Transforming growth factor-beta1 gene transfer is associated with the development of regulatory cells

TGF-β1 contributes to CD8+ Treg induction through p38 MAPK signaling in ovarian cancer microenvironment

CD8⁺ regulatory T cells (Tregs) contribute to cancer progression and immune evasion. We previously reported that CD8⁺ Tregs could be induced in vitro by co-culture of CD8⁺ T cells with the OC cell lines SKOV3/A2780. Here, we described the role of TGF-β1 in CD8⁺ Treg induction by the OC microenvironment. OC patients expressed high levels of TGF-β1, as did the co-culture supernatant from CD8⁺ T cells and SKOV3. Additionally, TGF-β1 levels were positively correlated with CD8⁺ Treg percentages in OC. Neutralization experiments, cytokine studies and proliferation assays revealed that the in vitro-induced CD8⁺Tregs depended at least partially on up-regulated expression of TGF-β1 to exert their suppressive function. CD8⁺ T cells cultured with SKOV3 exhibited marked activation of p38 MAPK than CD8⁺ T cells cultured alone, which could be inhibited by TGF-β1-neutralizing antibody. Moreover, the p38 specific inhibitor SB203580 dose-dependently blocked the TGF-β1 activated conversion of CD8⁺ T cells into CD8⁺ Tregs. These data suggested that in vitro-induction of CD8⁺ Tregs depended in part on TGF-β1 activation of p38 MAPK signaling. Therefore, p38 MAPK could be a therapeutic target in OC anti-tumor immunotherapy.

The role of lymphocytes in the development and treatment of alopecia areata

Alopecia areata (AA) development is associated with both innate and adaptive immune cell activation, migration to peri- and intra-follicular regions, and hair follicle disruption. Both CD4(+) and CD8(+) lymphocytes are abundant in AA lesions; however, CD8(+) cytotoxic T lymphocytes are more likely to enter inside hair follicles, circumstantially suggesting that they have a significant role to play in AA development. Several rodent models recapitulate important features of the human autoimmune disease and demonstrate that CD8(+) cytotoxic T lymphocytes are fundamentally required for AA induction and perpetuation. However, the initiating events, the self-antigens involved, and the molecular signaling pathways, all need further exploration. Studying CD8(+) cytotoxic T lymphocytes and their fate decisions in AA development may reveal new and improved treatment approaches.

Inhibition of αvβ6 promotes acute renal allograft rejection in nonhuman primates

The integrin αvβ6 activates latent transforming growth factor-β (TGF-β) within the kidney and may be a target for the prevention of chronic allograft fibrosis after kidney transplantation. However, TGF-β also has known immunosuppressive properties that are exploited by calcineurin inhibitors (CNIs); thus, the net benefit of αvβ6 inhibition remains undetermined. To assess the acute impact of interference with αvβ6 on acute rejection, we tested a humanized αvβ6-specific monoclonal antibody (STX-100) in a randomized, double-blinded, placebo-controlled nonhuman primate renal transplantation study to evaluate whether αvβ6 blockade alters the risk of acute rejection during CNI-based immunosuppression. Rhesus monkeys underwent renal allotransplantation under standard CNI-based maintenance immunosuppression; 10 biopsy-confirmed rejection-free animals were randomized to receive weekly STX-100 or placebo. Animals treated with STX-100 experienced significantly decreased rejection-free survival compared to placebo animals (p = 0.049). Immunohistochemical analysis confirmed αvβ6 ligand presence, and αvβ6 staining intensity was lower in STX-100-treated animals (p = 0.055), indicating an apparent blockade effect of STX-100. LAP, LTBP-1 and TGF-β were all decreased in animals that rejected on STX-100 compared to those that rejected on standard immunosuppression alone, suggesting a relevant effect of αvβ6 blockade on local TGF-β. These data caution against the use of αvβ6 blockade to achieve TGF-β inhibition in kidney transplantation.

Recipient-derived EDA fibronectin promotes cardiac allograft fibrosis

Advances in donor matching and immunosuppressive therapies have decreased the prevalence of acute rejection of cardiac grafts; however, chronic rejection remains a significant obstacle for long-term allograft survival. While initiating elements of anti-allograft immune responses have been identified, the linkage between these factors and the ultimate development of cardiac fibrosis is not well understood. Tissue fibrosis resembles an exaggerated wound healing response, in which extracellular matrix (ECM) molecules are central. One such ECM molecule is an alternatively spliced isoform of the ubiquitous glycoprotein fibronectin (FN), termed extra domain A-containing cellular fibronectin (EDA cFN). EDA cFN is instrumental in fibrogenesis; thus, we hypothesized that it might also regulate fibrotic remodelling associated with chronic rejection. We compared the development of acute and chronic cardiac allograft rejection in EDA cFN-deficient (EDA(-/-)) and wild-type (WT) mice. While EDA(-/-) mice developed acute cardiac rejection in a manner indistinguishable from WT controls, cardiac allografts in EDA(-/-) mice were protected from fibrosis associated with chronic rejection. Decreased fibrosis was not associated with differences in cardiomyocyte hypertrophy or intra-graft expression of pro-fibrotic mediators. Further, we examined expression of EDA cFN and total FN by whole splenocytes under conditions promoting various T-helper lineages. Conditions supporting regulatory T-cell (Treg) development were characterized by greatest production of total FN and EDA cFN, though EDA cFN to total FN ratios were highest in Th1 cultures. These findings indicate that recipient-derived EDA cFN is dispensable for acute allograft rejection responses but that it promotes the development of fibrosis associated with chronic rejection. Further, conditions favouring the development of regulatory T cells, widely considered graft-protective, may drive production of ECM molecules which enhance deleterious remodelling responses. Thus, EDA cFN may be a therapeutic target for ameliorating fibrosis associated with chronic cardiac allograft rejection.

Equine CD4(+) CD25(high) T cells exhibit regulatory activity by close contact and cytokine-dependent mechanisms in vitro

Horses are particularly prone to allergic and autoimmune diseases, but little information about equine regulatory T cells (Treg) is currently available. The aim of this study therefore was to investigate the existence of CD4(+) Treg cells in horses, determine their suppressive function as well as their mechanism of action. Freshly isolated peripheral blood mononuclear cells (PBMC) from healthy horses were examined for CD4, CD25 and forkhead box P3 (FoxP3) expression. We show that equine FoxP3 is expressed constitutively by a population of CD4(+) CD25(+) T cells, mainly in the CD4(+) CD25(high) subpopulation. Proliferation of CD4(+) CD25(-) sorted cells stimulated with irradiated allogenic PBMC was significantly suppressed in co-culture with CD4(+) CD25(high) sorted cells in a dose-dependent manner. The mechanism of suppression by the CD4(+) CD25(high) cell population is mediated by close contact as well as interleukin (IL)-10 and transforming growth factor-β1 (TGF-β1) and probably other factors. In addition, we studied the in vitro induction of CD4(+) Treg and their characteristics compared to those of freshly isolated CD4(+) Treg cells. Upon stimulation with a combination of concanavalin A, TGF-β1 and IL-2, CD4(+) CD25(+) T cells which express FoxP3 and have suppressive capability were induced from CD4(+) CD25(-) cells. The induced CD4(+) CD25(high) express higher levels of IL-10 and TGF-β1 mRNA compared to the freshly isolated ones. Thus, in horses as in man, the circulating CD4(+) CD25(high) subpopulation contains natural Treg cells and functional Treg can be induced in vitro upon appropriate stimulation. Our study provides the first evidence of the regulatory function of CD4(+) CD25(+) cells in horses and offers insights into ex vivo manipulation of Treg cells.

TGF-beta, IL-6, IL-17 and CTGF direct multiple pathologies of chronic cardiac allograft rejection

Cardiac transplantation is an effective treatment for heart failure refractive to therapy. Although immunosuppressive therapeutics have increased first year survival rates, chronic rejection remains a significant barrier to long-term graft survival. Chronic rejection manifests as patchy interstitial fibrosis, vascular occlusion and progressive loss of graft function. Recent evidence from experimental and patient studies suggests that the development of cardiomyocyte hypertrophy is another hallmark of chronic cardiac allograft rejection. This pathologic hypertrophy is tightly linked to the immune cytokine IL-6, which promotes facets of chronic rejection in concert with TGF-beta and IL-17. These factors potentiate downstream mediators, such as CTGF, which promote the fibrosis associated with the disease. In this article, we summarize contemporary findings that have revealed several elements involved in the induction and progression of chronic rejection of cardiac allografts. Further efforts to elucidate the interplay between these factors may direct the development of targeted therapies for this disease.

Connective tissue growth factor promotes fibrosis downstream of TGFbeta and IL-6 in chronic cardiac allograft rejection

Cardiac transplantation is an effective treatment for multiple types of heart failure refractive to therapy. Although immunosuppressive therapeutics have increased survival rates within the first year posttransplant, chronic rejection (CR) remains a significant barrier to long-term graft survival. Indicators of CR include patchy interstitial fibrosis, vascular occlusion and progressive loss of graft function. Multiple factors have been implicated in the onset and progression of CR, including TGFbeta, IL-6 and connective tissue growth factor (CTGF). While associated with CR, the role of CTGF in CR and the factors necessary for CTGF induction in vivo are not understood. To this end, we utilized forced expression and neutralizing antibody approaches. Transduction of allografts with CTGF significantly increased fibrotic tissue development, though not to levels observed with TGFbeta transduction. Further, intragraft CTGF expression was inhibited by IL-6 neutralization whereas TGFbeta expression remained unchanged, indicating that IL-6 effects may potentiate TGFbeta-mediated induction of CTGF. Finally, neutralizing CTGF significantly reduced graft fibrosis without reducing TGFbeta and IL-6 expression levels. These findings indicate that CTGF functions as a downstream mediator of fibrosis in CR, and that CTGF neutralization may ameliorate fibrosis and hypertrophy associated with CR.

Role of T cell TGFbeta signaling and IL-17 in allograft acceptance and fibrosis associated with chronic rejection

Chronic allograft rejection (CR) is the main barrier to long-term transplant survival. CR is a progressive disease defined by interstitial fibrosis, vascular neointimal development, and graft dysfunction. The underlying mechanisms responsible for CR remain poorly defined. TGFbeta has been implicated in promoting fibrotic diseases including CR, but is beneficial in the transplant setting due to its immunosuppressive activity. To assess the requirement for T cell TGFbeta signaling in allograft acceptance and the progression of CR, we used mice with abrogated T cell TGFbeta signaling as allograft recipients. We compared responses from recipients that were transiently depleted of CD4(+) cells (that develop CR and express intragraft TGFbeta) with responses from mice that received anti-CD40L mAb therapy (that do not develop CR and do not express intragraft TGFbeta). Allograft acceptance and suppression of graft-reactive T and B cells were independent of T cell TGFbeta signaling in mice treated with anti-CD40L mAb. In recipients transiently depleted of CD4(+) T cells, T cell TGFbeta signaling was required for the development of fibrosis associated with CR, long-term graft acceptance, and suppression of graft-reactive T and B cell responses. Furthermore, IL-17 was identified as a critical element in TGFbeta-driven allograft fibrosis. Thus, IL-17 may provide a therapeutic target for preventing graft fibrosis, a measure of CR, while sparing the immunosuppressive activity of TGFbeta.

Pirfenidone inhibits T-cell activation, proliferation, cytokine and chemokine production, and host alloresponses

BACKGROUND

We previously showed that pirfenidone, an anti-fibrotic agent, reduces lung allograft injury or rejection. In this study, we tested the hypothesis that pirfenidone has immune modulating activities and evaluated its effects on the function of T-cell subsets, which play important roles in allograft rejection.

METHOD

We first evaluated whether pirfenidone alters T-cell proliferation and cytokine release in response to T-cell receptor (TCR) activation, and whether pirfenidone alters regulatory T cells (CD4CD25) suppressive effects using an in vitro assay. Additionally, pirfenidone effects on alloantigen-induced T-cell proliferation in vivo were assessed by adoptive transfer of carboxyfluorescein diacetate succinimidyl ester-labeled T cells across a parent->F1 major histocompatibility complex mismatch, as well as using a murine heterotopic cardiac allograft model (BALB/c->C57BL/6).

RESULTS

Pirfenidone was found to inhibit the responder frequency of TCR-stimulated CD4 cell total proliferation in vitro and in vivo, whereas both CD4 and CD8 proliferation index were reduced by pirfenidone. Additionally, pirfenidone inhibited TCR-induced production of multiple pro-inflammatory cytokines and chemokines. Interestingly, there was no change on transforming growth factor-beta production by purified T cells, and pirfenidone had no effect on the suppressive properties of naturally occurring regulatory T cells. Pirfenidone alone showed a small but significant (P<0.05) effect on the in vivo allogeneic response, whereas the combination of pirfenidone and low dose rapamycin had more remarkable effect in reducing the alloantigen response with prolonged graft survival.

CONCLUSION

Pirfenidone may be an important new agent in transplantation, with particular relevance to combating chronic rejection by inhibiting both fibroproliferative and alloimmune responses.

Attenuation of allergen-induced airway hyperresponsiveness is mediated by airway regulatory T cells

Understanding the mechanisms involved in respiratory tolerance to inhaled allergens could potentially result in improved therapies for asthma and allergic diseases. Airway hyperresponsiveness (AHR) is a major feature of allergic asthma, thus the aim of the current study was to investigate mechanisms underlying suppression of allergen-induced AHR during chronic allergen exposure. Adult BALB/c mice were systemically sensitized with ovalbumin (OVA) in adjuvant and then challenged with a single 3 or 6 wk of OVA aerosols. Airway and parenchymal responses to inhaled methacholine (MCh), inflammatory cell counts, cytokines, OVA-specific IgE and IgG(1), parenchymal histology, and numbers of airway CD4(+)69(+) activated and CD4(+)25(+)FoxP3(+) regulatory T (Treg) cells were assessed 24 h after the final aerosol. Single OVA challenge resulted in AHR, eosinophilia, increased serum OVA-specific IgE, and T helper 2 (Th2) cytokines in bronchoalveolar lavage (BAL) but no difference in numbers of Treg compared with control mice. Three weeks of OVA challenges resulted in suppression of AHR and greater numbers of airway Treg cells and increased transforming growth factor-beta(1) (TGFbeta(1)) compared with control mice despite the presence of increased eosinophilia, OVA-specific IgE and IgG(1), and airway remodeling. Six weeks of OVA challenges restored AHR, whereas airway Treg numbers, TGFbeta(1), BAL eosinophilia, and Th2 cytokines returned to control levels. Partial in vivo depletion or adoptive transfer of Treg cells restored or inhibited AHR, respectively, but did not affect TGFbeta(1) or Th2 cytokine production. In conclusion, AHR suppression is mediated by airway Treg cells and potentially via a paracrine induction of TGFbeta(1) in the airways.

CD8+ suppressor T cells resurrected

This review focuses on the role of antigen-specific T cells that mediate active inhibition of immune responses over the past 35 years since their initial description. The field has experienced several changes in the accepted paradigm of such suppressor/regulatory T cells, from initial indications that such cells were CD8(+), to the view that such cells did not exist, to the identification of the transcription factor Foxp3 as a key orchestrator of inhibitory function. Although most Foxp3(+) cells in a resting animal are CD4(+)CD25(+) cells, Foxp3 expression and inhibitory function can be induced by antigens in the periphery by selective cytokine conditions, particularly TGF-beta. Such induced T cells occur within both the CD4 and the CD8 T-cell lineages and appear to mediate suppression by inhibiting the costimulatory activity of antigen-presenting cells and the production of inhibitory cytokines. Recent data generated by analysis of TCR Tg T cells that do not select many Foxp3-positive cells during thymic development are reviewed, emphasizing the pattern of "linked suppression" and focus of the relative potency of different mechanisms of suppression.

The regulation of Foxp3 expression in regulatory CD4(+)CD25(+)T cells: multiple pathways on the road

Regulatory T cells (Treg cells) have been well documented to have a crucial physiological role in preventing the development of autoimmune diseases and keeping self-tolerance. Foxp3, a recently identified member of the forkhead transcription factors, serves as a master regulator for the development and function of CD4(+)CD25(+)Treg cells. Though it is well defined that Foxp3 expression is sufficient to program CD4(+)CD25(+)Treg cell development, the physiological factors initiating intracellular Foxp3 expression remain poorly understood so far. In the present manuscript, we try to summarize the recent advances regarding the regulatory roles of T-cell receptor (TCR), co-stimulatory molecules, interleukin-2 (IL-2), transforming growth factor-beta (TGF-beta) and beyond pathways on Foxp3 expression.

Incomplete depletion and rapid regeneration of Foxp3+ regulatory T cells following anti-CD25 treatment in malaria-infected mice

Investigation of the role of regulatory T cells (Treg) in model systems is facilitated by their depletion using anti-CD25 Abs, but there has been considerable debate about the effectiveness of this strategy. In this study, we have compared the depletion and repopulation of CD4+CD25+Foxp3+ Treg in uninfected and malaria-infected mice using 7D4 and/or PC61 anti-CD25 Abs. We find that numbers and percentages of CD25(high) cells, but not Foxp3+ cells, are transiently reduced after 7D4 treatment, whereas treatment with PC61 alone or in combination with 7D4 (7D4 plus PC61) reduces but does not eliminate Foxp3+ cells for up to 2 wk. Importantly, all protocols fail to eliminate significant populations of CD25-Foxp3+ or CD25(low)Foxp3+ cells, which retain potent regulatory capacity. By adoptive transfer we show that repopulation of the spleen by CD25(high)Foxp3+ cells results from the re-expression of CD25 on peripheral populations of CD25-Foxp3+ but not from the conversion of peripheral Foxp3-) cells. CD25(high)Foxp3+ repopulation occurs more rapidly in 7D4-treated mice than in 7D4 plus PC61-treated mice, reflecting ongoing clearance of emergent CD25+Foxp3+ cells by persistent PC61 Ab. However, in 7D4 plus PC61-treated mice undergoing acute malaria infection, repopulation of the spleen by CD25+Foxp3+ cells occurs extremely rapidly, with malaria infection driving proliferation and CD25 expression in peripheral CD4+CD25-Foxp3+ cells and/or conversion of CD4+CD25-Foxp3- cells. Finally, we reveal an essential role for IL-2 for the re-expression of CD25 by Foxp3+ cells after anti-CD25 treatment and observe that TGF-beta is required, in the absence of CD25 and IL-2, to maintain splenic Foxp3+ cell numbers and a normal ratio of Treg:non-Treg cells.

Risk factors for early epithelial to mesenchymal transition in renal grafts

Epithelial-to-mesenchymal transition (EMT) of tubular epithelial cells (TECs) may participate in the pathogenesis of renal fibrosis. We performed a prospective study of EMT markers in protocol biopsies obtained 3 months after engraftment from 56 patients who received deceased donor kidneys and who had stable renal function. The presence of EMT was examined, and quantified by immunohistochemical staining for vimentin and translocation of beta-catenin to the cytoplasm. EMT status was defined as the presence of EMT markers in > or = 10% of TECs. EMT features were virtually absent in implantation biopsies, whereas 41% of the grafts were EMT-positive in the absence of advanced chronic allograft nephropathy. Thirteen patients (23%) had borderline changes or acute rejection. EMT features were more frequent in these patients than in those with normal kidney grafts (vimentin expression, p = 0.003; beta-catenin translocation, p = 0.002). EMT in grafts corresponded with elevated serum creatinine of the donor before the recovery of kidney (p = 0.02) and longer cold ischemia time (p = 0.02). In contrast, the donor age had no influence on the expression of EMT markers. These results suggest that EMT is an early and frequent phenomenon in kidney transplants that could be triggered by immunological and/or ischemic tubular injury.

Avenues for immunomodulation and graft protection by gene therapy in transplantation

Organ transplantation represents the only definitive therapy for many causes of end-organ failure. However, the universal success of this therapy is limited by chronic allograft rejection, the side effects of chronic immunosuppressive therapy, and a severe shortage of donor organs. Presently, the success of solid-organ transplantation depends on the continuous administration of toxic and nonspecific immunosuppressive agents, therapies that present risks for opportunistic infection, malignancy, and a variety of agent-specific side effects. To promote the use of transplantation with limited risk of long-term sequelae, three dominant research challenges emerge: (i) elimination of the need for exogenous immunosuppression by immunological tolerance induction; (ii) prevention of chronic rejection/graft dysfunction; and (iii) expansion of available organs for transplantation. Gene therapy may provide significant advances and solutions in each of these areas. Rejection of the graft in the immediate post-transplant period has been attacked through the transfer of immunomodulatory molecules in addition to tolerance inducing approaches. Chronic graft rejection may be similarly addressed through permanent tolerance induction or alternatively through the introduction of molecules to resist chronic graft damage. Genetic manipulation of stem cells may ultimately produce transgenic animals to serve as tissue donors to overcome the limited donor organ supply. This review will highlight ongoing developments in the translation of gene therapy approaches to the challenges inherent in transplantation.

Therapeutic targets in the treatment of allograft fibrosis

The dramatic improvements in short-term graft survival and acute rejection rates could only have been dreamed of 20 years ago. Late graft loss following kidney transplantation is now the critical issue of this decade. Frequently, graft loss is associated with the development of tubular atrophy and interstitial fibrosis within the kidney (i.e. chronic allograft nephropathy; CAN). Major treatment strategies in this disorder are non-specific and the focus of intervention has been on limiting injurious events. Following graft injury is a fibrogenesis phase featuring both proliferative and infiltrative responses mediated by chemokines, cytokines and growth factors. In particular, TGFbeta has been strongly implicated in the pathogenesis of chronic injury and epithelial-mesenchymal transformation (EMT) may be part of this process. The cascade of events results in matrix accumulation, due to either increased production and/or reduced degradation of matrix. Recent investigations into the pathogenesis of tissue fibrosis have suggested a number of new strategies to ameliorate matrix synthesis. While the majority of therapies have focused on TGFbeta, this may not be an ideal maneuver in transplant settings and alternative targets identified in other fibrotic diseases will be discussed. Attacking graft fibrosis should be a new focus in organ transplantation.