Only the CD62L+ subpopulation of CD4+CD25+ regulatory T cells protects from lethal acute GVHD

Donor regulatory T cells rapidly adapt to recipient tissues to control murine acute graft-versus-host disease

The adoptive transfer of regulatory T cells is a promising strategy to prevent graft-versus-host disease after allogeneic bone marrow transplantation. Here, we use a major histocompatibility complex-mismatched mouse model to follow the fate of in vitro expanded donor regulatory T cells upon migration to target organs. Employing comprehensive gene expression and repertoire profiling, we show that they retain their suppressive function and plasticity after transfer. Upon entering non-lymphoid tissues, donor regulatory T cells acquire organ-specific gene expression profiles resembling tissue-resident cells and activate hallmark suppressive and cytotoxic pathways, most evidently in the colon, when co-transplanted with graft-versus-host disease-inducing conventional T cells. Dominant T cell receptor clonotypes overlap between organs and across recipients and their relative abundance correlates with protection efficacy. Thus, this study reveals donor regulatory T cell selection and adaptation mechanisms in target organs and highlights protective features of Treg to guide the development of improved graft-versus-host disease prevention strategies.

Bending the Rules: Amplifying PD-L1 Immunoregulatory Function Through Flexible Polyethylene Glycol Synthetic Linkers

Immune checkpoint signaling, such as programmed cell death protein-1 (PD-1), is a key target for immunotherapy due to its role in dampening immune responses. PD-1 signaling in T cells is regulated by complex physicochemical and mechanical cues. However, how these mechanical forces are integrated with biochemical responses remains poorly understood. Our previous work demonstrated that the use of an immobilizing polyethylene glycol (PEG) linker on synthetic microgels for the presentation of a chimeric form of PD-L1, SA-PD-L1, lead to local regulatory responses capable of abrogating allograft rejection in a model of cell-based transplantation. We herein provide evidence that enhanced immune regulating function can be obtained when presentation of SA-PD-L1 is achieved through a longer more flexible PEG chain. Presentation of SA-PD-L1 through a linker of high molecular weight, and thus longer length (10 kDa, 60 nm in length), led to enhance conversion of naive T cells into T regulatory cells (Tregs) in vitro. In addition, using a subcutaneous implant model and protein tethered through three different linker sizes (6, 30, and 60 nm) to the surface of PEG hydrogels, we demonstrated that longer linkers promoted PD-1 immunomodulatory role in vivo through three main functions: (1) augmenting immune cell recruitment at the transplant site; (2) promoting the accumulation of naive Tregs expressing migratory markers; and (3) dampening CD8+ cytolytic molecule production while augmenting expression of exhaustion phenotypes locally. Notably, accumulation of Treg cells at the implant site persisted for over 30 days postimplantation, an effect not observed when protein was presented with the shorter version of the linkers (6 and 30 nm). Collectively, these studies reveal a facile approach by which PD-L1 function can be modulated through external tuning of synthetic presenting linkers. Impact statement Recently, there has been a growing interest in immune checkpoint molecules as potential targets for tolerance induction, including programmed cell death protein-1 (PD-1). However, how the mechanics of ligand binding to PD-1 receptor affect downstream activation signaling pathways remains unresolved. By taking advantage of the effect of polyethylene glycol chain length on molecule kinetics in an aqueous solution, we herein show that PD-L1 function can be amplified by adjusting the length of the grafting linker. Our results uncover a potential facile mechanism that can be exploited to advance the role of immune checkpoint ligands, in particular PD-L1, in tolerance induction for immunosuppression-free cell-based therapies.

Beyond FOXP3: a 20-year journey unravelling human regulatory T-cell heterogeneity

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3+CD4+CD25high CD127lowFOXP3+ phenotype. It is important to note that FOXP3+ Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4+ Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

Alpha-Synuclein-Specific Regulatory T Cells Ameliorate Parkinson's Disease Progression in Mice

Parkinson's disease (PD) is a long-term neurodegenerative disease characterized by dopaminergic neuronal loss and the aggregation of alpha-synuclein (α-syn) in the brain. Cell therapy using regulatory T cells (Tregs) has therapeutic potential on PD progression in a mouse model; however, several challenges were associated with its applications. Here, we propose a strategy for α-syn specific Treg expansion (α-syn Treg). We presented α-syn to T cells via dendritic cells. This method increased the mobility of Tregs towards the site of abundant α-syn in vitro (p < 0.01; α-syn Tregs versus polyclonal Tregs (poly Tregs)) and in vivo. Consequently, α-syn Tregs showed noteworthy neuroprotective effects against motor function deficits (p < 0.05, p < 0.01; α-syn Tregs versus poly Tregs), dopaminergic neuronal loss (p < 0.001; α-syn Tregs versus poly Tregs), and α-syn accumulation (p < 0.05; α-syn Tregs versus poly Tregs) in MPTP-induced PD mice. Furthermore, the adoptive transfer of α-syn Tregs exerted immunosuppressive effects on activated microglia, especially pro-inflammatory microglia, in PD mice. Our findings suggest that α-syn presentation may provide a significant improvement in neuroprotective activities of Tregs and suggest the effective clinical application of Treg therapy in PD.

Enforced gut homing of murine regulatory T cells reduces early graft-versus-host disease severity

Damage to the gastrointestinal tract following allogeneic hematopoietic stem cell transplantation is a significant contributor to the severity and perpetuation of graft-versus-host disease. In preclinical models and clinical trials, we showed that infusing high numbers of regulatory T cells reduces graft-versus-host disease incidence. Despite no change in in vitro suppressive function, transfer of ex vivo expanded regulatory T cells transduced to overexpress G protein-coupled receptor 15 or C-C motif chemokine receptor 9, specific homing receptors for colon or small intestine, respectively, lessened graft-versus-host disease severity in mice. Increased regulatory T cell frequency and retention within the gastrointestinal tissues of mice that received gut homing T cells correlated with lower inflammation and gut damage early post-transplant, decreased graft-versus-host disease severity, and prolonged survival compared with those receiving control transduced regulatory T cells. These data provide evidence that enforced targeting of ex vivo expanded regulatory T cells to the gastrointestinal tract diminishes gut injury and is associated with decreased graft-versus-host disease severity.

Maternal dendritic cells influence fetal allograft response following murine in-utero hematopoietic stem cell transplantation

BACKGROUND

Intrauterine hematopoietic stem cell transplantation (IUT), potentially curative in congenital haematological disease, is often inhibited by deleterious immune responses to donor cells resulting in subtherapeutic donor cell chimerism (DCC). Microchimerism of maternal immune cells (MMc) trafficked into transplanted recipients across the placenta may directly influence donor-specific alloresponsiveness, limiting DCC. We hypothesized that dendritic cells (DC) among trafficked MMc influence the development of tolerogenic or immunogenic responses towards donor cells, and investigated if maternal DC-depletion reduced recipient alloresponsiveness and enhanced DCC.

METHODS

Using transgenic CD11c.DTR (C57BL/6) female mice enabled transient maternal DC-depletion with a single dose of diphtheria toxin (DT). CD11c.DTR females and BALB/c males were cross-mated, producing hybrid pups. IUT was performed at E14 following maternal DT administration 24 h prior. Bone marrow-derived mononuclear cells were transplanted, obtained from semi-allogenic BALB/c (paternal-derived; pIUT), C57BL/6 (maternal-derived; mIUT), or fully allogenic (aIUT) C3H donor mice. Recipient F1 pups were analyzed for DCC, while maternal and IUT-recipient immune cell profile and reactivity were examined via mixed lymphocyte reactivity functional assays. T- and B-cell receptor repertoire diversity in maternal and recipient cells were examined following donor cell exposure.

RESULTS

DCC was highest and MMc was lowest following pIUT. In contrast, aIUT recipients had the lowest DCC and the highest MMc. In groups that were not DC-depleted, maternal cells trafficked post-IUT displayed reduced TCR & BCR clonotype diversity, while clonotype diversity was restored when dams were DC-depleted. Additionally, recipients displayed increased expression of regulatory T-cells and immune-inhibitory proteins, with reduced proinflammatory cytokine and donor-specific antibody production. DC-depletion did not impact initial donor chimerism. Postnatal transplantation without immunosuppression of paternal donor cells did not increase DCC in pIUT recipients; however there were no donor-specific antibody production or immune cell changes.

CONCLUSIONS

Though maternal DC depletion did not improve DCC, we show for the first time that MMc influences donor-specific alloresponsiveness, possibly by expanding alloreactive clonotypes, and depleting maternal DC promotes and maintains acquired tolerance to donor cells independent of DCC, presenting a novel approach to enhancing donor cell tolerance following IUT. This may have value when planning repeat HSC transplantations to treat haemoglobinopathies.

Engineered Treg cells as putative therapeutics against inflammatory diseases and beyond

Regulatory T (Treg) cells ensure tolerance against self-antigens, limit excessive inflammation, and support tissue repair processes. Therefore, Treg cells are currently attractive candidates for the treatment of certain inflammatory diseases, autoimmune disorders, or transplant rejection. Early clinical trials have proved the safety and efficacy of certain Treg cell therapies in inflammatory diseases. We summarize recent advances in engineering Treg cells, including the concept of biosensors for inflammation. We assess Treg cell engineering possibilities for novel functional units, including Treg cell modifications influencing stability, migration, and tissue adaptation. Finally, we outline perspectives of engineered Treg cells going beyond inflammatory diseases by using custom-designed receptors and read-out systems, aiming to use Treg cells as in vivo diagnostic tools and drug delivery vehicles.

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.

Prevention of acute GVHD using an orthogonal IL-2/IL-2Rβ system to selectively expand regulatory T cells in vivo

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative option for patients with hematological disorders and bone marrow (BM) failure syndromes. Graft-versus-host disease (GVHD) remains a leading cause of morbidity posttransplant. Regulatory T cell (Treg) therapies are efficacious in ameliorating GVHD but limited by variable suppressive capacities and the need for a high therapeutic dose. Here, we sought to expand Treg in vivo by expressing an orthogonal interleukin 2 receptor β (oIL-2Rβ) that would selectively interact with oIL-2 cytokine and not wild-type (WT) IL-2. To test whether the orthogonal system would preferentially drive donor Treg expansion, we used a murine major histocompatibility complex-disparate GVHD model of lethally irradiated BALB/c mice given T cell-depleted BM from C57BL/6 (B6) mice alone or together with B6Foxp3+GFP+ Treg or oIL-2Rβ-transduced Treg at low cell numbers that typically do not control GVHD with WT Treg. On day 2, B6 activated T cells (Tcons) were injected to induce GVHD. Recipients were treated with phosphate-buffered saline (PBS) or oIL-2 daily for 14 days, then 3 times weekly for an additional 14 days. Mice treated with oIL-2Rβ Treg and oIL-2 compared with those treated with PBS had enhanced GVHD survival, in vivo selective expansion of Tregs, and greater suppression of Tcon expansion in secondary lymphoid organs and intestines. Importantly, oIL-2Rβ Treg maintained graft-versus-tumor (GVT) responses in 2 distinct tumor models (A20 and MLL-AF9). These data demonstrate a novel approach to enhance the efficacy of Treg therapy in allo-HSCT using an oIL-2/oIL-2Rβ system that allows for selective in vivo expansion of Treg leading to GVHD protection and GVT maintenance.

Severely ill and high-risk COVID-19 patients exhibit increased peripheral circulation of CD62L+ and perforin+ T cells

Introduction

The emergence of SARS-CoV-2, which causes COVID-19, has led to over 400 million reported cases worldwide. COVID-19 disease ranges from asymptomatic infection to severe disease and may be impacted by individual immune differences.

Methods

We used multiparameter flow cytometry to compare CD4+ and CD8+ T cell responses in severe (ICU admitted) and non-severe (admitted to observational unit) hospitalized COVID-19 patients.

Results

We found that patients with severe COVID- 19 had greater frequencies of CD4+ T cells expressing CD62L compared to non-severe patients and greater frequencies of perforin+ CD8+ T cells compared to recovered patients. Furthermore, greater frequencies of CD62L+ CD4+ and CD8+ T cells were seen in severely ill diabetic patients compared to non-severe and non-diabetic patients, and increased CD62L+ CD4+ T cells were also seen in severely ill patients with hypertension.

Discussion

This is the first report to show that CD62L+ T cells and perforin+ T cells are associated with severe COVID-19 illness and are significantly increased in patients with high-risk pre-existing conditions including older age and diabetes. These data provide a potential biological marker for severe COVID-19.

Proximity-enabled covalent binding of IL-2 to IL-2Rα selectively activates regulatory T cells and suppresses autoimmunity

Interleukin-2 (IL-2) is a pleiotropic cytokine that orchestrates bidirectional immune responses via regulatory T cells (Tregs) and effector cells, leading to paradoxical consequences. Here, we report a strategy that exploited genetic code expansion-guided incorporation of the latent bioreactive artificial amino acid fluorosulfate-L-tyrosine (FSY) into IL-2 for proximity-enabled covalent binding to IL-2Rα to selectively promote Treg activation. We found that FSY-bearing IL-2 variants, such as L72-FSY, covalently bound to IL-2Rα via sulfur-fluoride exchange when in proximity, resulting in persistent recycling of IL-2 and selectively promoting the expansion of Tregs but not effector cells. Further assessment of L72-FSY-expanded Tregs demonstrated that L72-FSY maintained Tregs in a central memory phenotype without driving terminal differentiation, as demonstrated by simultaneously attenuated expression of lymphocyte activation gene-3 (LAG-3) and enhanced expression of programmed cell death protein-1 (PD-1). Subcutaneous administration of L72-FSY in murine models of pristane-induced lupus and graft-versus-host disease (GvHD) resulted in enhanced and sustained therapeutic efficacy compared with wild-type IL-2 treatment. The efficacy of L72-FSY was further improved by N-terminal PEGylation, which increased its circulatory retention for preferential and sustained effects. This proximity-enabled covalent binding strategy may accelerate the development of pleiotropic cytokines as a new class of immunomodulatory therapies.

Fibroblastic reticular cells mitigate acute GvHD via MHCII-dependent maintenance of regulatory T cells

Acute graft versus host disease (aGvHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT) inflicted by alloreactive T cells primed in secondary lymphoid organs (SLOs) and subsequent damage to aGvHD target tissues. In recent years, Treg transfer and/or expansion has emerged as a promising therapy to modulate aGvHD. However, cellular niches essential for fostering Tregs to prevent aGvHD have not been explored. Here, we tested whether and to what extent MHC class II (MHCII) expressed on Ccl19+ fibroblastic reticular cells (FRCs) shape the donor CD4+ T cell response during aGvHD. Animals lacking MHCII expression on Ccl19-Cre-expressing FRCs (MHCIIΔCcl19) showed aberrant CD4+ T cell activation in the effector phase, resulting in exacerbated aGvHD that was associated with significantly reduced expansion of Foxp3+ Tregs and invariant NK T (iNKT) cells. Skewed Treg maintenance in MHCIIΔCcl19 mice resulted in loss of protection from aGvHD provided by adoptively transferred donor Tregs. In contrast, although FRCs upregulated costimulatory surface receptors, and although they degraded and processed exogenous antigens after myeloablative irradiation, FRCs were dispensable to activate alloreactive CD4+ T cells in 2 mouse models of aGvHD. In summary, these data reveal an immunoprotective, MHCII-mediated function of FRC niches in secondary lymphoid organs (SLOs) after allo-HCT and highlight a framework of cellular and molecular interactions that regulate CD4+ T cell alloimmunity.

CD3e-immunotoxin spares CD62Llo Tregs and reshapes organ-specific T-cell composition by preferentially depleting CD3ehi T cells

CD3-epsilon(CD3e) immunotoxins (IT), a promising precision reagent for various clinical conditions requiring effective depletion of T cells, often shows limited treatment efficacy for largely unknown reasons. Tissue-resident T cells that persist in peripheral tissues have been shown to play pivotal roles in local and systemic immunity, as well as transplant rejection, autoimmunity and cancers. The impact of CD3e-IT treatment on these local cells, however, remains poorly understood. Here, using a new murine testing model, we demonstrate a substantial enrichment of tissue-resident Foxp3+ Tregs following CD3e-IT treatment. Differential surface expression of CD3e among T-cell subsets appears to be a main driver of Treg enrichment in CD3e-IT treatment. The surviving Tregs in CD3e-IT-treated mice were mostly the CD3e^dimCD62L^lo effector phenotype, but the levels of this phenotype markedly varied among different lymphoid and nonlymphoid organs. We also found notable variations in surface CD3e levels among tissue-resident T cells of different organs, and these variations drive CD3e-IT to uniquely reshape T-cell compositions in local organs. The functions of organs and anatomic locations (lymph nodes) also affected the efficacy of CD3e-IT. The multi-organ pharmacodynamics of CD3e-IT and potential treatment resistance mechanisms identified in this study may generate new opportunities to further improve this promising treatment.

M2c Macrophages Protect Mice from Adriamycin-Induced Nephropathy by Upregulating CD62L in Tregs

Regulatory T cells (Tregs) and M2c macrophages have been shown to exert potentially synergistic therapeutic effects in animals with adriamycin-induced nephropathy (AN), a model chronic proteinuric renal disease. M2c macrophages may protect against renal injury by promoting an increase in the number of Tregs in the renal draining lymph nodes of AN mice, but how they do so is unclear. In this study, we used an AN mouse model to analyze how M2c macrophages induce the migration of Tregs. Using flow cytometry, we found that M2c macrophages promoted the migration of Tregs from the peripheral blood to the spleen, thymus, kidney, and renal draining lymph nodes. At the same time, M2c macrophages significantly upregulated chemokine receptors and adhesion molecule in Tregs, including CCR4, CCR5, CCR7, CXCR5, and CD62L. Treating AN mice with monoclonal anti-CD62L antibody inhibited the migration of M2c macrophages and Tregs to the spleen, thymus, kidney, and renal draining lymph nodes. Taken together, our results suggest that M2c macrophages upregulate CD62L in Tregs and thereby promote their migration to inflammatory sites, where they exert renoprotective effects. These insights may aid the development of treatments against chronic kidney disease.

Responses of regulatory and effector T-cells to low-dose interleukin-2 differ depending on the immune environment after allogeneic stem cell transplantation

CD4⁺Foxp3⁺ regulatory T cells (Tregs) play a central role in the maintenance of immune tolerance after allogeneic hematopoietic stem cell transplantation (HSCT). Tregs promptly respond to low concentrations of IL-2 through the constitutive expression of high-affinity IL-2 receptors. It has been reported that low-dose IL-2 therapy increased circulating Tregs and improved clinical symptoms of chronic GVHD. Clinical studies of IL-2 therapy so far have mainly targeted patients in the chronic phase of transplantation when acute immune responses has subsided. However, the biological and clinical effects of exogenous IL-2 in an acute immune environment have not been well investigated. In the current study, we investigated the impact of exogenous IL-2 therapy on the post-transplant homeostasis of T cell subsets which influence the balance between GVHD and GVL in the acute phase, by setting the various immune environments early after HSCT in murine model. We initially found that 5,000 IU of IL-2 was enough to induce the active proliferation of Treg without influencing other conventional T cells (Tcons) when administered to normal mice. However, activated Tcons showed the response to the same dose of IL-2 in recipients after allogeneic HSCT. In a mild inflammatory environment within a threshold, exogenous IL-2 could effectively modulate Treg homeostasis with just limited influence to activated T cells, which resulted in an efficient GVHD suppression. In contrast, in a severely inflammatory environment, exogenous IL-2 enhanced activated T cells rather than Tregs, which resulted in the exacerbation of GVHD. Of interest, in an immune-tolerant state after transplant, exogenous IL-2 triggered effector T-cells to exert an anti-tumor effect with maintaining GVHD suppression. These data suggested that the responses of Tregs and effector T cells to exogenous IL-2 differ depending on the immune environment in the host, and the mutual balance of the response to IL-2 between T-cell subsets modulates GVHD and GVL after HSCT. Our findings may provide useful information in the optimization of IL-2 therapy, which may be personalized for each patient having different immune status.

Combined treatment of graft versus host disease using donor regulatory T cells and ruxolitinib

Donor derived regulatory T lymphocytes and the JAK1/2 kinase inhibitor ruxolitinib are currently being evaluated as therapeutic options in the treatment of chronic graft versus host disease (cGvHD). In this work, we aimed to determine if the combined use of both agents can exert a synergistic effect in the treatment of GvHD. For this purpose, we studied the effect of this combination both in vitro and in a GvHD mouse model. Our results show that ruxolitinib favors the ratio of thymic regulatory T cells to conventional T cells in culture, without affecting the suppressive capacity of these Treg. The combination of ruxolitinib with Treg showed a higher efficacy as compared to each single treatment alone in our GvHD mouse model in terms of GvHD incidence, severity and survival without hampering graft versus leukemia effect. This beneficial effect correlated with the detection in the bone marrow of recipient mice of the infused donor allogeneic Treg after the adoptive transfer.

CD28 Superagonist D665-mediated activation of mouse regulatory T cells maintains their phenotype without loss of suppressive quality

Regulatory T cells (Tregs) maintain immune homeostasis by regulating the activation of other immune cells. Preclinical studies show that the infusion of Tregs can promote immunological tolerance to allografts and prevent or cure multiple autoimmune diseases. However, Treg therapy is limited by high numbers of cells required to induce tolerance. In this study, we aimed at improving the in vitro expansion of sort purified mouse Tregs using the CD28 Superagonist (CD28-SA) D665 and comparing it to the conventional expansion using anti-CD3/anti-CD28 Dynabeads®. CD28-SA-stimulated Tregs expanded more than Dynabead®-stimulated Tregs while maintaining their phenotype by expressing the same level of CD4, CD25 and Foxp3. CD28-SA-expanded Tregs produced comparable amounts of IL-10 and TGFβ while showing a slightly superior suppressive capacity compared to Dynabead®-stimulated Tregs. Thus, stimulating murine Tregs with the CD28-SA is a promising alternative since it maintains their suppressive capacity without altering their phenotype and yields a higher fold expansion within 14 days.

Harnessing Treg Homeostasis to Optimize Posttransplant Immunity: Current Concepts and Future Perspectives

CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) are functionally distinct subsets of mature T cells with broad suppressive activity and have been shown to play an important role in the establishment of immune tolerance after allogeneic hematopoietic stem cell transplantation (HSCT). Tregs exhibit an activated phenotype from the stage of emigration from the thymus and maintain continuous proliferation in the periphery. The distinctive feature in homeostasis enables Tregs to respond sensitively to small environmental changes and exert necessary and sufficient immune suppression; however, on the other hand, it also predisposes Tregs to be susceptible to apoptosis in the inflammatory condition post-transplant. Our studies have attempted to define the intrinsic and extrinsic factors affecting Treg homeostasis from the acute to chronic phases after allogeneic HSCT. We have found that altered cytokine environment in the prolonged post-HSCT lymphopenia or peri-transplant use of immune checkpoint inhibitors could hamper Treg reconstitution, leading to refractory graft-versus-host disease. Using murine models and clinical trials, we have also demonstrated that proper intervention with low-dose interleukin-2 or post-transplant cyclophosphamide could restore Treg homeostasis and further amplify the suppressive function after HSCT. The purpose of this review is to reconsider the distinctive characteristics of post-transplant Treg homeostasis and discuss how to harness Treg homeostasis to optimize posttransplant immunity for developing a safe and efficient therapeutic strategy.

Immune Monitoring Assay for Extracorporeal Photopheresis Treatment Optimization After Heart Transplantation

Background

Extracorporeal photopheresis (ECP) induces immunological changes that lead to a reduced risk of transplant rejection. The aim of the present study was to determine optimum conditions for ECP treatment by analyzing a variety of tolerance-inducing immune cells to optimize the treatment.

Methods

Ten ECP treatments were applied to each of 17 heart-transplant patients from month 3 to month 9 post-HTx. Blood samples were taken at baseline, three times during treatment, and four months after the last ECP treatment. The abundance of subsets of tolerance-inducing regulatory T cells (T_regs) and dendritic cells (DCs) in the samples was determined by flow cytometry. A multivariate statistical model describing the immunological status of rejection-free heart transplanted patients was used to visualize the patient-specific immunological improvement induced by ECP.

Results

All BDCA⁺ DC subsets (BDCA1⁺ DCs: p < 0.01, BDCA2⁺ DCs: p < 0.01, BDCA3⁺ DCs: p < 0.01, BDCA4⁺ DCs: p < 0.01) as well as total T_regs (p < 0.01) and CD39⁺ T_regs (p < 0.01) increased during ECP treatment, while CD62L⁺ T_regs decreased (p < 0.01). The cell surface expression level of BDCA1 (p < 0.01) and BDCA4 (p < 0.01) on DCs as well as of CD120b (p < 0.01) on T_regs increased during the study period, while CD62L expression on T_regs decreased significantly (p = 0.04). The cell surface expression level of BDCA2 (p = 0.47) and BDCA3 (p = 0.22) on DCs as well as of CD39 (p = 0.14) and CD147 (p = 0.08) on T_regs remained constant during the study period. A cluster analysis showed that ECP treatment led to a sustained immunological improvement.

Conclusions

We developed an immune monitoring assay for ECP treatment after heart transplantation by analyzing changes in tolerance-inducing immune cells. This assay allowed differentiation of patients who did and did not show immunological improvement. Based on these results, we propose classification criteria that may allow optimization of the duration of ECP treatment.

The Role of Regulatory T Cells in Epicutaneous Immunotherapy for Food Allergy

In recent decades, a rapid increase in the prevalence of food allergies has led to extensive research on novel treatment strategies and their mechanisms. Mouse models have provided preliminary insights into the mechanism of epicutaneous immunotherapy (EPIT)-induced immune tolerance. In EPIT, antigen applied on the skin surface can be captured, processed, and presented in the lymph nodes (LNs) by Antigen-presenting cells (APCs). In the LNs, induction of regulatory T cells (Treg cells) requires both direct contact during antigen presentation and indirect mechanisms such as cytokines. Foxp3⁺CD62L⁺ Treg cells can exhibit the characteristics of hypomethylation of Foxp3 TSDR and Foxp3^-LAP⁺ Treg cells, which increase the expression of surface tissue-specific homing molecules to exert further sustained systemic immune tolerance. Studies have shown that EPIT is a potential treatment for food allergies and can effectively induce immune tolerance, but its mechanism needs further exploration. Here, we review Treg cells' role in immune tolerance induced by EPIT and provide a theoretical basis for future research directions, such as the mechanism of EPIT and the development of more effective EPIT treatments.

Hookworm treatment induces a decrease of suppressive regulatory T cell associated with a Th2 inflammatory response

Background

Like other helminths, hookworms (HW) induce a regulatory immune response able to modulate and dampen reactivity of the host to antigens. No data about the evolution of the immune response after treatment are available. We aim to phenotype the regulatory immune response during natural HW infection and its evolution after treatment.

Methodology

Twenty hookworm infected (HW+) and 14 non-infected subjects HW–from endemic area in the periphery of Ho Chi Minh City were included. Blood and feces samples were obtained before, 2 and 4 weeks after treatment with Albendazole 400mg. Additional samples were obtained at 3 and 12 months in the HW+ group. Hematological parameters, Treg (CD4+CD25^hiFoxP3^hi) and surface molecules (CD39, CD62L, ICOS, PD-1, CD45RA) were measured as well as inflammatory and lymphocytes differentiation cytokines such as IL-1β, IL-6, IFNγ, IL-4, IL-17, IL-10, IL-2 and TGFβ.

Results

HW+ subjects showed higher Treg, TregICOS+, Treg PD1-, TregCD62L+ and CD45RA+FoxP3^lo resting Treg (rTreg). CD45RA-FoxP3^lo non-suppressive Treg cells were also increased. No preferential Th1/Th2 orientation was observed, nor difference for IL-10 between two groups. After treatment, Treg, TregICOS+, TregCD62L+, Treg PD1- and rTreg decreased while IL-4 and IL-6 cytokines increased.

Conclusion

During HW infection, Treg are increased and characterized by a heterogeneous population: a highly suppressive as well as a non-suppressive T cells phenotype. After treatment, Treg with immune-suppressive phenotype exhibited a decrease parallel to an inflammatory Th2 response.

Function, Failure, and the Future Potential of Tregs in Type 1 Diabetes

Critical insights into the etiology of type 1 diabetes (T1D) came from genome-wide association studies that unequivocally connected genetic susceptibility to immune cell function. At the top of the susceptibility are genes involved in regulatory T-cell (Treg) function and development. The advances in epigenetic and transcriptional analyses have provided increasing evidence for Treg dysfunction in T1D. These are well supported by functional studies in mouse models and analysis of peripheral blood during T1D. For these reasons, Treg-based therapies are at the forefront of research and development and have a tangible probability to deliver a long-sought-after successful immune-targeted treatment for T1D. The current challenge in the field is whether we can directly assess Treg function at the tissue site or make informative interpretations based on peripheral data. Future studies focused on Treg function in pancreatic lymph nodes and pancreas could provide key insight into the ultimate mechanisms underlying Treg failure in T1D. In this Perspective we will provide an overview of current literature regarding Treg development and function in T1D and how this knowledge has been applied to Treg therapies.

Immunomodulatory Effects of Bendamustine in Hematopoietic Cell Transplantation

Bendamustine (BEN) is a unique alkylating agent with efficacy against a broad range of hematological malignancies, although investigations have only recently started to delve into its immunomodulatory effects. These immunomodulatory properties of BEN in the context of hematopoietic cell transplantation (HCT) are reviewed here. Pre- and post-transplant use of BEN in multiple murine models have consistently resulted in reduced GvHD and enhanced GvL, with significant changes to key immunological cell populations, including T-cells, myeloid derived suppressor cells (MDSCs), and dendritic cells (DCs). Further, in vitro studies find that BEN enhances the suppressive function of MDSCs, skews DCs toward cDC1s, enhances Flt3 expression on DCs, increases B-cell production of IL-10, inhibits STAT3 activation, and suppresses proliferation of T- and B-cells. Overall, BEN has a broad range of immunomodulatory effects that, as they are further elucidated, may be exploited to improve clinical outcomes. As such, clinical trials are currently underway investigating new potential applications of BEN in the setting of allogeneic HCT.

Separating the wheat from the chaff: Making sense of Treg heterogeneity for better adoptive cellular therapy

Regulatory T (Treg) cells are essential for immunological tolerance and can be used to suppress unwanted or excessive immune responses through adoptive cellular therapy. It is increasingly clear that many subsets of Treg cells exist, which have different functions and reside in different locations. Treg cell therapies may benefit from tailoring the selected subset to the tissue that must be protected as well as to characteristics of the immune response that must be suppressed, but little attention is given to this topic in current therapies. Here, we will discuss how three major axes of heterogeneity can be discerned among the Treg cell population, which determine function and lineage fidelity. A first axis relates to the developmental route, as Treg cells can be generated from immature T cells in the thymus or from already mature Tconv cells in the immunological periphery. Heterogeneity furthermore stems from activation history (naïve or effector) and location (lymphoid or peripheral tissues). Each of these axes bestows specific properties on Treg cells, which are further refined by additional processes leading to yet further variation. A critical aspect impacting on Treg cell heterogeneity is TCR specificity, which determines when and where Treg cells are generated as well as where they exhibit their effector functions. We will discuss the implications of this heterogeneity and the role of the TCR for the design of next generation adoptive cellular therapy with Treg cells.

High preharvest donor Foxp3 mRNA level predicts late relapse of acute lymphoblastic leukaemia after haematopoietic stem cell transplantation

Objectives

The curative effect of allogeneic haematopoietic stem cell transplantation (HSCT) for acute leukaemia is due in part to the donor T cell–mediated graft‐versus‐leukaemia immune reaction (GvL). Several studies have suggested that donor CD25+CD4+Foxp3+regulator T cells (Tregs) may decrease graft‐versus‐host disease (GvHD) without abrogating GVL. This notion may need modification in acute lymphoblastic leukaemia (ALL).

Methods

Foxp3 mRNA level was measured by qPCR in preharvest donor blood CD4+ T cells. The study comprised 45 patients with ALL in 1st or 2nd CR who received myeloablative HSCT using T‐replete bone marrow grafts.

Results

Relapse occurred in 17 patients median 363 days after HSCT. The relapse risk was estimated by Cox univariate and multivariate proportional hazard regression. The proportionality assumption was met by analysing the preharvest donor Foxp3 mRNA level as a time‐dependent covariate. Early relapse was not modified by the Foxp3 mRNA level. However, a higher Foxp3 mRNA level was associated with a significantly increased relapse risk after day 363 after transplantation, compatible with inhibition of GvL. In contrast, a higher preharvest donor CD4+ T‐cell concentration was associated with reduced relapse risk.

Conclusion

A higher preharvest donor Foxp3 mRNA level may be predictive of late ALL relapse after HSCT.

Fresh vs. frozen allogeneic peripheral blood stem cell grafts: A successful timely option

Cryopreservation of grafts has been established in autologous and cord blood transplantation, yet there is little experience regarding the effect of cryopreservation with sibling and unrelated grafts. We evaluated the effect of cryopreservation of grafts on allogeneic transplant outcomes using related, unrelated and haploidentical donors, including 958 patients, age 18-74 years (median 55) and using PBSC for various hematologic malignancies. Fresh grafts were received by 648 (68%) patients, 310 (32%) received cryopreserved. There was no difference between fresh vs cryopreserved grafts for neutrophil engraftment (P = .09), platelet engraftment (P = .11), graft failure (5.6% vs 6.8%, P = .46) and grade II-IV acute graft-vs-host disease (GVHD) (P = .71), moderate/severe chronic GVHD was observed in 176 (27%) vs 123 (40%) patients, respectively (P < .001). Multivariable analysis demonstrated no difference between fresh vs cryopreserved for OS (P = .39) and CIR (P = .08) while fresh grafts demonstrated borderline increased NRM (HR 1.27, 95% CI 1.02-1.59, P = .04). Of note, for patients with no or mild chronic GVHD, CIR was less for fresh compared to cryopreserved (HR = 0.67 for fresh, 95% CI 0.48-0.92, P = .01). We conclude there were no differences in engraftment and survival between fresh and cryopreserved grafts for allogeneic HCT, thus establishing cryopreservation to be a safe option for allogeneic HCT.

CD4+CD8+ T-Lymphocytes in Xenogeneic and Human Graft-versus-Host Disease

Mechanisms driving acute graft-versus-host disease (aGVHD) onset in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) are still poorly understood. To provide a detailed characterization of tissue-infiltrating T lymphocytes (TL) and search for eventual site-specific specificities, we developed a xenogeneic model of aGVHD in immunodeficient mice. Phenotypic characterization of xenoreactive T lymphocytes (TL) in diseased mice disclosed a massive infiltration of GVHD target organs by an original CD4⁺CD8⁺ TL subset. Immunophenotypic and transcriptional profiling shows that CD4⁺CD8⁺ TL comprise a major PD1⁺CD62L^−/+ transitional memory subset (>60%) characterized by low level expression of cytotoxicity-related transcripts. CD4⁺CD8⁺ TL produce high IL-10 and IL-13 levels, and low IL-2 and IFN-γ, suggestive of regulatory function. In vivo tracking of genetically labeled CD4⁺ or CD8⁺ TL subsequently found that CD4⁺CD8⁺ TL mainly originate from chronically activated cytotoxic TL (CTL). On the other hand, phenotypic profiling of CD3⁺ TL from blood, duodenum or rectal mucosa in a cohort of allo-HSCT patients failed to disclose abnormal expansion of CD4⁺CD8⁺ TL independent of aGVHD development. Collectively, our results show that acquisition of surface CD4 by xenoreactive CD8⁺ CTL is associated with functional diversion toward a regulatory phenotype, but rule out a central role of this subset in the pathogenesis of aGVHD in allo-HSCT patients.

Clinical-Grade Expanded Regulatory T Cells Are Enriched with Highly Suppressive Cells Producing IL-10, Granzyme B, and IL-35

In the setting of T cell-depleted, full-haplotype mismatched transplantation, adoptive immunotherapy with regulatory T cells (Tregs) and conventional T cells (Tcons) can prevent graft-versus-host disease (GVHD) and improve post-transplantation immunologic reconstitution and is associated with a powerful graft-versus-leukemia effect. To improve the purity and the quantity of the infused Tregs, good manufacturing practices (GMP)-compatible expansion protocols are needed. Here we expanded Tregs using an automated, clinical-grade protocol. Cells were extensively characterized in vitro, and their efficiency was tested in vivo in a mouse model. Tregs were selected by CliniMacs (CD4⁺CD25⁺, 94.5 ± 6.3%; FoxP3⁺, 63.7 ± 11.5%; CD127⁺, 20 ± 3%; suppressive activity, 60 ± 7%), and an aliquot of 100 × 10⁶ was expanded for 14 days using the CliniMACS Prodigy System, obtaining 684 ± 279 × 10⁶ cells (CD4⁺CD25⁺, 99.6 ± 0.2%; FoxP3⁺, 82 ± 8%; CD127⁺, 1.1 ± 0.8%; suppressive activity, 75 ± 12%). CD39 and CTLA4 expression levels increased from 22.4 ± 12% to 58.1 ± 13.3% (P < .05) and from 20.4 ± 6.7% to 85.4 ± 9.8% (P < .01), respectively. TIM3 levels increased from .4 ± .05% to 29 ± 16% (P < .05). Memory Tregs were the prevalent population, whereas naive Tregs almost disappeared at the end of the culture. mRNA analysis displayed significant increases in CD39, IL-10, granzyme B, and IL-35 levels at the end of culture period (P < .05). Conversely, IFNγ expression decreased significantly by day +14. Expanded Tregs were sorted according to TIM3, CD39, and CD62L expression levels (purity >95%). When sorted populations were analyzed, TIM3⁺ cells showed significant increases in IL-10 and granzyme B (P < .01) .When expanded Tregs were infused in an NSG murine model, mice that received Tcons only died of GVHD, whereas mice that received both Tcons and Tregs survived without GVHD. GMP grade expanded cells that display phenotypic and functional Treg characteristics can be obtained using a fully automated system. Treg suppression is mediated by multiple overlapping mechanisms (eg, CTLA-4, CD39, IL-10, IL-35, TGF-β, granzyme B). TIM3⁺ cells emerge as a potentially highly suppressive population. © 2020 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Human-Derived α1-Antitrypsin is Still Efficacious in Heavily Pretreated Patients with Steroid-Resistant Gastrointestinal Graft-versus-Host Disease

Almost one-half of patients developing graft-versus-host disease (GVHD) will not respond to standard first-line steroid treatment. Alpha-1 antitrypsin (AAT) is able to induce tolerance in preclinical models of GVHD. AAT alters the cytokine milieu, promotes a tolerogenic shift of dendritic cells, and skews effector T cells toward regulatory T cells. Gastrointestinal steroid-refractory (SR)-GVHD is a protein-losing enteropathy that might represent the optimal setting in which to use AAT. Here we analyze the outcomes of 16 patients treated with human-derived AAT in advanced-stage gut SR-GVHD, with two-thirds of the patients having failed at least 1 treatment for SR-GVHD. The overall response rate (ORR) was 44%, with a complete response (CR) rate of 27%. Gastrointestinal response was observed in 61% of patients. The median time to best response was 21 days (range, 6 to 26 days). At day 56 after AAT treatment, all CRs were maintained, and the ORR was 39%. The 1-year overall survival was 48% (95% confidence interval, 26% to 74%). Ancillary studies showed that AAT serum levels were in the normal range at the beginning of treatment, whereas fecal loss was elevated. AAT levels consistently rose after exogenous administration, but no correlation was found between serum levels and response. REG3α and IL-33 levels were associated with response while, in contrast to previous reports, regulatory T cells decreased during AAT treatment. This retrospective analysis supports a previous report of AAT as a promising agent in the management of gut SR-GVHD and should prompt its evaluation at an earlier stage.

CD52-negative T cells predict acute graft-versus-host disease after an alemtuzumab-based conditioning regimen

Allogeneic haematopoietic stem cell transplantation (HSCT) after a reduced-intensity conditioning (RIC) regimen with fludarabine, melphalan and alemtuzmab is an effective therapy for haematological malignancies. Alemtuzumab, a monoclonal antibody against CD52, a glycosylphosphatidylinositol-anchor-bound surface protein on lymphocytes, depletes T cells to prevent graft-versus-host disease (GVHD). Despite this, acute and chronic GVHD (a/cGVHD) remain life-threatening complications after HSCT. The aim of the present study was to identify parameters to predict GVHD. In 69 patients after HSCT, T-cell subsets were functionally analysed. Reconstitution of CD52^neg T cells and CD52^neg regulatory T cells (Tregs) correlated with onset, severity and clinical course of aGVHD. Patients with aGVHD showed significantly lower levels of CD52^pos T cells compared to patients with cGVHD or without GVHD (P < 0·001). Analysis of T-cell reconstitution revealed a percentage of <40% of CD52^pos CD4^pos T cells or CD52^pos Tregs at day +50 as a risk factor for the development of aGVHD. In contrast, CD52^neg Tregs showed significant decreased levels of glycoprotein A repetitions predominant (GARP; P < 0·001), glucocorticoid-induced TNFR-related protein (GITR; P < 0·001), chemokine receptor (CXCR3; P = 0·023), C-C chemokine receptor type 5 (CCR5; P = 0·004), but increased levels of immunoglobulin-like transcript 3 (ILT3; P = 0·001), as well as a reduced suppressive capacity. We conclude that reconstitution of CD52^neg T cells and CD52^neg Tregs is a risk factor for development of aGVHD.

IL-2 enhances ex vivo-expanded regulatory T-cell persistence after adoptive transfer

As regulatory T cell (Treg) adoptive therapy continues to develop clinically, there is a need to determine which immunomodulatory agents pair most compatibly with Tregs to enable persistence and stabilize suppressor function. Prior work has shown that mechanistic target of rapamycin inhibition can increase the stability of thymic Tregs. In this study, we investigated the transcriptomic signatures of ex vivo-expanded Tregs after adoptive transfer in the setting of clinically relevant immunosuppression using a nonhuman primate (NHP) model as a prelude to future transplant studies. Here, we found that adding interleukin-2 (IL-2) to rapamycin in vivo supported a logarithmic increase in the half-life of adoptively transferred carboxyfluorescein diacetate succinimidyl ester-labeled, autologous NHP Tregs, effectively doubling the number of cells in the peripheral blood Treg compartment compared with Treg infusion when rapamycin was given alone. Using single-cell transcriptomics, we found that transferred ex vivo-expanded Tregs initially exhibit a gene expression signature consistent with an activated state. Moreover, those cells with the highest levels of activation also expressed genes associated with p53-mediated apoptosis. In contrast, transferred Tregs interrogated at day +20 posttransfer demonstrated a gene signature more similar to published profiles of resting Tregs. Together, these preclinical data further support combining IL-2 and rapamycin in vivo as adjunctive therapy for ex vivo-expanded adoptively transferred Tregs and suggest that the activation status of ex vivo-expanded Tregs is critical to their persistence.

CD4+FOXP3+ Regulatory T Cell Therapies in HLA Haploidentical Hematopoietic Transplantation

Since their discovery CD4⁺FOXP3⁺ regulatory T cells (Tregs) represented a promising tool to induce tolerance in allogeneic hematopoietic cell transplantation. Preclinical models proved that adoptive transfer of Tregs or the use of compounds that can favor their function in vivo are effective for prevention and treatment of graft-vs.-host disease (GvHD). Following these findings, Treg-based therapies have been employed in clinical trials. Adoptive immunotherapy with Tregs effectively prevents GvHD induced by alloreactive T cells in the setting of one HLA haplotype mismatched hematopoietic transplantation. The absence of post transplant pharmacologic immunosuppression unleashes T-cell mediated graft-vs.-tumor (GvT) effect, which results in an unprecedented, almost complete control of leukemia relapse in this setting. In the present review, we will report preclinical studies and clinical trials that demonstrate Treg ability to promote donor engraftment, protect from GvHD and improve GvT effect. We will also discuss new strategies to further enhance in vivo efficacy of Treg-based therapies.

Efficient treatment of murine acute GvHD by in vitro expanded donor regulatory T cells

Acute graft-versus-host disease (aGvHD) is a frequent complication after allogeneic bone marrow/stem cell transplantation (BMT/SCT) induced by co-transplanted alloreactive conventional donor T cells. We previously demonstrated that the adoptive transfer of donor CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Treg) at the time of BMT prevents aGvHD in murine models. Yet, the therapeutic potential of donor Treg for the treatment of established aGvHD has not yet been studied in detail. We now used in vitro expanded phenotypically and functionally stable murine Treg to explore their therapeutic efficacy in haploidentical aGvHD models. Upon transfer donor Treg ameliorate clinical and histologic signs of aGvHD and significantly improve survival. They migrate to lymphoid as well as aGvHD target organs, predominantly the gastrointestinal tract, where they inhibit the proliferation of conventional T cells, reduce the influx of myeloid cells, and the accumulation of inflammatory cytokines. Successfully treated animals restore aGvHD-induced tissue damage in target organs and lymphoid tissues, thereby supporting lymphocyte reconstitution. The therapeutically applied Treg population survives long term without conversion into pathogenic effector T cells. These results demonstrate that donor Treg not only prevent aGvHD, but are also efficacious for the treatment of this life-threatening BMT complication.

Therapeutic use of regulatory T cells for graft-versus-host disease

Regulatory T cells (Treg cells) represent a CD4⁺ T-cell lineage that plays a critical role in restraining immune responses to self and foreign antigens and associated inflammation. Due to the suppressive function of Treg cells, inhibition or ablation of these cells can be used to boost the immunity against malignant cells. On the other hand, augmenting the activity of Treg cells can be employed for the treatment of inflammatory or autoimmune diseases and allogeneic conflicts associated with transplantation. Graft-versus-host disease (GvHD) is a leading cause of morbidity and mortality after haematopoietic stem cell transplantation (HSCT). In this review, we describe basic biological properties of Treg cells and their role in GvHD. We focus on the application of adoptive transfer of Treg cells and the therapeutic modulation of their activity for the prevention and treatment of GvHD in pre-clinical models and in clinical settings. We also discuss the main obstacles to applying Treg cell-based therapies for GvHD in clinical practice.

Basic fibroblast growth factor and agarose gel promote ​the ability of immune privilege of allogeneic cartilage transplantation in rats

Objective

Allogeneic cartilage transplantation is used to treat severe osteochondral defects or cartilaginous injury. However, acute immune rejection has been a key problem interfering with graft healing.

Methods

Full-thickness osteochondral defects were performed in Sprague Dawley rats. The allograft implants were set into the defect region. Blood and spleen samples from Postoperative Day 3 onward were collected for inflammatory cell analysis, including analysis of monocytes, natural killer cells, CD4⁺CD25⁺Foxp3⁺ regulatory T cells, CD4⁺ T cells, and CD8⁺ T cells. Gross observation and histologic staining (hematoxylin and eosin, toluidine blue) were carried out at the same time point to assess the repair effect of the cartilage graft and the degree of immune rejection.

Results

Treatment with basic fibroblast growth factor, agarose gel, and allogeneic cartilage was similar to that of the autologous group. The percentage of monocytes in allografts was at a higher level in the spleen and blood; the frequency of CD4⁺ T cells in the allogeneic group was higher than in the autologous group and the other agarose groups at 6 weeks after transplantation. The number of regulatory T cells in the autograft was increased from Postoperative Week 1; similar results were observed in groups containing basic fibroblast growth factor beginning at Postoperative Week 3.

Conclusions

Allogeneic cartilage transplantation induces acute immune rejection, which compromises the validity of the implant. The combination of basic fibroblast growth factor and agarose gel facilitates the goal of immune privilege and promotes the success of the allograft tissues.

The translational potential of this article

This study investigated the combination of basic fibroblast growth factor (bFGF) and agarose gel facilitates promotes the success of the allograft tissues transplantation. This work may help clinicians find a new way to repair articular cartilage damage. This will affect the treatment of articular cartilage movement injuries and arthritis.

Protease Activated Receptor 4 as a Novel Modulator of Regulatory T Cell Function

Regulatory T cells (Tregs) are a subpopulation of T cells that maintain immunological tolerance. In inflammatory responses the function of Tregs is tightly controlled by several factors including signaling through innate receptors such as Toll like receptors and anaphylatoxin receptors allowing an effective immune response to be generated. Protease-activated receptors (PARs) are another family of innate receptors expressed on multiple cell types and involved in the pathogenesis of autoimmune disorders. Whether proteases are able to directly modulate Treg function is unknown. Here, we show using two complimentary approaches that signaling through PAR-4 influences the expression of CD25, CD62L, and CD73, the suppressive capacity, and the stability of Tregs, via phosphorylation of FoxO1 and negative regulation of PTEN and FoxP3. Taken together, our results demonstrate an important role of PAR4 in tuning the function of Tregs and open the possibility of targeting PAR4 to modulate immune responses.

L-selectin: A Major Regulator of Leukocyte Adhesion, Migration and Signaling

L-selectin (CD62L) is a type-I transmembrane glycoprotein and cell adhesion molecule that is expressed on most circulating leukocytes. Since its identification in 1983, L-selectin has been extensively characterized as a tethering/rolling receptor. There is now mounting evidence in the literature to suggest that L-selectin plays a role in regulating monocyte protrusion during transendothelial migration (TEM). The N-terminal calcium-dependent (C-type) lectin domain of L-selectin interacts with numerous glycans, including sialyl Lewis X (sLe^x) for tethering/rolling and proteoglycans for TEM. Although the signals downstream of L-selectin-dependent adhesion are poorly understood, they will invariably involve the short 17 amino acid cytoplasmic tail. In this review we will detail the expression of L-selectin in different immune cell subsets, and its influence on cell behavior. We will list some of the diverse glycans known to support L-selectin-dependent adhesion, within luminal and abluminal regions of the vessel wall. We will describe how each domain within L-selectin contributes to adhesion, migration and signal transduction. A significant focus on the L-selectin cytoplasmic tail and its proposed contribution to signaling via the ezrin-radixin-moesin (ERM) family of proteins will be outlined. Finally, we will discuss how ectodomain shedding of L-selectin during monocyte TEM is essential for the establishment of front-back cell polarity, bestowing emigrated cells the capacity to chemotax toward sites of damage.

Rorc restrains the potency of ST2+ regulatory T cells in ameliorating intestinal graft-versus-host disease

Soluble stimulation-2 (ST2) is increased during graft-versus-host disease (GVHD), while Tregs that express ST2 prevent GVHD through unknown mechanisms. Transplantation of Foxp3- T cells and Tregs that were collected and sorted from different Foxp3 reporter mice indicated that in mice that developed GVHD, ST2+ Tregs were thymus derived and predominantly localized to the intestine. ST2-/- Treg transplantation was associated with reduced total intestinal Treg frequency and activation. ST2-/- versus WT intestinal Treg transcriptomes showed decreased Treg functional markers and, reciprocally, increased Rorc expression. Rorc-/- T cells transplantation enhanced the frequency and function of intestinal ST2+ Tregs and reduced GVHD through decreased gut-infiltrating soluble ST2-producing type 1 and increased IL-4/IL-10-producing type 2 T cells. Cotransfer of ST2+ Tregs sorted from Rorc-/- mice with WT CD25-depleted T cells decreased GVHD severity and mortality, increased intestinal ST2+KLRG1+ Tregs, and decreased type 1 T cells after transplantation, indicating an intrinsic mechanism. Ex vivo IL-33-stimulated Tregs (TregIL-33) expressed higher amphiregulin and displayed better immunosuppression, and adoptive transfer prevented GVHD better than control Tregs or TregIL-33 cultured with IL-23/IL-17. Amphiregulin blockade by neutralizing antibody in vivo abolished the protective effect of TregIL-33. Our data show that inverse expression of ST2 and RORγt in intestinal Tregs determines GVHD and that TregIL-33 has potential as a cellular therapy avenue for preventing GVHD.

Tailoring the homing capacity of human Tregs for directed migration to sites of Th1-inflammation or intestinal regions

Cell-based therapy with CD4⁺ FOXP3⁺ regulatory T cells (Tregs) is a promising strategy to limit organ rejection and graft-vs-host disease. Ongoing clinical applications have yet to consider how human Tregs could be modified to direct their migration to specific inflammation sites and/or tissues for more targeted immunosuppression. We show here that stable, homing-receptor-tailored human Tregs can be generated from thymic Tregs isolated from pediatric thymus or adult blood. To direct migration to Th1-inflammatory sites, addition of interferon-γ and IL-12 during Treg expansion produced suppressive, epigenetically stable CXCR3⁺ TBET⁺ FOXP3⁺ T helper (Th)1-Tregs. CXCR3 remained expressed after injection in vivo and Th1-Tregs migrated efficiently towards CXCL10 in vitro. To induce tissue-specific migration, addition of retinoic acid (RA) during Treg expansion induced expression of the gut-homing receptors α4β7-integrin and CCR9. FOXP3⁺ RA-Tregs had elevated expression of the functional markers latency-associated peptide and glycoprotein A repetitions predominant, increased suppressive capacity in vitro and migrated efficiently to healthy and inflamed intestine after injection into mice. Homing-receptor-tailored Tregs were epigenetically stable even after long-term exposure to inflammatory conditions, suppressive in vivo and characterized by Th1- or gut-homing-specific transcriptomes. Tailoring human thymic Treg homing during in vitro expansion offers a new and clinically applicable approach to improving the potency and specificity of Treg therapy.

Gata3 hypermethylation and Foxp3 hypomethylation are associated with sustained protection and bystander effect following epicutaneous immunotherapy in peanut-sensitized mice

Background

Epicutaneous immunotherapy (EPIT) is a promising method for treating food allergies. In animal models, EPIT induces sustained unresponsiveness and prevents further sensitization mediated by Tregs. Here, we elucidate the mechanisms underlying the therapeutic effect of EPIT, by characterizing the kinetics of DNA methylation changes in sorted cells from spleen and blood and by evaluating its persistence and bystander effect compared to oral immunotherapy (OIT).

Methods

BALB/c mice orally sensitized to peanut proteins (PPE) were treated by EPIT using a PPE‐patch or by PPE‐OIT. Another set of peanut‐sensitized mice treated by EPIT or OIT were sacrificed following a protocol of sensitization to OVA. DNA methylation was analyzed during immunotherapy and 8 weeks after the end of treatment in sorted cells from spleen and blood by pyrosequencing. Humoral and cellular responses were measured during and after immunotherapy.

Results

Analyses showed a significant hypermethylation of the Gata3 promoter detectable only in Th2 cells for EPIT from the 4th week and a significant hypomethylation of the Foxp3 promoter in CD62L⁺ Tregs, which was sustained only for EPIT. In addition, mice treated with EPIT were protected from subsequent sensitization and maintained the epigenetic signature characteristic for EPIT.

Conclusions

Our study demonstrates that EPIT leads to a unique and stable epigenetic signature in specific T‐cell compartments with downregulation of Th2 key regulators and upregulation of Treg transcription factors, likely explaining the sustainability of protection and the observed bystander effect.

Ex vivo expanded natural regulatory T cells from patients with end-stage renal disease or kidney transplantation are useful for autologous cell therapy

Novel concepts employing autologous, ex vivo expanded natural regulatory T cells (nTreg) for adoptive transfer has potential to prevent organ rejection after kidney transplantation. However, the impact of dialysis and maintenance immunosuppression on the nTreg phenotype and peripheral survival is not well understood, but essential when assessing patient eligibility. The current study investigates regulatory T-cells in dialysis and kidney transplanted patients and the feasibility of generating a clinically useful nTreg product from these patients. Heparinized blood from 200 individuals including healthy controls, dialysis patients with end stage renal disease and patients 1, 5, 10, 15, 20 years after kidney transplantation were analyzed. Differentiation and maturation of nTregs were studied by flow cytometry in order to compare dialysis patients and kidney transplanted patients under maintenance immunosuppression to healthy controls. CD127 expressing CD4⁺CD25^highFoxP3⁺ nTregs were detectable at increased frequencies in dialysis patients with no negative impact on the nTreg end product quality and therapeutic usefulness of the ex vivo expanded nTregs. Further, despite that immunosuppression mildly altered nTreg maturation, neither dialysis nor pharmacological immunosuppression or previous acute rejection episodes impeded nTreg survival in vivo. Accordingly, the generation of autologous, highly pure nTreg products is feasible and qualifies patients awaiting or having received allogenic kidney transplantation for adoptive nTreg therapy. Thus, our novel treatment approach may enable us to reduce the incidence of organ rejection and reduce the need of long-term immunosuppression.

Ex vivo generation of umbilical cord blood T regulatory cells expressing the homing markers CD62L and cutaneous lymphocyte antigen

Regulatory T cells (Tregs) are an important component of the immune system involved in regulation of immune cell proliferation and inflammatory responses and preventing autoimmune diseases. The use of Tregs in cellular therapy has recently been explored in clinical trials specifically evaluating the role of ex vivo expanded Tregs in the prevention of graft-versus-host disease during stem cell transplantation. The possibility of Treg use in the clinic requires clinical grade expansion of Tregs for development of cell therapy protocols and proper homing of Tregs to the intended target. Here we demonstrate a novel medium composition to expand CB Tregs, specifically upregulation the homing and activation markers CD62L and cutaneous lymphocyte antigen (CLA). CLA expression was uniquely acquired during activation of Tregs with subsequent loss or lack of expression with media change. This finding highlights the importance of proper growth conditions unique to Tregs that can alter expression of proteins and establishes a baseline for expanding marker specific Tregs that home and target unique tissues.

Bioimaging of alloantigen-stimulated regulatory T cells in rat vascularized composite allotransplantation

Background

Tipping the balance toward regulatory T cells (Tregs) through adoptive cell therapy has shown promise to induce transplantation tolerance. Although such strategy has been explored in many mice organ transplantation studies, less knowledge was available in rat systems. Furthermore, the behaviors of the transferred cells have not been well studied in real-time fashion.

Methods

Tregs from naïve LEW rats were purified in two steps with the autoMACS system. Immunosuppression potential of these cells was examined with mixed lymphocyte reaction. Following stimulation by the alloantigen in vitro, the purified Tregs were infused into the recipients of vascularized composite allotransplantation (VCA). Secondary allogeneic skin grafting challenge was performed on the recipients with long-term survived VCA. Live optical imaging was performed to track luciferase-expressing Tregs following infusion to the VCA recipients. Expression of relevant molecules was studied by flow cytometry or quantitative RT-PCR.

Results

Rat Tregs were enriched following two-step cell sorting and showed immunosuppressive capacity. Upon infusion into the VCA recipients that have been treated with antilymphocyte serum and short-term Cyclosporin A, the antigen-stimulated Tregs significantly prolonged VCA survival and induced donor-specific tolerance. Tracking of the infused bioluminescent Tregs showed their specific homing to lymph nodes, and then to the VCAs. Following secondary skin grafting, Tregs specifically gathered at the donor-derived skin that was not rejected by the recipient. The in vivo migratory pattern coincided with the altered expression of cell surface molecules of CD62L, CD103, CD134, and CD278, following donor-antigen stimulation. Elevated expression of CCR4 and CCL22 in allograft may also participate in recruiting Tregs for maintenance of VCA survival and promoting donor-specific tolerance.

Conclusion

Sorted Tregs induced donor-specific tolerance to VCA in rats. Live cell tracking demonstrated that activated CD4⁺CD25⁺FoxP3⁺ Tregs targeted primarily to the lymph nodes and VCA. The Tregs migrated to the secondary grafted donor skin and contributed to the maintenance of donor-specific tolerance. These behaviors were associated with phenotypic changes induced by donor antigen stimulation. Increased expression of CCR4 and CCL22 in VCA skin may also be relevant.

Third-party regulatory T cells prevent murine acute graft-versus-host disease

BACKGROUND/AIMS

Adoptive therapy with regulatory T (Treg) cells to prevent graft-versus-host disease (GVHD) would benefit from a strategy to improve homing to the sites of inflammation following hematopoietic stem cell transplantation (HSCT). Although donor-derived Treg cells have mainly been used in these models, third-party-derived Treg cells are a promising alternative for cell-based immunotherapy, as they can be screened for pathogens and cell activity, and banked for GVHD prevention. In this study, we explored major histocompatibility complex (MHC) disparities between Treg cells and conventional T cells in HSCT to evaluate the impact of these different cell populations on the prevention of acute GVHD, as well as survival after allogeneic transplantation.

METHODS

To induce acute GVHD, lethally irradiated BALB/c (H-2d) mice were transplanted with 5 × 105 T cell-depleted bone marrow cells and 5 × 105 CD4+CD25- splenic T cells from C57BL/6 (H-2b) mice. Recipients were injected with 5 × 105 cultured donor-, host-, or third-party-derived CD4+CD25+CD62L+ Treg cells (bone marrow transplantation + day 1).

RESULTS

Systemic infusion of three groups of Treg cell improved clinicopathological manifestations and survival in an acute GVHD model. Although donor-derived Treg cells were immunologically the most effective, the third-party-derived Treg cell therapy group displayed equal regulation of expansion of CD4+CD25+- Foxp3+ Treg cells and suppressive CD4+IL-17+ T-helper (Th17) cells in ex vivo assays compared with the donor- and host-derived groups.

CONCLUSION

Our findings demonstrate that the use of third-party Treg cells is a viable alternative to donor-derived Treg cellular therapy in clinical settings, in which human leukocyte antigen-matched donors are not always readily available.

Higher CD45RA+ Regulatory T Cells in the Graft Improves Outcome in Younger Patients Undergoing T Cell-Replete Haploidentical Transplantation: Where Donor Age Matters

To understand the phenomenon of early alloreactivity (EA) in younger children undergoing post-transplantation cyclophosphamide (PTCy)-based haploidentical transplantation, we studied the graft composition and the immune reconstitution in 32 consecutive patients (aged 2 to 25 years) undergoing PTCy and T cell costimulation blockade based peripheral blood stem cell transplantation with emphasis on CD45RA⁺ subset of regulatory T cells (Tregs). All but 1 engrafted, and 14 patients experienced EA (acute graft-versus-host disease grades II to IV, n = 8; and post-transplantation hemophagocytic syndrome, n = 6) with a cumulative incidence of 43.7%; 42% developed mild chronic graft-versus-host disease. The overall survival was 70.2% with a nonrelapse mortality of 16.8% at a median of 19 months. Age < 10 years, donor age > 45 years, and poor recovery of Tregs correlated with EA. Not Tregs but higher CD45RA⁺ Tregs in the graft was associated with less EA (11.7% versus 32.5%, P = .0001). Higher donor age correlated with a lower CD45RA⁺ Tregs in the graft (P = .01). However, only higher CD45RA⁺ Treg percentage in the graft favorably impacted EA as well as nonrelapse mortality and overall survival. Our study demonstrates a critical role for CD45RA⁺ Tregs in determining EA and outcome after PTCy-based haploidentical peripheral blood stem cell transplantation, and the age-related physiologic decline in this population might be responsible for adverse impact of donor age.

Utilization of leukapheresis and CD4 positive selection in Treg isolation and the ex-vivo expansion for a clinical application in transplantation and autoimmune disorders

Adoptive transfer of T regulatory cells (Tregs) is of great interest as a novel immunosuppressive therapy in autoimmune disorders and transplantation. Obtaining a sufficient number of stable and functional Tregs generated according to current Good Manufacturing Practice (cGMP) requirements has been a major challenge in introducing Tregs as a clinical therapy. Here, we present a protocol involving leukapheresis and CD4⁺ cell pre-enrichment prior to Treg sorting, which allows a sufficient number of Tregs for a clinical application to be obtained. With this method there is a decreased requirement for ex-vivo expansion. The protocol was validated in cGMP conditions. Our final Treg product passed all release criteria set for clinical applications. Moreover, during expansion Tregs presented their stable phenotype: percentage of CD4⁺CD25^hiCD127⁻ and CD4⁺FoxP3⁺ Tregs was > 95% and > 80%, respectively, and Tregs maintained proper immune suppressive function in vitro. Our results suggest that utilization of leukapheresis and CD4 positive selection during Treg isolation improves the likelihood of obtaining a sufficient number of high quality Treg cells during subsequent ex-vivo expansion and they can be applied clinically.

Harnessing Advances in T Regulatory Cell Biology for Cellular Therapy in Transplantation

Cellular therapy with CD4FOXP3 T regulatory (Treg) cells is a promising strategy to induce tolerance after solid-organ transplantation or prevent graft-versus-host disease after transfer of hematopoietic stem cells. Treg cells currently used in clinical trials are either polyclonal, donor- or antigen-specific. Aside from variations in isolation and expansion protocols, however, most therapeutic Treg cell-based products are much alike. Ongoing basic science work has provided considerable new insight into multiple facets of Treg cell biology, including their stability, homing, and functional specialization; integrating these basic science discoveries with clinical efforts will support the development of next-generation therapeutic Treg cells with enhanced efficacy. In this review, we summarize recent advances in knowledge of how Treg cells home to lymphoid and peripheral tissues, and control antibody production and tissue repair. We also discuss newly appreciated pathways that modulate context-specific Treg cell function and stability. Strategies to improve and tailor Treg cells for cell therapy to induce transplantation tolerance are highlighted.