A causal link between lymphopenia and autoimmunity

Specific myeloid signatures in peripheral blood differentiate active and rare clinical phenotypes of multiple sclerosis

Current understanding of Multiple Sclerosis (MS) pathophysiology implicates perturbations in adaptive cellular immune responses, predominantly T cells, in Relapsing-Remitting forms (RRMS). Nevertheless, from a clinical perspective MS is a heterogeneous disease reflecting the heterogeneity of involved biological systems. This complexity requires advanced analysis tools at the single-cell level to discover biomarkers for better patient-group stratification. We designed a novel 44-parameter mass cytometry panel to interrogate predominantly the role of effector and regulatory subpopulations of peripheral blood myeloid subsets along with B and T-cells (excluding granulocytes) in MS, assessing three different patient cohorts: RRMS, PPMS (Primary Progressive) and Tumefactive MS patients (TMS) (n=10, 8, 14 respectively). We further subgrouped our cohort into inactive or active disease stages to capture the early underlying events in disease pathophysiology. Peripheral blood analysis showed that TMS cases belonged to the spectrum of RRMS, whereas PPMS cases displayed different features. In particular, TMS patients during a relapse stage were characterized by a specific subset of CD11c+CD14+ CD33+, CD192+, CD172+-myeloid cells with an alternative phenotype of monocyte-derived macrophages (high arginase-1, CD38, HLA-DR-low and endogenous TNF-a production). Moreover, TMS patients in relapse displayed a selective CD4 T-cell lymphopenia of cells with a Th2-like polarised phenotype. PPMS patients did not display substantial differences from healthy controls, apart from a trend toward higher expansion of NK cell subsets. Importantly, we found that myeloid cell populations are reshaped under effective disease-modifying therapy predominantly with glatiramer acetate and to a lesser extent with anti-CD20, suggesting that the identified cell signature represents a specific therapeutic target in TMS. The expanded myeloid signature in TMS patients was also confirmed by flow cytometry. Serum neurofilament light-chain levels confirmed the correlation of this myeloid cell signature with indices of axonal injury. More in-depth analysis of myeloid subsets revealed an increase of a subset of highly cytolytic and terminally differentiated NK cells in PPMS patients with leptomeningeal enhancement (active-PPMS), compared to those without (inactive-PPMS). We have identified previously uncharacterized subsets of circulating myeloid cells and shown them to correlate with distinct disease forms of MS as well as with specific disease states (relapse/remission).

Distinct CD4+ T cell signature in ANA-positive young adult patients

Failure of immune tolerance can lead to autoantibody production resulting in autoimmune diseases, a broad spectrum of organ-specific or systemic disorders. Immune tolerance mechanisms regulate autoreactive T and B cells, yet some lymphocytes escape and promote autoantibody production. CD4+ T cell dysregulation, characterized by decreased or impaired regulatory cells (Tregs) and/or accumulation of memory and effector T cells such as TH17, plays a crucial role in the pathogenesis of these diseases. Antinuclear antibody (ANAs) testing is used as a first step for the diagnosis of autoimmune disorders, although most ANA-positive individuals do not have nor will develop an autoimmune disease. Studying the differences of T cell compartment among healthy blood donors, ANA-negative patients and ANA-positive patients, in which loss of tolerance have not led to autoimmunity, may improve our understanding on how tolerance mechanisms fail. Herein, we report that ANA-positive patients exhibit a distinct distribution of T cell subsets: significantly reduced frequencies of recent thymic emigrants (RTE) and naïve T cells, and significantly increased frequencies of central memory T cells, TH2 and TH17 cells; modulations within the T cell compartment are most profound within the 18-40 year age range. Moreover, CD4+ T cells in ANA-positive patients are metabolically active, as determined by a significant increase in mTORC1 and mTORC2 signals, compared to ANA-negative patients and healthy blood donors. No significant impairment of Treg numbers or pro-inflammatory cytokine production was observed. These results identify a unique T cell signature associated with autoantibody production in the absence of autoimmune disease.

Characterization of Autoimmune Thyroid Disease in a Cohort of 73 Paediatric Patients Affected by 22q11.2 Deletion Syndrome: Longitudinal Single-Centre Study

Background. Chromosome 22q11.2 Deletion Syndrome (22q11.2DS) is the most frequent microdeletion syndrome and is mainly characterized by congenital cardiac defects, dysmorphic features, hypocalcemia, palatal dysfunction, developmental delay, and impaired immune function due to thymic hypoplasia or aplasia. Thyroid anomalies are frequently reported in patients with 22q11.2DS, although only a few well-structured longitudinal studies about autoimmune thyroid disease (ATD) have been reported. Aim. To longitudinally evaluate the frequency of thyroid anomalies and ATD in patients with 22q11.2DS. Patients and Methods. Pediatric patients with a confirmed genetic diagnosis of 22q11.2DS were recruited and followed up on longitudinally. Clinical, biochemical, and immunological data were collected, as well as thyroid function, autoimmunity, and thyroid sonographic data. Results. The study included 73 children with 22q11.2DS, with a mean follow-up duration of 9.51 ± 5.72 years. In all, 16 of the 73 enrolled patients (21.9%) developed ATD before 18 years of age (mean age 12.92 ± 3.66 years). A total of 20.5% developed Hashimoto’s Thyroiditis (HT), of whom 50% required L-thyroxine treatment; 1.4% developed Graves Disease. Thyroid hypoplasia was found in 6/16 patients with ATD and left lobe hypoplasia in 9/16 patients. These features were also found in patients affected by 22q11.2DS without ATD. Among patients who developed ATD, at the first altered ultrasound scan, the most frequent anomalies suggestive of thyroiditis were inhomogeneous echotexture, diffuse or irregular hypo-echogenicity, and vascular overflow. Conclusion. We strongly recommend periodic screening of thyroid function and for autoimmunity in patients affected by 22q11.2DS. Along with blood tests, ultrasound scans of the thyroid gland should be performed periodically since some patients who go on to develop an ATD could have specific anomalies on ultrasound prior to any other anomaly.

Lymphopenia and Mechanisms of T-Cell Regeneration

Chronic lymphopenia, in particular, T-lymphocyte deficiency, increases the risk of death from cancer, cardiovascular and respiratory diseases and serves as a risk factor for a severe course and poor outcome of infectious diseases such as COVID-19. The regeneration of T-lymphocytes is a complex multilevel process, many questions of which still remain unanswered. The present review considers two main pathways of increasing the T-cell number in lymphopenia: production in the thymus and homeostatic proliferation in the periphery. Literature data on the signals that regulate each pathway are summarized. Their contribution to the quantitative and qualitative restoration of the immune cell pool is analyzed. The features of CD4⁺ and CD8⁺ T-lymphocytes’ regeneration are considered.

Immune Regulatory Cell Bias Following Alemtuzumab Treatment in Relapsing-Remitting Multiple Sclerosis

Alemtuzumab is a highly effective treatment for relapsing-remitting multiple sclerosis. It selectively targets the CD52 antigen to induce profound lymphocyte depletion, followed by recovery of T and B cells with regulatory phenotypes. We previously showed that regulatory T cell function is restored with cellular repletion, but little is known about the functional capacity of regulatory B-cells and peripheral blood monocytes during the repletion phase. In this study (ClinicalTrials.gov ID# NCT03647722) we simultaneously analyzed the change in composition and function of both regulatory lymphocyte populations and distinct monocyte subsets in cross-sectional cohorts of MS patients prior to or 6, 12, 18, 24 or 36 months after their first course of alemtuzumab treatment. We found that the absolute number and percentage of cells with a regulatory B cell phenotype were significantly higher after treatment and were positivity correlated with regulatory T cells. In addition, B cells from treated patients secreted higher levels of IL-10 and BDNF, and inhibited the proliferation of autologous CD4⁺CD25^- T cell targets. Though there was little change in monocytes populations overall, following the second annual course of treatment, CD14⁺ monocytes had a significantly increased anti-inflammatory bias in cytokine secretion patterns. These results confirmed that the immune system in alemtuzumab-treated patients is altered in favor of a regulatory milieu that involves expansion and increased functionality of multiple regulatory populations including B cells, T cells and monocytes. Here, we showed for the first time that functionally competent regulatory B cells re-appear with similar kinetics to that of regulatory T-cells, whereas the change in anti-inflammatory bias of monocytes does not occur until after the second treatment course. These findings justify future studies of all regulatory cell types following alemtuzumab treatment to reveal further insights into mechanisms of drug action, and to identify key immunological predictors of durable clinical efficacy in alemtuzumab-treated patients.

Lymphocyte Counts and Multiple Sclerosis Therapeutics: Between Mechanisms of Action and Treatment-Limiting Side Effects

Although the detailed pathogenesis of multiple sclerosis (MS) is not completely understood, a broad range of disease-modifying therapies (DMTs) are available. A common side effect of nearly every MS therapeutic agent is lymphopenia, which can be both beneficial and, in some cases, treatment-limiting. A sound knowledge of the underlying mechanism of action of the selected agent is required in order to understand treatment-associated changes in white blood cell counts, as well as monitoring consequences. This review is a comprehensive summary of the currently available DMTs with regard to their effects on lymphocyte count. In the first part, we describe important general information about the role of lymphocytes in the course of MS and the essentials of lymphopenic states. In the second part, we introduce the different DMTs according to their underlying mechanism of action, summarizing recommendations for lymphocyte monitoring and definitions of lymphocyte thresholds for different therapeutic regimens.

COVID-19 Immunobiology: Lessons Learned, New Questions Arise

There is strong evidence that COVID-19 pathophysiology is mainly driven by a spatiotemporal immune deregulation. Both its phenotypic heterogeneity, spanning from asymptomatic to severe disease/death, and its associated mortality, are dictated by and linked to maladaptive innate and adaptive immune responses against SARS-CoV-2, the etiologic factor of the disease. Deregulated interferon and cytokine responses, with the contribution of immune and cellular stress-response mediators (like cellular senescence or uncontrolled inflammatory cell death), result in innate and adaptive immune system malfunction, endothelial activation and inflammation (endothelitis), as well as immunothrombosis (with enhanced platelet activation, NET production/release and complement hyper-activation). All these factors play key roles in the development of severe COVID-19. Interestingly, another consequence of this immune deregulation, is the production of autoantibodies and the subsequent development of autoimmune phenomena observed in some COVID-19 patients with severe disease. These new aspects of the disease that are now emerging (like autoimmunity and cellular senescence), could offer us new opportunities in the field of disease prevention and treatment. Simultaneously, lessons already learned from the immunobiology of COVID-19 could offer new insights, not only for this disease, but also for a variety of chronic inflammatory responses observed in autoimmune and (auto)inflammatory diseases.

Autoimmunity and COVID-19 - The microbiotal connection

Background and aims

The novel SARS-CoV-2 has been rattling the world since its outbreak in December 2019, leading to the COVID-19 pandemic. The learning curve of this new virus has been steep, with a global scientific community desperate to learn how the virus is transmitted, how it replicates, why it causes such a wide spectrum of disease manifestations, resulting in none or few symptoms in some. Others are burdened by an intense immune response that resembles the cytokine storm syndrome (CSS), which leads to severe disease manifestations, often complicated by fatal acute respiratory distress syndrome and death. Research efforts have been focusing on finding effective cures and vaccinations for this virus.

The presence of SARS-CoV-2 in the gastrointestinal (GI) tract, represented by several GI manifestations, has led to its investigation as a target for the virus and as an indicator of disease severity. The response of the microbiome (which is heavily linked to immunity) to the novel SARS-CoV-2 virus, and its role in igniting the exaggerated immune response has therefore become a focus of interest. The objective of our study was to gather the data connecting between the microbiome, the GI tract and COVID-19 and to investigate whether these reported alterations in the gut microbiome bear any resemblance to those seen in lupus, the prototypical autoimmune disease. Confirming such changes may become the steppingstone to potential therapies that may prevent transmission, progression and immune related manifestations of COVID-19, via manipulation of the gut microbiota.

Methods

We performed an extensive literature review, utilizing the Pubmed search engine and Google Scholar for studies evaluating the microbiome in COVID-19 patients and compared results with studies evaluating the microbiome in lupus. We searched for the terms: microbiome, dysbiosis, COVID-19, SARS-CoV-2, gastrointestinal as well as lupus and autoimmune. While there were hundreds of articles which referred to gastrointestinal manifestations in COVID-19, to date only 4 studies investigated the gastrointestinal microbiome in this setting. We compared the similarities between microbiome of COVID-19 patients and lupus patients.

Results

We found that there are several similar processes of immune dysregulation in patients with COVID-19 and in those with lupus, with several other alterations seen in other pathological states. Some of these similarities include loss of microbiota biodiversity, increased representation of pathobionts, which are microbes associated with inflammation and disease (i.e Proteobacteria) and a relative decrease of symbionts, which are protective microbes, associated with anti-inflammatory properties (i.e Lactobacillus). Compromise to the intestinal barrier has also been reported in both.

Conclusions

We conclude that the gastrointestinal tract contributes to the disease manifestations in COVID-19. Whether gastrointestinal dysbiosis is the cause or effect of gastrointestinal manifestations and several severe systemic manifestations, which may be the response to an increased pro-inflammatory environment, is still debatable and warrants further investigation. Given the resemblance of the microbiome in COVID-19 patients to that seen in lupus patients, it becomes clearer why several therapies used in autoimmune conditions are currently under investigation for the treatment of COVID-19 patients. Moreover, these findings should promote further investigating the utility of manipulation of the microbiome, via nutritional supplementation or even fecal transplantations, interventions that may alter the course of the disease, and potentially prevent disease transmission at low cost and low risk.

Alemtuzumab-induced Alopecia areata - a case report and systematic literature review of adverse events associated with Alemtuzumab

Alemtuzumab is currently approved for the treatment of active relapsing-remitting multiple sclerosis (RRMS). Despite the efficacy of this therapy several side effects in the skin have been noted during or after infusion including vitiligo, alopecia areata, malignant skin tumors and infections. Awareness of these effects and their treatment is of essential interdisciplinary importance. This minireview provides an overview of the dermatological side effects described in the current literature. We also suggest pathomechanisms underlying these phenomena. To introduce this review, we present the case of a woman with RRMS who developed severe alopecia areata for the first time on alemtuzumab.

Autologous hematopoietic stem cell transplantation restores the suppressive capacity of regulatory B cells in systemic sclerosis patients

OBJECTIVES

The rationale of autologous hematopoietic stem cell transplantation (AHSCT) for autoimmune diseases is that high-dose immunosuppression eradicates autoreactive T and B cells, and the infused autologous hematopoietic stem cells promote reconstitution of a naive and self-tolerant immune system. The aim of this study was to evaluate the reconstitution of different B cell subsets, both quantitatively and functionally, in systemic sclerosis (SSc) patients treated with AHSCT.

METHODS

Peripheral blood was harvested from twenty-two SSc patients before transplantation and at 30, 60, 120, 180 and 360 days post-AHSCT. Immunophenotyping of B cell subsets, B cell cytokine production, signaling pathways, and suppressive capacity of regulatory B cells (Bregs) were assessed by flow cytometry.

RESULTS

Naïve B cell frequencies increased from 60 to 360 days post-AHSCT, compared to pre-transplantation. Conversely, memory B cell frequencies decreased during the same period. Plasma cell frequencies transiently decreased at 60 days post-AHSCT. IL-10-producing Bregs CD19+CD24hiCD38hi and CD19+CD24hiCD27+ frequencies increased at 180 days. Moreover, the phosphorylation of ERK1/2 and p38MAPK proteins increased in B cells reconstituted post-AHSCT. Notably, CD19+CD24hiCD38hi Bregs recovered their ability to suppress production of Th1 cytokines by CD4+ T cells at 360 days post-AHSCT. Finally, IL-6 and TGF-β1-producing B cells decreased following AHSCT.

CONCLUSION

Taken together, these results suggest improvements in immunoregulatory and anti-fibrotic mechanisms after AHSCT for SSc, which may contribute to reestablishment of self-tolerance and clinical remission.

Insights Into the Involvement of Circular RNAs in Autoimmune Diseases

Circular RNAs (circRNAs) are single-stranded, endogenous, non-coding RNA (ncRNA) molecules formed by the backsplicing of messenger RNA (mRNA) precursors and have covalently closed circular structures without 5′-end caps and 3′-end polyadenylation [poly(A)] tails. CircRNAs are characterized by abundant species, stable structures, conserved sequences, cell- or tissue-specific expression, and widespread and stable presence in many organisms. Therefore, circRNAs can be used as biomarkers for the prediction, diagnosis, and treatment of a variety of diseases. Autoimmune diseases (AIDs) are caused by defects in immune tolerance or abnormal immune regulation, which leads to damage to host organs. Due to the complexity of the pathophysiological processes of AIDs, clinical therapeutics have been suboptimal. The emergence of circRNAs sheds new light on the treatment of AIDs. In particular, circRNAs mainly participate in the occurrence and development of AIDs by sponging targets. This review systematically explains the formation, function, mechanism, and characteristics of circRNAs in the context of AIDs. With a deeper understanding of the pathophysiological functions of circRNAs in the pathogenesis of AIDs, circRNAs may become reasonable, accurate, and effective biomarkers for the diagnosis and treatment of AIDs in the future.

Prevalence and pathogenicity of autoantibodies in patients with idiopathic CD4 lymphopenia

BACKGROUNDIdiopathic CD4 lymphopenia (ICL) is defined by persistently low CD4+ cell counts (<300 cells/μL) in the absence of a causal infection or immune deficiency and can manifest with opportunistic infections. Approximately 30% of ICL patients develop autoimmune disease. The prevalence and breadth of their autoantibodies, however, and their potential contribution to pathogenesis of ICL remain unclear.METHODSWe hybridized 34 and 51 ICL patients' sera to a 9,000-human-proteome array and to a 128-known-autoantigen array, respectively. Using a flow-based method, we characterized the presence of anti-lymphocyte Abs in the whole cohort of 72 patients, as well as the Ab functional capability of inducing Ab-dependent cell-mediated cytotoxicity (ADCC), complement deposition, and complement-dependent cytotoxicity (CDC). We tested ex vivo the activation of the classical complement pathway on ICL CD4+ T cells.RESULTSAll ICL patients had a multitude of autoantibodies mostly directed against private (not shared) targets and unrelated quantitatively or qualitatively to the patients' autoimmune disease status. The targets included lymphocyte intracellular and membrane antigens, confirmed by the detection by flow of IgM and IgG (mostly IgG1 and IgG4) anti-CD4+ cell Abs in 50% of the patients, with half of these cases triggering lysis of CD4+ T cells. We also detected in vivo classical complement activation on CD4+ T cells in 14% of the whole cohort.CONCLUSIONOur data demonstrate that a high prevalence of autoantibodies in ICL, some of which are specific for CD4+ T cells, may contribute to pathogenesis, and may represent a potentially novel therapeutic target.TRIAL REGISTRATIONClinicalTrials.gov NCT00867269.FUNDINGNIAID and National Institute of Arthritis and Musculoskeletal and Skin Diseases of the NIH.

Expanding mechanistic insights into the pathogenesis of idiopathic CD4+ T cell lymphocytopenia

Idiopathic CD4+ T cell lymphocytopenia (ICL) is a heterogeneous syndrome presenting with persistent CD4+ T cell lymphopenia of unknown origin, and opportunistic infections in some patients. The underlying pathogenesis and appropriate management remain understudied. In this issue of the JCI, Perez-Diez and Wong et al. assessed the prevalence of autoantibodies from the sera of 51 adult ICL patients (out of a cohort of 72). Some patients showed high levels of IgG and IgM autoantibodies against numerous autoantigens, and some autoantibodies were specific for lymphocytes. The researchers implicate these autoantibodies as a possible pathogenic mechanism responsible for the reduction in circulating CD4+ T cells. This study goes beyond defining a mechanism in a complex, poorly defined disease; it also brings a renewed focus on ICL that will likely result in improved diagnostic evaluation and treatment.

Autoinflammatory and autoimmune conditions at the crossroad of COVID-19

Coronavirus disease 2019 (COVID-19) has been categorized as evolving in overlapping phases. First, there is a viral phase that may well be asymptomatic or mild in the majority, perhaps 80% of patients. The pathophysiological mechanisms resulting in minimal disease in this initial phase are not well known. In the remaining 20% of cases, the disease may become severe and/or critical. In most patients of this latter group, there is a phase characterized by the hyperresponsiveness of the immune system. A third phase corresponds to a state of hypercoagulability. Finally, in the fourth stage organ injury and failure occur. Appearance of autoinflammatory/autoimmune phenomena in patients with COVID-19 calls attention for the development of new strategies for the management of life-threatening conditions in critically ill patients. Antiphospholipid syndrome, autoimmune cytopenia, Guillain-Barré syndrome and Kawasaki disease have each been reported in patients with COVID-19. Here we present a scoping review of the relevant immunological findings in COVID-19 as well as the current reports about autoinflammatory/autoimmune conditions associated with the disease. These observations have crucial therapeutic implications since immunomodulatory drugs are at present the most likely best candidates for COVID-19 therapy. Clinicians should be aware of these conditions in patients with COVID-19, and these observations should be considered in the current development of vaccines.

Anti-CD52 blocks EAE independent of PD-1 signals and promotes repopulation dominated by double-negative T cells and newly generated T and B cells

Lymphocyte depletion using anti-CD52 antibody effectively reduces relapses of multiple sclerosis (MS). To begin to understand what mechanisms might control this outcome, we examined the effect of a murine-CD52-specific mAb on the depletion and repopulation of immune cells in mice with experimental autoimmune encephalomyelitis (EAE), a model of MS. We tested whether the tolerance-promoting receptor programmed cell death protein-1 (PD-1) is required for disease remission post anti-CD52, and found that PD-1-deficient mice with a more severe EAE were nevertheless effectively treated with anti-CD52. Anti-CD52 increased the proportions of newly generated T cells and double-negative (DN) T cells while reducing newly generated B cells; the latter effect being associated with a higher expression of CD52 by these cells. In the longer term, anti-CD52 caused substantial increases in the proportion of newly generated lymphocytes and DN T cells in mice with EAE. Thus, the rapid repopulation of lymphocytes from central lymphoid organs post anti-CD52 may limit further disease. Furthermore, these data identify DN T cells, a subset with immunoregulatory potential, as a significant hyperrepopulating subset following CD52-mediated depletion.

Keratinocyte growth factor impairs human thymic recovery from lymphopenia

BACKGROUND

The lymphocyte-depleting antibody alemtuzumab is a highly effective treatment of relapsing-remitting multiple sclerosis (RRMS); however 50% of patients develop novel autoimmunity post-treatment. Most at risk are individuals who reconstitute their T-cell pool by proliferating residual cells, rather than producing new T-cells in the thymus; raising the possibility that autoimmunity might be prevented by increasing thymopoiesis. Keratinocyte growth factor (palifermin) promotes thymopoiesis in non-human primates.

METHODS

Following a dose-tolerability sub-study, individuals with RRMS (duration ≤10 years; expanded disability status scale ≤5·0; with ≥2 relapses in the previous 2 years) were randomised to placebo or 180mcg/kg/day palifermin, given for 3 days immediately prior to and after each cycle of alemtuzumab, with repeat doses at M1 and M3. The interim primary endpoint was naïve CD4+ T-cell count at M6. Exploratory endpoints included: number of recent thymic-emigrants (RTEs) and signal-joint T-cell receptor excision circles (sjTRECs)/mL of blood. The trial primary endpoint was incidence of autoimmunity at M30.

FINDINGS

At M6, individuals receiving palifermin had fewer naïve CD4+T-cells (2.229x107/L vs. 7.733x107/L; p=0.007), RTEs (16% vs. 34%) and sjTRECs/mL (1100 vs. 3396), leading to protocol-defined termination of recruitment. No difference was observed in the rate of autoimmunity between the two groupsConclusion: In contrast to animal studies, palifermin reduced thymopoiesis in our patients. These results offer a note of caution to those using palifermin to promote thymopoiesis in other settings, particularly in the oncology/haematology setting where alemtuzumab is often used as part of the conditioning regime.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01712945Funding: MRC and Moulton Charitable Foundation.

Alemtuzumab as Treatment for Multiple Sclerosis

Alemtuzumab, the first monoclonal antibody to be used as a therapy and the first to be humanized, was introduced into the treatment of multiple sclerosis in 1991 after its successful use in hematology, oncology, and transplantation medicine. One phase 2 and two phase 3 trials of this lymphocyte-depleting agent have established alemtuzumab's superior efficacy to interferon β-1a over the short term (2-3 years) with greater relapse rate reduction, reduced accumulation of disability, and more frequent sustained improvement in disability. Longer-term extension studies show durable effects on slowing cerebral atrophy over 6 years and maintained low relapse rates over 10 years, despite roughly half of patients not needing further dosing. Homeostatic proliferation of residual T cells after alemtuzumab-induced lymphopenia is probably responsible for its most common side effects: secondary autoimmunity 1 or 2 years after the last infusion of alemtuzumab affecting the thyroid gland (30% of patients), platelets (1%), or renal glomeruli (0.1%). With the prerequisite of patient and physician adherence to a prolonged safety-monitoring protocol, alemtuzumab offers durable high efficacy from infrequent dosing.

Strain differences in thymic atrophy in rats immunized for EAE correlate with the clinical outcome of immunization

An accumulating body of evidence suggests that development of autoimmune pathologies leads to thymic dysfunction and changes in peripheral T-cell compartment, which, in turn, perpetuate their pathogenesis. To test this hypothesis, thymocyte differentiation/maturation in rats susceptible (Dark Agouti, DA) and relatively resistant (Albino Oxford, AO) to experimental autoimmune encephalomyelitis (EAE) induction was examined. Irrespective of strain, immunization for EAE (i) increased the circulating levels of IL-6, a cytokine causally linked with thymic atrophy, and (ii) led to thymic atrophy reflecting partly enhanced thymocyte apoptosis associated with downregulated thymic IL-7 expression. Additionally, immunization diminished the expression of Thy-1, a negative regulator of TCRαβ-mediated signaling and activation thresholds, on CD4+CD8+ TCRαβ^lo/hi thymocytes undergoing selection and thereby impaired thymocyte selection/survival. This diminished the generation of mature CD4+ and CD8+ single positive TCRαβ^hi thymocytes and, consequently, CD4+ and CD8+ recent thymic emigrants. In immunized rats, thymic differentiation of natural regulatory CD4+Foxp3+CD25+ T cells (nTregs) was particularly affected reflecting a diminished expression of IL-7, IL-2 and IL-15. The decline in the overall thymic T-cell output and nTreg generation was more pronounced in DA than AO rats. Additionally, differently from immunized AO rats, in DA ones the frequency of CD28- cells secreting cytolytic enzymes within peripheral blood CD4+ T lymphocytes increased, as a consequence of thymic atrophy-related replicative stress (mirrored in CD4+ cell memory pool expansion and p16^INK4a accumulation). The higher circulating level of TNF-α in DA compared with AO rats could also contribute to this difference. Consistently, higher frequency of cytolytic CD4+ granzyme B+ cells (associated with greater tissue damage) was found in spinal cord of immunized DA rats compared with their AO counterparts. In conclusion, the study indicated that strain differences in immunization-induced changes in thymopoiesis and peripheral CD4+CD28- T-cell generation could contribute to rat strain-specific clinical outcomes of immunization for EAE.

C1q restrains autoimmunity and viral infection by regulating CD8+ T cell metabolism

Deficiency of C1q, the initiator of the complement classical pathway, is associated with the development of systemic lupus erythematosus (SLE). Explaining this association in terms of abnormalities in the classical pathway alone remains problematic because C3 deficiency does not predispose to SLE. Here, using a mouse model of SLE, we demonstrate that C1q, but not C3, restrains the response to self-antigens by modulating the mitochondrial metabolism of CD8⁺ T cells, which can themselves propagate autoimmunity. C1q deficiency also triggers an exuberant effector CD8⁺ T cell response to chronic viral infection leading to lethal immunopathology. These data establish a link between C1q and CD8⁺ T cell metabolism and may explain how C1q protects against lupus, with implications for the role of viral infections in the perpetuation of autoimmunity.

Regenerating Immunotolerance in Multiple Sclerosis with Autologous Hematopoietic Stem Cell Transplant

Multiple sclerosis (MS) is an inflammatory disorder of the central nervous system where evidence implicates an aberrant adaptive immune response in the accrual of neurological disability. The inflammatory phase of the disease responds to immunomodulation to varying degrees of efficacy; however, no therapy has been proven to arrest progression of disability. Recently, more intensive therapies, including immunoablation with autologous hematopoietic stem cell transplantation (AHSCT), have been offered as a treatment option to retard inflammatory disease, prior to patients becoming irreversibly disabled. Empirical clinical observations support the notion that the immune reconstitution (IR) that occurs following AHSCT is associated with a sustained therapeutic benefit; however, neither the pathogenesis of MS nor the mechanism by which AHSCT results in a therapeutic benefit has been clearly delineated. Although the antigenic target of the aberrant immune response in MS is not defined, accumulated data suggest that IR following AHSCT results in an immunotolerant state through deletion of pathogenic clones by a combination of direct ablation and induction of a lymphopenic state driving replicative senescence and clonal attrition. Restoration of immunoregulation is evidenced by changes in regulatory T cell populations following AHSCT and normalization of genetic signatures of immune homeostasis. Furthermore, some evidence exists that AHSCT may induce a rebooting of thymic function and regeneration of a diversified naïve T cell repertoire equipped to appropriately modulate the immune system in response to future antigenic challenge. In this review, we discuss the immunological mechanisms of IR therapies, focusing on AHSCT, as a means of recalibrating the dysfunctional immune response observed in MS.

Density dependent re-tuning of autoreactive T cells alleviates their pathogenicity in a lymphopenic environment

Peripheral T cell tolerance is challenging to induce in partially lymphopenic hosts and this is relevant for clinical situations involving transplant tolerance. While the shortage of regulatory cells is thought to be one reason for this, T cell-intrinsic tolerance processes such as anergy are also poorly triggered in such hosts. In order to understand the latter, we used a T cell deficient mouse model system where adoptively transferred autoreactive T cells are significantly tolerized in a cell intrinsic fashion, without differentiation to regulatory T cells. Intriguingly these T cells often retain sufficient effector functions to trigger autoimmune pathology. Here we find that the high population density of the autoreactive T cells that accumulated in such a host limits the progression of the cell-intrinsic tolerance process in T cells. Accordingly, reducing the cell density during a second transfer allowed T cells to further tune down their responsiveness to antigenic stimulation. The retuning of T cells was reflected by a loss of the T cell's abilities to proliferate, produces cytokines or help B cells. We further suggest, based on altering the levels of chronic antigen using miniosmotic pumps, that the effects of cell-density on T cell re-tuning may reflect the effective changes in the antigen dose perceived by individual T cells. This could proportionally elicit more negative feedback downstream of the TCR. Consistent with this, the retuned T cells showed signaling defects both proximal and distal to the TCR. Therefore, similar to the immunogenic activation of T cells, cell-intrinsic T cell tolerance may also involve a quantitative and progressive process of tuning down its antigen-responsiveness. The progress of such tuning seems to be stabilized at multiple intermediate stages by factors such as cell density, rather than just absolute antigen levels.

The ERM Protein Moesin Regulates CD8+ Regulatory T Cell Homeostasis and Self-Tolerance

The ezrin-radixin-moesin (ERM) proteins are a family of membrane-associated proteins that link membrane proteins with actin filaments in the cell cortex and regulate many cellular processes, including cell shape determination, membrane transport, and signal transduction. Lymphocytes predominantly express two ERM members, ezrin and moesin. Mutations in the moesin gene in humans are associated with primary immunodeficiency with profound lymphopenia, and moesin-deficient mice exhibit a similar lymphopenia phenotype. In this study, we show that aging moesin-deficient mice develop a systemic lupus erythematosus-like autoimmune phenotype, which is characterized by elevated serum autoantibody levels and glomerulonephritis. Younger moesin-deficient mice exhibited elevated basal levels of several Ig isotypes and enhanced Ab affinity maturation upon immunization. Germinal center B cells and follicular helper T cells spontaneously accumulated in unimmunized mice, and CD8⁺CD44⁺CD122⁺Ly49⁺ regulatory T (CD8⁺ Tregs) cells, which inhibit the expansion of follicular helper T cells, were severely reduced in these mice. Isolated CD8⁺ Treg cells from moesin-deficient mice showed impaired proliferation in response to IL-15, which was accompanied by defects in STAT5 activation and IL-15Rα internalization, suggesting that moesin plays a key role in IL-15-mediated signaling. These findings underscore the importance of moesin in IL-15-dependent CD8⁺ Treg cell homeostasis and, thus, the control of self-tolerance.

Human neonatal thymectomy induces altered B-cell responses and autoreactivity

An association between T‐cell lymphopenia and autoimmunity has long been proposed, but it remains to be elucidated whether T‐cell lymphopenia affects B‐cell responses to autoantigens. Human neonatal thymectomy (Tx) results in a decrease in T‐cell numbers and we used this model to study the development of autoreactivity. Two cohorts of neonatally thymectomized individuals were examined, a cohort of young (1–5 years post‐Tx, n = 10–27) and older children (>10 years, n = 26), and compared to healthy age‐matched controls. T‐cell and B‐cell subsets were assessed and autoantibody profiling performed. Early post‐Tx, a decrease in T‐cell numbers (2.75 × 10⁹/L vs. 0.71 × 10⁹/L) and an increased proportion of memory T cells (19.72 vs. 57.43%) were observed. The presence of autoantibodies was correlated with an increased proportion of memory T cells in thymectomized children. No differences were seen in percentages of different B‐cell subsets between the groups. The autoantigen microarray showed a skewed autoantibody response after Tx. In the cohort of older individuals, autoantibodies were present in 62% of the thymectomized children, while they were found in only 33% of the healthy controls. Overall, our data suggest that neonatal Tx skews the autoantibody profile. Preferential expansion and preservation of Treg (regulatory T) cell stability and function, may contribute to preventing autoimmune disease development after Tx.

Foxp3-independent mechanism by which TGF-β controls peripheral T cell tolerance

Peripheral T cell tolerance is promoted by the regulatory cytokine TGF-β and Foxp3-expressing Treg cells. However, whether TGF-β and Treg cells are part of the same regulatory module, or exist largely as distinct pathways to repress self-reactive T cells remains incompletely understood. Using a transgenic model of autoimmune diabetes, here we show that ablation of TGF-β receptor II (TβRII) in T cells, but not Foxp3 deficiency, resulted in early-onset diabetes with complete penetrance. The rampant autoimmune disease was associated with enhanced T cell priming and elevated T cell expression of the inflammatory cytokine GM-CSF, concomitant with pancreatic infiltration of inflammatory monocytes that triggered immunopathology. Ablation of the GM-CSF receptor alleviated the monocyte response and inhibited disease development. These findings reveal that TGF-β promotes T cell tolerance primarily via Foxp3-independent mechanisms and prevents autoimmunity in this model by repressing the cross talk between adaptive and innate immune systems.

Intestinal microbiota link lymphopenia to murine autoimmunity via PD-1+CXCR5-/dim B-helper T cell induction

T cell lymphopenia results in peripheral homeostatic expansion to maintain the T cell immune system, which is termed lymphopenia-induced proliferation (LIP). LIP is a potential risk for expanding autoreactive clones to become pathogenic in human and murine autoimmune diseases. However, the ontogeny of T cells that induce autoantibody production by autoreactive B cells in LIP remains unclear. Transfer of CD4⁺CD25⁻ conventional T (Tc) cells into T-cell-deficient athymic nude mice has been previously reported as a LIP-induced autoimmune model which develops organ-specific autoimmune diseases and systemic antinuclear antibodies (ANAs). We show here that via LIP in this model, Tc cells proliferated and differentiated into PD-1⁺CXCR5^−/dim B-helper T cells, which promoted splenic germinal center (GC) formation, provided help for autoantibody-producing B cells, and had distinctive features of follicular helper T (Tfh) cells except that they do not express high CXCR5. Intestinal microbiota were essential for their generation, since depletion of them in recipient mice by antibiotics resulted in a reduction of LIP-induced PD-1⁺CXCR5^−/dim B-helper T cells and an amelioration of autoimmune responses. Our findings will contribute to the elucidation of the mechanism of lymphopenia-induced autoimmunity and autoantibody production, and will pave the way for microbiota-targeted novel therapeutic approaches to systemic autoimmune diseases.

Toward revision of antimicrobial therapies in hematopoietic stem cell transplantation: target the pathogens, but protect the indigenous microbiota

Host microbiota plays important roles in providing colonization resistance to pathogens and instructing development and function of the immune system. Antibiotic treatments intended to target pathogens further weaken the host defenses and may paradoxically increase the risk of systemic infections. This consequence is especially problematic in patients undergoing hematopoietic stem cell transplantation, where the mucosal defenses are already weakened by the conditioning regimens. This review discusses the roles that indigenous microbiota plays in protecting the host and maintaining immune homeostasis. In addition, we highlight possible strategies that are being developed to allow targeted antimicrobial therapy against pathogens, while minimizing the harm to indigenous microbiota.

Adoptive Cell Therapy with Tregs to Improve Transplant Outcomes: The Promise and the Stumbling Blocks

The contribution of regulatory T cells (Treg) to the induction and maintenance of tolerance is well-recognized in rodents and may contribute to long-term human organ allograft survival. The therapeutic efficacy of adoptively-transferred Treg in promoting tolerance to organ allografts is well-recognized in mouse models. Early phase 1/2 clinical studies of Treg therapy have been conducted in patients with type-1 (autoimmune) diabetes and refractory Crohn's disease, and for inhibition of graft-versus-host disease following bone marrow transplantation with proven safety. The feasibility of adoptive Treg therapy in the clinic is subject to various parameters, including optimal cell source, isolation procedure, expansion, target dose, time of infusion, as well as generation of a GMP-cell product. Several phase 1/2 Treg dose-escalation studies are underway in organ transplantation. Recent evidence suggests that additional factors are critical to ensure Treg safety and efficacy in allograft recipients, including Treg characterization, stability, longevity, trafficking, concomitant immunosuppression, and donor antigen specificity. Accordingly, Treg therapy in the context of organ transplantation may prove more challenging in comparison to other prospective clinical settings of Treg immunotherapy, such as type-1 diabetes.

[Primary immunodeficiency and autoimmunity]

Many evidences highlight that immunodeficiency and autoimmunity are two sides of a same coin. Primary immune deficiencies (PIDs), which are rare mono- or multigenic defects of innate or adaptative immunity, frequently associate with autoimmunity. Analyses of single-gene defects in immune pathways of families with PIDs, by new tools of molecular biology (next genome sequencing technologies), allowed a better understanding of the ways that could both drive immune defect with immune deficiency and autoimmunity. Moreover, genes implicated in rare single-gene defects are now known to be also involved in polygenic conventional autoimmune diseases. Here, we describe the main autoimmune symptoms occurring in PIDs and the underlying mechanisms that lead to autoimmunity in immunodeficiency. We review the links between autoimmunity and immunodeficiency and purpose some principles of care for patients with PIDs and autoimmunity.

Impact of Human Mutant TGFβ1/Fc Protein on Memory and Regulatory T Cell Homeostasis Following Lymphodepletion in Nonhuman Primates

Transforming growth factor β1 (TGFβ1) plays a key role in T cell homeostasis and peripheral tolerance. We evaluated the influence of a novel human mutant TGFβ1/Fc (human IgG4 Fc) fusion protein on memory CD4⁺ and CD8⁺ T cell (Tmem) responses in vitro and their recovery following antithymocyte globulin (ATG)-mediated lymphodepletion in monkeys. TGFβ1/Fc induced Smad2/3 protein phosphorylation in rhesus and human peripheral blood mononuclear cells and augmented the suppressive effect of rapamycin on rhesus Tmem proliferation after either alloactivation or anti-CD3/CD28 stimulation. In combination with IL-2, the incidence of CD4⁺ CD25^hi Foxp3^hi regulatory T cells (Treg) and Treg:Th17 ratios were increased. In lymphodepleted monkeys, whole blood trough levels of infused TGFβ1/Fc were maintained between 2 and 7 μg/mL for 35 days. Following ATG administration, total T cell numbers were reduced markedly. In those given TGFβ1/Fc infusion, CD8⁺ T cell recovery to predepletion levels was delayed compared to controls. Additionally, numbers of CD4⁺ CD25^hi CD127^lo Treg increased at 4-6 weeks after depletion but subsequently declined to predepletion levels by 12 weeks. In all monkeys, CD4⁺ CD25^hi Foxp3^hi Treg/CD4⁺ IL-17⁺ cell ratios were reduced, particularly after stopping TGFβ1/Fc infusion. Thus, human TGFβ1/Fc infusion may delay Tmem recovery following lymphodepletion in nonhuman primates. Combined (low-dose) IL-2 infusion may be required to improve the Treg:Th17 ratio following lymphodepletion.

Idiopathic CD4 lymphocytopenia with sensorimotor polyneuropathy

A, 21-years-old, male, presented with acute onset, gradually progressive, predominantly distal, symmetrical weakness of both upper and lower limbs with arreflexia. He had impaired sensations in glove and stocking distribution with distal gradient. He was found to have absolute CD4 + cell count of 188 cells/μL, absolute CD8 cell count, 532 cells/μL and CD4: CD8 ratio of 0.35. Electrophysiology revealed reduced to absent CMAP amplitude as well as SNAPs in various nerves of upper and lower limbs, along with normal conduction velocity and normal F wave latencies. Pattern evoked visual potentials were prolonged, on both sides, P100 being 130 ms, on right and 108 ms, on left side. In the follow up of 2 years, he showed spontaneous but gradual clinical improvement but his electrophysiological parameters as well as CD 4+ cells count did not show any significant improvement.

Targeting Homeostatic T Cell Proliferation to Control Beta-Cell Autoimmunity

Immunomodulation of the autoreactive T cell response is considered a major strategy to control beta-cell autoimmunity, both in the natural history of type 1 diabetes and in islet transplantation, which can be affected by autoimmunity recurrence. So far, these strategies have had modest results, prompting efforts to define novel cellular and molecular targets to control autoreactive T cell expansion and activation. Novel findings highlighted the important role of the homeostatic cytokine interleukin-7 in inducing proliferation and differentiation of autoreactive T cell clones that causes beta-cell autoimmunity. In this review, we discuss recent evidences and novel findings on the role of IL-7 mediated homeostatic T cell proliferation in the process of beta-cell destruction and evidences of how targeting IL-7 and its receptor could be an innovative and effective strategy to control beta-cell autoimmunity.

Distinct roles of T-cell lymphopenia and the microbial flora for gastrointestinal and CNS autoimmunity

T-cell lymphopenia is a major risk factor for autoimmunity. Here we describe congenic Lewis (LEW) rats with a loss-of-function mutation in the Gimap5 gene, leading to a 92% reduction in peripheral T-cell numbers. Gimap5-deficient LEW rats developed eosinophilic autoimmune gastroenteritis accompanied by a 40-fold increase in IgE serum levels. This phenotype was ameliorated by antibiotic treatment, indicating a critical role of the microbial flora in the development of inflammatory bowel disease. Interestingly, Gimap5-deficient LEW rats showed strongly aggravated experimental autoimmune encephalomyelitis (EAE) after immunization with guinea pig myelin basic protein. This phenotype, however, persisted after antibiosis, confirming that the enhanced CNS autoimmune response in T-cell lymphopenic Gimap5-deficient LEW rats was unrelated to the composition of the microbial flora. Rather, it seems that it was caused by the 7-fold increase in the percentage of activated T cells producing IL-17 and IFN-γ, and the skewed T-cell receptor (TCR) repertoire, both of which were the result of T-cell lymphopenia and not affected by antibiosis. This notion was supported by the observation that adoptive T-cell transfer corrected the TCR repertoire and improved EAE. Collectively, our findings confirm a critical albeit differential role of T-cell lymphopenia in the susceptibility to organ-specific autoimmune responses.-Fischer, H. J., Witte, A.-K., Walter, L., Gröne, H.-J., van den Brandt, J., Reichardt, H. M. Distinct roles of T-cell lymphopenia and the microbial flora for gastrointestinal and CNS autoimmunity.

A septin requirement differentiates autonomous and contact-facilitated T cell proliferation

T cell proliferation is initiated by T cell antigen receptor (TCR) triggering and/or by soluble growth factors. In characterizing T cells lacking the septin cytoskeleton, we found that successful cell division has discrete septin-dependent and -independent pathways. Septin-deficient T cells failed cytokinesis when prompted by pharmacological activation or cytokines. In contrast, cell division was independent of septins when cell-cell contacts, such as those from antigen-presenting cells, provided a niche. This septin-independent pathway was mediated by phosphatidylinositol-3-OH kinase activation through a combination of integrins and co-stimulatory signals. We could differentiate cytokine- versus antigen-driven expansion in vivo and thus demonstrate that targeting septins has strong potential to moderate detrimental bystander or homeostatic cytokine-driven proliferation without influencing expansion driven by conventional antigen-presentation.

PTPN2 attenuates T-cell lymphopenia-induced proliferation

When the peripheral T-cell pool is depleted, T cells undergo homoeostatic expansion. This expansion is reliant on the recognition of self-antigens and/or cytokines, in particular interleukin-7. The T cell-intrinsic mechanisms that prevent excessive homoeostatic T-cell responses and consequent overt autoreactivity remain poorly defined. Here we show that protein tyrosine phosphatase N2 (PTPN2) is elevated in naive T cells leaving the thymus to restrict homoeostatic T-cell proliferation and prevent excess responses to self-antigens in the periphery. PTPN2-deficient CD8(+) T cells undergo rapid lymphopenia-induced proliferation (LIP) when transferred into lymphopenic hosts and acquire the characteristics of antigen-experienced effector T cells. The enhanced LIP is attributed to elevated T-cell receptor-dependent, but not interleukin-7-dependent responses, results in a skewed T-cell receptor repertoire and the development of autoimmunity. Our results identify a major mechanism by which homoeostatic T-cell responses are tuned to prevent the development of autoimmune and inflammatory disorders.

Lymphopenia-induced proliferation in the absence of functional Autoimmune regulator (Aire) induces colitis in mice

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by mutations in Autoimmune regulator (Aire), a transcriptional regulator of negative selection in thymus. However, Aire is also expressed in periphery, but the full range of Aire's peripheral function is unknown. Here, we transferred lymphocytes from wildtype donors into lymphopenic recipients with or without functional Aire. Following cell proliferation thus took place in Aire-sufficient or deficient environment. The wildtype lymphocytes hyperproliferated and induced disease in lymphopenic Aire(-/-) but not in Aire(+/+) recipients. The disease was characterized by diarrhea, inflammation, and colitis, and in some recipients pancreatitis, gastritis, and hepatitis was also found. Our results identify Aire as an important regulator of peripheral T cell homeostasis in gastrointestinal tissues. Given a suitable trigger the absence of peripheral Aire leads to dysregulated T cell proliferation and disease.

Systemic LPS Translocation Activates Cross-Presenting Dendritic Cells but Is Dispensable for the Breakdown of CD8+ T Cell Peripheral Tolerance in Irradiated Mice

Lymphodepletion is currently used to enhance the efficacy of cytotoxic T lymphocyte adoptive transfer immunotherapy against cancer. This beneficial effect of conditioning regimens is due, at least in part, to promoting the breakdown of peripheral CD8⁺ T cell tolerance. Lymphodepletion by total body irradiation induces systemic translocation of commensal bacteria LPS from the gastrointestinal tract. Since LPS is a potent activator of the innate immune system, including antigen presenting dendritic cells, we hypothesized that LPS translocation could be required for the breakdown of peripheral tolerance observed in irradiated mice. To address this issue, we have treated irradiated mice with antibiotics in order to prevent LPS translocation and utilized them in T cell adoptive transfer experiments. Surprisingly, we found that despite of completely blocking LPS translocation into the bloodstream, antibiotic treatment did not prevent the breakdown of peripheral tolerance. Although irradiation induced the activation of cross-presenting CD8⁺ dendritic cells in the lymphoid tissue, LPS could not solely account for this effect. Activation of dendritic cells by mechanisms other than LPS translocation is sufficient to promote the differentiation of potentially autoreactive CD8⁺ T cells into effectors in irradiated mice. Our data indicate that LPS translocation is dispensable for the breakdown of CD8⁺ T cell tolerance in irradiated mice.

Reversible lacrimal gland-protective regulatory T-cell dysfunction underlies male-specific autoimmune dacryoadenitis in the non-obese diabetic mouse model of Sjögren syndrome

CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells are required to maintain immunological tolerance; however, defects in specific organ-protective Treg cell functions have not been demonstrated in organ-specific autoimmunity. Non-obese diabetic (NOD) mice spontaneously develop lacrimal and salivary gland autoimmunity and are a well-characterized model of Sjögren syndrome. Lacrimal gland disease in NOD mice is male-specific, but the role of Treg cells in this sex-specificity is not known. This study aimed to determine if male-specific autoimmune dacryoadenitis in the NOD mouse model of Sjögren syndrome is the result of lacrimal gland-protective Treg cell dysfunction. An adoptive transfer model of Sjögren syndrome was developed by transferring cells from the lacrimal gland-draining cervical lymph nodes of NOD mice to lymphocyte-deficient NOD-SCID mice. Transfer of bulk cervical lymph node cells modelled the male-specific dacryoadenitis that spontaneously develops in NOD mice. Female to female transfers resulted in dacryoadenitis if the CD4(+) CD25(+) Treg-enriched population was depleted before transfer; however, male to male transfers resulted in comparable dacryoadenitis regardless of the presence or absence of Treg cells within the donor cell population. Hormone manipulation studies suggested that this Treg cell dysfunction was mediated at least in part by androgens. Surprisingly, male Treg cells were capable of preventing the transfer of dacryoadenitis to female recipients. These data suggest that male-specific factors promote reversible dysfunction of lacrimal gland-protective Treg cells and, to our knowledge, form the first evidence for reversible organ-protective Treg cell dysfunction in organ-specific autoimmunity.

Porcine reproductive and respiratory syndrome (PRRS): an immune dysregulatory pandemic

Porcine reproductive and respiratory disease syndrome (PRRS) is a viral pandemic that especially affects neonates within the “critical window” of immunological development. PRRS was recognized in 1987 and within a few years became pandemic causing an estimated yearly $600,000 economic loss in the USA with comparative losses in most other countries. The causative agent is a single-stranded, positive-sense enveloped arterivirus (PRRSV) that infects macrophages and plasmacytoid dendritic cells. Despite the discovery of PRRSV in 1991 and the publication of >2,000 articles, the control of PRRS is problematic. Despite the large volume of literature on this disease, the cellular and molecular mechanisms describing how PRRSV dysregulates the host immune system are poorly understood. We know that PRRSV suppresses innate immunity and causes abnormal B cell proliferation and repertoire development, often lymphopenia and thymic atrophy. The PRRSV genome is highly diverse, rapidly evolving but amenable to the generation of many mutants and chimeric viruses for experimental studies. PRRSV only replicates in swine which adds to the experimental difficulty since no inbred well-defined animal models are available. In this article, we summarize current knowledge and apply it toward developing a series of provocative and testable hypotheses to explain how PRRSV immunomodulates the porcine immune system with the goal of adding new perspectives on this disease.

Inflammation and lymphopenia trigger autoimmunity by suppression of IL-2-controlled regulatory T cell and increase of IL-21-mediated effector T cell expansion

The dynamic interplay between regulatory T cells (T(regs)) and effector T cells (T(effs)) governs the balance between tolerance and effector immune responses. Perturbations of T(reg) frequency and function or imbalances in T(reg)/T(eff) levels are associated with the development of autoimmunity. The factors that mediate these changes remain poorly understood and were investigated in this study in murine autoimmune arthritis. T(regs) displayed a stable phenotype in arthritic mice and were fully functional in in vitro suppression assays. However, their expansion was delayed relative to T(effs) (T follicular helper cells and Th17 cells) during the early stages of autoimmune reactivity. This imbalance is likely to have led to insufficient T(reg) control of T(effs) and induced autoimmunity. Moreover, a counterregulatory and probably IL-7-driven increase in thymic T(reg) production and recruitment to inflamed tissues was too slow for disease prevention. Increased T(eff) over T(reg) expansion was further aggravated by inflammation and lymphopenia. Both these conditions contribute to autoimmune pathogenesis and were accompanied by decreases in the availability of IL-2 and increases in levels of IL-21. IL-2 neutralization or supplementation was used to show that T(reg) expansion mainly depended on this cytokine. IL-21R(-/-) cells were used to demonstrate that IL-21 promoted the maintenance of T(effs). Thus, at inflammatory sites in experimental arthritis, a deficit in IL-2 hampers T(reg) proliferation, whereas exaggerated IL-21 levels overwhelm T(reg) control by supporting T(eff) expansion. This identifies IL-2 and IL-21 as targets for manipulation in therapies for autoimmunity.

Innate immune cell CD45 regulates lymphopenia-induced T cell proliferation

The leukocyte-specific tyrosine phosphatase, CD45, severely impacts T cell development and activation by modulating TCR signaling. CD45-deficient (CD45KO) mice have reduced peripheral T cell numbers where CD8 T cells are underrepresented. In this article, we show that CD45KO mice are unable to support efficient homeostatic proliferation, affecting CD8 T cells more than CD4 T cells. Using CD45-RAG1 double-deficient (45RAGKO) mice, we show that lymphopenia-induced proliferation (LIP) of CD45-sufficient T cells is defective in a host environment lacking CD45 on innate immune cells. We identify two deficiencies in the 45RAGKO mice that affect LIP. One involves CD11c(+) cells and the second the production of IL-7 by lymphoid stromal cells. CD45KO dendritic cells were not defective in foreign Ag-induced T cell proliferation, yet CD45KO CD11c(+) cells were unable to rescue the spontaneous LIP in the 45RAGKO mice. This was in contrast with the CD45-sufficient CD11c(+) cells that partially rescued this spontaneous proliferation and did so without affecting IL-7 levels. The absence of CD45 also led to reduced IL-7 production by lymphoid stromal cells, suggesting an indirect effect of CD45 on innate immune cells in influencing IL-7 production by lymphoid stromal cells. These findings demonstrate a novel role for CD45 on innate immune cells in promoting lymphopenia-induced T cell proliferation and suggest that innate immune cells may communicate with stromal cells to regulate IL-7 production.

On the origin of immunopathology

Stranded between medicine and experimental biology, immunology is buried in its own problems and remains distant from important areas of current biology, such as evolutionary theory, developmental biology and cognitive sciences. Immunology has treated the living system merely as the place or dimension in which immune activity takes place, inserted on a misleading axis (progressive responsiveness versus no response; memory versus tolerance) which neglects the analysis of a robustly stable dynamics which is always present and is neither tolerance nor immunity-a problem currently approached as one of "regulatory" activity. However, a regulatory response also demands regulation, leading to an endless recursion and the adoption of a stimulus-response framework inevitably drives us away from the physiological processes in which lymphocytes are involved. Herein, we propose that immunological physiology, like everything else in the body is dynamic and conservative. Immunopathology, including inherited immunodeficiencies, severe forms of infectious diseases, allergy and autoimmune diseases, are interferences with this stability which frequently include oligoclonal expansions of T lymphocytes. We suggest that this decrease in clonal diversity results from a loss of the stabilizing connectivity among lymphocytes and are not simply markers of immunopathology, but are rather expressions of basic pathogenic mechanisms. The so-called autoimmune diseases are examples of this disequilibrium. In the last decade the characterization of an enormous and diversified commensal microbiota has posed a new and pressing problem: how to explain the harmonic conviviality with trillions of foreign macromolecules. In addition, robustly stable relations towards macromolecular diet can be established by simple ingestion, a state presently labeled as "oral tolerance", a problem that has been buffered for decades as anti-inflammatory protection of the gut. A major change in terminology is necessary to describe this new panorama. We focus on two important gaps in immunological discussions: (a) the organism, seen simultaneously as the medium with which the immune system is constantly in touch and as the entity that mediates the contact with external materials; and (b) the observer, the immunologist, who operates as a human being in human languaging with other human beings, and characterizes immunological specificity. We acknowledge that we are proposing radical departures from current dogma and that we should justify them. Most of what we propose stem form a way of seeing called Biology of Cognition and Language, that derives from ideas of the neurobiologist/philosopher Humberto Maturana, also known as "autopoiesis theory".

Mode of action and clinical studies with alemtuzumab

The lymphocyte depleting anti-CD52 monoclonal antibody alemtuzumab has been used in Cambridge, UK, as an experimental treatment of multiple sclerosis since 1991. One phase-2 trial (CAMMS-223) and two phase-3 studies (CARE-MS1 and CARE-MS2) have confirmed its efficacy in treatment-naive patients, and have established superiority over interferon beta-1a in patients who continue to relapse in spite of first-line therapy (Cohen et al., 2012; Coles et al., 2008; Coles et al., 2012a; Coles et al., 2012b). Despite causing a prolonged T cell lymphopenia, significant infections have not been an issue following treatment; rather alemtuzumab's primary safety concern is secondary autoimmunity, occurring up to five years after treatment and maximally at two years: 30% of patients develops thyroid autoimmunity, and 1% develops idiopathic thrombocytopenic purpura (ITP). In addition, 4 out of 1486 patients (<0.3%) treated on the commercially sponsored studies developed glomerulonephritis. Two of these patients developed anti-glomerular basement membrane disease, a condition which may result in renal failure unless treated aggressively. In September 2013, the European Medicine Agency (EMA) ruled that the benefit-to-risk balance for alemtuzumab was favourable, approving it as a first-line therapy for adults with active relapsing remitting multiple sclerosis (under the trade name Lemtrada). Lemtrada is now also approved as a treatment of multiple sclerosis in Canada, Australia, Switzerland, Israel, Mexico and Brazil. However, in December 2013, Lemtrada failed to gain approval from the U.S. Food and Drug Administration (FDA), with concerns over trial design and safety stated as the main reasons. In this review we describe our local experience and explain the rationale behind its initial use as a treatment of multiple sclerosis and behind the design of the commercially sponsored trials, summarising their key findings. We also sum up our understanding of its mechanism of action.

Delay in cART initiation results in persistent immune dysregulation and poor recovery of T-cell phenotype despite a decade of successful HIV suppression

Background

Successful combination antiretroviral therapy (cART) increases levels of CD4+ T-cells, however this increase may not accurately reflect long-term immune recovery since T-cell dysregulation and loss of T-cell homeostasis often persist. We therefore assessed the impact of a decade of effective cART on immune regulation, T-cell homeostasis, and overall T-cell phenotype.

Methods

We conducted a retrospective study of 288 HIV+ cART-naïve patients initiating therapy. We identified 86 individuals who received cART for at least a decade, of which 44 consistently maintained undetectable plasma HIV-RNA levels throughout therapy. At baseline, participants were classified into three groups according to pre-treatment CD4+ T-cell counts: Group I (CD4<200 cells/mm³); Group II (CD4: 200–350 cells/mm³); Group III (CD4>350 cells/mm³). Outcomes of interest were: (1) CD4+ T-cell count restoration (CD4>532 cells/mm³); (2) normalization of CD4:CD8 T-cell ratio (1.2–3.3); (3) maintenance of CD3+ T-cell homeostasis (CD3: 65%–85% of peripheral lymphocytes); (4) normalization of the complete T-cell phenotype (TCP).

Results

Despite a decade of sustained successful cART, complete T-cell phenotype normalization only occurred in 16% of patients, most of whom had initiated therapy at high CD4+ T-cell counts (>350 cells/mm³). The TCP parameter that was the least restored among patients was the CD4:CD8 T-cell ratio.

Conclusions

Failure to normalize the complete T-cell phenotype was most apparent in patients who initiated cART with a CD4+ T-cell count <200 cells/mm³. The impact of this impaired T-cell phenotype on life-long immune function and potential comorbidities remains to be elucidated.

Naive CD4 T-cell activation identifies MS patients having rapid transition to progressive MS

Objective:

Our objective was to determine whether altered naive CD4 T-cell biology contributes to development of disease progression in secondary progressive multiple sclerosis (SPMS).

Methods:

We compared the naive CD4 T-cell gene expression profiles of 19 patients with SPMS and 14 healthy controls (HCs) using a whole-genome microarray approach. We analyzed surface protein expression of critical genes by flow cytometry after T-cell receptor (TCR) stimulation of naive CD4 T cells isolated from HCs and patients with SPMS.

Results:

Hierarchical clustering segregated patients with SPMS into 2 subgroups: SP-1, which had a short duration of relapsing-remitting multiple sclerosis (MS), and SP-2, which had a long duration of relapsing-remitting MS. SP-1 patients upregulated numerous immune genes, including genes within TCR and toll-like receptor (TLR) signaling pathways. SP-2 patients showed immune gene downregulation in comparison with HCs. We identified an SP-1–specific transcriptional signature of 3 genes (TLR4, TLR2, and chemokine receptor 1), and these genes had higher surface protein expression in SP-1 than in SP-2. After TCR stimulation for 48 hours, only SP-1 showed a progressive linear increase in TLR2 and TLR4 protein expression.

Conclusions:

Differences in naive CD4 T-cell biology, notably of TCR and TLR signaling pathways, identified patients with MS with more rapid conversion to secondary progression, a critical determinant of long-term disability in MS.

Low DPP4 expression and activity in multiple sclerosis

Multiple sclerosis (MS) is a prototypic Th1/Th17 chronic autoimmune disease of the central nervous system. Dipeptidyl peptidase 4 (DPP4 or CD26) is a multifunctional molecule involved in autoimmune diseases' pathophysiology. We sought to integrate disparate pieces of data and analyze the plasma levels of sDPP4, DPP activity and DPP4 surface expression on T-cells in 129 MS patients with different clinical forms and 53 healthy controls, across two independent cohorts. Herein, we provide new evidence that sDPP4 concentration and DPP activity are significantly lower in MS patients than controls (p < 0.0001 and p < 0.01, respectively). In contrast, the frequency of circulating CD8(+)DPP4(hi) T-cells (p = 0.02) was increased in MS patients. This is the first study that simultaneously analyzes DPP4 expression and function in a large cohort of MS patients. Our data indicate a putative role for DPP4 in MS pathophysiology and suggest that a deeper understanding of surface versus shed DPP4 biology is warranted.

Human autoimmunity after lymphocyte depletion is caused by homeostatic T-cell proliferation

The association between lymphopenia and autoimmunity is recognized, but the underlying mechanisms are poorly understood and have not been studied systematically in humans. People with multiple sclerosis treated with the lymphocyte-depleting monoclonal antibody alemtuzumab offer a unique opportunity to study this phenomenon; one in three people develops clinical autoimmunity, and one in three people develops asymptomatic autoantibodies after treatment. Here, we show that T-cell recovery after alemtuzumab is driven by homeostatic proliferation, leading to the generation of chronically activated (CD28(-)CD57(+)), highly proliferative (Ki67(+)), oligoclonal, memory-like CD4 and CD8 T cells (CCR7(-)CD45RA(-) or CCR7(-)CD45RA(+)) capable of producing proinflammatory cytokines. Individuals who develop autoimmunity after treatment are no more lymphopenic than their nonautoimmune counterparts, but they show reduced thymopoiesis and generate a more restricted T-cell repertoire. Taken together, these findings demonstrate that homeostatic proliferation drives lymphopenia-associated autoimmunity in humans.