Tregs In Recipients Research Articles

Antibody-Suppressor CXCR5+CD8+ T Cells Are More Potent Regulators of Humoral Alloimmunity after Kidney Transplant in Mice Compared to CD4+ Regulatory T Cells.

Adoptive cell therapy (ACT), especially with CD4+ regulatory T cells (CD4+ Tregs), is an emerging therapeutic strategy to minimize immunosuppression and promote long-term allograft acceptance, although much research remains to realize its potential. In this study, we investigated the potency of novel Ab-suppressor CXCR5+CD8+ T cells (CD8+ TAb-supp) in comparison with conventional CD25highFoxp3+CD4+ Tregs for suppression of humoral alloimmunity in a murine kidney transplant (KTx) model of Ab-mediated rejection (AMR). We examined quantity of peripheral blood, splenic and graft-infiltrating CD8+ TAb-supp, and CD4+ Tregs in KTx recipients and found that high alloantibody-producing CCR5 knockout KTx recipients have significantly fewer post-transplant peripheral blood and splenic CD8+ TAb-supp, as well as fewer splenic and graft-infiltrating CD4+ Tregs compared with wild-type KTx recipients. ACT with alloprimed CXCR5+CD8+ T cells reduced alloantibody titer, splenic alloprimed germinal center (GC) B cell quantity, and improved AMR histology in CCR5 knockout KTx recipients. ACT with alloprimed CD4+ Treg cells improved AMR histology without significantly inhibiting alloantibody production or the quantity of splenic alloprimed GC B cells. Studies with TCR transgenic mice confirmed Ag specificity of CD8+ TAb-supp-mediated effector function. In wild-type recipients, CD8 depletion significantly increased alloantibody titer, GC B cells, and severity of AMR pathology compared with isotype-treated controls. Anti-CD25 mAb treatment also resulted in increased but less pronounced effect on alloantibody titer, quantity of GC B cells, and AMR pathology than CD8 depletion. To our knowledge, this is the first report that CD8+ TAb-supp cells are more potent regulators of humoral alloimmunity than CD4+ Treg cells.

Differentiation of regulatory myeloid and T-cells from adult human hematopoietic stem cells after allogeneic stimulation.

Donor hematopoietic stem cell (DHSC) infusions are increasingly being studied in transplant patients for tolerance induction. To analyze the fate of infused DHSCs in patients, we developed an in vitro culture system utilizing CD34+DHSCs stimulated with irradiated allogeneic cells in cytokine supplemented medium long-term. Flow cytometric analyses revealed loss of the CD34 marker and an increase in CD33+ myeloid and CD3+ T-cell proportion by 10.4% and 72.7%, respectively, after 21 days in culture. T-cells primarily expressed TcR-αβ and were of both CD4+ and CD8+ subsets. Approximately 80% of CD3+ T cells lacked expression of the co-stimulatory receptor CD28. The CD4+ compartment was predominated by CD4+CD25+CD127-FOXP3+ Tregs (>50% CD4+CD127- compartment) with <1% of all leukocytes exhibiting a CD4+CD127+ phenotype. Molecular analyses for T-cell receptor excision circles showed recent and increased numbers of TcR rearrangements in generated T cells over time suggesting de novo differentiation from DHSCs. CD33+ myeloid cells mostly expressed HLA-DR, but lacked expression of co-stimulatory receptors CD80 and CD83. When studied as modulators in primary mixed lymphocyte reactions where the cells used to stimulate the DHSC were used as responders, the DHSC-lines and their purified CD8+, CD4+, CD33+ and linage negative subsets inhibited the responses in a dose-dependent and non-specific fashion. The CD8+ cell-mediated inhibition was due to direct lysis of responder cells. Extrapolation of these results into the clinical situation would suggest that DHSC infusions into transplant recipients may generate multiple subsets of donor "chimeric" cells and promote recipient Treg development that could regulate the anti-donor immune response in the periphery. These studies have also indicated that T cell maturation can occur in vitro in response to allogeneic stimulation without the pre-requisite of a thymic-like environment or NOTCH signaling stimulatory cell line.

Deciphering Antigen Specificity of Protective Regulatory T Cell Clones in Patients after Allogeneic Stem Cell Transplantation

Introduction: Clonal expansion of donor regulatory T cells (Tregs) in recipients of allogeneic stem cell transplantations (allo-SCT) is associated with the absence of acute graft-versus-host disease (aGVHD). Therefore, we hypothesize that antigen-specific donor Tregs prevent aGVHD. In this project, we aim to identify the cognate antigen of expanded Treg clones in patients after allo-SCT. Methods: We recruited 177 consecutive patients undergoing allo-SCT for acute myeloid leukemia without severe infection and CMV-reactivation for this study. Healthy adults matching patients' sex and age served as the control group. We sorted CD3 +CD4 +CD25 hiCD127 low Tregs from peripheral blood mononuclear cell samples collected early after transplantation (21 to 36 days, median 27 days), and we performed single-cell RNA sequencing (scRNAseq) to profile Treg transcriptome including both TCR alpha and beta chain. To determine the antigen specificity of a given TCR, we adapted a cytokine-capturing antigen-screening system (Lee and Meyerson, Sci Immunol, 2021). We built the system by 1) expressing designated TCRαβ chains in Jurkat cells, and 2) expressing cell-surface interleukin-2 capture mAb, corresponding MHC-II molecules, and CD74-fused epitope libraries in HEK293T cells serving as antigen-presenting cells (APCs). By co-culturing both modified cell lines, we can perform high-throughput screening of pooled candidates. To obtain epitope-encoding minigenes, we either used RNA fragmentation to generate candidates randomly or customized oligonucleotide synthesis to encode the tiled human proteome. To scale down the diversity of the synthetic library, we utilized NetMHCIIpan (DTU Health Tech) for MHC-II binding affinity prediction. By sequencing the CD74-fused minigene after screening out APCs with the highest cytokine intensity on the cell surface, we can decode the peptide sequence recognized by the given TCR. We have validated the cytokine-capturing antigen-screening system using a CMV-specific TCR and its cognate antigen. Results: In total, we analyzed six patients with and six patients without aGVHD. ScRNAseq showed that the FOXP3 + Treg population in patients without aGVHD shared more transcriptional similarities with healthy control as compared to patients with aGVHD. Due to lymphocytopenia, Tregs are extremely low in numbers early after allo-SCT, but clustering analysis revealed highly clonal expanded populations of Tregs with various degrees of activation. Notably, one patient without aGVHD was found to have a distinct Treg-dominant CD4 population, and a markedly abundant Treg clone (&amp;gt;15% of the entire Treg repertoire) was found to be parts of both FOXP3 + and FOXP3 - clusters. We then transduced the most abundant TCR into JM-T, the TCR-deficient Jurkat cell. We used an RNA-fragmented randomized library for the first screening, in which we identified one shared epitope in three independent screenings of high frequency. We then moved on to perform screenings for synthesized candidate pools predicted by NetMHCIIpan, representing human proteome and common post-allo-SCT infections. Currently, we are analyzing sequencing reads from parallel screenings and attempting direct expansion of IL-2 + sort-outs. Conclusion: By expanding our established screening system, we aim to elucidate the antigens of multiple clonal expanded TCR candidates from the same patient. Identification of specific antigens leading to clonal Treg expansion and protection from GVHD holds the potential for the development of targeted cell therapies.

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.

Recirculating Foxp3+ regulatory T cells are restimulated in the thymus under Aire control.

Thymically-derived Foxp3+ regulatory T cells (Treg) critically control immunological tolerance. These cells are generated in the medulla through high affinity interactions with medullary thymic epithelial cells (mTEC) expressing the Autoimmune regulator (Aire). Recent advances have revealed that thymic Treg contain not only developing but also recirculating cells from the periphery. Although Aire is implicated in the generation of Foxp3+ Treg, its role in the biology of recirculating Treg remains elusive. Here, we show that Aire regulates the suppressive signature of recirculating Treg independently of the remodeling of the medullary 3D organization throughout life where Treg reside. Accordingly, the adoptive transfer of peripheral Foxp3+ Treg in AireKO recipients led to an impaired suppressive signature upon their entry into the thymus. Furthermore, recirculating Treg from AireKO mice failed to attenuate the severity of multiorgan autoimmunity, demonstrating that their suppressive function is altered. Using bone marrow chimeras, we reveal that mTEC-specific expression of Aire controls the suppressive signature of recirculating Treg. Finally, mature mTEC lacking Aire were inefficient in stimulating peripheral Treg both in polyclonal and antigen-specific co-culture assays. Overall, this study demonstrates that Aire confers to mTEC the ability to restimulate recirculating Treg, unravelling a novel function for this master regulator in Treg biology.

Dysregulated regulatory T cell responses target fibroblasts and lead to chronic rejection after heart transplantation

Abstract Suppressive and reparative regulatory T cell (Treg) functions are described. However, in transplantation (Tx), recipient immune responses to persistent MHC differences will sustain injury and impact repair. The development of immunosuppressant-resistant graft vasculopathy and fibrosis, or chronic rejection (CR) remains a leading cause of death post-heart Tx (HTx) and may reflect failed tissue repair. We tested the hypothesis that Treg repair responses become dysregulated due to sustained alloreactive immune responses. Our studies utilized IL-33 as a model injury signal, or damage-associated molecular pattern (DAMP) and B6 (H-2b) CD45.1+ mice received heterotopic HTx from MHCII-mismatched Bm12 (H2-I-Abm12) donors that were IL-33-deficient or competent. On day (d)14, scRNAseq and CITE-seq were used to compare CD45.1+ cells from HTx digests (n=4). IL-33 modulated &amp;gt;800 genes in HTx-infiltrating Treg, including the growth factor amphiregulin (Areg; 2.25x; P=0.0241). Areg is implicated in tissue repair, yet when B6 Foxp3YFP-CrexAregfl/fl and Foxp3YFP-Cre mice receiving Bm12 HTx were assessed at d100 (n=6–10), the deletion of Areg in Treg protected against CR. Using IncuCyte Live-Cell imaging, it was clear that Areg from Treg stimulated fibroblast proliferation and migration. Tregs stimulated with IL-2 alone or with IL-33 were assessed at d14 or d21 for CpG methylation of Treg-associated genes. These data revealed that sustained exposure to IL-33 increased methylation of Foxp3, suggesting that sustained DAMP stimulation makes Treg unstable. In total, our studies identify how a sustained and dysregulated repair response involving interactions between fibroblasts and recipient Treg contributes to the progression of HTx CR. Supported by grants from NIH (F30AI147437, T32 CA082084) (GKD), NIH (R01HL122489, R01AR073527) (HRT)

Nrf2 Is a Critical Mediator of CD4 T Cell-Induced Acute Graft-Versus-Host Disease

Recent studies have shown that, in contrast to typical proliferating lymphocytes, alloreactive T (allo-T) cells can be specifically killed by apoptosis through compounds that lead to generation of intracellular reactive oxygen species. Nuclear factor erythroid-derived 2-like 2 (Nrf2) is an ubiquitously expressed transcription factor well-known for its role in regulating the cellular redox pathway, but little is known about its involvement in T-cell biology. In this study, we examined the contribution of Nrf2 to allo-T cells in the context of an allogeneic hematopoietic cell transplant (allo-HCT).To study the role of Nrf2 in T cell function, we first assessed the expression pattern of Nrf2 in activated T cells. We found that total cellular and nuclear Nrf2 expression in T cells were significantly increased 24 hours after in vitro α-CD3/CD28 stimulation (p<0.001), as well as in vivo in donor allo-T cells on day 14 in a well-established MHC-disparate murine allo-HSC model (C57BL/6→BALB/c) (p<0.05) (Fig 1). We next examined the effects of Nrf2 deficiency on T cell alloreactivity by transplanting WT or Nrf2-/- donor T cells in MHC-disparate (C57BL/6→BALB/c), as well as MHC-matched, minor antigen mismatched (C57BL/6→LP) murine models. In both models, allo-HCT recipients of Nrf2-/- donor T cells had significantly less acute graft-versus-host disease (GVHD)-induced mortality (p<0.01), morbidity (p<0.001), and intestinal pathology (p<0.05) (Fig 2a). To test if Nrf2 differentially regulates CD4+ versus CD8+ T cell function, we mixed and matched WT versus Nrf2-/- CD4+ and CD8+ T cells for transplant. Compared to allo-HCT recipients of donor WT CD4+: WT CD8+ T cells, we observed similar GVHD mortality in allo-HCT recipients of donor WT CD4+: Nrf2-/- CD8+ T cells, while we saw reduced GVHD mortality in allo-HCT recipients of donor Nrf2-/- CD4+: WT CD8+ T cells (p<0.01) (Fig 2b). These data support the notion that Nrf2 predominately regulates donor CD4+ and is dispensable for CD8+ T cells during allo-activation and the development of GVHD.We assessed if Nrf2 could affect polarization of donor CD4 T cells after allo-HCT, and found a two-fold increase in the proportion and absolute numbers of CD25+Foxp3+ regulatory T cells (Tregs) in the spleens of donor Nrf2-/- T cell allo-HCT recipients on day 7 post transplant (p<0.001) (Fig 3a). We next examined if Nrf2-deficiency results in greater induction of Tregs (iTregs) or stabilization of natural Tregs (nTregs). While we found an equal fraction of WT and Nrf2-/- naïve CD4+ T cells induced towards Tregs in vitro, we saw a significantly greater percentage of donor Nrf2-/- Tregs expressing Helios, a marker for thymus-derived nTregs, compared to donor WT Tregs in allo-HCT recipients on day 7 (p<0.01) (Fig 3b). Recent studies have suggested that Helios is required to stabilize the expression of FoxP3, and thus, the abundance and inhibitory activity of Tregs in inflammatory settings. In keeping with this notion, we discovered an increase in the cellular FoxP3 protein expression within donor Nrf2-/- Tregs in allo-HCT recipients (p<0.01) (Fig 3c). To further elucidate the biological significance of Nrf2 function on nTregs, we removed CD4+CD25+ putative Tregs from the donor inoculum and transplanted only conventional T cells (Fig 3d). We found that the survival advantage with donor Nrf2-/- T cells was abolished when Tregs were depleted from the donor graft, suggesting that Nrf2 expression in donor T cells negatively regulates nTregs during allo-activation, most likely through downregulation of Helios and FoxP3 expression.Finally, to determine if Nrf2 was critical for T-cell mediated GVT activities, we challenged allo-HCT recipients with A20 (B-cell lymphoma) cells. Using bioluminescent imaging, we found that Nrf2-/- allo-T cells were equally efficient in clearing tumor burdens, and along with their mitigated GVHD activities, resulting in a significantly improved survival outcome.Taken together, we identified a novel role of Nrf2 in CD4+ T cells in the context of allo-HCT. Nrf2 negatively regulated CD4+ nTreg through Helios downregulation during GVHD, but appeared to be dispensable in CD8+ mediated antitumor responses, further highlighting the possibility of separating GVT from GVHD activities. Our findings suggest that targeted manipulation of Nrf2 activities in allo-T cells may offer a useful clinical strategy to mitigate GVHD while preserving GVT responses. [Display omitted] DisclosuresJenq:Seres: Research Funding. van den Brink:PureTech Health: Consultancy; Seres: Research Funding; Jazz Pharmaceuticals: Consultancy; Therakos Institute: Other: Speaking engagement.

Cord Blood Regulatory T Cells for Prevention of Graft Versus Host Disease

Background: Regulatory T-cells (Tregs) are a T-cell subset capable of suppressing effector T-cells (Teffs) and, when given at the time of allogeneic hematopoietic stem cell transplantation (Allo-SCT), have been shown to prevent graft v. host disease (GVHD). We previously demonstrated that cord blood (CB) Tregs can be ex vivo expanded to clinically meaningful doses and prevent GVHD in a xenogenic mouse model. The efficacy of the ex vivo expanded CB Tregs in preventing GVHD was markedly improved with fucosylation, which adds fucose resulting in creation of a siayl-Lewis X moiety found on P-selectin ligand, thereby facilitating trafficking through the endothelium into inflammatory sites. We hypothesized that adoptive therapy with fucosylated Tregs could prevent GVHD even when given at suboptimal Tregs:Teffs ratios. We conducted a Phase I clinical trial to evaluate the clinical safety of fucosylated CB Treg infusion for GVHD prophylaxis (ww.clinicaltrials.gov NCT02423915). We now report on 5 patients who received GVHD prophylaxis with 3rdparty, ex-vivo expanded CB Tregs at a dose level of 1.0 x10e6 cells/ kg (2 un-fucosylated and 3 fucosylated CB Treg products).Patients and methods: A 3rd party CB unit with at least 3/6 HLA matching to the recipient was selected. Treg isolation and expansion was performed as shown previously. When indicated, expanded CB Tregs were incubated with substrate (GDP β-fucose) and fucosyltrasferase-VI (FT6) enzyme (TZ101, Targazyme, Carlsbad, CA) for 30 minutes, washed and infused on day -1. The first 2 patients underwent double cord transplant with Flu/Cy/TBI reduced intensity conditioning and received unfucosylated CB Tregs at a dose of 1 x 10e6/kg. The subsequent 3 patients underwent peripheral blood (PB) matched unrelated donor (MUD) transplant with Fludarabine/ Melphalan myeloablative conditioining and received fucosylated CB Tregs at a dose of 1 x 10e6/kg. All patients received additional pharmacologic GVHD prophylaxis with sirolimus and mycophenolate mofetil. All patients received their designated CB Treg dose. The median proportion of CD4+25+CD127- in the infused Treg product was 96% (94-98%). Expanded CB Treg product showed suppression of T cell proliferation using CFSE assay. For the first 2 patients, the infused graft Teffs dose was at least 12 times more than the CB Tregs and for the subsequent 3 patients, the dose of infused Teffs dose was at least 132 times more than that of the infused fucosylated CB Tregs. No infusion toxicities were observed.Results: All patients receiving fucosylated CB Tregs followed by PB MUD transplants exhibited non-infectious high fevers up to 40οC accompanied by an erythematous rash starting on post-transplant day +5 that lasted for 5-7 days and resolved after steroid administration (IV methylprednisolone 1mg/kg) for 24-96 hours. Skin biopsies were consistent with engraftment syndrome and not GVHD. All 5 patients engrafted at a median of 13 days. The three patients who received fucosylated CB Tregs and one of two patients receiving untreated CB Tregs developed ≥ grade II acute GVHD at a median of day +22 which had completely resolved by day 130 post-transplant. One patient had late onset aGVHD. No cGVHD was documented in any patient. One recipient of non-fucosylated Tregs died on day +40 due to unrelated causes (intracranial bleeding). No GVHD was observed in this patient. PB Flow cytometric analysis revealed an increase in inflammatory T-cell subsets in the first week post-transplant with a concurrent bimodal increase in the Treg populations on day -1 and day +7 (figure 1A). NK and DC but not B cell subsets were significantly increased. A consistent increase in the cell populations secreting IFNү, IL-4 and IL-17 was observed in the post-transplant period and a bi-modal increase in the IL-10 secreting cells was observed on Day -1 and Day +7 consistent with the circulating Treg cells (figure 1B).Conclusions: Our group is the first to show safety of infusing 3rd party, ex-vivo expanded CB Tregs in a PB MUD transplant setting. At a dose level of 1.0 x 10e6 /kg, 3rd party CB Tregs were administered without acute infusional toxicity and no negative impact on engraftment. The cause for the high fevers observed in the fucosylated CB Treg recipients is unclear at this time. We are now enrolling additional patients with unfucosylated Tregs in a PB MUD transplant setting to investigate the mechanisms underlying this phenomenon. [Display omitted] DisclosuresKhoury:Kiromics: Research Funding; Angle: Research Funding; Stemline Therapeutics: Research Funding; Pfizer: Research Funding.

A Prospective Controlled Trial to Evaluate Safety and Efficacy of in vitro Expanded Recipient Regulatory T Cell Therapy and Tocilizumab Together With Donor Bone Marrow Infusion in HLA-Mismatched Living Donor Kidney Transplant Recipients (Trex001).

Background: The induction of donor-specific immunological tolerance could improve outcome after kidney transplantation. However, no tolerance protocol is available for routine clinical use. Chimerism-based regimens hold promise, but their widespread application is impeded in part by unresolved safety issues. This study tests the hypothesis that therapy with polyclonal recipient regulatory T cells (Tregs) and anti-IL6R (tocilizumab) leads to transient chimerism and achieves pro-tolerogenic immunomodulation in kidney transplant recipients also receiving donor bone marrow (BM) without myelosuppressive conditioning of the recipient.Methods/design: A prospective, open-label, controlled, single-center, phase I/IIa academic study is performed in HLA-mismatched living donor kidney transplant recipients.Study group: Recipients of the study group receive in vitro expanded recipient Tregs and a donor bone marrow cell infusion within 3 days after transplantation and tocilizumab for the first 3 weeks post-transplant. In addition they are treated with thymoglobulin, belatacept, sirolimus, and steroids as immunosuppression. Starting 6 months post-transplant, sirolimus and steroids are withdrawn in a step-wise manner in stable patients.Control group: Recipients of the control group are treated with thymoglobulin, belatacept, sirolimus, and steroids as immunosuppression. Co-primary endpoints of safety (impaired graft function [eGFR <35 mL/min/1.73 m2], graft-vs.-host disease or patient death by 12 months) and efficacy (total leukocyte donor chimerism within 28 days post-transplant) are assessed. Secondary endpoints include frequency of biopsy-proven acute rejection episodes and subclinical rejection episodes on surveillance biopsies, assessment of kidney graft function, and the evaluation whether the study protocol leads to detectable changes in the immune system indicative of pro-tolerogenic immune modulation.Discussion: The results of this trial will provide evidence whether treatment with recipient Tregs and donor BM is feasible, safe and efficacious in leading to transient chimerism. If successful, this combination cell therapy has the potential to become a novel treatment option for immunomodulation in organ transplantation without the toxicities associated with myelosuppressive recipient conditioning.Trial registration: European Clinical Trials Database EudraCT Nr 2018-003142-16 and clinicaltrials.gov NCT03867617.

Adoptive Therapy with Cord Blood T Regulatory Cells Enhances Anti-Myeloma Efficacy of T Cell Based Immunotherapies

Background. Inflammatory tumor microenvironment leads to T cell exhaustion in multiple myeloma leading to treatment failure and relapse. Specifically, T cell based therapies including bispecific antibodies and chimeric antigen receptor (CAR) T cell are associated with the additional side effects of non-specific T cell activation and cytokine release syndrome. Adoptive therapy with allogeneic cord blood (CB) T regulatory (Treg) cell therapy has been shown to be safe with clinical efficacy in a wide range of diseases including graft vs. host disease (GvHD), inflammatory bone marrow failures and COVID-19 induced acute respiratory distress syndrome. Furthermore, combination of Tregs with donor lymphocyte infusion (DLI) has led to resolution of leukemia relapse without GvHD flare up. We hypothesize that co-administration of Tregs with adoptive T cell based therapy will improve myeloma outcomes. Methods. 3x106 GFP-labeled MM.1S cells were injected into NSG mice followed by 5x106 CD3+ T conventional (Tcon) cells on day 14. In a subset of the Tcon treated mice, 1x107 CB Treg cells were injected on day 47, 54 and 61. Mice were followed every other day for weight and GvHD score. Non-invasive bioluminescent imaging (BLI) was performed serially. Weekly blood draw was performed for cell analysis and cytokine assays. At the time of euthanasia, blood, spleen and bone marrow were harvested for histopathology and flow analysis. In a subsequent experiment, intra-peritoneal injection of the bi-specific antibody against CD3 and BCMA (BCMA-BiTE) was administered in the xenogenic myeloma model in the presence or absence of CB Treg cells. Pan T cells were injected into all mice to facilitate the anti-tumor action of BiTE. Results. Both Tcon and Tcon+Treg recipients maintained their body weight compared to myeloma alone or myeloma + Treg arm (Figure A). All mice showed evidence of tumor growth by day 20 (Figure A). Widespread MM.1S cell growth in the myeloma only mice at day 27 was demonstrated by BLI whereas no measurable tumor growth was evident in Tcon recipients or Tcon+Treg recipients. By day 69, Tcon only mice were significantly increased tumor growth compared to Tcon+Treg recipients (Figure B). While circulating multiple myeloma cells were detected in myeloma alone and myeloma+Treg arm, no such evidence was detectable in the Tcon or Tcon+Treg recipients. However, upon euthanasia, extramedullary relapse of myeloma as retroperitoneal mass was detected in Tcon recipient (Figure C). Addition of Treg + BiTE led to a similar degree of tumor control compared to BiTE alone treated mice, however, a significant weight loss was observed in this arm (Figure D) with a corresponding high GvHD score (Figure E). Furthermore, addition of CB Treg cells led to decrease of T cell exhaustion phenotypic markers (data not shown). Conclusion. We are the first to show that CB Treg cells can be administered in combination with the T-cell based immunotherapies directed against myeloma. Such a strategy should be examined in the clinical setting. Figure Disclosures Nishimoto: Bayer Yakuhin, Ltd:: Research Funding; Janssen Pharmaceutical K.K.:: Research Funding. Sadeghi:Cellenkos Inc.: Current Employment. Shah:GSK, Amgen, Indapta Therapeutics, Sanofi, BMS, CareDx, Kite, Karyopharm: Consultancy; BMS, Janssen, Bluebird Bio, Sutro Biopharma, Teneobio, Poseida, Nektar: Research Funding. Patel:Nektar: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Cellectis: Research Funding; Takeda: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Oncopeptides: Consultancy; Poseida: Research Funding; Precision Biosciences: Research Funding; Bristol Myers Squibb: Consultancy, Research Funding. Parmar:Cellenkos Inc.: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties, Research Funding.

Adoptive Cord Blood T Regulatory Cell Therapy Leads to Resolution of Inflammation and Decreased Proteinuria in Lupus Nephritis

Background. Systemic lupus erythematosus (SLE) is associated with widespread inflammation with multi-organ involvement where renal failure is the most dreaded and fatal complication. Adoptive therapy with cord blood (CB) derived T regulatory cells has been shown to improve outcomes in disease driven by inflammation including graft versus host disease (GvHD), inflammatory bone marrow disorder, COVID-19 induced acute respiratory distress syndrome. We hypothesize that CB Treg therapy can treat lupus nephritis. Methods. The suppressive abilities of CB Tregs expressing CD4+CD25highCD127lowFoxP3+ were assayed by human cytokines assay kits (IL-10, IFN-γ, IP-10, TNF-α, IL-6, and IL-17A) in the cell culture supernatants. For examining the efficacy of CB Tregs in vivo, SLE xenograft model was created with female Rag2-/-γc-/- mice transplanted with 3x106 human SLE-peripheral blood mononuclear cells (PBMCs) by intravenous injection on day 0. The mice were allowed to develop disease and on day 30 post-transplant, they were divided into 2 groups: i) control and ii) treatment. 1x107 ex vivo-expanded, cryopreserved, allogeneic, non-HLA matchedCB Tregs were injected into SLE xenografts intravenously once per week for 4 weeks through the tail vein. Serial blood draws were performed for the phenotypic analysis, cytokine assay and anti-double stranded (ds)DNA IgG antibody analysis. Serial examination of the urine samples was performed for creatinine and albumin quantification. Histopathologic examination of the harvested organs was performed at the time of planned euthanasia at 13 weeks. Results. Co-culture of CB Tregs with the pathogenic SLE-PBMCs decreased the secretion of inflammatory cytokines including IFN-γ, IP-10, TNF-α, IL-6, and IL-17A (Figure A) with a reciprocal increase in the secretion of the anti-inflammatory IL-10 cytokine (Figure B). Adoptive therapy with CB Treg cells led to a significant decrease in circulating CD8+ effector T cells and an increase in CD4+ helper T cells (Figure C). CB Treg recipients showed preserved weight gain (Figure D), lower GvHD score (Figure E) and improved overall survival (Figure F). A significant decrease in proteinuria at 9 weeks post-transplant (Figure G) correlated with a decrease in anti-dsDNA IgG Ab levels (Figure H) and soluble CD40 ligand levels (Figure I). Histopathological results from two index cases from each arm (Figure J) demonstrated that CB Treg recipients show reduced T-cells (CD3+) (Figure K) and B-cells (CD20+) (Figure L) in the kidneys, as well as a decrease in the lymphoid infiltration into glomeruli and renal parenchyma as compared to the control arm (Figure M). Conclusion. We are the first to demonstrate the benefit of allogeneic CB Treg cell therapy for treatment of lupus nephritis. We propose to examine such a strategy in the clinical setting. Figure Disclosures Nishimoto: Janssen Pharmaceutical K.K.:: Research Funding; Bayer Yakuhin, Ltd:: Research Funding. Sadeghi:Cellenkos Inc.: Current Employment. Parmar:Cellenkos Inc.: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties, Research Funding.

Cord Blood Regulatory T Cells Prevent Mutiple Myeloma Progression By Suppressing Inflammation

Introduction: Regulatory T cells (Tregs) are potent immunosuppressors and are being developed as adoptive immunotherapy for inflammatory disorders and autoimmune diseases. Specifically, cord blood (CB) Tregs are emerging as a promising treatment for graft vs. host disease (GVHD) as well as immune mediated bone marrow failure disorders including aplastic anemia, hypoplastic myelodysplasia and primary myelofibrosis. We and others have shown that when compared to peripheral blood (PB), CB Tregs have a higher expression of Helios, a marker of thymic Tregs; exert superior suppression on proliferating conventional T cells and do not secrete inflammatory IL-17 or express RORүt under stressful conditions. Such a stable suppressor profile coupled with their ready availability as an off-the-shelf product positions CB Tregs to be a very attractive therapeutic agent. Since multiple myeloma, a plasma cell clonal malignancy, exists in an inflammatory microenvironment of hematopoietic and non-hematopoietic cells which is likely related to disease progression, we hypothesized that adoptive therapy with CB Tregs may block myeloma progression by exerting their anti-inflammatory function. Methods: We used the NOD-SCID IL2rγnull (NSG) mice to first establish the myeloma tumor model, where mice were injected intravenously via tail vein with 3 x 106 Firefly luciferase labeled MM1S cells. For generating CB Tregs for adoptive therapy, Treg cell enrichment was performed from the whole CB unit using CD25+ magnetic beads and LS column (MIltenyl) followed by continuous culture in the presence of CD3/28 T-cell activator beads, and human recombinant interleukin-2 for 14 days. Expanded CB Treg phenotype was confirmed using flow cytometry analysis and the in-vitro suppressive capacity was assessed by CellTrace Violet Cell Proliferation assay. The mice were injected intravenously via tail vein with Firefly luciferase labeled MM1S cells on day 0 with or without 10 x 106 ex-vivo expanded CB Treg cells on day -1. We monitored the progression of MM1S cells by in vivo bioluminescence imaging (BLI) using the IVIS imaging system (Xenogen) 10 minutes after intraperitoneal injection of D-luciferin. Imaging data were analyzed and quantified with Living Image Software (Xenogen). We also assessed the weight and survival as well as the plasma cytokines levels. At the time of euthanasia, organs were harvested and analyzed for myeloma burden by using immunohistochemistry as well as flow analysis. Results: The expanded CB Tregs showed a consistent phenotype of CD4+25+127-FoxP3high and more than 80% suppression of the proliferating conventional T cells (Tcons). The progression of MM1S cells in the mice injected with CB Treg (n=9) was significantly delayed as shown in figure 1A, where minimal evidence of myeloma cells is visualized on day 31 compared to widespread tumor in the control arm (n=9). CB Treg recipients preserved their weight for a longer time (Figure 1B) and had improved overall survival (p=0.039) (Figure 1C). The prevention of development of myeloma by CB Tregs correlated with the lower levels of the inflammatory cytokine, interleukin-6 (IL-6) (murine) especially on day 35 post myeloma inoculation (Figure 1D). The circulating myeloma cells in the CB Treg recipients were significantly lower as compared to control mice. Upon euthanasia on day 25 post inoculation, myeloma cells were barely detectable in bone marrow and spleen in the CB Treg recipients as compared to large tumor burden in the control arm (Figure 1E). Conclusions: Our results demonstrate that ex-vivo expanded CB Treg cells prevent the growth of myeloma cells in a xenogenic model via suppression of inflammatory cytokines such as IL-6. These data provide additional insight to the underpinnings of myeloma progression and may contribute to the development of the novel immunotherapies in the future. Figure 1 Disclosures Shah: University of California, San Francisco: Employment; Genentech, Seattle Genetics, Oncopeptides, Karoypharm, Surface Oncology, Precision biosciences GSK, Nektar, Amgen, Indapta Therapeutics, Sanofi: Membership on an entity's Board of Directors or advisory committees; Indapta Therapeutics: Equity Ownership; Celgene, Janssen, Bluebird Bio, Sutro Biopharma: Research Funding; Poseida: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Nkarta: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kite: Consultancy, Membership on an entity's Board of Directors or advisory committees; Teneobio: Consultancy, Membership on an entity's Board of Directors or advisory committees. Orlowski:Poseida Therapeutics, Inc.: Research Funding. Parmar:Cellenkos Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Single Injection of Cord Blood Regulatory T Cells Can Delay the Manifestations of Systemic Lupus Erythematosus

Background: Systemic Lupus Erythematosus (SLE) is a chronic inflammatory autoimmune disorder with multi-organ involvement, including skin rash, joint pain, neurological dysfunction, pulmonary fibrosis, vasculitis, and renal failure. Previously it has been reported that SLE patients have a lower percentage of regulatory T cells (Tregs) and when compared to healthy population, Tregs derived from SLE patients show defect in their suppressor function. Our group at MD Anderson Cancer Center has already shown that a significantly lower dose of cord blood (CB) Tregs as compared to conventional T cells (Tcon) in the donor graft is able to prevent graft vs host disease (GVHD). Furthermore, adoptive therapy with CB Tregs is being explored as a therapy for bone marrow failure including aplastic anemia as a single agent in the non-transplant setting. Therefore, we hypothesized that adoptive therapy with CB Tregs may be utilized for the treatment of SLE. Method: For examining the efficacy of CB Tregs in vivo, we developed a humanized SLE model, where female Rag2-/-γc-/- mice were transplanted with 3 ~ 4 x 106 human SLE-PBMCs by intravenous injection on day 0. The mice were allowed to develop disease (control) and at 1 weeks post-transplant a single dose of 1x107 CB Tregs was injected through the tail vein (treatment). Mice peripheral blood (PB) was assessed weekly for their cell compartment composition by using flow cytometry; double stranded DNA (dsDNA IgG) and plasma cytokines. Mice were monitored twice per week for weight loss, GVHD score and survival. Weekly urine collection was performed to analyze for albumin and creatinine. At the time of euthanasia, harvested organs were analyzed by flow cytometry, and immunohistochemistry. Result: Single injection of CB Tregs was sufficient to slow down the phenotype of SLE as shown in figure 1A, where the physical appearance of CB Treg treated mice was significantly better than the control and it correlated with a significantly lesser CD3+ infiltrates in the spleen of the treatment vs. control mice (Figure 1B) and a similar finding was observed in the CD20 infiltrate in the renal tissue (data not shown). While a widespread parakeratosis in the skin of the control mice, almost complete resolution was observed in the treatment arm (figure 1C). In addition, a lack of lymphoid infiltrate in the kidney and resolution of splenic lymphoid hyperplasia was observed in the CB Treg recipients (data not shown). In another experiment, we studied the role of weekly injection of 1x107 CB Tregs with the first injection administered at week 4 after the lupus inoculation. Significant improvement was observed in the urine albumin (p&lt;0.02) (Fig 1D) as well as urine creatinine (p&lt;0.0006) levels; which correlated with the significant improvement in the dsDNA IgG levels in the treatment arm compared to control (Fig 1E), respectively. We also measure the durability of single dose CB Treg injection, where a decrease in the 5-week plasma inflammatory cytokines including sCD40L (Fig 1F); TNFα (Fig 1G) and IFNγ (Fig 1H) was observed irrespective of CB Treg injection on day+7 or day+28 after the lupus PBMC injection. Conclusion: We conclude that adoptive therapy with CB Tregs is a viable option for SLE and additional studies are planned to optimize the dose and schedule details. Figure 1 Disclosures Khoury: Angle: Research Funding; Stemline Therapeutics: Research Funding; Kiromic: Research Funding. Iyer:Seattle Genetics, Inc.: Research Funding; Novartis: Research Funding; Bristol-Myers Squibb: Research Funding; Genentech/Roche: Research Funding; Incyte: Research Funding; Arog: Research Funding. Parmar:Cellenkos Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Immunomodulation Followed by Antigen-Specific Treg Infusion Controls Islet Autoimmunity.

Optimal immune-based therapies for type 1 diabetes (T1D) should restore self-tolerance without inducing chronic immunosuppression. CD4+Foxp3+ regulatory T cells (Tregs) are a key cell population capable of facilitating durable immune tolerance. However, clinical trials with expanded Tregs in T1D and solid-organ transplant recipients are limited by poor Treg engraftment without host manipulation. We showed that Treg engraftment and therapeutic benefit in nonautoimmune models required ablative host conditioning. Here, we evaluated Treg engraftment and therapeutic efficacy in the nonobese diabetic (NOD) mouse model of autoimmune diabetes using nonablative, combinatorial regimens involving the anti-CD3 (αCD3), cyclophosphamide (CyP), and IAC (IL-2/JES6-1) antibody complex. We demonstrate that αCD3 alone induced substantial T-cell depletion, impacting both conventional T cells (Tconv) and Tregs, subsequently followed by more rapid rebound of Tregs Despite robust depletion of host Tconv and host Tregs, donor Tregs failed to engraft even with interleukin-2 (IL-2) support. A single dose of CyP after αCD3 depleted rebounding host Tregs and resulted in a 43-fold increase in donor Treg engraftment, yet polyclonal donor Tregs failed to reverse diabetes. However, infusion of autoantigen-specific Tregs after αCD3 alone resulted in robust Treg engraftment within the islets and induced remission in all mice. This novel combinatorial therapy promotes engraftment of autoantigen-specific donor Tregs and controls islet autoimmunity without long-term immunosuppression.

Transplantation tolerance in nonhuman primates and humans.

This review focuses on our recent studies involving nonmyeloablative bone marrow transplantation as an approach to inducing organ allograft tolerance across MHC barriers in nonhuman primates and in patients. The clinical studies are focused on mechanisms of tolerance involved in a protocol carried out at Massachusetts General Hospital in HLA-mismatched haploidentical combinations for the induction of renal allograft tolerance. These studies, in which chimerism was only transient and GVHD did not occur, suggest an early role for donor-specific regulatory T cells in tolerance induction, followed by partial and gradual deletion of donor-reactive T cells. We utilized high-throughput sequencing methodologies in a novel way to identify and track large numbers of alloreactive T cell receptors (TCRs). This method has been shown to identify biologically significant alloreactive TCRs in transplant patients and pointed to clonal deletion as a major mechanism of long-term tolerance in these patients. More recently, we adapted this sequencing method to optimally identify the donor-specific regulatory T cell (Treg) repertoire. Interrogation of the early posttransplant repertoire demonstrated expansion of donor-specific Tregs in association with tolerance. Our studies suggest a role for the kidney graft in tolerance by these mechanisms in patients who had only transient chimerism. Nonhuman primate studies indicate that other organs, including the heart, the lungs and the liver, are less readily tolerated following a period of transient mixed chimerism. Our efforts to extend the reach of mixed chimerism for tolerance induction beyond the kidney are therefore focused on the addition of recipient Tregs to the protocol. This approach has the potential to enhance chimerism while further reducing the risk of GVHD.

Notch-1 Inhibition Promotes Immune Regulation in Transplantation Via Regulatory T Cell-Dependent Mechanisms.

Transplantation is the treatment of choice for many patients with end-stage organ disease. Despite advances in immunosuppression, long-term outcomes remain suboptimal, hampered by drug toxicity and immune-mediated injury, the leading cause of late graft loss. The development of therapies that promote regulation while suppressing effector immunity is imperative to improve graft survival and minimize conventional immunosuppression. Notch signaling is a highly conserved pathway pivotal to T-cell differentiation and function, rendering it a target of interest in efforts to manipulate T cell-mediated immunity. We investigated the pattern of Notch-1 expression in effector and regulatory T cells (Tregs) in both murine and human recipients of a solid-organ transplant. Using a selective human anti-Notch-1 antibody (aNotch-1), we examined the effect of Notch-1 receptor inhibition in full major histocompatibility complex-mismatch murine cardiac and lung transplant models, and in a humanized skin transplant model. On the basis of our findings, we further used a genetic approach to investigate the effect of selective Notch-1 inhibition in Tregs. We observed an increased proportion of Tregs expressing surface and intracellular (activated) Notch-1 in comparison with conventional T cells, both in mice with transplants and in the peripheral blood of patients with transplants. In the murine cardiac transplant model, peritransplant administration of aNotch-1 (days 0, 2, 4, 6, 8, and 10) significantly prolonged allograft survival in comparison with immunoglobulin G-treated controls. Similarly, aNotch-1 treatment improved both histological and functional outcomes in the murine lung transplant model. The use of aNotch-1 resulted in a reduced proportion of both splenic and intragraft conventional T cells, while increasing the proportion of Tregs. Furthermore, Tregs isolated from aNotch-1-treated mice showed enhanced suppressive function on a per-cell basis, confirmed with selective Notch-1 deletion in Tregs (Foxp3EGFPCreNotch1fl/fl). Notch-1 blockade inhibited the mammalian target of rapamycin pathway and increased the phosphorylation of STAT5 (signal transducer and activator of transcription 5) in murine Tregs. Notch-1low Tregs isolated from human peripheral blood exhibited more potent suppressive capacity than Notch-1high Tregs. Last, the combination of aNotch-1 with costimulation blockade induced long-term tolerance in a cardiac transplant model, and this tolerance was dependent on CTLA-4 (cytotoxic T-lymphocyte-associated antigen-4) signaling. Our data reveal a promising, clinically relevant approach for immune modulation in transplantation by selectively targeting Notch-1.

Intrapulmonary Immune Regulation by Pre-Transplant Infusion of Recipient-Derived Regulatory T Cells in a Rat Model of Ex Vivo Lung Perfusion Followed by Transplantation

Purpose Regulatory T cells (Tregs) are a potential therapeutic option in lung transplantation (LTx). We have shown that expanded recipient Tregs can be seeded pre-transplant in the donor lung graft using normothermic ex vivo lung perfusion (EVLP). Here, we examined whether this therapy can alleviate lung injury early post-transplant. Methods Study design is shown in Fig A. CD4+CD25hi Tregs were isolated from Wistar Kyoto rats (WKy, RT1l) and expanded for 7d-14d. Fischer 344 (F344 RT1lv1) heart-lung blocks were flushed and placed on EVLP. Lungs were perfused with SteenTM solution (37°C, 4h). Expanded Tregs (5-120 × 106) were infused after 1h. Control lungs received no Tregs. The right lung was used for assessment at end-EVLP, and left LTx into WKy recipients was performed after 60min cold preservation. Necropsy was performed on day 3 post-LTx. Results Wet-dry ratio was lower in Treg-treated grafts compared to controls (Fig B). Transcripts for FoxP3, IL-10, CTLA-4 and GITR were elevated in Treg-treated grafts (Fig B). Tregs isolated from the right donor lung at end-EVLP suppressed CD4+CD25− T cell proliferation in vitro (Fig C). On day 3 post-LTx, ICAM1 and CD44 (adhesion molecules) expression on both CD4+ and CD8+ T cells were lower in Treg-treated grafts compared to untreated controls (Fig D). Histologically, both Treg-treated and control grafts had minor lung injury and cellular rejection on day 3 post-LTx: acute lung injury scores (4.10 ± 1.66 and 3.88 ± 1.36), ISHLT A grades (0.60 ± 0.516 and 0.625 ± 0.744), B grades (0.400 ± 0.516 and 0.313 ± 0.458). Conclusion Expanded recipient Tregs directly delivered to the lung allograft prior to transplantation exert immune regulatory effects in vivo and in vitro. Further work is needed to optimize this pre-transplant therapeutic approach.

Different phenotypes of CD4+CD25+Foxp3+ regulatory T cells in recipients post liver transplantation

CD4+ regulatory T cells (Tregs) play an important role in inducing immune tolerance in organ transplantation, which can be divided into CD45RA+Tregs (resting Tregs, rTregs) and CD45RO+Tregs (activated Tregs, aTregs). Currently, the expressions and phenotypic changes of Tregs in recipients after liver transplantation (LT) is unknown. We therefore investigated the expression and transformation of rTregs and aTregs in 83 cases of recipients with normal status post-LT. The percentages of CD45RA, CD45RO, CD31 in CD4+Tregs were detected by flow cytometry and the effective factors were analyzed. In LT recipients, the percentage of CD45RO+Tregs in CD4+Tregs was higher than that of CD45RA+Tregs. There was significant difference in the ratio of positive Foxp3 between CD45RA+Tregs and CD45RO+Tregs. Percentage of CD45RA+Tregs was higher in pediatric group than that in adult group, whereas percentage of CD45RO+Tregs was lower in the pediatric group. However, it was different only in CD45RO+Tregs in various survival periods post-LT. In conclusion, Tregs pool in human was heterogeneous post-LT and contained different subsets in phenotypes. Upon stimulation by donor graft, percentages of CD4+Tregs and CD45RO+Tregs were increased post-LT and most of rTregs was transformed into aTregs in peripheral blood, and rTregs and aTregs were both related to recipients' ages.

Early expansion of donor-specific Tregs in tolerant kidney transplant recipients

Allograft tolerance, in which a graft is accepted without long-term immunosuppression, could overcome numerous obstacles in transplantation. Human allograft tolerance has been intentionally induced across HLA barriers via combined kidney and bone marrow transplantation (CKBMT) with a regimen that induces only transient chimerism. Tregs are enriched early after CKBMT. While deletional tolerance contributes to long-term tolerance, the role of Tregs remains unclear. We have optimized a method for identifying the donor-specific Treg repertoire and used it to interrogate the fate of donor-specific Tregs after CKBMT. We expanded Tregs with several different protocols. Using functional analyses and T cell receptor sequencing, we found that expanding sorted Tregs with activated donor B cells identified the broadest Treg repertoire with the greatest potency and donor specificity of suppression. This method outperformed both alloantigen stimulation with CTLA4Ig and sequencing of CFSElo cells from the primary mixed lymphocyte reaction. In 3 tolerant and 1 nontolerant CKBMT recipients, we sequenced donor-specific Tregs before transplant and tracked them after transplant. Preexisting donor-specific Tregs were expanded at 6 months after CKBMT in tolerant patients and were reduced in the nontolerant patient. These results suggest that early expansion of donor-specific Tregs is involved in tolerance induction following CKBMT.

A Phase I Clinical Trial with Ex Vivo Expanded Recipient Regulatory T cells in Living Donor Kidney Transplants

There is considerable interest in therapeutic transfer of regulatory T cells (Tregs) for controlling aberrant immune responses. Initial clinical trials have shown the safety of Tregs in hematopoietic stem cell transplant recipients and subjects with juvenile diabetes. Our hypothesis is that infusion(s) of Tregs may induce transplant tolerance thus avoiding long-term use of toxic immunosuppressive agents that cause increased morbidity/mortality. Towards testing our hypothesis, we conducted a phase I dose escalation safety trial infusing billions of ex vivo expanded recipient polyclonal Tregs into living donor kidney transplant recipients. Despite variability in recipient’s renal disease, our expansion protocol produced Tregs which met all release criteria, expressing >98% CD4+CD25+ with <1% CD8+ and CD19+ contamination. Our product displayed >80% FOXP3 expression with stable demethylation in the FOXP3 promoter. Functionally, expanded Tregs potently suppressed allogeneic responses and induced the generation of new Tregs in the recipient’s allo-responders in vitro. Within recipients, expanded Tregs amplified circulating Treg levels in a sustained manner. Clinically, all doses of Treg therapy tested were safe with no adverse infusion related side effects, infections or rejection events up to two years post-transplant. This study provides the necessary safety data to advance Treg cell therapy to phase II efficacy trials.