The promise of CD4+FoxP3+ regulatory T-cell manipulation in vivo: applications for allogeneic hematopoietic stem cell transplantation

Concomitant use of interleukin-2 and tacrolimus suppresses follicular helper T cell proportion and exerts therapeutic effect against lupus nephritis in systemic lupus erythematosus-like chronic graft versus host disease

Introduction

Defective interleukin-2 (IL-2) production contributes to immune system imbalance in patients with systemic erythematosus lupus (SLE). Recent clinical studies suggested that low-dose IL-2 treatment is beneficial for SLE and the therapeutic effect is associated with regulatory T cell (Treg) expansion. Pharmacological calcineurin inhibition induces a reduction in the number of Tregs because they require stimulation of T cell receptor signaling and IL-2 for optimal proliferation. However, the activation of T cell receptor signaling is partially dispensable for the expansion of Tregs, but not for that of conventional T cells if IL-2 is present.

Aim

We examined whether addition of IL-2 restores the Treg proportion even with concurrent use of a calcineurin inhibitor and if the follicular helper T cell (Tfh) proportion is reduced in an SLE-like murine chronic graft versus host disease model.

Methods

Using a parent-into-F1 model, we investigated the effect of IL-2 plus tacrolimus on Treg and Tfh proportions and the therapeutic effect.

Results

Treatment with a combination of IL-2 and tacrolimus significantly delayed the initiation of proteinuria and decreased the urinary protein concentration, whereas tacrolimus or IL-2 monotherapy did not significantly attenuate proteinuria. Phosphorylation of signal transducer and activator of transcription 3, a positive regulator of Tfh differentiation, was reduced by combination treatment, whereas phosphorylation of signal transducer and activator of transcription 5, a negative regulator, was not reduced.

Conclusion

Addition of calcineurin inhibitors as adjunct agents may be beneficial for IL-2-based treatment of lupus nephritis.

Regulatory T Cell Amelioration of Graft-versus-Host Disease following Allogeneic/Xenogeneic Hematopoietic Stem Cell Transplantation Using Mobilized Mouse and Human Peripheral Blood Donors

The present studies examined experimental transplant outcomes using mobilized peripheral blood from mice and humans together with FoxP3+Treg cells. Donor mice were treated with filgrastim and / or plerixafor and their peripheral blood (PB) displayed significant elevations in hematopoietic stem and progenitor populations. Some of these PB donors were concurrently administered a Treg expansion strategy consisting of a TL1A-Ig fusion protein low dose rIL-2. A significant increase (4-5x) in the frequency Tregs occurred during mobilization. C3H.SW PB was collected from mobilized and Treg unexpanded ("TrUM") or mobilized and Treg expanded ("TrEM") donors and transplanted into MHC-matched B6 (H2b) recipients. Recipients of TrEM, exhibited significantly reduced weight loss and clinical GVHD scores compared to recipients of TrUM. Notably, recipients of TrEM exhibited comparable GVL activity to TrUM recipients against leukemia levels. Next, huTregs (CD4+CD25+CD127lo) from a healthy human PB mobilized donor were expanded ex-vivo prior to transplant into NSG/ NOD-scid IL2Rgammanull mice. We found that treatment with ex-vivo expanded huTregs resulted in significant reduction of lethality and clinical xGVHD scores. Notably, post-transplant, PB huTregs levels remained elevated and the frequency of huCD4+Tconv and CD8+ cells was diminished supporting the improved xGVHD outcomes. These findings demonstrated that the use of mPB containing elevated Treg levels significantly reduced GVHD following "MUD" and MHC-mismatched mouse HSCT without loss of GVL activity. Moreover, utilizing ex-vivo expanded huTregs from a mobilized PB donor and added back to donor PB ameliorated xGVHD. In total, these studies support the notion that in vivo or ex-vivo manipulation of donor Tregs together with mobilized peripheral blood could provide therapeutic approaches to improve aHSCT outcomes.

In or out of control: Modulating regulatory T cell homeostasis and function with immune checkpoint pathways

Regulatory T cells (Tregs) are the master regulators of immunity and they have been implicated in different disease states such as infection, autoimmunity and cancer. Since their discovery, many studies have focused on understanding Treg development, differentiation, and function. While there are many players in the generation and function of truly suppressive Tregs, the role of checkpoint pathways in these processes have been studied extensively. In this paper, we systematically review the role of different checkpoint pathways in Treg homeostasis and function. We describe how co-stimulatory and co-inhibitory pathways modulate Treg homeostasis and function and highlight data from mouse and human studies. Multiple checkpoint pathways are being targeted in cancer and autoimmunity; therefore, we share insights from the clinic and discuss the effect of experimental and approved therapeutics on Treg biology.

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.

Lactobacillus supports Clostridiales to restrict gut colonization by multidrug-resistant Enterobacteriaceae

Infections by multidrug-resistant Enterobacteriaceae (MRE) are life-threatening to patients. The intestinal microbiome protects against MRE colonization, but antibiotics cause collateral damage to commensals and open the way to colonization and subsequent infection. Despite the significance of this problem, the specific commensals and mechanisms that restrict MRE colonization remain largely unknown. Here, by performing a multi-omic prospective study of hospitalized patients combined with mice experiments, we find that Lactobacillus is key, though not sufficient, to restrict MRE gut colonization. Lactobacillus rhamnosus and murinus increase the levels of Clostridiales bacteria, which induces a hostile environment for MRE growth through increased butyrate levels and reduced nutrient sources. This mechanism of colonization resistance, an interaction between Lactobacillus spp. and Clostridiales involving cooperation between microbiota members, is conserved in mice and patients. These results stress the importance of exploiting microbiome interactions for developing effective probiotics that prevent infections in hospitalized patients.

Multidrug-resistant Enterobacteriaceae (MRE) represent a major threat for patients’ health. Here, the authors describe how cooperation between gut commensal bacteria (Lactobacillus spp. And Clostridiales) restrict MRE colonization in mice and patients

Combinations of anti-GITR antibody and CD28 superagonist induce permanent allograft acceptance by generating type 1 regulatory T cells

Type 1 regulatory T (Tr1) cells represent a subset of IL-10-producing CD4⁺Foxp3^- T cells and play key roles in promoting transplant tolerance. However, no effective pharmacological approaches have been able to induce Tr1 cells in vivo. We herein report the combined use of a CD28 superagonist (D665) and anti-glucocorticoid-induced tumor necrosis factor receptor-related protein monoclonal antibody (G3c) to induce Tr1 cells in vivo. Large amounts of IL-10/interferon-γ-co-producing CD4⁺Foxp3^- Tr1 cells were generated by D665-G3c sequential treatment in mice. Mechanistic studies suggested that D665-G3c induced Tr1 cells via transcription factors Prdm1 and Maf. G3c contributed to Tr1 cell generation via the activation of mitogen-activated protein kinase-signal transducer and activator of transcription 3 signaling. Tr1 cells suppressed dendritic cell maturation and T cell responses and mediated permanent allograft acceptance in fully major histocompatibility complex-mismatched mice in an IL-10-dependent manner. In vivo Tr1 cell induction is a promising strategy for achieving transplant tolerance.

Emerging translational strategies and challenges for enhancing regulatory T cell therapy for graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for many types of cancer. Genetic disparities between donor and host can result in immune-mediated attack of host tissues, known as graft versus host disease (GVHD), a major cause of morbidity and mortality following HSCT. Regulatory CD4+ T cells (Tregs) are a rare cell type crucial for immune system homeostasis, limiting the activation and differentiation of effector T cells (Teff) that are self-reactive or stimulated by foreign antigen exposure. Adoptive cell therapy (ACT) with Treg has demonstrated, first in murine models and now in patients, that prophylactic Treg infusion can also suppress GVHD. While clinical trials have demonstrated Treg reduce severe GVHD occurrence, several impediments remain, including Treg variability and practical need for individualized Treg production for each patient. Additionally, there are challenges in the use of in vitro expansion techniques and in achieving in vivo Treg persistence in context of both immune suppressive drugs and in lymphoreplete patients being treated for GVHD. This review will focus on 3 main translational approaches taken to improve the efficacy of tTreg ACT in GVHD prophylaxis and development of treatment options, following HSCT: genetic modification, manipulating TCR and cytokine signaling, and Treg production protocols. In vitro expansion for Treg ACT presents a multitude of approaches for gene modification to improve efficacy, including: antigen specificity, tissue targeting, deletion of negative regulators/exhaustion markers, resistance to immunosuppressive drugs common in GVHD treatment. Such expansion is particularly important in patients without significant lymphopenia that can drive Treg expansion, enabling a favorable Treg:Teff ratio in vivo. Several potential therapeutics have also been identified that enhance tTreg stability or persistence/expansion following ACT that target specific pathways, including: DNA/histone methylation status, TCR/co-stimulation signaling, and IL-2/STAT5 signaling. Finally, this review will discuss improvements in Treg production related to tissue source, Treg subsets, therapeutic approaches to increase Treg suppression and stability during tTreg expansion, and potential for storing large numbers of Treg from a single production run to be used as an off-the-shelf infusion product capable of treating multiple recipients.

Recipient Tregs: Can They Be Exploited for Successful Hematopoietic Stem Cell Transplant Outcomes?

Human and mouse CD4⁺FoxP3⁺ T cells (Tregs) comprise non-redundant regulatory compartments which maintain self-tolerance and have been found to be of potential therapeutic usefulness in autoimmune disorders and transplants including allogeneic hematopoietic stem cell transplantation (allo-HSCT). There is substantial literature interrogating the application of donor derived Tregs for the prevention of graft versus host disease (GVHD). This Mini-Review will focus on the recipient's Tregs which persist post-transplant. Although treatment in patients with low dose IL-2 months post-HSCT are encouraging, manipulating Tregs in recipients early post-transplant is challenging, in part likely an indirect consequence of damage to the microenvironment required to support Treg expansion of which little is understood. This review will discuss the potential for manipulating recipient Tregs in vivo prior to and after HSCT (fusion proteins, mAbs). Strategies that would circumvent donor/recipient peripheral blood harvest, cell culture and ex-vivo Treg expansion will be considered for the translational application of Tregs to improve HSCT outcomes.

Exosomes Secreted by Mesenchymal Stem Cells Induce Immune Tolerance to Mouse Kidney Transplantation via Transporting LncRNA DANCR

Mesenchymal stem cells induce kidney transplant tolerance by increasing regulatory T (Treg) cells. Bone marrow mesenchymal stem cell exosomes (BMMSC-Ex) promote Treg cell differentiation. Long non-coding RNA differentiation antagonizing non-protein coding RNA (DANCR) is expressed in BMMSCs and can be encapsulated in exosomes. We aimed to explore the role of DANCR in BMMSC-Ex in immune tolerance after kidney transplantation and related mechanism. The isogenic/allograft kidney transplantation mouse model was established, and levels of serum creatinine (SCr) were determined. Hematoxylin-eosin staining was conducted to detect the inflammation, and immunohistochemistry was performed to detect the infiltration of CD4+ T cells. Levels of IFN-γ, IL-17, and IL-2 were examined by ELISA. Flow cytometry was conducted to determine Treg cells. In the allograft group, the inflammatory response was severe, CD4+ T cell infiltration, SCr levels, and plasma rejection-related factors were up-regulated, while injection of BMMSC-Ex reversed the results. BMMSC-Ex increased Treg cells in kidney transplantation mice. Interference with DANCR reversed the promoting effect of BMMSC-Ex on Treg cell differentiation. DANCR bound to SIRT1, promoted ubiquitination and accelerated its degradation. The injection of BMMSC-Ex (after interference with DANCR) promoted SIRT1 levels, inflammatory response, CD4+ T cell infiltration, SCr levels, and plasma rejection related factors' expression, while Treg cells were decreased. LncRNA DANCR in BMMSC-Ex promoted Treg cell differentiation and induced immune tolerance of kidney transplantation by down-regulating SIRT1 expression in CD4+ T cells.

CD4+ T-cell reconstitution predicts survival outcomes after acute graft-versus-host-disease: a dual-center validation

Acute graft-versus-host-Disease (aGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). We previously showed that early CD4+ T-cell immune reconstitution (IR; CD4+ IR) predicts survival after HCT. Here, we studied the relation between CD4+ IR and survival in patients developing aGVHD. Pediatric patients undergoing first allogeneic HCT at University Medical Center Utrecht (UMC)/Princess Máxima Center (PMC) or Memorial Sloan Kettering Cancer Center (MSK) were included. Primary outcomes were nonrelapse mortality (NRM) and overall survival (OS), stratified for aGVHD and CD4+ IR, defined as ≥50 CD4+ T cells per μL within 100 days after HCT or before aGVHD onset. Multivariate and time-to-event Cox proportional hazards models were applied, and 591 patients (UMC/PMC, n = 276; MSK, n = 315) were included. NRM in patients with grade 3 to 4 aGVHD with or without CD4+ IR within 100 days after HCT was 30% vs 80% (P = .02) at UMC/PMC and 5% vs 67% (P = .02) at MSK. This was associated with lower OS without CD4+ IR (UMC/PMC, 61% vs 20%; P = .04; MSK, 75% vs 33%; P = .12). Inadequate CD4+ IR before aGVHD onset was associated with significantly higher NRM (74% vs 12%; P < .001) and inferior OS (24% vs 78%; P < .001). In this retrospective analysis, we demonstrate that early CD4+ IR, a simple and robust marker predictive of outcomes after HCT, is associated with survival after moderate to severe aGVHD. This association must be confirmed prospectively but suggests strategies to improve T-cell recovery after HCT may influence survival in patients developing aGVHD.

High proportion of terminally differentiated regulatory T cells after allogeneic hematopoietic stem cell transplantation

It is now well-established that regulatory T cells (Treg) represent a heterogeneous group of CD4⁺ T cells. Previous studies have demonstrated that Treg homeostasis was impacted by allogeneic hematopoietic cell transplantation (allo-HCT) and particularly so in patients with chronic graft-versus-host disease (GVHD). Here, we first assessed the ability of various Treg subsets to phosphorylate STAT5 in response to IL-2 or IL-7 stimulation in vitro. We then compared the frequencies of different Treg subtypes in healthy controls as well as in allo-HCT patients with or without chronic GVHD. The highest phosphorylated STAT5 (pSTAT5) signal in response to IL-2 was observed in the CD45RO⁺CD26^-CD39⁺HLA-DR⁺ Treg fraction. In contrast, naive Treg were mostly less susceptible to IL-2 stimulation in vitro. Following IL-7 stimulation, most Treg subpopulations upregulated pSTAT5 expression but to a lesser extent than conventional T cells. Compared to healthy controls, allo-HCT patients had lower frequencies of the naive CD45RA^brightCD26⁺ Treg subpopulation but higher frequencies of the most differentiated memory CD45RO⁺CD26^-CD39⁺ Treg subpopulations. Further, unbiased analysis revealed that six Treg clusters characterized by high expression of CD25, HLA-DR, and ICOS were significantly more frequent in patients with no or with limited chronic GVHD than in those with moderate/severe chronic GVHD.

How to Make an Immune System and a Foreign Host Quickly Cohabit in Peace? The Challenge of Acute Graft-Versus-Host Disease Prevention After Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) has been used as cellular immunotherapy against hematological cancers for more than six decades. Its therapeutic efficacy relies on the cytoreductive effects of the conditioning regimen but also on potent graft-versus-tumor (GVT) reactions mediated by donor-derived immune cells. However, beneficial GVT effects may be counterbalanced by acute GVHD (aGVHD), a systemic syndrome in which donor immune cells attack healthy tissues of the recipient, resulting in severe inflammatory lesions mainly of the skin, gut, and liver. Despite standard prophylaxis regimens, aGVHD still occurs in approximately 20–50% of alloHCT recipients and remains a leading cause of transplant-related mortality. Over the past two decades, advances in the understanding its pathophysiology have helped to redefine aGVHD reactions and clinical presentations as well as developing novel strategies to optimize its prevention. In this review, we provide a brief overview of current knowledge on aGVHD immunopathology and discuss current approaches and novel strategies being developed and evaluated in clinical trials for aGVHD prevention. Optimal prophylaxis of aGVHD would prevent the development of clinically significant aGVHD, while preserving sufficient immune responsiveness to maintain beneficial GVT effects and immune defenses against pathogens.

Limited efficacy of rapamycin monotherapy in vascularized composite allotransplantation

BACKGROUND

Vascularized composite allotransplantation (VCA) is a novel and life-enhancing procedure to restore a patient's function and/or appearance. Current immunosuppression in VCA recipients is based on calcineurin inhibitor (CNI) therapy that can lead to severe complications, such that inducing immune tolerance is a major goal of VCA research. In contrast to CNI, rapamycin (RPM) is thought to be beneficial to the development of immune tolerance by suppressing T-effector cells (Teffs) and expanding T-regulatory (Treg) cells. However, we found high dose RPM monotherapy prolonged VCA survival by only a few days, leading us to explore the mechanisms responsible.

METHODS

A mouse orthotopic forelimb transplantation model (BALB/c- > C57BL/6) was established using WT mice, as well as C57BL/6 recipients with conditional deletion of T-bet within their Treg cells. Events in untreated VCA recipients or those receiving RPM or FK506 therapy were analyzed by flow-cytometry, histopathology and real-time qPCR.

RESULTS

Therapy with RPM (2 mg/kg/d, p < .005) or FK506 (2 mg/kg/d, p < .005) each prolonged VCA survival. In contrast to FK506, RPM increased the ratio of splenic Treg to Teff cells (p < .05) by suppressing Teff and expanding Treg cells. While the proportion of activated splenic CD4 + Foxp3- T cells expressing IFN-γ were similar in control and RPM-treated groups, RPM decreased the proportions ICOS+ and CD8+ IFN-γ + splenic T cells. However, RPM also downregulated CXCR3+ expression by Tregs, and forelimb allografts had reduced infiltration by CXCR3+ Treg cells. In addition, allograft recipients whose Tregs lacked T-bet underwent accelerated rejection compared to WT mice despite RPM therapy.

CONCLUSIONS

We demonstrate that while RPM increased the ratio of Treg to Teff cells and suppressed CD8+ T cell allo-activation, it failed to prevent CD4 Teff cell activation and impaired CXCR3-dependent Treg graft homing, thereby limiting the efficacy of RPM in VCA recipients.

Use of Tregs as a cell-based therapy via CD39 for benign prostate hyperplasia with inflammation

Benign prostatic hyperplasia (BPH) occurs most commonly among older men, often accompanied by chronic tissue inflammation. Although its aetiology remains unclear, autoimmune dysregulation may contribute to BPH. Regulatory T cells (Tregs) prevent autoimmune responses and maintain immune homeostasis. In this study, we aimed to investigate Tregs frequency, phenotype, and function in BPH patients and to evaluate adoptive transfer Tregs for immunotherapy in mice with BPH via CD39. Prostate specimens and peripheral blood from BPH patients were used to investigate Treg subsets, phenotype and Treg‐associated cytokine production. Sorted CD39^+/− Tregs from healthy mice were adoptively transferred into mice before or after testosterone propionate administration. The Tregs percentage in peripheral blood from BPH patients was attenuated, exhibiting low Foxp3 and CD39 expression with low levels of serum IL‐10, IL‐35 and TGF‐β. Immunohistochemistry revealed Foxp3+ cells were significantly diminished in BPH prostate with severe inflammatory. Although the Tregs subset was comprised of more effector/memory Tregs, CD39 was still down‐regulated on effector/memory Tregs in BPH patients. Before or after testosterone propionate administration, no alterations of BPH symptoms were observed due to CD39‐ Tregs in mice, however, CD39⁺Tregs existed more potency than Tregs to regulate prostatic hyperplasia and inhibit inflammation by decreasing IL‐1β and PSA secretion, and increasing IL‐10 and TGF‐β secretion. Furthermore, adoptive transfer with functional Tregs not only improved prostate hyperplasia but also regulated muscle cell proliferation in bladder. Adoptive transfer with Tregs may provide a novel method for the prevention and treatment of BPH clinically.

Unleashing the cure: Overcoming persistent obstacles in the translation and expanded use of hematopoietic stem cell-based therapies

Hematopoietic stem cell transplantation (HSCT) is broadly used for treating and curing hematological cancers and various disorders of the blood and immune system. However, its true therapeutic potential remains vastly constrained by significant scientific and technical hurdles that preclude expansion to new indications and limit the number of patients who could benefit from, gain access to, or financially afford the procedure. To define and overcome these challenges, the California Institute for Regenerative Medicine (CIRM) held multiple workshops related to HSCT and has subsequently invested in a new generation of approaches to address the most compelling needs of the field, including new sources of healthy and immunologically compatible hematopoietic stem cells for transplant; safe and efficient genome modification technologies for correction of inherited genetic defects and other forms of gene therapy; safer and more tractable transplantation procedures such as nongenotoxic conditioning regimens, methods to accelerate immune reconstitution and recovery of immune function, and innovations to minimize the risk of immune rejection; and other life‐threatening complications from transplant. This Perspective serves to highlight these needs through examples from the recent CIRM‐funded and other notable investigations, presents rationale for comprehensive, systematic, and focused strategies to unleash the full potential of HSCT, thereby enabling cures for a greatly expanded number of disorders and making HSCT feasible, accessible, and affordable to all who could benefit.

The role of regulatory T cells in graft-versus-host disease management

Introduction: Despite improvements in human leukocyte antigen (HLA) matching algorithms and supportive care, graft-versus-host disease (GVHD) remains the leading cause of non-relapse morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HSCT). Acute GVHD, typically occurring in the first 100 days post-HSCT, is mediated by mature effector T cells from the donor (graft) that become activated after encountering alloantigens in the recipient (host). Chronic GVHD, characterized by aberrant immune responses to both autoantigens and alloantigens, occurs later and arises from a failure to develop tolerance after HSCT. CD4+ CD25+ CD127- FOXP3+ regulatory T cells (Tregs) function to suppress auto- and alloreactive immune responses and are key mediators of immune tolerance.Areas covered: In this review, authors discuss the biologic and therapeutic roles of Tregs in acute and chronic GVHD, including in vivo and ex vivo strategies for Treg expansion and adoptive Treg cellular therapy.Expert opinion: Although they comprise only a small subset of circulating CD4 + T cells, Tregs play an important role in establishing and maintaining immune tolerance following allogeneic HSCT. The development of GVHD has been associated with reduced Treg frequency or numbers. Consequently, the immunosuppressive properties of Tregs are being harnessed in clinical trials for GVHD prevention and treatment.