B-cell development : one problem, multiple solutions.

Interspecies variations in the processes of B-cell development and repertoire generation contrast with the greater consistency of T-cell development. B-cell development in mice and humans, with postnatal B-cell generation of new repertoire in the bone marrow throughout life, is regarded as the 'standard' pattern. In contrast, accounts of B cells in birds, sheep, cattle, rabbits and pigs (the 'other' species) describe cessation of gene diversification in the perinatal period, with the gut-associated lymphoid tissue (GALT) functioning as the primary lymphoid organ thereafter. It has become customary to regard the developmental pathways of T and B cells within any individual species as being as dissimilar as the functions of the two mature cell types. Reinterpretation of B-cell development patterns in different species is overdue in response to two types of reports. The first of these describe T-B 'crossover', specifically the intrathymic production of B cells and the extrathymic production of T cells. The second attests to the extent of sharing of B-cell developmental features across the two groups of species. We propose that, as is a feature of other haematopoietic cells, a menu of alternative B- and T-cell pathways has been retained and shared across species. A single pathway usually predominates in any species, masking alternatives. The observed predominance of any pathway is determined by factors such as placental permeability, extent of maturation of the immune system by birth and the feasibility of direct experimental intervention in development

Glutamic Acid Decarboxylase-Derived Epitopes with Specific Domains Expand CD4+CD25+ Regulatory T Cells

BACKGROUND:CD4(+)CD25(+) regulatory T cell (Treg)-based immunotherapy is considered a promising regimen for controlling the progression of autoimmune diabetes. In this study, we tested the hypothesis that the therapeutic effects of Tregs in response to the antigenic epitope stimulation depend on the structural properties of the epitopes used. METHODOLOGY/PRINCIPAL FINDINGS:Splenic lymphocytes from nonobese diabetic (NOD) mice were stimulated with different glutamic acid decarboxylase (GAD)-derived epitopes for 7-10 days and the frequency and function of Tregs was analyzed. We found that, although all expanded Tregs showed suppressive functions in vitro, only p524 (GAD524-538)-expanded CD4(+)CD25(+) T cells inhibited diabetes development in the co-transfer models, while p509 (GAD509-528)- or p530 (GAD530-543)-expanded CD4(+)CD25(+) T cells had no such effects. Using computer-guided molecular modeling and docking methods, the differences in structural characteristics of these epitopes and the interaction mode (including binding energy and identified domains in the epitopes) between the above-mentioned epitopes and MHC class II I-A(g7) were analyzed. The theoretical results showed that the epitope p524, which induced protective Tregs, possessed negative surface-electrostatic potential and bound two chains of MHC class II I-A(g7), while the epitopes p509 and p530 which had no such ability exhibited positive surface-electrostatic potential and bound one chain of I-A(g7). Furthermore, p524 bound to I-A(g7) more stably than p509 and p530. Of importance, we hypothesized and subsequently confirmed experimentally that the epitope (GAD570-585, p570), which displayed similar characteristics to p524, was a protective epitope by showing that p570-expanded CD4(+)CD25(+) T cells suppressed the onset of diabetes in NOD mice. CONCLUSIONS/SIGNIFICANCE:These data suggest that molecular modeling-based structural analysis of epitopes may be an instrumental tool for prediction of protective epitopes to expand functional Tregs

Modulation of T Cell Function by Combination of Epitope Specific and Low Dose Anticytokine Therapy Controls Autoimmune Arthritis

Innate and adaptive immunity contribute to the pathogenesis of autoimmune arthritis by generating and maintaining inflammation, which leads to tissue damage. Current biological therapies target innate immunity, eminently by interfering with single pro-inflammatory cytokine pathways. This approach has shown excellent efficacy in a good proportion of patients with Rheumatoid Arthritis (RA), but is limited by cost and side effects. Adaptive immunity, particularly T cells with a regulatory function, plays a fundamental role in controlling inflammation in physiologic conditions. A growing body of evidence suggests that modulation of T cell function is impaired in autoimmunity. Restoration of such function could be of significant therapeutic value. We have recently demonstrated that epitope-specific therapy can restore modulation of T cell function in RA patients. Here, we tested the hypothesis that a combination of anti-cytokine and epitope-specific immunotherapy may facilitate the control of autoimmune inflammation by generating active T cell regulation. This novel combination of mucosal tolerization to a pathogenic T cell epitope and single low dose anti-TNFα was as therapeutically effective as full dose anti-TNFα treatment. Analysis of the underlying immunological mechanisms showed induction of T cell immune deviation

Human Antigen-Specific Regulatory T Cells Generated by T Cell Receptor Gene Transfer

Therapies directed at augmenting regulatory T cell (Treg) activities in vivo as a systemic treatment for autoimmune disorders and transplantation may be associated with significant off-target effects, including a generalized immunosuppression that may compromise beneficial immune responses to infections and cancer cells. Adoptive cellular therapies using purified expanded Tregs represents an attractive alternative to systemic treatments, with results from animal studies noting increased therapeutic potency of antigen-specific Tregs over polyclonal populations. However, current methodologies are limited in terms of the capacity to isolate and expand a sufficient quantity of endogenous antigen-specific Tregs for therapeutic intervention. Moreover, FOXP3+ Tregs fall largely within the CD4+ T cell subset and are thus routinely MHC class II-specific, whereas class I-specific Tregs may function optimally in vivo by facilitating direct tissue recognition.To overcome these limitations, we have developed a novel means for generating large numbers of antigen-specific Tregs involving lentiviral T cell receptor (TCR) gene transfer into in vitro expanded polyclonal natural Treg populations. Tregs redirected with a high-avidity class I-specific TCR were capable of recognizing the melanoma antigen tyrosinase in the context of HLA-A*0201 and could be further enriched during the expansion process by antigen-specific reactivation with peptide loaded artificial antigen presenting cells. These in vitro expanded Tregs continued to express FOXP3 and functional TCRs, and maintained the capacity to suppress conventional T cell responses directed against tyrosinase, as well as bystander T cell responses. Using this methodology in a model tumor system, murine Tregs designed to express the tyrosinase TCR effectively blocked antigen-specific effector T cell (Teff) activity as determined by tumor cell growth and luciferase reporter-based imaging.These results support the feasibility of class I-restricted TCR transfer as a promising strategy to redirect the functional properties of Tregs and provide for a more efficacious adoptive cell therapy

Analysis of single nucleotide polymorphisms in the FAS and CTLA-4 genes of peripheral T-cell lymphomas

Angioimmunoblastic T-cell lymphoma (AILT) represents a subset of T-cell lymphomas but resembles an autoimmune disease in many of its clinical aspects. Despite the phenotype of effector T-cells and high expression of FAS and CTLA-4 receptor molecules, tumor cells fail to undergo apoptosis. We investigated single nucleotide polymorphisms (SNPs) of the FAS and CTLA-4 genes in 94 peripheral T-cell lymphomas. Although allelic frequencies of some FAS SNPs were enriched in AILT cases, none of these occurred at a different frequency compared to healthy individuals. Therefore, SNPs in these genes are not associated with the apoptotic defect and autoimmune phenomena in AILT

T cells at the site of autoimmune inflammation show increased potential for trogocytosis

CD4+ T cells acquire membrane fragments from antigen-presenting-cells via a process termed trogocytosis. Identifying which CD4+ T cells undergo trogocytosis in co-culture with Ag-loaded APC can enrich for antigen-reactive T cells without knowledge of their fine specificity or cytokine-production profiles. We sought to assess the suitability of this method to identify disease relevant effector and regulatory T cells during autoimmune inflammation. Trogocytosis efficiently identified MBP-reactive T cells in vitro and ex-vivo following immunization. However, Foxp3+ regulatory T cells constitutively displayed a higher rate of trogocytosis than their Foxp3- counterparts which limits the potential of trogocytosis to identify antigen-reactive Treg cells. During inflammation a locally elevated rate of trogocytosis (seen in both effector and regulatory T cells isolated from the inflamed CNS) precludes the use of trogocytosis as a measure of antigenic reactivity among cells taken from inflammatory sites. Our results indicate trogocytosis detection can enrich for Ag-reactive conventional T cells in the periphery but is limited in its ability to identify Ag-reactive Treg or T effector cells at sites of inflammation. Increased trogocytosis potential at inflammatory sites also draws into the question the biological significance of this phenomenon during inflammation, in Treg mediated suppression and for the maintenance of tolerance in health and disease

The therapeutic potential of regulatory T cells for the treatment of autoimmune disease

IntroductionImmune tolerance remains the holy grail of therapeutic immunology in the fields of organ and tissue transplant rejection, autoimmune diseases, and allergy and asthma. We have learned that FoxP3(+)CD4(+) regulatory T cells play a vital role in both the induction and maintenance of self-tolerance.Areas coveredIn this opinion piece, we highlight regulatory T cells (Treg) cell biology and novel immune treatments to take advantage of these cells as potent therapeutics. We discuss the potential to utilize Treg and Treg-friendly therapies to replace current general immunosuppressives and induce tolerance as a path towards a drug-free existence without associated toxicities.Expert opinionFinally, we opine on the fact that biomedicine sits on the cusp of a new revolution: the use of human cells as versatile therapeutic engines. We highlight the challenges and opportunities associated with the development of a foundational cellular engineering science that provides a systematic framework for safely and predictably regulating cellular behaviors. Although Treg therapy has become a legitimate clinical treatment, development of the therapy will require a better understanding of the underlying Treg biology, manufacturing advances to promote cost effectiveness and combinations with other drugs to alter the pathogenicity/regulatory balance