IL-17 contributes to CD4-mediated graft-versus-host disease

Helper T-cell differentiation in graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective therapeutic option for many malignant diseases. However, the efficacy of allo-HSCT is limited by the occurrence of destructive graft-versus-host disease (GVHD). Since allogeneic T cells are the driving force in the development of GVHD, their activation, proliferation, and differentiation are key factors to understanding GVHD pathogenesis. This review focuses on one critical aspect: the differentiation and function of helper T (Th) cells in acute GVHD. We first summarize well-established subsets including Th1, Th2, Th17, and T-regulatory cells; their flexibility, plasticity, and epigenetic modification; and newly identified subsets including Th9, Th22, and T follicular helper cells. Next, we extensively discuss preclinical findings of Th-cell lineages in GVHD: the networks of transcription factors involved in differentiation, the cytokine and signaling requirements for development, the reciprocal differentiation features, and the regulation of microRNAs on T-cell differentiation. Finally, we briefly summarize the recent findings on the roles of T-cell subsets in clinical GVHD and ongoing strategies to modify T-cell differentiation for controlling GVHD in patients. We believe further exploration and understanding of the immunobiology of T-cell differentiation in GVHD will expand therapeutic options for the continuing success of allo-HSCT.

Current data on IL-17 and Th17 cells and implications for graft versus host disease

Human interleukin 17 was first described in 1995 as a new cytokine produced primarily by activated T CD4+ cells that stimulate the secretion of IL-6 and IL-8 by human fibroblasts, besides increasing the expression of ICAM-1. Various authors have reported that IL-17A has a role in the protection of organisms against extracellular bacteria and fungi due to the capacity of IL-17A to recruit neutrophils to the areas of infection, evidencing a pathological role in various models of autoimmune diseases, such as experimental autoimmune encephalitis and arthritis. The participation of IL-17A has also been described in the acute rejection of organ transplants and graft versus host disease. However, the greatest revolution in research with IL-17 happened in 2000, when it was proposed that IL-17 cannot be classified as Th1 or Th2, but rather, simply as a new lineage of IL-17-producing T-cells. These findings modified the previously established Th1/Th2 paradigm, leading to the definition of the CD3+ CD4+ Th17 cellular subtype and establishment of a new model to explain the origin of various immune events, as well as its implication in the graft versus host disease that is discussed in depth in this article.

Chronic dry eye disease is principally mediated by effector memory Th17 cells

Recent experimental and clinical data suggest that there is a link between dry eye disease (DED) and T-cell-mediated immunity. However, whether these immune responses are a consequence or cause of ocular surface inflammation remains to be determined. Thus far, only models of acute DED have been used to derive experimental data. This is in contrast to clinical DED which usually presents as a chronic disease. In the present study, using a murine model of chronic DED, it was established that the chronic phase of the disease is accompanied by T helper type 17 (Th17) responses at the ocular surface and that a significant memory T-cell population can be recovered from chronic DED. This memory response is predominantly mediated by Th17 cells. Moreover, adoptive transfer of this memory T-cell population was shown to induce more severe and rapidly progressing DED than did the adoptive transfer of its effector or naive counterparts. Not only do these results clearly demonstrate that effector memory Th17 cells are primarily responsible for maintaining the chronic and relapsing course of DED, but they also highlight a potentially novel therapeutic strategy for targeting memory immune responses in patients with DED.

The identification and characteristics of IL-22-producing T cells in acute graft-versus-host disease following allogeneic bone marrow transplantation

Graft-versus-host disease (GVHD) remains the major obstacle for allogeneic bone marrow transplantation, in which many proinflammatory cytokines secreted by alloreactive donor T cells are involved. Role of IL-22 as a member of IL-10 family in GVHD is still disputed and the properties of IL-22-producing cells are unclear. We demonstrated here that CD4⁺ T cells but not CD8⁺ T cells involved in GVHD were the main cellular source of donor-derived IL-22. Th1 and Th17 cells were detected not only express classical cytokine IFN-γ or IL-17, but also contributed to IL-22 secretion in GVHD. Th22 cells characterized by the independent secretion of IL-22 were identified and occupied almost half percentage of IL-22-producing CD4⁺ T cells. The frequency of IL-22-producing CD4⁺ T cells showed dynamic changes with the development of GVHD. Finally, we observed that IL-22-producing CD4⁺ T cells in GVHD mouse carried CD62L⁻CD44(high/low) surface markers. In conclusion, we illuminate the characteristics of donor-derived IL-22-producing CD4⁺ T cells, which may have potent implication for further study of pathogenesis of GVHD.

IL-17 gene ablation does not impact Treg-mediated suppression of graft-versus-host disease after bone marrow transplantation

Regulatory T cell (Treg) immunotherapy is a promising strategy for the treatment of graft rejection responses and autoimmune disorders. Our and other laboratories have shown that the transfer of highly purified CD4(+)CD25(+)Foxp3(+) natural Treg can prevent lethal graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation across both major and minor histocompatibility barriers. However, recent evidence suggests that the Treg suppressive phenotype can become unstable, a phenomenon that can culminate in Treg conversion into IL-17-producing cells. We hypothesized that the intense proinflammatory signals released during an ongoing alloreaction might redirect a fraction of the transferred Treg to the Th17 cell fate, thereby losing immunosuppressive potential. We therefore sought to evaluate the impact of Il17 gene ablation on Treg stability and immunosuppressive capacity in a major MHC mismatch model. We show that although Il17 gene ablation results in a mildly enhanced Treg immunosuppressive ability in vitro, such improvement is not observed when IL-17-deficient Treg are used for GVHD suppression in vivo. Similarly, when we selectively blocked IL-1 signaling in Treg, that was shown to be necessary for Th17 conversion, we did not detect any improvement on Treg-mediated GVHD suppressive ability in vivo. Furthermore, upon ex vivo reisolation of transferred wild-type Treg, we detected little or no Treg-mediated IL-17 production upon GVHD induction. Our results indicate that blocking Th17 conversion does not affect the GVHD suppressive ability of highly purified natural Treg in vivo, suggesting that IL-17 targeting is not a valuable strategy to improve Treg immunotherapy after hematopoietic cell transplantation.

Immune Regulation and Oxidative Stress Reduction by Preimplantation Factor following Syngeneic or Allogeneic Bone Marrow Transplantation

Bone marrow transplantation (BMT), a well-established treatment for hematological diseases, is frequently hampered by graft-versus-host disease (GVHD) and/or by infections due to delay in immune restoration. Prelmplantation Factor (PIF) is an embryo-derived peptide whose physiological function is to regulate local and systemic immunity and promote transplant acceptance. Synthetic PIF’s effectiveness to regulate immune response following BMT was herein examined in murine model. PIF administration reduced GVHD following allogenic BMT, decreased skin, liver, and colon inflammation and down regulated GVHD-associated gene expression in the liver. iNOS gene expression was reduced both in liver and colon. In syngeneic BMT, PIF administration reduced proinflammatory genes expression and promoted mice weight recovery up to two months after transplantation. PIF immune-regulatory effects were mediated via interaction with monocytes, resulting in decreased iNOS expression and NO secretion in-vitro. Overall, we demonstrate that by regulating immune response after BMT, PIF reduces inflammation and oxidative stress, leading to transplant success.

c-Rel in GVHD biology: a missing link

Graft-versus-host disease (GVHD) is a major complication associated with allogeneic bone marrow transplantation (BMT). Recent advances in the treatment of lymphoid malignancies with BMT include exploring mechanisms that can inhibit GVHD while maintaining graft-versus-leukemic (GVL) effects. In this issue of the European Journal of Immunology, Yu et al. [Eur. J. Immunol. 2013.43: 2327-2337] demonstrate efficient separation of GVHD and GVL by abrogating c-Rel in T cells. Intrinsic c-Rel deficiency in T cells resulted in complete protection against GVHD in both major and minor histocompatibility mismatched murine models of BMT. Protection against GVHD was associated with a decreased presence of Th1 and Th17 cells with a concomitant increase in Treg-cell numbers. Interestingly, an intrinsic defect of c-Rel also resulted in decreased expression of the Th1-associated chemokine receptor CXCR3. Finally, the absence of c-Rel maintained GVL effects with significant tumor clearance in murine recipients. These data suggest that specific targeting of the T-cell-specific transcription factor c-Rel can inhibit GVHD while maintaining GVL effects.

Increased plasmacytoid dendritic cells and RORγt-expressing immune effectors in cutaneous acute graft-versus-host disease

The role of PDCs and Th17 cells is not well understood in the pathogenesis of aGVHD. We evaluated PDC and Th17 cells in skin biopsies of 38 patients at diagnosis of aGVHD. The biopsies were tested by immunohistochemistry for the expression of BDCA2, a typical marker of PDCs. We found an increase of BDCA2(+) cells in the skin of the patients with aGVHD. Moreover, we observed a strong expression of the type I IFN-inducible protein Mx1 in the skin of the patients with aGVHD, compared with that of those without it, suggesting that PDCs produce type I IFN. We also analyzed the expression of two Th17 surface markers-CD161 and CCR6-and RORγt, the key transcription factor that orchestrates the differentiation of Th17 cells. Significantly higher numbers of RORγt(+), CD161(+), and CCR6(+) cells were counted in the skin of the patients with aGVHD than in the skin of those who underwent allo-SCT and in whom aGVHD did not develop. This study provides evidence for a role of Th17-mediated responses and a potential new pathophysiological link between PDCs and Th17 in human cutaneous aGVHD.

The Nlrp3 inflammasome regulates acute graft-versus-host disease

Conditioning therapies before transplantation induce the release of uric acid, which triggers the NLRP3 inflammasome and IL-1β production contributing to graft-versus-host disease.

The success of allogeneic hematopoietic cell transplantation is limited by acute graft-versus-host disease (GvHD), a severe complication accompanied by high mortality rates. Yet, the molecular mechanisms initiating this disease remain poorly defined. In this study, we show that, after conditioning therapy, intestinal commensal bacteria and the damage-associated molecular pattern uric acid contribute to Nlrp3 inflammasome–mediated IL-1β production and that gastrointestinal decontamination and uric acid depletion reduced GvHD severity. Early blockade of IL-1β or genetic deficiency of the IL-1 receptor in dendritic cells (DCs) and T cells improved survival. The Nlrp3 inflammasome components Nlrp3 and Asc, which are required for pro–IL-1β cleavage, were critical for the full manifestation of GvHD. In transplanted mice, IL-1β originated from multiple intestinal cell compartments and exerted its effects on DCs and T cells, the latter being preferentially skewed toward Th17. Compatible with these mouse data, increased levels of active caspase-1 and IL-1β were found in circulating leukocytes and intestinal GvHD lesions of patients. Thus, the identification of a crucial role for the Nlrp3 inflammasome sheds new light on the pathogenesis of GvHD and opens a potential new avenue for the targeted therapy of this severe complication.

Role of non-HLA gene polymorphisms in graft-versus-host disease

A large number of reports have associated various non-HLA gene polymorphisms with the risk and severity of graft-versus-host disease (GVHD). To date, candidate gene studies and genome-wide association studies have been performed to investigate such non-HLA gene polymorphisms in relation to GVHD. Candidate gene studies are hypothesis-driven and cost-effective, whereas genome-wide association studies have the potential to discover new gene polymorphisms, including possible biomarkers and therapeutic targets. Some gene polymorphisms have the potential to affect protein function or gene expression, or to encode minor histocompatibility antigens. Non-HLA genotyping for genes influencing GVHD prior to transplantation should provide useful information that will facilitate choosing the donor, type of graft, conditioning treatment, and GVHD prophylaxis. However, attention should be paid to the need for validation studies and ethical issues.

Enhanced and aberrant T cell trafficking following total body irradiation: a gateway to graft-versus-host disease?

Pre-transplant conditioning regimens play a major role in triggering graft-versus-host disease (GVHD). This study investigated the effect of irradiation on donor T cell trafficking to lymphoid and non-lymphoid tissues by comparing the migration of carboxy-fluorescein diacetate succinimidyl ester-labelled, naïve donor T lymphocytes in vivo in irradiated and non-irradiated syngeneic mice recipients. Recruitment of adoptively transferred naïve T cells to secondary lymphoid organs was increased in irradiated mice and naïve T cells also aberrantly localized to non-lymphoid tissues. Irradiation also induced aberrant effector memory T cell migration into lymph nodes and their localization to homing-privileged non-lymphoid sites, such as the gut. The presence of a minor histocompatibility mismatch further enhanced the aberrant accumulation of T cells in both lymphoid and non-lymphoid tissue, whilst their migratory pattern was not modified as compared to fully matched irradiated recipients. These effects correlated with decreased permeability of, and the secretion of chemotactic factors by the endothelium. Our findings are consistent with the possibility that excessive, dysregulated extravasation of T cells induced by irradiation promotes the development of GVHD.

c-Rel is an essential transcription factor for the development of acute graft-versus-host disease in mice

Transcription factors of the Rel/NF-κB family are known to play different roles in immunity and inflammation, although the putative role of c-Rel in transplant tolerance and graft-versus-host disease (GVHD) remains elusive. We report here that T cells deficient for c-Rel have a dramatically reduced ability to cause acute GVHD after allogeneic bone marrow transplantation using major and minor histocompatibility mismatched murine models. In the study to understand the underlying mechanisms, we found that c-Rel(-/-) T cells had a reduced ability to expand in lymphoid organs and to infiltrate in GVHD target organs in allogeneic recipients. c-Rel(-/-) T cells were defective in the differentiation into Th1 cells after encountering alloantigens, but were enhanced in the differentiation toward Foxp3(+) regulatory T (Treg) cells. Furthermore, c-Rel(-/-) T cells had largely preserved activity to mediate graft-versus-leukemia response. Taken together, our findings indicate that c-Rel plays an essential role in T cells in the induction of acute GVHD, and suggest that c-Rel can be a potential target for therapeutic intervention in allogeneic hematopoietic cell transplantation in the clinic.

IL-22 deficiency in donor T cells attenuates murine acute graft-versus-host disease mortality while sparing the graft-versus-leukemia effect

Acute graft-versus-host disease (aGVHD) remains a major complication following allogeneic hematopoietic cell transplantation (allo-HCT), limiting the success of this therapy. Many proinflammatory cytokines secreted following the conditioning regimen have been linked to aGVHD initiation. Interleukin-22 (IL-22) is a cytokine related to IL-10 for its structure and is secreted by T helper type 17 (TH17) cells and innate immune cells. Given the paradoxical role of IL-22 in inflammation with both protective or proinflammatory functions, we investigated whether IL-22 could have a role in aGVHD pathophysiology in a mouse allo-HCT model. In this study, we show that IL-22 deficiency in donor T cells can decrease the severity of aGVHD, while limiting systemic and local inflammation in aGVHD target organs. In addition, we found that Foxp3+ regulatory T cells (Treg cells) were increased in recipient mice that received IL-22-deficient T cells, suggesting that Treg were involved in the reduced severity of GVHD. Finally, we found that the graft-versus-leukemia (GVL) effect mediated by donor T cells was preserved in the absence of IL-22. Overall, these data suggest that targeting of IL-22 may represent a valid approach towards decreasing aGVHD severity after allo-HCT while preserving the GVL effect.

The expression of Th17-associated cytokines in human acute graft-versus-host disease

The role of Th17 cells and Th17-associated cytokines in the development of acute graft-versus-host disease (aGVHD) in clinical allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients is not well established. In the current study, a cohort of 69 allo-HSCT patients was examined for the percentages of Th17 and FoxP3(+) Treg cells and the expressions of RORγt and FoxP3 in peripheral blood mononuclear cells (PBMCs). The Th17 percentage and RORγt expression were significantly higher, whereas Treg percentage and FoxP3 expression were significantly lower in severe aGVHD (grade 3 to 4) and mild aGVHD (grade 1 to 2) patients than in patients without aGVHD (grade 0) and healthy donors. We then investigated the expressions of Th17-associated cytokines, including TGF-β, IL-6, IL-1β, IL-17, IL-21, IL-22, IL-23, as well as IL-23R in the PBMCs of patients after allo-HSCT. The expressions of IL-17 and IL-22 in CD4(+) T cells were also examined. The results showed that the expressions of IL-6, IL-1β, IL-17, IL-21, IL-23, and IL-23R were all increased, whereas IL-22 expression was decreased in aGVHD patients. The changes were also correlated with the severity of aGVHD. We also investigated the dynamic changes of Th17/Treg cells and Th17-associated cytokines in patients during the onset and resolution of aGVHD. The results demonstrated a reciprocal relationship between Treg and Th17 cells. Th17-associated cytokine expressions, namely IL-17 and IL-23, were closely related to the occurrence and resolution of aGVHD. We conclude that the dynamic balance between the Th17 and FoxP3(+) Treg cells and the changes of Th17-associated cytokines could be the indicators of the disease progression and promising candidates of prognostic biomarkers of aGVHD.

PLZF confers effector functions to donor T cells that preserve graft-versus-tumor effects while attenuating GVHD

Efforts to limit GVHD mediated by alloreactive donor T cells after allogeneic bone marrow transplantation are limited by a concomitant decrease in graft-versus-tumor (GVT) activity and increased possibilities of tumor relapse. Using a novel approach, we adoptively transferred conventional T cells expressing the transcription factor promyelocytic leukemia zinc finger (PLZF), which confers effector properties resembling invariant natural killer T cells, such as copious production of cytokines under suboptimal stimulation. PLZF expression in T-cell allografts attenuates expansion of alloreactive T cells, leading to lower GVHD. Intact alloreactivity-driven antitumor cytokine responses result in preserved GVT effects, leading to improved survival. Our findings suggest that therapy with PLZF-overexpressing T cells would result in overall improved outcomes due to less GVHD and intact GVT effects.

Homeostatic proliferation of naive CD4+ T cells in mesenteric lymph nodes generates gut-tropic Th17 cells

Homeostatic proliferation of naive T cells in the spleen and cutaneous lymph nodes supplies memory-phenotype T cells. The "systemic" proliferative responses divide distinctly into fast or slow cell division rates. The fast proliferation is critical for generation of effector memory T cells. Because effector memory T cells are abundant in the lamina propria of the intestinal tissue, "gut-specific" homeostatic proliferation of naive T cells may be important for generation of intestinal effector memory T cells. However, such organ-specific homeostatic proliferation of naive T cells has not yet been addressed. In this study, we examined the gut-specific homeostatic proliferation by transferring CFSE-labeled naive CD4(+) T cells into sublethally irradiated mice and separately evaluating donor cell division and differentiation in the intestine, mesenteric lymph nodes (MLNs), and other lymphoid organs. We found that the fast-proliferating cell population in the intestine and MLNs had a gut-tropic α4β7(+) Th17 phenotype and that their production was dependent on the presence of commensal bacteria and OX40 costimulation. Mesenteric lymphadenectomy significantly reduced the Th17 cell population in the host intestine. Furthermore, FTY720 treatment induced the accumulation of α4β7(+)IL-17A(+) fast-dividing cells in MLNs and eliminated donor cells in the intestine, suggesting that MLNs rather than intestinal tissues are essential for generating intestinal Th17 cells. These results reveal that MLNs play a central role in inducing gut-tropic Th17 cells and in maintaining CD4(+) T cell homeostasis in the small intestine.

Rejection and regulation: a tight balance

PURPOSE OF REVIEW

Achieving allograft tolerance is the holy grail of transplantation. However, tolerance and rejection are two extreme ends of a scale that can be tipped in either direction. We review the novel effector and regulatory mechanisms involved and factors that tip the balance in favor of rejection or regulation.

RECENT FINDINGS

It is increasingly recognized that established T-cell phenotypes could change their commitments. New data point to the plasticity of Th17 cells in vivo with a reciprocal balance of Th17 cells and regulatory T cells (Tregs) driven by the local cytokine environment. Treg-cell profiles have been linked to acute and chronic allograft outcomes, and emerging data also indicate a novel role of a regulatory B-cell population. Current research efforts are looking into factors that tip the balance toward allograft tolerance by targeting cytokines, novel costimulatory pathways such as T-cell immunoglobulin mucin molecules, and components of innate immunity, particularly dendritic cells.

SUMMARY

The balance of effector and regulatory mechanisms contributing to allograft outcome is very complex. It is likely that targeting multiple pathways will be required to achieve tolerance. Further studies are warranted to define this balance and identify optimal combination of therapeutic interventions.

Essentials of Th17 cell commitment and plasticity

CD4(+) T helper (Th) cells exist in a variety of epigenetic states that determine their function, phenotype, and capacity for persistence. These polarization states include Th1, Th2, Th17, and Foxp3(+) T regulatory cells, as well as the more recently described T follicular helper, Th9, and Th22 cells. Th17 cells express the master transcriptional regulator retinoic acid-related orphan receptor γ thymus and produce canonical interleukin (IL)-17A and IL-17F cytokines. Th17 cells display a great degree of context-dependent plasticity, as they are capable of acquiring functional characteristics of Th1 cells. This late plasticity may contribute to the protection against microbes, plays a role in the development of autoimmunity, and is necessary for antitumor activity of Th17 cells in adoptive cell transfer therapy models. Moreover, plasticity of this subset is associated with higher in vivo survival and self-renewal capacity and less senescence than Th1 polarized cells, which have less plasticity and more phenotypic stability. New findings indicate that subset polarization of CD4(+) T cells not only induces characteristic patterns of surface markers and cytokine production but also has a maturational aspect that affects a cell's ability to survive, respond to secondary stimulation, and form long-term immune memory.

Pharmacologic prophylaxis regimens for acute graft-versus-host disease: past, present and future

Abstract Acute graft-versus-host disease (GVHD) has compromised and continues to compromise the benefits associated with allogeneic hematopoietic cell transplant to cure malignant and non-malignant diseases. Pharmacologic interventions to prevent GVHD have emerged as a major objective of research in the immunology and transplant fields. A better understanding of the pathobiology behind the GVHD process has led the way to novel approaches and medications. Here we review the present arsenal of medications used to prevent GVHD, focusing on past experience and the current evidence, and discuss future potential targets.

Decreased levels of circulating IL17-producing CD161+CCR6+ T cells are associated with graft-versus-host disease after allogeneic stem cell transplantation

The C-type lectin-like receptor CD161 is a well-established marker for human IL17-producing T cells, which have been implicated to contribute to the development of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (allo-SCT). In this study, we analyzed CD161⁺ T cell recovery, their functional properties and association with GVHD occurrence in allo-SCT recipients. While CD161⁺CD4⁺ T cells steadily recovered, CD161^hiCD8⁺ T cell numbers declined during tapering of Cyclosporine A (CsA), which can be explained by their initial growth advantage over CD161^neg/lowCD8⁺ T cells due to ABCB1-mediated CsA efflux. Interestingly, occurrence of acute and chronic GVHD was significantly correlated with decreased levels of circulating CD161⁺CD4⁺ as well as CD161^hiCD8⁺ T cells. In addition, these subsets from transplanted patients secreted high levels of IFNγ and IL17. Moreover, we found that CCR6 co-expression by CD161⁺ T cells mediated specific migration towards CCL20, which was expressed in GVHD biopsies. Finally, we demonstrated that CCR6⁺ T cells indeed were present in these CCL20⁺ GVHD-affected tissues. In conclusion, we showed that functional CD161⁺CCR6⁺ co-expressing T cells disappear from the circulation and home to GVHD-affected tissue sites. These findings support the hypothesis that CCR6⁺CD161-expressing T cells may be involved in the immune pathology of GVHD following their CCL20-dependent recruitment into affected tissues.

STAT3 transcription factor promotes instability of nTreg cells and limits generation of iTreg cells during acute murine graft-versus-host disease

Acute graft-versus-host disease (GvHD) is a major cause of mortality in allogeneic bone marrow transplantation (BMT), for which administration of FoxP3(+) regulatory T (Treg) cells has been proposed as a therapy. However, the phenotypic stability of Treg cells is controversial, and STAT3-dependent cytokines can inhibit FoxP3 expression. We assessed whether the elimination of STAT3 in T cells could limit the severity of GvHD. We found STAT3 limited FoxP3(+) Treg cell numbers following allogeneic BMT by two pathways: instability of natural Treg (nTreg) cells and inhibition of induced Treg (iTreg) cell polarization from naive CD4(+) T cells. Deletion of STAT3 within only the nTreg cell population was not sufficient to protect against lethal GvHD. In contrast, transfer of STAT3-deficient naive CD4(+) T cells increased FoxP3(+) Treg cells post-BMT and prevented lethality, suggesting that the consequence of STAT3 signaling may be greater for iTreg rather than nTreg cells during GvHD.

IFN-γ production by allogeneic Foxp3+ regulatory T cells is essential for preventing experimental graft-versus-host disease

It is emerging that CD4+Foxp3+ regulatory T (Treg) cells can produce the proinflammatory cytokine IFN-γ when stimulated in a Th1 cytokine environment. In this study, we report that Foxp3+ Treg cells readily produced IFN-γ in vivo in a highly inflammatory model of graft-versus-host disease (GVHD) and during a Th1-dominated immune response to intracellular bacteria. Moreover, stimulation in vitro via TCR in the presence of IL-12 alone was sufficient to induce IFN-γ production by Treg cells in a dose-dependent manner. Transfer of donor Treg cells can prevent lethal GVHD; therefore, we used this model as a robust readout for in vivo Treg function. Interestingly, >50% of allogeneic donor, but not residual recipient Foxp3+ Treg cells produced IFN-γ after transplantation, suggesting that this cytokine production was alloantigen specific. These IFN-γ producers were stable Foxp3+ Treg cells because methylation analysis of the Foxp3 gene locus of transferred and reisolated Treg cells during GVHD showed a fully demethylated Treg-specific-demethylated region. Next, we addressed whether IFN-γ production was supporting or rather impairing the immunosuppressive function of Treg cells during GVHD. Blocking of IFN-γ with specific mAb completely abolished the beneficial effect of donor Treg cells. We could further show that only wild-type Treg cells, but not Treg cells from IFN-γ-deficient donor mice, prevented GVHD. This indicated that Treg cell-intrinsic IFN-γ production was required for their protective function. In conclusion, our data show that IFN-γ produced by Foxp3+ Treg cells has essential immune-regulatory functions that are required for prevention of experimental GVHD.

Inorganic arsenic represses interleukin-17A expression in human activated Th17 lymphocytes

Trivalent inorganic arsenic [As(III)] is an efficient anticancer agent used to treat patients suffering from acute promyelocytic leukemia. Recently, experimental studies have clearly demonstrated that this metalloid can also cure lymphoproliferative and/or pro-inflammatory syndromes in different murine models of chronic immune-mediated diseases. T helper (Th) 1 and Th17 lymphocytes play a central role in development of these diseases, in mice and humans, especially by secreting the potent pro-inflammatory cytokine interferon-γ and IL-17A, respectively. As(III) impairs basic functions of human T cells but its ability to modulate secretion of pro-inflammatory cytokines by differentiated Th lymphocytes is unknown. In the present study, we demonstrate that As(III), used at concentrations clinically achievable in plasma of patients, has no effect on the secretion of interferon-γ from Th1 cells but almost totally blocks the expression and the release of IL-17A from human Th17 lymphocytes co-stimulated for five days with anti-CD3 and anti-CD28 antibodies, in the presence of differentiating cytokines. In addition, As(III) specifically reduces mRNA levels of the retinoic-related orphan receptor (ROR)C gene which encodes RORγt, a key transcription factor controlling optimal IL-17 expression in fully differentiated Th17 cells. The metalloid also blocks initial expression of IL-17 gene induced by the co-stimulation, probably in part by impairing activation of the JNK/c-Jun pathway. In conclusion, our results demonstrate that As(III) represses expression of the major pro-inflammatory cytokine IL-17A produced by human Th17 lymphocytes, thus strengthening the idea that As(III) may be useful to treat inflammatory immune-mediated diseases in humans.

Cytokine profiles in various graft-versus-host disease target organs following hematopoietic stem cell transplantation

Previous studies using genetic-deficient murine models suggest that different T-helper subsets may contribute to different types of tissue damages in graft-versus-host disease (GvHD). However, there is limited information available on the distribution of T-helper cytokines in the various GvHD target tissues. In the current study, an acute GvHD murine model was set up to directly assess the in situ cytokine profiles in various GvHD tissue lesions; in addition, we also studied GvHD tissues from patients who had undergone bone marrow transplantation procedures. We observed that interferon-γ (IFN-γ was dominant in murine liver and gastrointestinal tissue lesions, whereas IFN-γ and interleukin 17 (IL-17) were abundant in murine skin lesions. Furthermore, in human GvHD tissues, interleukin 4 (IL-4) and IFN-γ were predominant in liver lesions and colon lesions, respectively, while no specific cytokine was prevalent in human GvHD skin lesions. In addition, a low ratio of CD4(+) T helper (Th) versus CD8(+) T cytotoxic (Tc) cells in human GvHD tissue lesions, especially in the liver, was detected, and this contrasts with the situation in murine GvHD tissues where CD4(+) Th cells were predominant. Dual staining for CD markers and cytokine expression showed that IFN-γ-secreting T cells were enriched in all murine GvHD target tissue lesions, and Tc1 and Tc2 cells were predominant in human GvHD colon and liver sections, respectively. However, IFN-γ(+) Th1, IL-17(+) Th17, IFN-γ(+) Tc1, and IL-17(+) Tc17 cells were slightly more frequent in human skin lesions compared to IL-4(+) Th2 and IL-4(+) Tc2 cells. To sum up, these results suggest that differences in cytokine imbalances may significantly contribute to tissue-specific pathogenesis in GvHD target organs, and CD8(+) Tc cells may play an important role in human GvHD induction.

Attenuation of acute graft-versus-host disease in the absence of the transcription factor RORγt

Graft-versus-host disease (GVHD) remains the most significant complication after allogeneic stem cell transplantation. Previously, acute GVHD had been considered to be mediated predominantly by Th1-polarized T cells. Recently, investigators have identified a second proinflammatory lineage of T cells termed Th17 that is critically dependent on the transcription factor retinoic acid-related orphan receptor (ROR)γt. In this study, we have evaluated the role of Th17 cells in murine acute GVHD by infusing donor T cells lacking RORC and as a consequence the isoform RORγt. Recipients given donor CD4(+) and CD8(+) T cells lacking RORC had significantly attenuated acute GVHD and markedly decreased tissue pathology in the colon, liver, and lung. Using a clinically relevant haploidentical murine transplantation model, we showed that RORC(-/-) CD4(+) T cells alone diminished the severity and lethality of acute GVHD. This was not found when CD4(+) T cells from RORC(-/-) mice were given to completely mismatched BALB/c mice, and it was correlated with absolute differences in the generation of TNF in the colon after transplant. Thus, CD4(+) T cell expression of RORC is important in the pathogenesis of acute GVHD.

On the interactions between mesenchymal stem cells and regulatory T cells for immunomodulation in transplantation

Experimental studies have established the use of mesenchymal stem cells (MSC) as a candidate immunosuppressive therapy. MSC exert their immunomodulatory function through the inhibition of CD4⁺ and CD8⁺ T cell proliferation. It is unknown whether MSC impair the immunosuppressive function of regulatory T cells (Treg). In vitro and in vivo studies suggest that MSC mediate their immunomodulatory effects through the induction of Treg. In this review we will focus on the interactions between MSC and Treg, and evaluate the consequences of these cellular interplays for prospective MSC immunotherapy in organ transplantation.

Advances in graft-versus-host disease biology and therapy

Allogeneic haematopoietic stem cell transplantation is used to treat a variety of disorders, but its efficacy is limited by the occurrence of graft-versus-host disease (GVHD). The past decade has brought impressive advances in our understanding of the role of stimulatory and suppressive elements of the adaptive and innate immune systems from both the donor and the host in GVHD pathogenesis. New insights from basic immunology, preclinical models and clinical studies have led to novel approaches for prevention and treatment. This Review highlights the recent advances in understanding the pathophysiology of GVHD and its treatment, with a focus on manipulations of the immune system that are amenable to clinical application.

The IL-17 differentiation pathway and its role in transplant outcome

The limitations of allogeneic transplantation are graft-versus-host disease (both acute and chronic), infection, and relapse. Acute GVHD has traditionally been thought of as a Th1-mediated disease with inflammatory cytokines (eg, interferon [IFN]-γ and tumor necrosis factor [TNF]) and cellular cytolysis mediating apoptotic target tissue damage in skin, gut, and liver. Chronic GVHD has not fit neatly into either Th1 or Th2 (eg, IL-4, IL-13) paradigms. Increasingly, the Th17 pathway of differentiation has been shown to play important roles in acute and chronic GVHD (aGVHD, cGVHD), particularly in relation to skin and lung disease. Here we discuss the IL-17 pathway of T cell differentiation and the accumulating evidence suggesting it represents an important new target for the control of deleterious alloimmune responses.

Arsenic trioxide prevents murine sclerodermatous graft-versus-host disease

Chronic graft-versus-host disease (GVHD) follows allogeneic hematopoietic stem cell transplantation. It results from alloreactive processes induced by minor MHC incompatibilities triggered by activated APCs, such as plasmacytoid dendritic cells (pDCs), and leading to the activation of CD4 T cells. Therefore, we tested whether CD4(+) and pDCs, activated cells that produce high levels of reactive oxygen species, could be killed by arsenic trioxide (As(2)O(3)), a chemotherapeutic drug used in the treatment of acute promyelocytic leukemia. Indeed, As(2)O(3) exerts its cytotoxic effects by inducing a powerful oxidative stress that exceeds the lethal threshold. Sclerodermatous GVHD was induced in BALB/c mice by body irradiation, followed by B10.D2 bone marrow and spleen cell transplantation. Mice were simultaneously treated with daily i.p. injections of As(2)O(3). Transplanted mice displayed severe clinical symptoms, including diarrhea, alopecia, vasculitis, and fibrosis of the skin and visceral organs. The symptoms were dramatically abrogated in mice treated with As(2)O(3). These beneficial effects were mediated through the depletion of glutathione and the overproduction of H(2)O(2) that killed activated CD4(+) T cells and pDCs. The dramatic improvement provided by As(2)O(3) in the model of sclerodermatous GVHD that associates fibrosis with immune activation provides a rationale for the evaluation of As(2)O(3) in the management of patients affected by chronic GVHD.

Plasmacytoid dendritic cells and Th17 immune response contribution in gastrointestinal acute graft-versus-host disease

The contribution of Th17 cells in acute graft-versus-host disease (aGVHD) has been demonstrated in aGVHD mouse models. However, their contribution in human gastrointestinal aGVHD remains unclear. We evaluated Th17 cells in a cohort of 23 patients at diagnosis of aGVHD. In this study, we have shown that the absolute number of Th17 cells using the CCR6 and CD161 markers were significantly higher in the intestinal mucosa of patients with aGVHD compared with intestinal mucosa of patients without aGVHD. Moreover, in keeping with the increase of CCR6+ and CD161+ T cells, RORγt the key transcription factor that orchestrates the differentiation of Th17 cells, was significantly increased in the intestinal mucosa of patients with aGVHD compared with intestinal mucosa of patients without aGVHD (P=0.01). Since plasmacytoid dendritic cells (PDCs) have been reported to drive the differentiation of the Th17 subset, we quantified PDCs in these patients. PDC CD123+ cells were increased in the intestinal mucosa of patients with aGVHD. Furthermore, the number of CD123+ PDCs paralleled the histological grade of aGVHD, providing evidence for a role of Th17-mediated responses and a potential new pathophysiological link between PDCs and Th17 in human aGVHD.

Altered balance between Th1 and Th17 cells in circulation is an indicator for the severity of murine acute GVHD

Disbalance of Th1 and Th17 can lead to inflammatory diseases and autoimmunity. Acute graft-versus-host disease (GVHD) is now considered as a compound and dysregulated immune response. Both Th1 and Th17 have been implicated in the pathophysiology of acute GVHD. Disbalance of Th1 and Th17 may also play a critical role in mediating acute GVHD. In this study, we investigated the Th1/Th17 imbalance in peripheral blood through out the pathological process of acute GVHD, using a GVHD model of C57BL/6 (H-2(b)) donor to BALB/c (H-2(d)) recipient. We also analyzed the correlation between Th1/Th17 ratio and severity of acute GVHD, and explored the potential function of Th1/Th17 imbalance in acute GVHD. Recipients received 5×10(6) spleen cells (SP) underwent more severe acute GVHD, compared with the ones received 5×10(5) SP. Severe GVHD bearing recipients had much higher proportion of Th1 cells but lower proportion of Th17 cells, compared with mild GVHD bearing ones. The Th1/Th17 ratios in both groups underwent relative changes according to the changing proportions of Th1 and Th17 cells and showed positive correlation with clinical scores of acute GVHD. We describe the changing proportions of Th1 and Th17 cells in acute GVHD, and we find that Th1/Th17 ratio is an accurate indicator for predicting the severity of acute GVHD.

Th17 alloimmunity prevents neonatal establishment of lymphoid chimerism in IL-4-deprived mice

Immune responses in newborn mice are known to be biased toward the helper type 2 phenotype. This may account for their propensity to develop tolerance. Herein, we evaluated the effects of IL-4 deprivation on CD4(+) T-cell activities elicited by neonatal exposure to allogeneic spleen cells. We showed that chimerism, Th2-type polarization and pathology, as well as skin allograft acceptance were inhibited in BALB/c mice immunized at birth with (A/J x BALB/c) F(1) spleen cells upon in vivo IL-4 neutralization. While IL-4 neutralization inhibited the development of Th2 cells in this model, it led to the accumulation of IL-17A, IL-17F, IL-22, IL-6 and RORγt mRNA in the spleen or graft tissues. Moreover, IL-4 deprivation led to the differentiation of donor-specific Th17 cells with a concomitant Th1 response characterized by IFN-γ production. The Th17-type response emerging in IL-4-deprived mice was found to mediate both intragraft neutrophil infiltration and the abrogation of B-cell chimerism. Neutralization of this Th17 response failed however to restore functional skin graft acceptance. Collectively, our observations indicate that the neonatal Th2 response opposes the development of Th17 cells, and that Th17 cells are responsible for controlling lymphoid chimerism in mice neonatally injected with semiallogeneic cells.

Synthetic retinoid Am80 ameliorates chronic graft-versus-host disease by down-regulating Th1 and Th17

Chronic GVHD (cGVHD) is a main cause of late death and morbidity after allogeneic hematopoietic cell transplantation, but its pathogenesis remains unclear. We investigated the roles of Th subsets in cGVHD with the use of a well-defined mouse model of cGVHD. In this model, development of cGVHD was associated with up-regulated Th1, Th2, and Th17 responses. Th1 and Th2 responses were up-regulated early after BM transplantation, followed by a subsequent up-regulation of Th17 cells. Significantly greater numbers of Th17 cells were infiltrated in the lung and liver from allogeneic recipients than those from syngeneic recipients. We then evaluated the roles of Th1 and Th17 in cGVHD with the use of IFN-γ-deficient and IL-17-deficient mice as donors. Infusion of IFN-γ(-/-) or IL-17(-/-) T cells attenuated cGVHD in the skin and salivary glands. Am80, a potent synthetic retinoid, regulated both Th1 and Th17 responses as well as TGF-β expression in the skin, resulting in an attenuation of cutaneous cGVHD. These results suggest that Th1 and Th17 contribute to the development of cGVHD and that targeting Th1 and Th17 may therefore represent a promising therapeutic strategy for preventing and treating cGVHD.

Blocking IL-21 signaling ameliorates xenogeneic GVHD induced by human lymphocytes

In rodent graft-versus-host disease (GVHD) models, anti-IL-21 neutralizing mAb treatment ameliorates lethality and is associated with decreases in Th1 cytokine production and gastrointestinal tract injury. GVHD prevention was dependent on the in vivo generation of donor-inducible regulatory T cells (Tregs). To determine whether the IL-21 pathway might be targeted for GVHD prevention, skin and colon samples obtained from patients with no GVHD or grade 2 to 4 GVHD were analyzed for IL-21 protein expression. By immunohistochemistry staining, IL-21 protein-producing cells were present in all gastrointestinal tract samples and 54% of skin samples obtained from GVHD patients but not GVHD-free controls. In a human xenogeneic GVHD model, human IL-21-secreting cells were present in the colon of GVHD recipients and were associated with elevated serum IL-21 levels. A neutralizing anti-human IL-21 mAb given prophylactically significantly reduced GVHD-associated weight loss and mortality, resulting in a concomitant increase in Tregs and a decrease in T cells secreting IFN-γ or granzyme B. Based on these findings, anti-IL-21 mAb could be considered for GVHD prevention in the clinic.

A novel monoclonal antibody specific to mouse IL-17

IL-17 is secreted by T helper (Th) 17 cells, and might play important roles in host defense against extracellular bacterial infection and fungal infection and contribute to the pathogenesis of various autoimmune inflammatory diseases. Here we have, for the first time, generated the monoclonal antibody against the rat IL-17 protein, which is secreted by T helper (Th) 17 cells. Enzyme-linked immunosorbent assay (ELISA) and Western immunoblotting were used to screen the hybridomas. As a result, one MAb named Y11 (IgG1) was characterized, which was effective in detecting the recombinant and the cellular protein. Then the MAb was used to detect the expression of IL-17 in rat intestine graft tissues by immunohistochemical analysis. Thus, Y11 could be considered a useful tool for studies of IL-17 expression and function.

Genomics of fish IL-17 ligand and receptors: a review

Interleukin-17 (IL-17) is a cytokine family composed of six ligands (A-F). Especially, the IL-17A and IL-17F are best characterized cytokines of IL-17 family cytokine. These are produced by Th17 cells and induce the expression of many mediators of inflammation properties. In addition, the five member of IL-17 receptor family (RA-RE) have been identified in mammals. Although the research on fish IL-17 is a little to date, this review discusses some of the recent advances in research on IL-17 ligand and receptor genes in fish. IL-17 family member was chosen from the fish genome database, and its structure and phylogeny is analyzed in detail. Moreover, invertebrate IL-17 genes are also discussed, and the isolation and current status of fish IL-17 receptor genes are summarized. Comparative genomic analysis of the IL-17 family among mammals, teleost and invertebrates provided new insights. Novel IL-17 ligand (IL-17N) was identified from teleost, moreover it was suggested that IL-17N may be a teleost specific ligand by synteny and phylogenetic analysis. On the other hand, IL-17 receptors are well conserved between mammal and teleost, the five member of IL-17 receptor family: IL-17RA-RE were found on the teleost genome. In addition, the IL-17RA gene was duplicated in tandem on the stickleback and medaka genome. Knowledge about the IL-17 ligand/receptor in fish is very limited. Therefore this review will hopefully encourage future studies of IL-17 in fish.

Bone marrow and the control of immunity

Bone marrow is thought to be a primary hematopoietic organ. However, accumulated evidences demonstrate that active function and trafficking of immune cells, including regulatory T cells, conventional T cells, B cells, dendritic cells, natural killer T (NKT) cells, neutrophils, myeloid-derived suppressor cells and mesenchymal stem cells, are observed in the bone marrow. Furthermore, bone marrow is a predetermined metastatic location for multiple human tumors. In this review, we discuss the immune network in the bone marrow. We suggest that bone marrow is an immune regulatory organ capable of fine tuning immunity and may be a potential therapeutic target for immunotherapy and immune vaccination.

A genetic variant in the IL-17 promoter is functionally associated with acute graft-versus-host disease after unrelated bone marrow transplantation

Interleukin IL-17 is a proinflammatory cytokine that has been implicated in the pathogenesis of various autoimmune diseases. The single nucleotide polymorphism (SNP), rs2275913, in the promoter region of the IL-17 gene is associated with susceptibility to ulcerative colitis. When we examined the impact of rs2275913 in a cohort consisting of 438 pairs of patients and their unrelated donors transplanted through the Japan Marrow Donor Program, the donor IL-17 197A allele was found to be associated with a higher risk of acute graft-versus-host disease (GVHD; hazard ratio [HR], 1.46; 95% confidence interval [CI], 1.00 to 2.13; P = 0.05). Next, we investigated the functional relevance of the rs2275913 SNP. In vitro stimulated T cells from healthy individuals possessing the 197A allele produced significantly more IL-17 than those without the 197A allele. In a gene reporter assay, the 197A allele construct induced higher luciferase activity than the 197G allele, and the difference was higher in the presence of T cell receptor activation and was abrogated by cyclosporine treatment. Moreover, the 197A allele displayed a higher affinity for the nuclear factor activated T cells (NFAT), a critical transcription factor involved in IL-17 regulation. These findings substantiate the functional relevance of the rs2275913 polymorphism and indicate that the higher IL-17 secretion by individuals with the 197A allele likely accounts for their increased risk for acute GVHD and certain autoimmune diseases.

Pretransplantation assessments and symptom profiles: predicting transplantation-related toxicity and improving patient-centered outcomes

With the advent of reduced-intensity conditioning regimens and improvements in supportive care, hematopoietic cell transplantation (HCT) has become increasingly available to older adults and medically vulnerable populations with hematologic diseases. However, adverse outcomes including long-term treatment-related distress, disability (frailty), and death remain important concerns in this population. In other areas of oncology, comprehensive geriatric assessments have been used to stratify patients for treatment-related risk, and patient-reported outcomes (PROs) have helped in understanding treatment-related toxicity from a patient perspective. However, these powerful tools have not yet become widely used in HCT. Here, we review the theories and available data that support the development of pretreatment functional assessments and longitudinal PRO sampling in HCT. We discuss the potential for these techniques to improve transplantation outcomes through risk stratification, interventional studies, and predictive models that incorporate genetic and biomarker data. Predicting and understanding long-term transplantation-related toxicity through functional assessments and PROs will be critical to calculating the risk/benefit ratio of aggressive therapies in older patient populations, and we contend that functional assessments and PRO sampling should become standard parts of the routine evaluation of HCT patients.

Type I-IFNs control GVHD and GVL responses after transplantation

Although the effects of type II-IFN (IFN-γ) on GVHD and leukemia relapse are well studied, the effects of type I-interferon (type I-IFN, IFN-α/β) remain unclear. We investigated this using type I-IFN receptor-deficient mice and exogenous IFN-α administration in established models of GVHD and GVL. Type I-IFN signaling in host tissue prevented severe colon-targeted GVHD in CD4-dependent models of GVHD directed toward either major histocompatibility antigens or multiple minor histocompatibility antigens. This protection was the result of suppression of donor CD4+ T-cell proliferation and differentiation. Studies in chimeric recipients demonstrated this was due to type I-IFN signaling in hematopoietic tissue. Consistent with this finding, administration of IFN-α during conditioning inhibited donor CD4+ proliferation and differentiation. In contrast, CD8-dependent GVHD and GVL effects were enhanced when type I-IFN signaling was intact in the host or donor, respectively. This finding reflected the ability of type I-IFN to both sensitize host target tissue/leukemia to cell-mediated cytotoxicity and augment donor CTL function. These data confirm that type I-IFN plays an important role in defining the balance of GVHD and GVL responses and suggests that administration of the cytokine after BM transplantation could be studied prospectively in patients at high risk of relapse.