Treg suppression of immunity within inflamed allogeneic grafts

Vimentin modulates regulatory T cell receptor-ligand interactions at distal pole complex, leading to dysregulated host response to viral pneumonia

Forkhead box P3 (Foxp3)+ regulatory T cells (Tregs) resolve acute inflammation and repair the injured lung after viral pneumonia. Vimentin is a critical protein in the distal pole complex (DPC) of Tregs. This study reveals the inhibitory effect of vimentin on the suppressive and reparative capacity of Tregs. Treg-specific deletion of vimentin increases Helios+interleukin-18 receptor (IL-18R)+ Tregs, suppresses inflammatory immune cells, and enhances tissue repair, protecting Vimfl/flFoxp3YFP-cre mice from influenza-induced lung injury and mortality. Mechanistically, vimentin suppresses the induction of amphiregulin, an epidermal growth factor receptor (EGFR) ligand necessary for tissue repair, by sequestering IL-18R to the DPC and restricting receptor-ligand interactions. We propose that vimentin in the DPC of Tregs functions as a molecular switch, which could be targeted to regulate the immune response and enhance tissue repair in patients with severe viral pneumonia.

Capecitabine mitigates cardiac allograft rejection via inhibition of TYMS-Mediated Th1 differentiation in mice

OBJECTIVES

Previous studies elucidated that capecitabine (CAP) works as an anti-tumor agent with putative immunosuppressive effects. However, the intricate mechanisms underpinning these effects remain to be elucidated. In this study, we aimed to unravel the molecular pathways by which CAP exerts its immunosuppressive effects to reduce allograft rejection.

METHODS

Hearts were transplanted from male BALB/c donors to male C57BL/6 recipients and treated with CAP for seven days. The rejection of these heart transplants was assessed using a range of techniques, including H&E staining, immunohistochemistry, RNA sequencing, LS-MS/MS, and flow cytometry. In vitro, naïve CD4+ T cells were isolated and cultured under Th1 condition medium with varying treatments, flow cytometry, LS-MS/MS were employed to delineate the role of thymidine synthase (TYMS) during Th1 differentiation.

RESULTS

CAP treatment significantly mitigated acute allograft rejection and enhanced graft survival by reducing graft damage, T cell infiltration, and levels of circulating pro-inflammatory cytokines. Additionally, it curtailed CD4+ T cell proliferation and the presence of Th1 cells in the spleen. RNA-seq showed that TYMS, the target of CAP, was robustly increased post-transplantation in splenocytes. In vitro, TYMS and its metabolic product dTMP were differentially expressed in Th0 and Th1, and were required after activation of CD4+ T cell and Th1 differentiation. TYMS-specific inhibitor, raltitrexed, and the metabolite of capecitabine, 5-fluorouracil, could inhibit the proliferation and differentiation of Th1. Finally, the combined use of CAP and the commonly used immunosuppressant rapamycin can induce long-term survival of allograft.

CONCLUSION

CAP undergoes metabolism conversion to interfere pyrimidine metabolism, which targets TYMS-mediated differentiation of Th1, thereby playing a significant role in mitigating acute cardiac allograft rejection in murine models.

Mesenchymal stem cells pretreated with interferon-gamma attenuate renal fibrosis by enhancing regulatory T cell induction

Mesenchymal stem cells (MSCs) exert their anti-inflammatory and anti-fibrotic effects by secreting various humoral factors. Interferon-gamma (IFN-γ) can enhance these effects of MSCs, and enhancement of regulatory T (Treg) cell induction is thought to be an underlying mechanism. However, the extent to which Treg cell induction by MSCs pretreated with IFN-γ (IFN-γ MSCs) ameliorates renal fibrosis remains unknown. In this study, we investigated the effects of Treg cell induction by IFN-γ MSCs on renal inflammation and fibrosis using an siRNA knockdown system. Administration of IFN-γ MSCs induced Treg cells and inhibited infiltration of inflammatory cells in ischemia reperfusion injury (IRI) rats more drastically than control MSCs without IFN-γ pretreatment. In addition, administration of IFN-γ MSCs more significantly attenuated renal fibrosis compared with control MSCs. Indoleamine 2,3-dioxygenase (IDO) expression levels in conditioned medium from MSCs were enhanced by IFN-γ pretreatment. Moreover, IDO1 knockdown in IFN-γ MSCs reduced their anti-inflammatory and anti-fibrotic effects in IRI rats by reducing Treg cell induction. Our findings suggest that the increase of Treg cells induced by enhanced secretion of IDO by IFN-γ MSCs played a pivotal role in their anti-fibrotic effects. Administration of IFN-γ MSCs may potentially be a useful therapy to prevent renal fibrosis progression.

A humanized IL-2 mutein expands Tregs and prolongs transplant survival in preclinical models

Long-term organ transplant survival remains suboptimal, and life-long immunosuppression predisposes transplant recipients to an increased risk of infection, malignancy, and kidney toxicity. Promoting the regulatory arm of the immune system by expanding Tregs may allow immunosuppression minimization and improve long-term graft outcomes. While low-dose IL-2 treatment can expand Tregs, it has a short half-life and off-target expansion of NK and effector T cells, limiting its clinical applicability. Here, we designed a humanized mutein IL-2 with high Treg selectivity and a prolonged half-life due to the fusion of an Fc domain, which we termed mIL-2. We showed selective and sustainable Treg expansion by mIL-2 in 2 murine models of skin transplantation. This expansion led to donor-specific tolerance through robust increases in polyclonal and antigen-specific Tregs, along with enhanced Treg-suppressive function. We also showed that Treg expansion by mIL-2 could overcome the failure of calcineurin inhibitors or costimulation blockade to prolong the survival of major-mismatched skin grafts. Validating its translational potential, mIL-2 induced a selective and sustainable in vivo Treg expansion in cynomolgus monkeys and showed selectivity for human Tregs in vitro and in a humanized mouse model. This work demonstrated that mIL-2 can enhance immune regulation and promote long-term allograft survival, potentially minimizing immunosuppression.

Adenosinergic metabolism pathway: an emerging target for improving outcomes of solid organ transplantation

Extracellular nucleotides are widely recognized as crucial modulators of immune responses in peripheral tissues. Adenosine triphosphate (ATP) and adenosine are key components of extracellular nucleotides, the balance of which contributes to immune homeostasis. Under tissue injury, ATP exerts its pro-inflammatory function, while the adenosinergic pathway rapidly degrades ATP to immunosuppressive adenosine, thus inhibiting excessive and uncontrolled inflammatory responses. Previous reviews have explored the immunoregulatory role of extracellular adenosine in various pathological conditions, especially inflammation and malignancy. However, current knowledge regarding adenosine and adenosinergic metabolism in the context of solid organ transplantation remains fragmented. In this review, we summarize the latest information on adenosine metabolism and the mechanisms by which it suppresses the effector function of immune cells, as well as highlight the protective role of adenosine in all stages of solid organ transplantation, including reducing ischemia reperfusion injury during organ procurement, alleviating rejection, and promoting graft regeneration after transplantation. Finally, we discuss the potential for future clinical translation of adenosinergic pathway in solid organ transplantation.

Delayed graft rejection in autoimmune islet transplantation via biomaterial immunotherapy

The induction of operational immune tolerance is a major goal in beta-cell replacement strategies for the treatment of type 1 diabetes. Our group previously reported long-term efficacy via biomaterial-mediated programmed death ligand 1 (PD-L1) immunotherapy in islet allografts in nonautoimmune models. In this study, we evaluated autoimmune recurrence and allograft rejection during islet transplantation in spontaneous nonobese diabetic (NOD) mice. Graft survival and metabolic function were significantly prolonged over 60 days in recipients of syngeneic islets receiving the biomaterial-delivered immunotherapy, but not in control animals. The biomaterial-mediated PD-L1 immunotherapy resulted in delayed allograft rejection in diabetic NOD mice compared with controls. Discrimination between responders and nonresponders was attributed to the enriched presence of CD206+ program death 1+ macrophages and exhausted signatures in the cytotoxic T cell compartment in the local graft microenvironment. Notably, draining lymph nodes had similar remodeling in innate and adaptive immune cell populations. This work establishes that our biomaterial platform for PD-L1 delivery can modulate immune responses to transplanted islets in diabetic NOD mice and, thus, can provide a platform for the development of immunologic strategies to curb the allo- and autoimmune processes in beta-cell transplant recipients.

Interleukin-21 modulates balance between regulatory T cells and T-helper 17 cells in chronic hepatitis B virus infection

BACKGROUND

Chronic HBV infection is always accompanied by differences in the balance between regulatory T cells (Tregs) and T-helper 17 (Th17) cells in infection phases. IL-21 plays an important role in the progression of chronic HBV infection. Thus, the aim of our study was to investigate the role of the regulatory function of IL-21 in maintaining the balance between Tregs and Th17 cells in chronic HBV infection.

METHODS

Twenty-five chronic HBV-infected patients in the immune-tolerant (IT) phase and 23 chronic hepatitis B (CHB) patients were recruited in this study. Cytokines production was measured by ELISA. The mRNA expression levels were determined by qPCR. CD4+T cells were stimulated with or without IL-21. Tregs and Th17 cells were measured by flow cytometry. pSTAT3 and STAT3 expression was assessed by Western blotting.

RESULTS

The concentration of IL-21 in the serum of CHB were significantly higher than that in the serum from IT patients, and IL-21 and IL-21R levels in the PBMCs from CHB were higher than those from IT patients. IL-21 promoted Th17 cells differentiation and function but inhibited Treg cells differentiation and function by activating STAT3 signaling pathways, upregulating RORγt expression, downregulating Foxp3 expression, by increasing IL-17and IL-22 secretion, and decreasing TGF-β secretion in chronic HBV infection. The proportion of Tregs and TGF-β concentrations in CHB was significantly lower than that in IT patients. Furthermore, the percentage of Th17 cells and the IL-17 concentration in CHB was markedly higher than that in IT patients, causing a reduction in the Tregs/Th17 ratio in CHB patients.

CONCLUSIONS

Our results suggest that IL-21 may contribute to inflammation in chronic HBV infection by modulating the balance between Treg and Th17 cells.

Revisiting regulatory T cells as modulators of innate immune response and inflammatory diseases

Regulatory T cells (Treg) are known to be critical for the maintenance of immune homeostasis by suppressing the activation of auto- or allo-reactive effector T cells through a diverse repertoire of molecular mechanisms. Accordingly, therapeutic strategies aimed at enhancing Treg numbers or potency in the setting of autoimmunity and allogeneic transplants have been energetically pursued and are beginning to yield some encouraging outcomes in early phase clinical trials. Less well recognized from a translational perspective, however, has been the mounting body of evidence that Treg directly modulate most aspects of innate immune response under a range of different acute and chronic disease conditions. Recognizing this aspect of Treg immune modulatory function provides a bridge for the application of Treg-based therapies to common medical conditions in which organ and tissue damage is mediated primarily by inflammation involving myeloid cells (mononuclear phagocytes, granulocytes) and innate lymphocytes (NK cells, NKT cells, γδ T cells and ILCs). In this review, we comprehensively summarize pre-clinical and human research that has revealed diverse modulatory effects of Treg and specific Treg subpopulations on the range of innate immune cell types. In each case, we emphasize the key mechanistic insights and the evidence that Treg interactions with innate immune effectors can have significant impacts on disease severity or treatment. Finally, we discuss the opportunities and challenges that exist for the application of Treg-based therapeutic interventions to three globally impactful, inflammatory conditions: type 2 diabetes and its end-organ complications, ischemia reperfusion injury and atherosclerosis.

Tregs integrate native and CAR-mediated costimulatory signals for control of allograft rejection

Tregs expressing chimeric antigen receptors (CAR-Tregs) are a promising tool to promote transplant tolerance. The relationship between CAR structure and Treg function was studied in xenogeneic, immunodeficient mice, revealing advantages of CD28-encoding CARs. However, these models could underrepresent interactions between CAR-Tregs, antigen-presenting cells (APCs), and donor-specific Abs. We generated Tregs expressing HLA-A2-specific CARs with different costimulatory domains and compared their function in vitro and in vivo using an immunocompetent model of transplantation. In vitro, the CD28-encoding CAR had superior antigen-specific suppression, proliferation, and cytokine production. In contrast, in vivo, Tregs expressing CARs encoding CD28, ICOS, programmed cell death 1, and GITR, but not 4-1BB or OX40, all extended skin allograft survival. To reconcile in vitro and in vivo data, we analyzed effects of a CAR encoding CD3ζ but no costimulatory domain. These data revealed that exogenous costimulation from APCs can compensate for the lack of a CAR-encoded CD28 domain. Thus, Tregs expressing a CAR with or without CD28 are functionally equivalent in vivo, mediating similar extension of skin allograft survival and controlling the generation of anti-HLA-A2 alloantibodies. This study reveals a dimension of CAR-Treg biology and has important implications for the design of CARs for clinical use in Tregs.

Enhancing longevity of immunoisolated pancreatic islet grafts by modifying both the intracapsular and extracapsular environment

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease characterized by autoimmune destruction of pancreatic β cells. Transplantation of immunoisolated pancreatic islets might treat T1DM in the absence of chronic immunosuppression. Important advances have been made in the past decade as capsules can be produced that provoke minimal to no foreign body response after implantation. However, graft survival is still limited as islet dysfunction may occur due to chronic damage to islets during islet isolation, immune responses induced by inflammatory cells, and nutritional issues for encapsulated cells. This review summarizes the current challenges for promoting longevity of grafts. Possible strategies for improving islet graft longevity are also discussed, including supplementation of the intracapsular milieu with essential survival factors, promotion of vascularization and oxygenation near capsules, modulation of biomaterials, and co-transplantation of accessory cells. Current insight is that both the intracapsular as well as the extracapsular properties should be improved to achieve long-term survival of islet-tissue. Some of these approaches reproducibly induce normoglycemia for more than a year in rodents. Further development of the technology requires collective research efforts in material science, immunology, and endocrinology. STATEMENT OF SIGNIFICANCE: Islet immunoisolation allows for transplantation of insulin producing cells in absence of immunosuppression and might facilitate the use of xenogeneic cell sources or grafting of cells obtained from replenishable cell sources. However, a major challenge to date is to create a microenvironment that supports long-term graft survival. This review provides a comprehensive overview of the currently identified factors that have been demonstrated to be involved in either stimulating or reducing islet graft survival in immunoisolating devices and discussed current strategies to enhance the longevity of encapsulated islet grafts as treatment for type 1 diabetes. Although significant challenges remain, interdisciplinary collaboration across fields may overcome obstacles and facilitate the translation of encapsulated cell therapy from the laboratory to clinical application.

Exosomes, MDSCs and Tregs: A new frontier for GVHD prevention and treatment

The development of graft versus host disease (GVHD) represents a long-standing complication of allogeneic hematopoietic cell transplantation (allo-HCT). Different approaches have been used to control the development of GVHD with most relying on variations of chemotherapy drugs to eliminate allo-reactive T cells. While these approaches have proven effective, it is generally accepted that safer, and less toxic GVHD prophylaxis drugs are required to reduce the health burden placed on allo-HCT recipients. In this review, we will summarize the emerging concepts revolving around three biologic-based therapies for GVHD using T regulatory cells (Tregs), myeloid-derived-suppressor-cells (MDSCs) and mesenchymal stromal cell (MSC) exosomes. This review will highlight how each specific modality is unique in its mechanism of action, but also share a common theme in their ability to preferentially activate and expand Treg populations in vivo. As these three GVHD prevention/treatment modalities continue their path toward clinical application, it is imperative the field understand both the biological advantages and disadvantages of each approach.