T-cell Pool Research Articles

The fate of CD4+ T cells under tolerance‐inducing stimulation: a modeling perspective

Non-depleting anti-CD4 monoclonal antibodies (MAbs) induce long-term dominant tolerance mediated by regulatory T cells in several animal models of transplantation, allergy and autoimmunity. However, despite many studies on tolerance induction following CD4 blockade, the consequences of this intervention on T-cell kinetics are still unknown. Mathematical models have been useful to understand lymphocyte dynamics, estimating rates of proliferation and cell death following an intervention. Using the same strategy, we found that CD4(+) T cells activated in vitro in the presence of non-depleting anti-CD4 MAbs are prevented from undergoing optimal proliferation and show a higher frequency of apoptosis. Although the changes are small, during the course of a proliferative response, they lead to very distinct final levels of cell numbers. The importance of these mechanisms, predicted by the mathematical model, was validated by showing that lck-driven Bcl-x(L) transgenic mice, bearing T cells resistant to apoptosis, fail to become tolerant to skin grafts following CD4-blockade. Our data show that, in addition to induction of regulatory T cells, CD4 blockade has a marked effect in the effector T-cell pool by the combined action of hindering proliferation while favoring apoptosis. It is, therefore, the combination of all those mechanisms that leads to stable tolerance.

Signal transducer and activator of transcription 3 (Stat3) contributes to T‐cell homeostasis by regulating pro‐survival Bcl‐2 family genes

The naive T-cell pool in peripheral lymphoid tissues is fairly stable in terms of number, diversity and functional capabilities in spite of the absence of prominent stimuli. This stability is attributed to continuous tuning of the composition of the T-cell pool by various homeostatic signals. Despite extensive research into the link between signal transducer and activator of transcription 3 (Stat3) and T-cell survival, little is known about how Stat3 regulates homeostasis by maintaining the required naive T-cell population in peripheral lymphoid organs. We assessed whether the elimination of Stat3 in T cells limits T-cell survival. We demonstrated that the proportion and number of single-positive thymocytes as well as T cells in the spleen and lymph nodes were significantly decreased in the Stat3-deficient group as a result of the enhanced susceptibility of Stat3-deleted T lymphocytes to apoptosis. Importantly, expression of the anti-apoptotic Bcl-2 and Bcl-xL was markedly decreased in Stat3-deleted single-positive thymocytes and T lymphocytes, suggesting that Stat3 helps to maintain the T-cell pool in the resting condition by promoting the expression of Bcl-2 family genes. These findings suggest the importance of Stat3 in the integration of homeostatic cues for the maintenance and functional tuning of the T-cell pool.

Differential requirement for CCR4 in the maintenance but not establishment of the invariant Vγ5(+) dendritic epidermal T-cell pool.

Thymocytes expressing the invariant Vγ5 γδT-cell receptor represent progenitors of dendritic epidermal T-cells (DETC) that play an important immune surveillance role in the skin. In contrast to the bulk of αβT-cell development, Vγ5+ DETC progenitor development occurs exclusively in fetal thymus. Whilst αβT-cell development is known to require chemokine receptor mediated migration through distinct thymus regions, culminating in medullary entry and thymic egress, the importance and control of intrathymic migration for DETC progenitors is unclear. We recently revealed a link between Vγ5+ DETC progenitor development and medullary thymic epithelial cells expressing Aire, a known regulator of thymic chemokine expression, demonstrating that normal Vγ5+ DETC progenitor development requires regulated intramedullary positioning. Here we investigate the role of chemokines and their receptors during intrathymic Vγ5+ DETC progenitor development and establishment of the DETC pool in the skin. We report that thymic medullary accumulation of Vγ5+ DETC progenitors is a G-protein coupled receptor dependent process. However, this process occurs independently of Aire’s influences on intrathymic chemokines, and in the absence of CCR4 and CCR7 expression by DETC progenitors. In contrast, analysis of epidermal γδT-cells at neonatal and adult stages in CCR4−/− mice reveals that reduced numbers of DETC in adult epidermis are not a consequence of diminished intrathymic embryonic development, nor deficiencies in initial epidermal seeding in the neonate. Collectively, our data reveal differences in the chemokine receptor requirements for intrathymic migration of αβ and invariant γδT-cells, and highlight a differential role for CCR4 in the maintenance, but not initial seeding, of DETC in the epidermis.

Lung Inflammation and Thymic Atrophy after Bleomycin Are Controlled by the Prostaglandin D2Receptor DP1

Acute lung injury (ALI) can be accompanied by secondary systemic manifestations. In a model of ALI induced by bleomycin (bleo), we examined the response of D prostanoid receptor 1 (DP1)-deficient mice (DP1(-/-)) to better understand these processes. DP1 deficiency aggravated the toxicity of bleo as indicated by enhanced body weight loss, mortality, and lung inflammation including bronchoalveolar permeability and neutrophilia. Thymic atrophy was also observed after bleo and was strongly exacerbated in DP1(-/-) mice. This resulted from the enhanced depletion of immature T lymphocytes in the thymus of DP1(-/-) mice, a phenomenon usually related to increased glucocorticoid release in blood. Serum corticosterone was more elevated in DP1(-/-) mice after bleo than in wild-type (wt) mice. Thymocytes of DP1(-/-) mice were not more sensitive to dexamethasone in vitro, and systemic delivery of dexamethasone or peritoneal inflammation after LPS induced a similar thymic atrophy in wt and DP1(-/-) mice, indicating that pulmonary DP1 was critical to the control of thymic atrophy after bleo. DP1(-/-) mice showed increased lung and/or blood mediators involved in neutrophil recruitment and/or glucocorticoid production/thymic atrophy (osteopontin, leukemia inhibitory factor, and keratinocyte-derived chemokine) after bleo. Finally, local pulmonary DP1 activation or inhibition in wt mice abrogated or amplified thymic atrophy after bleo, respectively. Altogether, our data reveal that ALI can perturb the systemic T-cell pool by inducing thymic atrophy and that both pathological processes are controlled by the pulmonary DP1 receptor. This new pathway represents a potential therapeutic target in ALI.

CD28 controls the development of innate‐like CD8+T cells by promoting the functional maturation of NKT cells

NK T cells(NKT cells) share functional characteristics and homing properties that are distinct from conventional T cells. In this study, we investigated the contribution of CD28 in the functional development of γδ NKT and αβ NKT cells in mice. We show that CD28 promotes the thymic maturation of promyelocytic leukemia zinc finger(+) IL-4(+) NKT cells and upregulation of LFA-1 expression on NKT cells. We demonstrate that the developmental defect of γδ NKT cells in CD28-deficient mice is cell autonomous. Moreover, we show in both wild-type C57BL/6 mice and in downstream of tyrosine kinase-1 transgenic mice, a mouse model with increased numbers of γδ NKT cells, that CD28-mediated regulation of thymic IL-4(+) NKT cells promotes the differentiation of eomesodermin(+) CD44(high) innate-like CD8(+) T cells. These findings reveal a previously unappreciated mechanism by which CD28 controls NKT-cell homeostasis and the size of the innate-like CD8(+) T-cell pool.

Reshaping of T-lymphocyte compartment in adult prepubertaly ovariectomised rats: A putative role for progesterone deficiency

This study explores the role of ovarian hormones in the phenotypic shaping of peripheral T-cell pool over the reproductive lifespan of rats. For this purpose, 2-month-old prepubertally ovariectomised (Ox) rats, showing oestrogen and progesterone deficiency, and 11-month-old Ox rats, exhibiting only progesterone deficiency, were examined for thymus output, and cellularity and composition of major TCRαβ+ peripheral blood lymphocyte (PBL) and splenocyte subsets. Although ovariectomy increased thymic output in both 2- and 11-month-old rats, the count of both CD4+ and CD8+ PBLs and splenocytes increased only in the former. In the blood and spleen of 11-month-old Ox rats only the count of CD8+ cells increased. Although ovariectomy affected the total CD4+ count in none of the examined compartments from the 11-month-old rats, it increased CD4+FoxP3+ PBL and splenocyte relative proportions over those in the age-matched controls. The age-related differences in the cellularity and the major subset composition in Ox rats were linked to the differences in the ovarian steroid hormone levels registered in 2- and 11-month-old rats. The administration of progesterone to Ox rats during the seven days before the sacrificing confirmed contribution of this hormone deficiency to the ovariectomy-induced changes in the TCRαβ+ PBL and splenocyte pool from 11-month-old rats. The expansion of the CD8+ splenocyte subset in the 11-month-old Ox rats reflected increases in cellularity of memory and, particularly, naïve cells. This was due to greater thymic output of CD8+ cells and homeostatic proliferation than apoptosis in 11-month-old Ox rats when compared with age-matched sham-Ox control rats. The homeostatic changes within CD8+ splenocyte pool from 11-month-old Ox rats, most likely, reflected the enhanced splenic IL-7 and TGF-β mRNA expression. Overall, in adult female rats, circulating oestrogen and progesterone provide maintenance of T-cell counts, a diversity of T-cell repertoire, and the main T-cell subset composition in the periphery. Progesterone deficiency affects mainly the CD8+ lymphocyte compartment through increasing thymic CD8+ cell export and upsetting homeostatic regulation within the CD8+ splenocyte pool. These alterations were reversible through progesterone supplementation.

Toward eliminating HLA class I expression to generate universal cells from allogeneic donors

AbstractLong-term engraftment of allogeneic cells necessitates eluding immune-mediated rejection, which is currently achieved by matching for human leukocyte antigen (HLA) expression, immunosuppression, and/or delivery of donor-derived cells to sanctuary sites. Genetic engineering provides an alternative approach to avoid clearance of cells that are recognized as “non-self” by the recipient. To this end, we developed designer zinc finger nucleases and employed a “hit-and-run” approach to genetic editing for selective elimination of HLA expression. Electro-transfer of mRNA species coding for these engineered nucleases completely disrupted expression of HLA-A on human T cells, including CD19-specific T cells. The HLA-Aneg T-cell pools can be enriched and evade lysis by HLA-restricted cytotoxic T-cell clones. Recognition by natural killer cells of cells that had lost HLA expression was circumvented by enforced expression of nonclassical HLA molecules. Furthermore, we demonstrate that zinc finger nucleases can eliminate HLA-A expression from embryonic stem cells, which broadens the applicability of this strategy beyond infusing HLA-disparate immune cells. These findings establish that clinically appealing cell types derived from donors with disparate HLA expression can be genetically edited to evade an immune response and provide a foundation whereby cells from a single donor can be administered to multiple recipients.

HIV immune activation drives increased Eomes expression in memory CD8 T cells in association with transcriptional downregulation of CD127

During HIV infection distinct mechanisms drive immune activation of the CD4 and CD8 T cells leading to CD4 T-cell depletion and expansion of the CD8 T-cell pool. This immune activation is polyclonal and extends beyond HIV-specific T cells. One consequence of this immune activation is a profound decrease in IL-7Rα (CD127) expression on memory CD8 T cells. The mechanisms leading to this are unknown and because of the potential impact of reduced IL-7 signaling in memory T cells specific to HIV and other pathogens, in the present study we examined the molecular mechanisms implicated in this downregulation of CD127. Membrane bound (mIL7RA) and soluble (sIL7RA) mRNA expression was determined by qRT-PCR. CD127, Eomesodermin (Eomes) and T-bet expression in healthy controls and HIV-infected patients were studied by flow cytometry. CD127 downregulation occurs at the transcriptional level for both mIL7RA and sIL7RA alternative spliced forms in the CD127 memory CD8 T cells. CD127 memory CD8 T cells exhibited increased Eomes expression and an 'effector-like' gene profile. These changes were associated with higher HIV-RNA levels. Following combination antiretroviral therapy (cART), there was an increase in CD127 expression over an extended period of time (>5 months) which was associated with decreased Eomes expression. CD127 is downregulated at a transcriptional level in memory CD8 T cells in association with upregulation of Eomes expression.

OP0267 The influence of latent cytomegalovirus (CMV) infection on T-cell-phenotype in children with juvenile idiopathic arthritis (JIA)

BackgroundLife-long latent CMVinfection seems to diminish the size of the naive and the early memory T-cell pool and to drive Th1 polarization within the immune system. Previous studies in patients...

AB1110 The role of violations of the apoptosis in the formation juvenile idiopathic arthritis

BackgroundJuvenile idiopathic arthritis (JIA) – is a chronic systemic autoimmune disease that is a characterized by articular lesion with synovial hyperplasia and cellular infiltration. One of the pathogenetic mechanisms of...

AB0054 No evidence for premature immunosenescence in newly diagnosed, non treated, shared epitope-positive patients with rheumatoid arthritis

BackgroundThe peripheral T-cell pool in chronic autoimmune syndromes, such as Rheumatoid Arthritis (RA) displays features associated with senescence of the immune system. Immunosenescence is characterized by increased frequencies of terminally...

Clinical and pharmacodynamic (PD) results of a phase I trial with AMP-224 (B7-DC Fc) that binds to the PD-1 receptor.

3044 Background: PD-1/B7-H1 (PD-L1) axis blockade can reinvigorate T cells, and overcome tumor immune evasion of multiple tumor types. AMP-224 is the first recombinant B7-DC-Fc fusion protein tested in patients that binds to and modulates the PD-1 axis through a unique MOA. The MoA hypothesis for AMP-224 is depletion of PD-1high expressing T-cells representing exhausted effector cells. Subsequent replenishment of the T-cell pool with functional T-cells may restore immune function. Methods: Patients with advanced solid tumors received low dose CTX on Day 0, followed by AMP-224 (IV infusion) on Days 1 and 15 of each 28-day cycle in doses ranging from 0.3 to 30 mg/kg. Blood samples were assessed serially for changes in lymphocyte subsets, PD-1HIT cells and T cell effector function. IHC staining of paired biopsies for B7-H1, CD8, PD-1, CD4 and FoxP3 was performed to assess immunological status of the tumor at baseline and following treatment and then relative to peripheral readouts. Results: 42 patients (83% melanoma) were treated with varying doses of AMP-224 [0.3 mg/kg (n = 6); 1 mg/kg (n=4); 3 mg/kg (n = 4); 10 mg/kg (n = 22); 30 mg/kg (n = 6)]. Infusion reactions were common (69% across dose cohorts) and occurred mostly at higher doses (86% at the 10 mg/kg dose). No drug-related inflammatory adverse events were identified contrary to PD-1 blocking antibodies. Fresh pre-treatment biopsies were collected from 33/42 (78.5%) patients and paired biopsies have been collected thus far from 19/36 (52.7%) patients on study. 31% of baseline tumors were B7-H1+. Several PD readouts in the periphery showed reductions in PD-1HIcells and emergence of a functional T cell response (increases in IFNg+, TNFa+, IL-2+ CD4 and CD8 T cells) in individual patients where partial response, stable disease, and mixed responses were seen. Conclusions: Data from peripheral readouts is consistent with hypothesized AMP-224 MoA. B7-H1+ was not always predictive of functional response to AMP-224 immunotherapy. Comprehensive PD readouts and evaluation of PK/PD relationships will be presented and may ultimately predict restoration of immune competence even in the presence of initial disease progression. Clinical trial information: NCT01352884.

Skewing of the CD4+ T-Cell Pool Toward Monofunctional Antigen-Specific Responses in Patients With Immune Reconstitution Inflammatory Syndrome in The Gambia

A common complication of starting antiretroviral therapy (ART) for human immunodeficiency virus (HIV) is the development of immune reconstitution inflammatory syndrome (IRIS) in approximately 25% of patients. Despite similarities with paradoxical reactions to tuberculosis and reversal reactions in leprosy, the exact mechanisms, and therefore potential determinants, of IRIS are still unknown. In this longitudinal cohort study, we analyzed 20 patients who developed IRIS following initiation of ART and 16 patients who did not, matched for ART time point. Peripheral blood mononuclear cells were stimulated overnight with a positive control antigen and 2 tuberculosis-specific antigens (purified protein derivative [PPD] and ESAT-6/CFP10), followed by polychromatic flow cytometry for analysis of cytokine production from CD4(+) and CD8(+) T cells. Responses to PPD were significantly higher in IRIS patients compared to controls during the IRIS time point, but CD4(+) and CD8(+) T-cell responses to the positive control stimulation were significantly lower in IRIS patients at all time points. Furthermore, whereas control patients had rejuvenated polyfunctional T-cell responses by 3 months after ART, IRIS patients were strikingly monofunctional (generally interferon γ alone), even up to 6 months of ART in response to all stimulations. Our findings suggest that the peripheral T-cell responses to the underlying pathogen are exaggerated in IRIS patients but that the overall quality of the peripheral T-cell pool is significantly reduced compared to non-IRIS patients. Furthermore, these effects are apparent at least up to 3 months after cessation of IRIS.

Continuous immunosurveillance of oligodendrocyte antigens leads to the generation of effector T-cell pools that might contribute to CNS autoimmune disease (P3123)

Abstract Immunosurveillance of antigens from the CNS is tightly regulated in order to avoid autoimmune disease, such as multiple sclerosis. To test how CNS antigens are recognized by the peripheral immune system, we created transgenic mice having constitutive or inducible expression of EGFP-fused model neoantigens in myelinating glial cells. We examined the level of systemic priming to CNS neoantigens and compared it to priming from non-immune privileged gut tissue. We report here that the level of the EGFP-triple peptide in both the constitutive and inducible models is sufficiently high in the CNS to induce neoantigen-specific T cell priming in the periphery; however, there is no recruitment of these cells to the CNS. Immunosurveillance of CNS antigens in the peripheral immune tissues is enhanced during neuroinflammation, during which time activated neoantigen-specific T cells accumulate in the CNS. These data suggest that CNS antigens are surveilled in the periphery, leading to the generation of effector T cell pools. Additional inflammatory signals from the CNS induce the migration of effector T cells, which form microclusters with dendritic cells and autophagic oligodendrocytes that leads to the amplification of CNS inflammation. Increased immunosurveillance and inflammation might contribute to the chronic phase of CNS autoimmune disease. These new models can help us dissect the mechanisms of disease initiation and maintenance that is of clinical importance.

T-cell reconstitution after allogeneic stem cell transplantation: assessment by measurement of the sjTREC/ TREC ratio and thymic naive T cells

The immune reconstitution after allogeneic hematopoietic stem cell transplantation comprises thymus-dependent and thymus-independent pathways. We wanted to improve the understanding of this complex process using two different measurements at definite checkpoints of T-cell neogenesis. We therefore assessed the thymus-dependent pathway by combining measurements of single joint T-cell receptor excision circles (sjTREC) and β T-cell receptor excision circles (βTREC) in an improved quantitative light-cycler hybridization polymerase chain reaction assay. In a subgroup of patients, we additionally assessed the proliferation kinetics of the CD31(+) thymic naïve cell population, which corresponds to recent thymic emigrants by six-color immunostaining. After the establishment of normal values in 22 healthy volunteers, we applied our polymerase chain reaction to 66 patients undergoing allogeneic hematopoietic stem cell transplantation at a median age of 44 years. It took more than 2 years after transplant to restore the pre-transplant thymic proliferation capacity. Only one third of the patients in our longitudinal study reached age-adjusted normal values for both sjTREC and βTREC at a median follow-up of 558 days, with acute graft-versus-host disease being the most prominent negative factor by univariate analysis. We observed several patterns of sjTREC and βTREC recovery suggesting different mechanisms of thymic damage in individual patients. In a comparison of CD31(+) thymic naïve cells between volunteers and patients after transplant we found a significantly higher peak proliferation rate within the latter population in the first year after transplantation. The combination of measurements of sjTREC and βTREC by our simplified polymerase chain reaction assay provides insight about the stage of T-cell development affected by different types of damage and may help to choose the correct therapeutic intervention. Besides the sole thymic T-cell neogenesis, proliferation within the CD31(+) thymic naïve cell compartment contributed to the replenishment of the naïve T-cell pool after transplantation.

B-Cell Lymphopoiesis Is Regulated by Cathepsin L

Cathepsin L (CTSL) is a ubiquitously expressed lysosomal cysteine peptidase with diverse and highly specific functions. The involvement of CTSL in thymic CD4+ T-cell positive selection has been well documented. Using CTSLnkt/nkt mice that lack CTSL activity, we have previously demonstrated that the absence of CTSL activity affects the homeostasis of the T-cell pool by decreasing CD4+ cell thymic production and increasing CD8+ thymocyte production. Herein we investigated the influence of CTSL activity on the homeostasis of peripheral B-cell populations and bone marrow (BM) B-cell maturation. B-cell numbers were increased in lymph nodes (LN), spleen and blood from CTSLnkt/nkt mice. Increases in splenic B-cell numbers were restricted to transitional T1 and T2 cells and to the marginal zone (MZ) cell subpopulation. No alterations in the proliferative or apoptosis levels were detected in peripheral B-cell populations from CTSLnkt/nkt mice. In the BM, the percentage and the absolute number of pre-pro-B, pro-B, pre-B, immature and mature B cells were not altered. However, in vitro and in vivo experiments showed that BM B-cell production was markedly increased in CTSLnkt/nkt mice. Besides, BM B-cell emigration to the spleen was increased in CTSLnkt/nkt mice. Colony-forming unit pre-B (CFU pre-B) assays in the presence of BM stromal cells (SC) and reciprocal BM chimeras revealed that both BM B-cell precursors and SC would contribute to sustain the increased B-cell hematopoiesis in CTSLnkt/nkt mice. Overall, our data clearly demonstrate that CTSL negatively regulates BM B-cell production and output therefore influencing the homeostasis of peripheral B cells.

Human mast cells drive memory CD4+ T cells toward an inflammatory IL-22+ phenotype

Mast cells are key components of the skin microenvironment in psoriasis, yet their functional role in this T-cell-mediated inflammatory disorder remains to be elucidated. To define the impact of T-cell/mast-cell cognate interactions on the cytokines produced by TH cells. We used human primary mast cells and effector/memory CD4(+) T cells for in vitro coculture experiments, and we analyzed TH cells responses by using cytometry. CD4(+) T-cell/mast-cell conjugates in skin lesions from patients with psoriasis were analyzed by using 3-color immunohistochemistry and confocal microscopy. We show that IFN-γ-primed human mast cells formed productive immunologic synapses with antigen-experienced CD4(+) T cells. These interactions promoted the generation of TH22 and IL-22/IFN-γ-producing TH cells from the circulating memory CD4(+) T-cell pool via a TNF-α/IL-6-dependent mechanism. An analysis of human psoriatic skin biopsies showed a rich infiltrate of IL-22(+)CD4(+) T cells frequently found in contact with mast cells. Moreover, most of these mast-cell-conjugated lymphocytes coexpressed IFN-γ, suggesting that IL-22(+)IFN-γ(+) CD4(+) T cells are generated in vivo on interaction with mast cells. Our findings identify human mast cells as functional partners of TH cells, shaping their responses toward IL-22 production.

Mesenchymal stromal cells as a means of controlling pathological T-cell responses in allogeneic islet transplantation

To evaluate the potential for mesenchymal stromal cells (MSCs) to regulate T-cell responses responsible for graft destruction following allogeneic islet transplantation (AIT). Despite a high level of primary graft function being observed in most individuals following AIT, the majority of recipients require exogenous insulin within 5 years, presumably due to graft attrition. Although this process is not fully understood, recent evidence suggests that a combination of chronic allograft rejection and/or the recrudescence of anti-islet autoimmunity govern islet loss. Emerging reports highlight that the pathology of AIT may involve the proliferation, effector function and homeostatic expansion of alloreactive and autoreactive T-cell pools. MSCs exhibit several desirable characteristics, which may advocate their use in AIT. This includes the capacity to suppress alloreactive and autoimmune T-cell responses, and promote a cytokine environment that is likely to be graft protective. However, further work is needed to clarify if MSCs can function in the setting of immune suppression and discern how they may effect T-cell effector functions and influence homeostatic expansion. MSCs exhibit the potential to regulate the T-cell-driven processes that underlie disease pathology in AIT, but further study may be required to maximize their therapeutic efficacy.

Infectious Tolerance as Candidate Therapy for Type 1 Diabetes: Transfer of Immunoregulatory Properties from Human Regulatory T Cells to Other T Cells and Proinflammatory Dendritic Cells

Type 1 diabetes is a T-cell-mediated autoimmune disease in which the insulin-producing cells in the islets of Langerhans are selectively destroyed. Although symptomatic insulin therapy is able to control glucose levels in the blood, many patients do not obtain the desired glycemic control, which increases the risk of diabetic complications. While many immunotherapeutic efforts to intervene in the disease process focus on systemic immune-suppressive therapies, antigen-specific immune modulation represents an attractive alternative. Dendritic cells modulated with 1.25(OH)2 vitamin D3, and dexamethasone (tolerogenic DCs) loaded with islet antigens induce Ag-specific regulatory CD4 T cells (iaTregs), offering a tissue-specific intervention therapy. iaTregs exert their function via linked suppression to diminish effector cells by modulating pro-inflammatory DCs to upregulate inhibitory receptors. In turn, these re-educated mature DCs induce IL-10-producing cells from the naïve T-cell pool. Thus, tolerogenic DCs transfer regulatory properties to pro-inflammatory DCs via iaTregs (i.e., infectious tolerance). In this review, we describe the current knowledge regarding regulatory mechanisms of these tolerogenic DCs and the Tregs that they induce, and we propose that cell therapy with human tolerogenic DCs provides new opportunities for immune intervention in patients with autoimmune diseases.

Effect of natalizumab on circulating CD4+ T-cells in multiple sclerosis.

In multiple sclerosis (MS), treatment with the monoclonal antibody natalizumab effectively reduces the formation of acute lesions in the central nervous system (CNS). Natalizumab binds the integrin very late antigen (VLA)-4, expressed on the surface of immune cells, and inhibits VLA-4 dependent transmigration of circulating immune-cells across the vascular endothelium into the CNS. Recent studies suggested that natalizumab treated MS patients have an increased T-cell pool in the blood compartment which may be selectively enriched in activated T-cells. Proposed causes are sequestration of activated T-cells due to reduced extravasation of activated and pro-inflammatory T-cells or due to induction of VLA-4 mediated co-stimulatory signals by natalizumab. In this study we examined how natalizumab treatment altered the distribution of effector and memory T-cell subsets in the blood compartment and if T-cells in general or myelin-reactive T-cells in particular showed signs of increased immune activation. Furthermore we examined the effects of natalizumab on CD4+ T-cell responses to myelin in vitro. Natalizumab-treated MS patients had significantly increased numbers of effector-memory T-cells in the blood. In T-cells from natalizumab-treated MS patients, the expression of TNF-α mRNA was increased whereas the expression of fourteen other effector cytokines or transcription factors was unchanged. Natalizumab-treated MS patients had significantly decreased expression of the co-stimulatory molecule CD134 on CD4+CD26HIGH T-cells, in blood, and natalizumab decreased the expression of CD134 on MBP-reactive CD26HIGHCD4+ T-cells in vitro. Otherwise CD4+ T-cells from natalizumab-treated and untreated MS patients showed similar responses to MBP. In conclusion natalizumab treatment selectively increased the effector memory T-cell pool but not the activation state of T-cells in the blood compartment. Myelin-reactive T-cells were not selectively increased in natalizumab treated MS.