Ongoing somatic hypermutation of the rearranged VH but not of the V-lambda gene in EBV-transformed rheumatoid factor-producing lymphoblastoid cell line

Epstein-Barr virus as a potentiator of autoimmune diseases

The Epstein-Barr virus (EBV) is epidemiologically associated with development of autoimmune diseases, including systemic lupus erythematosus, Sjögren syndrome, rheumatoid arthritis and multiple sclerosis. Although there is well-established evidence for this association, the underlying mechanistic basis remains incompletely defined. In this Review, we discuss the role of EBV infection as a potentiator of autoimmune rheumatic diseases. We review the EBV life cycle, viral transcription programmes, serological profiles and lytic reactivation. We discuss the epidemiological and mechanistic associations of EBV with systemic lupus erythematosus, Sjögren syndrome, rheumatoid arthritis and multiple sclerosis. We describe the potential mechanisms by which EBV might promote autoimmunity, including EBV nuclear antigen 1-mediated molecular mimicry of human autoantigens; EBV-mediated B cell reprogramming, including EBV nuclear antigen 2-mediated dysregulation of autoimmune susceptibility genes; EBV and host genetic factors, including the potential for autoimmunity-promoting strains of EBV; EBV immune evasion and insufficient host responses to control infection; lytic reactivation; and other mechanisms. Finally, we discuss the therapeutic implications and potential therapeutic approaches to targeting EBV for the treatment of autoimmune disease.

Gastric DLBCL clonal evolution as function of patient age

Diffuse large B cell lymphoma (DLBCL) is the most common type of NHL, accounting for about 40% of NHL cases, and is one of the most aggressive lymphomas. DLBCL is widespread in individuals aged more than 50 years old, with a maximum incidence in the seventh decade, but it may also occur in younger patients. DLBCL may occur in any immune system tissue, including those around the gastrointestinal tract, and even in the stomach, though gastric DLBCL has yet to be sufficiently investigated. This study aimed to understand changes in gastric Diffuse Large B cell lymphoma (gastric DLBCL) development with age. Immunoglobulin (Ig) heavy chain variable region genes were amplified from sections of nine preserved biopsies, from patients whose age varied between 25 and 89 years, sequenced and analyzed. We show first that identification of the malignant clone based on the biopsies is much less certain than was previously assumed; and second that, contrary to expectations, the repertoire of gastric B cell clones is more diverse among the elderly DLBCL patients than among the young.

Effect of Interleukins on Antibody Production by Epstein-Barr Virus Transformed B Cells

During the past few decades, monoclonal antibodies (MAbs) have become an increasingly used tool in diagnostics, therapeutics, and biomedical research. Several methods have been employed to produce MAbs, one of which is the immortalization of B cells by Epstein-Barr virus (EBV). Despite its simplicity, this procedure was never routinely adopted due to its poor efficiency and short-lived antibody (Ab) production. Various adjustments to the basic procedure were introduced, including the addition of certain cytokines and CpG oligodeoxynucleotides, which were shown to improve EBV infectivity and cloning efficiency. The objective of this study was to manipulate culture conditions of the EBV-transformed human lymphocytes, lymphoblastoid cell lines (LCLs), by the timely addition of stimuli including CpG and various interleukins. Such manipulations are aimed at improving LCL proliferative activity and enhancing the cell lines' immortalization potential as well as their Ab production. To accomplish this, IgG(+) B cells were isolated from peripheral blood of a hepatitis B vaccinated, anti-HB Ab-positive volunteer. These cells were infected with EBV and incubated in the presence of CpG DNA 2006 motifs, recombinant human interleukin-2 (rhIL-2), rhIL-4, rhIL-6, and rhIL-21, individually and in combinations. Cells were then restimulated for 2 weeks with the same ILs. The effect of these ILs on anti-HB Ab production and the proliferation of the EBV-transformed lymphocytes were investigated. The current study demonstrates that treatment of LCL cultures with rhIL-2, rh-IL4, rhIL-6, and rhIL-21, individually and in combination, increased to varying degrees the proliferative activity and Ab production of these cells. The addition of IL-4 alone was able to sustain increase in anti-HB Ab despite IL-4 withdrawal. This study suggests that with further optimization ILs can have an enhancing effect on LCL immortalization potential and Ab production capacity.

Genomic variation in the porcine immunoglobulin lambda variable region

Production of a vast antibody repertoire is essential for the protection against pathogens. Variable region germline complexity contributes to repertoire diversity and is a standard feature of mammalian immunoglobulin loci, but functional V region genes are limited in swine. For example, the porcine lambda light chain locus is composed of 23 variable (V) genes and 4 joining (J) genes, but only 10 or 11 V and 2 J genes are functional. Allelic variation in V and J may increase overall diversity within a population, yet lead to repertoire holes in individuals lacking key alleles. Previous studies focused on heavy chain genetic variation, thus light chain allelic diversity is not known. We characterized allelic variation of the porcine immunoglobulin lambda variable (IGLV) region genes. All intact IGLV genes in 81 pigs were amplified, sequenced, and analyzed to determine their allelic variation and functionality. We observed mutational variation across the entire length of the IGLV genes, in both framework and complementarity determining regions (CDRs). Three recombination hotspot motifs were also identified suggesting that non-allelic homologous recombination is an evolutionarily alternative mechanism for generating germline antibody diversity. Functional alleles were greatest in the most highly expressed families, IGLV3 and IGLV8. At the population level, allelic variation appears to help maintain the potential for broad antibody repertoire diversity in spite of reduced gene segment choices and limited germline sequence modification. The trade-off may be a reduction in repertoire diversity within individuals that could result in an increased variation in immunity to infectious disease and response to vaccination.

Production of human monoclonal antibodies by the epstein-barr virus method

Epstein-Barr virus (EBV) is a herpes virus which in vitro efficiently immortalizes nearly all human B lymphocytes. The lymphoblastoid diploid cell lines (LCL's) thus generated preserve the characteristics of the cells initially infected by the virus: the cells produce and secrete immunoglobulins and also express these molecules on their surface. A selection of specific antibody-producing cells (i.e., antigen-committed cells) before EBV-infection or when LCL's have already been established, enables isolation of monoclonal cell lines that secrete specific antibodies. If selection of antigen-committed cells is not feasible, secretion of specific antibodies by cloned LCL's in limiting dilution cultures enables isolation of the desired cell lines. The method allows the production of human IgM, IgG, IgA, and IgE monoclonal antibodies from any individual. Monoclonal antibodies produced by the EBV method resemble the antibody repertoire of the donor of the lymphocytes. Human monoclonal antibodies are promising reagents for passive immunization.

Antibody repertoire development in fetal and neonatal piglets. XII. Three IGLV genes comprise 70% of the pre-immune repertoire and there is little junctional diversity

We characterized 239 lambda rearrangements from fetal and germfree (GF) piglets to: (1) determine if transcripts recovered from the earliest sites of B cell lymphogenesis were unique (2) determine what proportion of the genome is used to form the pre-immune repertoire (3) estimate the degree of somatic hypermutation and junctional diversity during ontogeny and (4) test whether piglets maintained germfree in isolators (GF piglets) have a more diversified repertoire than fetal piglets. We show that all expressed lambda genes belong to the IGLV3 and IGLV8 families and only IGLJ2 and IGLJ3 were expressed and used equally throughout fetal and neonatal life. Only genes of the IGLV8 family were used in yolk sac and fetal liver and in these tissues, IGLV8-10 comprised >50%. However, the IGLV8 genes recovered at these early sites of B cell lymphogenesis were recovered at all stages of development. Thus, no unique lambda rearrangement was recovered at the first sites of B cell development. The frequency of somatic hypermutation (SHM) in fetal piglets was ~5.9 per Kb equivalent, mutation were concentrated in CDR regions and did not increase in GF piglets. The average CDR3 length was 30 nt ± 2.7 and did not change in GF piglets. Similar to the heavy chain pre-immune repertoire in this species, three IGLV genes account for ~70% of the repertoire. Unlike the heavy chain repertoire, junctional diversity was very limited.

Epstein-Barr virus infection of naïve B cells in vitro frequently selects clones with mutated immunoglobulin genotypes: implications for virus biology

Epstein-Barr virus (EBV), a lymphomagenic human herpesvirus, colonises the host through polyclonal B cell-growth-transforming infections yet establishes persistence only in IgD⁺ CD27⁺ non-switched memory (NSM) and IgD⁻ CD27⁺ switched memory (SM) B cells, not in IgD⁺ CD27⁻ naïve (N) cells. How this selectivity is achieved remains poorly understood. Here we show that purified N, NSM and SM cell preparations are equally transformable in vitro to lymphoblastoid cells lines (LCLs) that, despite upregulating the activation-induced cytidine deaminase (AID) enzyme necessary for Ig isotype switching and Ig gene hypermutation, still retain the surface Ig phenotype of their parental cells. However, both N- and NSM-derived lines remain inducible to Ig isotype switching by surrogate T cell signals. More importantly, IgH gene analysis of N cell infections revealed two features quite distinct from parallel mitogen-activated cultures. Firstly, following 4 weeks of EBV-driven polyclonal proliferation, individual clonotypes then become increasingly dominant; secondly, in around 35% cases these clonotypes carry Ig gene mutations which both resemble AID products and, when analysed in prospectively-harvested cultures, appear to have arisen by sequence diversification in vitro. Thus EBV infection per se can drive at least some naïve B cells to acquire Ig memory genotypes; furthermore, such cells are often favoured during an LCL's evolution to monoclonality. Extrapolating to viral infections in vivo, these findings could help to explain how EBV-infected cells become restricted to memory B cell subsets and why EBV-driven lymphoproliferative lesions, in primary infection and/or immunocompromised settings, so frequently involve clones with memory genotypes.

Epstein-Barr virus (EBV), a growth-transforming virus linked to several B cell lymphomas in man, is usually carried as an asymptomatic latent infection in B lymphocytes. Such virus carriage selectively involves memory, but not naive, B cells. How this selectivity is achieved is poorly understood since we find that naive and memory cell types are equally susceptible to infection and growth transformation to lymphoblastoid cell lines in vitro. Here we ask if EBV-transformation of purified naïve B cells can induce key features of memory cells, namely immunoglobulin (Ig) class switching and Ig gene mutation. We find that EBV does not induce Ig class switching (though the infected cells remain responsive to exogenous switch signals) but can induce Ig gene mutation. Thus, within 4 weeks of infecting naive B cell preparations, one can often detect cells carrying Ig mutations which appear to have arisen by somatic hypermutation in vitro. Furthermore, in many cases such cells become dominant during clonal evolution of the emergent EBV-transformed cell line. Overall these findings suggest a possible explanation as to why EBV is selectively found in memory B cell populations in vivo and why EBV-positive lymphoproliferative lesions/lymphomas so frequently involve clones with mutated Ig genotypes.

Somatic hypermutation targeting is influenced by location within the immunoglobulin V region

The observed mutation pattern in immunoglobulin (Ig) V genes from peripheral B cells is influenced by several mechanisms, including the targeting of AID to specific DNA motifs, negative selection of B cells unable to express Ig receptor, and positive selection of B cells that carry affinity-increasing mutations. These influences, combined with biased codon usage, produce the well-known pattern of increased replacement mutation frequency in the CDR regions, and decreased replacement frequency in the framework regions. Through the analysis of over 12,000 mutated sequences, we show that the specific location in the V gene also significantly influences mutation accumulation. While this position-specific effect is partially explained by selection, it appears independently of the CDR/FWR structure. To further explore the specific targeting of SHM, we propose a statistical formalism describing the mutation probability of a sequence through the multiplication of independent probabilities. Using this model, we show that C→G (or G→C) mutations are almost as frequent as C→T and G→A mutations, in contrast with C→A (or G→T) mutations, which are as any other mutation. The proposed statistical framework allows us to precisely quantify the effect of V gene position, mutation substitution type, and micro-sequence specificity on the observed mutation pattern.

Preferential targeting of somatic hypermutation to hotspot motifs and hypermutable sites and generation of mutational clusters in the IgVH alleles of a rheumatoid factor producing lymphoblastoid cell line

Epstein-Barr virus transforms human peripheral B cells into lymphoblastoid cell lines (LCL) that secrete specific antibodies. Our previous studies showed that a monoclonal LCL that secretes a rheumatoid factor expressed activation-induced cytidine deaminase (AID) and displayed an ongoing process of somatic hypermutation (SHM) at a frequency of 1.7×10⁻³ mut/bp in its productively rearranged IgVH gene. The present work shows that SHM similarly affects the nonproductive IgVH allele of the same culture. Sequencing of multiple cDNA clones derived from cellular subclones of the parental culture, showed that both alleles exhibited an ongoing mutational process with mutation rates of 2-3×10⁻⁵ mut/bp×generation with a high preference for C/G transition mutations and lack of a significant strand bias. About 50% of the mutations were targeted to the underlined C/G bases in the WRCH/DGYW and RCY/RGY hotspot motifs, indicating that they were due to the initial phase of AID activity. Mutations were targeted to the VH alleles and not to the Cμ or to the GAPDH genes. Genealogical trees showed a stepwise accumulation of only 1-3 mutations per branch of the tree. Unexpectedly, 27% of all the mutations in the two alleles occurred repeatedly and independently within certain sites (not necessarily the canonical hotspot motifs) in cellular clones belonging to different branches of the lineage tree. Furthermore, some of the mutations seem to arise as recurrent mutational clusters, independently generated in different cellular clones. Statistical analysis showed that it is very unlikely that these clusters were due to random targeting of equally accessible hotspots, indicating the presence of 'hypermutable sites' that generate recurring mutational clusters in the IgVH alleles. Intrinsic hypermutable sites may enhance affinity maturation and generation of effective mutated antibody repertoires against invading pathogens.

Immunotherapy for Alzheimer's disease

Patients with Alzheimer's disease (AD) express severe cognitive deficiencies with a concurrent increase in brain deposits of aggregated amyloid-beta (Abeta), a catabolic derivative of the ubiquitous amyloid precursor protein (APP). Interference in the homeostasis of Abeta has been suggested as a treatment for AD patients. In AD murine models it has been shown that active and passive immunization against Abeta alters the equilibrium of the different forms of Abeta in brain and serum, leading to a concomitant cognitive improvement. Generally, the clinical trials that followed the study of the murine AD model confirmed the results of the AD models, although safety issues advocate the passive vaccination approach rather than the active one. However, passive vaccination of patients with monoclonal antibodies derived from nonhuman sources is limited. Anti-Abeta IgM and IgG antibodies, which are present in the serum of every healthy individual and probably play a role in the homeostasis of Abeta in healthy subjects, might be beneficial to AD patients, as shown for the effect exerted by the commercial preparation of intravenous immunoglobulin. Human monoclonal anti-Abeta antibodies, which correspond to the ubiquitous anti-Abeta antibodies, are plausible candidates for future immunotherapy of AD patients.