Transplantation tolerance: Clinical potential of regulatory T cells

Immunomodulatory functions of microorganisms in tissue regenerative healing

External pathogenic microorganisms and commensal microorganisms in the body have either harmful or beneficial impacts on the regenerative repair of tissues, and the immune system plays a crucial regulatory role in this process. This review summarises our current understanding of microorganism-immune system interactions, with a focus on how these interactions impact the renewal and repair ability of tissues, including skin, bone, gut, liver, and nerves. This review concludes with a discussion of the mechanisms by which microbes act on various types of immune cells to affect tissue regeneration, offers potential strategies for using microbial therapies to enhance the regenerative repair function of tissues, and suggest novel therapeutic approaches for regenerative medicine. STATEMENT OF SIGNIFICANCE: Microbiological communities have crucial impacts on human health and illness by participating in energy collection and storage and performing various metabolic processes. External pathogenic microorganisms and commensal microorganisms in the body have either harmful or beneficial impacts on the regenerative repair of tissues, and the immune system plays a critical regulatory role in this process. This study reviews the important correlation between microorganisms and the immune system and investigates the mechanism of various microorganism that participate in the regeneration and repair of tissues and organs by modulating immune system.

Matching for HLA-DR excluding diabetogenic HLA-DR3 and HLA-DR4 predicts insulin independence after pancreatic islet transplantation

Introduction

In pancreatic islet transplantation, the exact contribution of human leukocyte antigen (HLA) matching to graft survival remains unclear. Islets may be exposed to allogenic rejection but also the recurrence of type 1 diabetes (T1D). We evaluated the HLA-DR matching, including the impact of diabetogenic HLA-DR3 or HLA-DR4 matches.

Methods

We retrospectively examined the HLA profile in 965 transplant recipients and 2327 islet donors. The study population was obtained from patients enrolled in the Collaborative Islet Transplant Registry. We then identified 87 recipients who received a single-islet infusion. Islet-kidney recipients, 2nd islet infusion, and patients with missing data were excluded from the analysis (n=878).

Results

HLA-DR3 and HLA-DR4 were present in 29.7% and 32.6% of T1D recipients and 11.6% and 15.8% of the donors, respectively. We identified 52 T1D islet recipients mismatched for HLA-DR (group A), 11 with 1 or 2 HLA-DR-matches but excluding HLA-DR3 and HLA- DR4 (group B), and 24 matched for HLA-DR3 or HLA-DR4 (group C). Insulin-independence was maintained in a significantly higher percentage of group B recipients from year one through five post-transplantation (p<0.01). At five-year post-transplantation, 78% of group B was insulin-independent compared to 24% (group A) and 35% (group C). Insulin-independence correlated with significantly better glycemic control (HbA1c <7%), fasting blood glucose, and reduced severe hypoglycemic events. Matching HLA-A-B-DR (≥3) independently of HLA- DR3 or HLA-DR4 matching did not improve graft survival.

Conclusion

This study suggests that matching HLA-DR but excluding the diabetogenic HLA-DR3 and/or 4 is a significant predictor for long-term islet survival.

Tolerance in liver transplantation: Biomarkers and clinical relevance

Transplantation is the optimal treatment for end-stage organ failure, and modern immunosuppression has allowed important progress in short-term outcomes. However, immunosuppression poorly influences chronic rejection and elicits chronic toxicity in current clinical practice. Thus, a major goal in transplantation is to understand and induce tolerance. It is well established that human regulatory T cells expressing the transcription factor FoxP3 play important roles in the maintenance of immunological self-tolerance and immune homeostasis. The major regulatory T cell subsets and mechanisms of expansion that are critical for induction and long-term maintenance of graft tolerance and survival are being actively investigated. Likewise, other immune cells, such as dendritic cells, monocyte/macrophages or natural killer cells, have been described as part of the process known as "operational tolerance". However, translation of these results towards clinical practice needs solid tools to identify accurately and reliably patients who are going to be tolerant. In this way, a plethora of genetic and cellular biomarkers is raising and being validated worldwide in large multi-center clinical trials. Few of the studies performed so far have provided a detailed analysis of the impact of immunosuppression withdrawal on pre-existing complications derived from the long-term administration of immunosuppressive drugs and the side effects associated with them. The future of liver transplantation is aimed to develop new therapies which increase the actual low tolerant vs non-tolerant recipients ratio.

Treg/Th17 imbalance in malignant pleural effusion partially predicts poor prognosis

Accumulating evidence shows that an imbalance in regulatory T cells (Tregs)/T helper IL-17-producing cells (Th17) exists in malignant pleural effusion (MPE). However, the cause of this phenomenon in MPE and the underlying mechanism remain uncertain. The percentages of Tregs and Th17 cells in MPE and parapneumonic effusion (PPE) were determined by flow cytometry. Their specific transcription factors, forkhead box P3 (FoxP3) and retinoic acid-related orphan receptor γt (RORγt); related cytokines, interleukin-6 (IL-6), IL-17, IL-10, and transforming growth factor-β1 (TGF‑β1); and chemokines, C-C motif ligand 17 (CCL17) and CCL20, were analyzed by real-time PCR and ELISA, respectively. Compared to patients with PPE, patients with MPE presented a higher percentage of Tregs but a lower frequency of Th17 cells. Foxp3 mRNA expression level in the cells in the pleural effusion was significantly increased in patients with MPE compared to the levels in patients with PPE (MPE vs. PPE: 3.05±0.62 vs. 0.52±0.11, p=0.0012). It was also noted that high levels of IL-10, TGF-β1 and CCL17 were observed in MPE when compared to PPE (MPE vs. PPE: IL-10, 166.3±39.53 vs. 40.38±10.92 pg/ml, p=0.0307; TGF-β1, 10,720±1,274 vs. 1,747±293.2 pg/ml, p<0.0001; CCL17, 341.1±88.22 vs. 119.2±19.80 pg/ml, p=0.0427). Furthermore, a high ratio of Tregs/Th17 cells in MPE was highly correlated to poor survival. An alteration in CCL17 and CCL20 might contribute to the Treg/Th17 imbalance in MPE, which partially predicts a poor prognosis in patients with lung cancer.

Cell-based therapies for myocardial repair: emerging role for bone marrow-derived mesenchymal stem cells (MSCs) in the treatment of the chronically injured heart

Accumulating data support the use of bone marrow (BM)-derived MSCs in animal models (e.g., swine) to restore cardiac function and tissue perfusion in chronic cardiac injury. Based on results obtained in swine, we are currently conducting phase I/II clinical trials to address the safety, cell type, cell dose, delivery technique, and efficacy of MSCs in patients with chronic heart failure. MSCs for these trials are isolated from harvested BM and then processed and expanded for intracardiac injection. The BM-MSCs in use for the clinical trials are of clinical grade having been processed successfully in an FDA-approved cGMP facility.

Immunological challenges and therapies in xenotransplantation

Xenotransplantation, or the transplantation of cells, tissues, or organs between different species, was proposed a long time ago as a possible solution to the worldwide shortage of human organs and tissues for transplantation. In this setting, the pig is currently seen as the most likely candidate species. In the last decade, progress in this field has been remarkable and includes a better insight into the immunological mechanisms underlying the rejection process. Several immunological hurdles nonetheless remain, such as the strong antibody-mediated and innate or adaptive cellular immune responses linked to coagulation derangements, precluding indefinite xenograft survival. This article reviews our current understanding of the immunological mechanisms involved in xenograft rejection and the potential strategies that may enable xenotransplantation to become a clinical reality in the not-too-distant future.

Survival of free and encapsulated human and rat islet xenografts transplanted into the mouse bone marrow

Bone marrow was recently proposed as an alternative and potentially immune-privileged site for pancreatic islet transplantation. The aim of the present study was to assess the survival and rejection mechanisms of free and encapsulated xenogeneic islets transplanted into the medullary cavity of the femur, or under the kidney capsule of streptozotocin-induced diabetic C57BL/6 mice. The median survival of free rat islets transplanted into the bone marrow or under the kidney capsule was 9 and 14 days, respectively, whereas that of free human islets was shorter, 7 days (bone marrow) and 10 days (kidney capsule). Infiltrating CD8⁺ T cells and redistributed CD4⁺ T cells, and macrophages were detected around the transplanted islets in bone sections. Recipient mouse splenocytes proliferated in response to donor rat stimulator cells. One month after transplantation under both kidney capsule or into bone marrow, encapsulated rat islets had induced a similar degree of fibrotic reaction and still contained insulin positive cells. In conclusion, we successfully established a small animal model for xenogeneic islet transplantation into the bone marrow. The rejection of xenogeneic islets was associated with local and systemic T cell responses and macrophage recruitment. Although there was no evidence for immune-privilege, the bone marrow may represent a feasible site for encapsulated xenogeneic islet transplantation.

New concepts of immune modulation in xenotransplantation

The shortage of human organs for transplantation has focused research on the possibility of transplanting pig organs into humans. Many factors contribute to the failure of a pig organ graft in a primate. A rapid innate immune response (natural anti-pig antibody, complement activation, and an innate cellular response; e.g., neutrophils, monocytes, macrophages, and natural killer cells) is followed by an adaptive immune response, although T-cell infiltration of the graft has rarely been reported. Other factors (e.g., coagulation dysregulation and inflammation) appear to play a significantly greater role than in allotransplantation. The immune responses to a pig xenograft cannot therefore be controlled simply by suppression of T-cell activity. Before xenotransplantation can be introduced successfully into the clinic, the problems of the innate, coagulopathic, and inflammatory responses will have to be overcome, most likely by the transplantation of organs from genetically engineered pigs. Many of the genetic manipulations aimed at protecting against these responses also reduce the adaptive response. The T-cell and elicited antibody responses can be prevented by the biological and/or pharmacologic agents currently available, in particular, by costimulation blockade-based regimens. The exogenous immunosuppressive regimen may be significantly reduced by the presence of a graft from a pig transgenic for a mutant (human) class II transactivator gene, resulting in down-regulation of swine leukocyte antigen class II expression, or from a pig with "local" vascular endothelial cell expression of an immunosuppressive gene (e.g., CTLA4-Ig). The immunomodulatory efficacy of regulatory T cells or mesenchymal stromal cells has been demonstrated in vitro but not yet in vivo.

Potential regulatory role of in vitro-expanded Vδ1 T cells from human peripheral blood

γδ T cells represent a relevant proportion of T lymphocytes that express T cell receptors (TCRs) encoded by the γ and δ T cell receptor genes. Whereas the most circulating γδ T cell type, Vδ2 T cells, has been described and studied intensively, the potential role of Vδ1 T cells remains largely unclear. Here, we identified that expanded peripheral blood Vδ1 T cells stimulated with anti-human TCR Vδ1 monoclonal antibody (mAb) in vitro predominantly expressed forkhead box p3 (Foxp3). In addition, these cells also expressed other regulatory T cell-related molecules, such as CD25, glucocorticoid-induced TNFR family-related protein and cytotoxic T lymphocyte-associated protein-4 (CTLA-4), and held the potent capacity for the production of transforming growth factor beta 1 (TGF-β1). These autocrine and/or paracrine TGF-β1 could bind TGF-β1 receptors on Vδ1 T cells and induce sustained Foxp3 expression. Moreover, Foxp3 expression coincided with high CD25 expression. CD25(high) Vδ1 T cells exhibited stronger suppression on CD4(+) T cell proliferation compared with TGF-β1-induced CD25(high) CD4(+) regulatory T cells. Therefore, our phenotypic and functional analyses first demonstrate the potential regulatory property of anti-human TCR Vδ1 mAb-activated Vδ1 T cells. These results will broaden our understanding about the role of peripheral blood Vδ1 T cells under physical and pathological conditions.

Regulatory T cells in allogeneic stem cell transplantation

Growing evidence suggests that cellular adoptive immunotherapy is becoming an attractive though challenging approach in regulating tumor immunity and alloresponses in clinical transplantation. Naturally arising CD4+CD25+Foxp3+ regulatory T cells (Treg) have emerged as a key component in this regard. Over the last decade, a large body of evidence from preclinical models has demonstrated their crucial role in auto- and tumor immunity and has opened the door to their “first-in-man” clinical application. Initial studies in clinical allogeneic stem cell transplantation are very encouraging and may pave the way for other applications. Further improvements in Treg ex vivo or in vivo expansion technologies will simplify their global clinical application. In this review, we discuss the current knowledge of Treg biology and their potential for cell-based immunotherapy in allogeneic stem cell transplantation.

Potential of T-regulatory cells to protect xenografts

PURPOSE OF REVIEW

Immunological barriers still preclude clinical xenotransplantation. The protective role of CD4(+)CD25(+)Foxp3(+) T-regulatory cells (Treg) in allotransplantation is well described and, therefore, could represent a promising therapeutical tool for xenotransplantation. This review addresses the latest findings on Treg in xenotransplantation research.

RECENT FINDINGS

In vivo, costimulation blockade-based strategies including anti-CD154 monoclonal antibodies (mAbs) in combination with rapamycin or anti-LFA-1 mAb prolonged both concordant and discordant islets xenografts survival in a Treg-dependent manner. In vitro, IL-10 secretion was shown to be critical for the suppression of xenogeneic responses mediated by Treg. Moreover, transgenic expression of inducible costimulator-immunoglobulin or PD-L1 on porcine endothelial cells inhibited human T-cell proliferation in vitro and was associated with the induction of Treg and IL-10 secretion. CXCR3 mediated the recruitment of Treg to pig endothelium. Finally, the recruitment of human Treg was enhanced by the immobilization of human CCL17 on pig endothelium.

SUMMARY

There is increasing evidence for the potential of CD4(+)CD25(+)Foxp3(+) Treg to protect xenografts. Induction of Treg in recipients and/or recruitment of human Treg to pig endothelium may represent novel strategies to prevent cell-mediated rejection in pig-to-human xenotransplantation.

Increased Th17 cell frequency concomitant with decreased Foxp3+ Treg cell frequency in the peripheral circulation of patients with carotid artery plaques

OBJECTIVE AND DESIGN

We investigated a possible imbalance between T helper (Th)17 and CD4+ CD25+ forkhead/winged helix transcription factor (Foxp3) T regulatory (Treg) cells in patients with carotid artery plaques.

MATERIAL OR SUBJECTS

From November 2009 to September 2010, we enrolled 126 males and 104 females with mean age 68.24 ± 6.71 years.

TREATMENT

Based on carotid artery sonography, the 230 subjects were categorized into three groups: plaque negative; stable plaques; and unstable plaques.

METHODS

Th17 and Treg cell frequencies, relevant plasma cytokines (IL-17, IL-6, IL-23, and TNF-α), and RORγt mRNA levels were determined.

RESULTS

Compared to plaque negative, Th17 cells, Th17-related cytokines (IL-17, IL-6, IL-23, and TNF-α), and RORγt mRNA levels were higher with stable plaques, and highest with unstable plaques. The opposite trend was found for Treg cells, Treg-related cytokines (IL-10 and TGF-β1), and Foxp3 mRNA. Th17 cell frequencies were significantly negatively correlated with Treg cell frequencies.

CONCLUSIONS

Our investigation demonstrated that there is a Th17/Treg functional imbalance in patients with unstable carotid atherosclerotic plaques. Th17 cells may promote atherogenesis, while Treg cells may have a protective role against atherosclerosis plaques. An imbalance of Th17/Treg cells may offer a new direction for the treatment of atherosclerosis.

Learning to live together: harnessing regulatory T cells to induce organ transplant tolerance

The discovery of immune cells with regulatory effects has created considerable excitement for their potential use in inducing tolerance to transplanted tissues. Despite the fact that these cells possess essential functions in vivo, attempts to translate them into effective clinical therapies has proved challenging due to a number of unanticipated complexities in their behavior. This article provides a broad summary of research done to understand the largest of the regulatory cell subtypes, namely CD4+Foxp3+ Regulatory T cells (T(Regs)). Special attention will be paid to current and future difficulties in using T(Regs) clinically, as well as room for improvement and innovation in this field.