disrupted genes that are important for B cell development in mice. At the same time, functional studies of human B cell differentiation, together with analysis of naturally occurring mutations that disrupt this process, have progressed rapidly. This has provided insight into the pathogenesis of lymphoproliferative and immunodeficiency diseases as well as a clearer view of normal developmental events. In this chapter we have reviewed human B cell differentiation with particular emphasis on newly emerging concepts. We also discussed CD5, a pan-T cell antigen that is expressed in low levels on a subpopulation of B cells implicated in the pathogenesis of chronic lymphocytic leukaemia (CLL). Finally, we discussed the issue of restricted variable region gene usage during B cell ontogeny and in CLL.