Title: Regulatory T-cell therapy for autoimmune and autoinflammatory diseases: The next frontier
Abstract: Forkhead box P3–expressing regulatory T (Treg) cells are essential for self-tolerance, with an emerging role in tissue repair and regeneration. Their ability to traffic to tissue and perform complex therapeutic tasks in response to the tissue microenvironment make them an attractive candidate for drug development. Early experiences of Treg cell therapy in patients with graft-versus-host disease, type 1 diabetes, and organ transplantation have shown that it is feasible, safe, and potentially efficacious in some settings. Many ongoing trials in patients with a wide variety of diseases will further enhance our knowledge about the optimal approaches for Treg cell manufacturing and dosing. We review the current preclinical rationale supporting Treg cell therapy in a variety of disease settings ranging from tissue transplantation, autoimmune diseases, and non–immune-mediated inflammatory settings. We point out challenges in development of Treg cell therapy and speculate how synthetic biology can be used to enhance the feasibility and efficacy of Treg cell therapy for autoimmune and autoinflammatory diseases. Forkhead box P3–expressing regulatory T (Treg) cells are essential for self-tolerance, with an emerging role in tissue repair and regeneration. Their ability to traffic to tissue and perform complex therapeutic tasks in response to the tissue microenvironment make them an attractive candidate for drug development. Early experiences of Treg cell therapy in patients with graft-versus-host disease, type 1 diabetes, and organ transplantation have shown that it is feasible, safe, and potentially efficacious in some settings. Many ongoing trials in patients with a wide variety of diseases will further enhance our knowledge about the optimal approaches for Treg cell manufacturing and dosing. We review the current preclinical rationale supporting Treg cell therapy in a variety of disease settings ranging from tissue transplantation, autoimmune diseases, and non–immune-mediated inflammatory settings. We point out challenges in development of Treg cell therapy and speculate how synthetic biology can be used to enhance the feasibility and efficacy of Treg cell therapy for autoimmune and autoinflammatory diseases. Regulatory T (Treg) cells are a small subset (5% to 10%) of peripheral CD4+ T cells that are essential for maintaining immunologic tolerance. Decreased Treg cell numbers or function have been described in the setting of many autoimmune diseases in both patients and animal models.1Miyara M. Gorochov G. Ehrenstein M. Musset L. Sakaguchi S. Amoura Z. Human FoxP3+ regulatory T cells in systemic autoimmune diseases.Autoimmun Rev. 2011; 10: 744-755Crossref PubMed Scopus (171) Google Scholar, 2Dominguez-Villar M. Hafler D.A. Regulatory T cells in autoimmune disease.Nat Immunol. 2018; 19: 665-673Crossref PubMed Scopus (2) Google Scholar Importantly, adoptive transfer of Treg cells has been shown to ameliorate autoimmune disease and prevent transplant rejection in mouse models.3Tang Q. Bluestone J.A. Regulatory T-cell therapy in transplantation: moving to the clinic.Cold Spring Harb Perspect Med. 2013; 3Crossref PubMed Scopus (110) Google Scholar These preclinical data have spurred the development of experimental Treg cell therapies, many of which are currently in clinical trials. In this review we will discuss the unique biology of Treg cells and describe both current clinical applications of and emerging approaches to Treg cell therapy, including important outstanding questions in the field (Table I).Table ISome unknowns in Treg cell therapyTreg cell biology and genetic engineering•Relative effect of Treg cells on DCs versus effector T cells in patients•Importance of localization of Treg cells to inflamed tissue versus lymph nodes•In vivo stability of Treg cell phenotype in patients•Effects of transgenic expression of chimeric antigen receptors or antigen-specific TCRs on Treg cell function in patientsTreg cell product manufacturing•Optimal starting materials and Treg cell isolation methods•Effect that the patient's disease state has on Treg cell manufacturing outcomes•Optimal culture conditions and length of culture to maximize Treg cell efficacy•Treg cell product phenotypes associated with better clinical outcomesTreg cell therapy clinical trial design•Conditions with greatest potential benefit of Treg cell therapy•Optimal Treg cell dosing•Role of other drugs administered with Treg cell therapy•Timing of Treg cell dose(s) Open table in a new tab Treg cells express the lineage-defining transcription factor forkhead box P3 (FOXP3) and a specific epigenetic signature throughout the genome.4Fontenot J.D. 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Miyao T. et al.Active demethylation of the Foxp3 locus leads to the generation of stable regulatory T cells within the thymus.J Immunol. 2013; 190: 3180-3188Crossref PubMed Scopus (96) Google Scholar, 8Polansky J.K. Kretschmer K. Freyer J. Floess S. Garbe A. Baron U. et al.DNA methylation controls Foxp3 gene expression.Eur J Immunol. 2008; 38: 1654-1663Crossref PubMed Scopus (424) Google Scholar Treg cells develop in the thymus (thymic regulatory T [tTreg] cells) from immature thymocytes in response to self-antigen stimulation during T-cell development. Treg cells can also develop in the periphery from mature T cells (peripheral regulatory T [pTreg] cells) through exposure to specific microenvironments, particularly at mucosal sites in the presence of commensal microbiota.7Toker A. Engelbert D. Garg G. Polansky J.K. Floess S. 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Comparative analysis of protocols to induce human CD4+Foxp3+ regulatory T cells by combinations of IL-2, TGF-beta, retinoic acid, rapamycin and butyrate.PLoS One. 2016; 11: e0148474Crossref PubMed Scopus (26) Google Scholar In this review we will be focusing primarily on freshly isolated Treg cells from peripheral blood, which are used in most clinical trials and consist predominantly of tTreg cells. A small number of Treg cells with limited TCR specificities can control diverse effector cells in a given tissue environment, a property termed dominant tolerance.11Legoux F.P. Lim J.B. Cauley A.W. Dikiy S. Ertelt J. Mariani T.J. et al.CD4+ T cell tolerance to tissue-restricted self antigens is mediated by antigen-specific regulatory T cells rather than deletion.Immunity. 2015; 43: 896-908Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar For example, a few thousand Treg cells specific for a mouse islet–specific hybrid peptide12Stadinski B.D. Delong T. Reisdorph N. 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Continuous requirement for the TCR in regulatory T cell function.Nat Immunol. 2014; 15: 1070-1078Crossref PubMed Scopus (180) Google Scholar The versatility of their suppressive functions makes Treg cells effective guardians of immune homeostasis. Treg cells suppress locally through direct contact and paracrine actions in the tissue in which they reside. Thus their ability to traffic to and accumulate in specific tissue is vital to their function, deploying different combinations of suppressive activities in response to tissue microenvironments. Resting Treg cells express CD62L and CCR7 to home to secondary lymphoid tissue to control activation and clonal expansion of other T cells.22Smigiel K.S. Richards E. Srivastava S. Thomas K.R. Dudda J.C. Klonowski K.D. et al.CCR7 provides localized access to IL-2 and defines homeostatically distinct regulatory T cell subsets.J Exp Med. 2014; 211: 121-136Crossref PubMed Scopus (121) Google Scholar Depending on the context of their activation, Treg cells can mimic the phenotypes of TH1, TH2, TH17, and follicular helper T effector cells through expression of the transcription factors T-bet, GATA-3, retinoic acid–related orphan receptor γT, and B-cell lymphoma 6, which drive the differentiation of these effector cells.23Levine A.G. Mendoza A. Hemmers S. Moltedo B. Niec R.E. Schizas M. et al.Stability and function of regulatory T cells expressing the transcription factor T-bet.Nature. 2017; 546: 421-425Crossref PubMed Scopus (34) Google Scholar, 24Kim B.S. Lu H. Ichiyama K. Chen X. Zhang Y.B. 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Samstein R.M. Liang Y. Kas A. et al.CD4+ regulatory T cells control TH17 responses in a Stat3-dependent manner.Science. 2009; 326: 986-991Crossref PubMed Scopus (567) Google Scholar This additional layer of effector transcriptional program endows Treg-, TH1-, TH2-, and TH17-like properties through expression of chemokine receptors and adhesion molecules to “shadow” distinct effectors to suppress inflammation in the target tissue (Fig 1). Importantly, adoptive cell therapy (ACT) of Treg cells could potentially exploit subsets of Treg cells to improve targeting of Treg cells to specific tissues and organs. In addition to their role in suppressing effector immunity, Treg cells also contribute to tissue homeostasis and repair.29Li J. Tan J. Martino M.M. Lui K.O. Regulatory T-cells: potential regulator of tissue repair and regeneration.Front Immunol. 2018; 9: 585Crossref PubMed Scopus (1) Google Scholar, 30Panduro M. Benoist C. Mathis D. 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Fifty clinical trials of ACT of polyclonal Treg cell therapy have been completed or are ongoing in immune and nonimmune inflammatory disease settings (Fig 2, as listed at clinicaltrials.gov; also see Gliwinski et al42Gliwinski M. Iwaszkiewicz-Grzes D. Trzonkowski P. Cell-based therapies with T regulatory cells.BioDrugs. 2017; 31: 335-347Crossref PubMed Scopus (6) Google Scholar for a table). This work has been accomplished largely with ex vivo–expanded Treg cells, which are isolated based on cell-surface receptor expression (generally CD4+CD25+CD127− cells) and then expanded by using polyclonal activation through the TCR.43Putnam A.L. Brusko T.M. Lee M.R. Liu W. Szot G.L. Ghosh T. et al.Expansion of human regulatory T-cells from patients with type 1 diabetes.Diabetes. 2009; 58: 652-662Crossref PubMed Scopus (220) Google Scholar, 44Putnam A.L. Safinia N. Medvec A. Laszkowska M. Wray M. 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Preventing graft-versus-host disease (GvHD) after allogeneic stem cell transplantation was one of the first preclinical demonstrations of efficacy of Treg cell therapy.47Cohen J.L. Trenado A. Vasey D. Klatzmann D. Salomon B.L. CD4(+)CD25(+) immunoregulatory T cells: new therapeutics for graft-versus-host disease.J Exp Med. 2002; 196: 401-406Crossref PubMed Scopus (533) Google Scholar, 48Edinger M. Hoffmann P. Ermann J. Drago K. Fathman C.G. Strober S. et al.CD4+CD25+ regulatory T cells preserve graft-versus-tumor activity while inhibiting graft-versus-host disease after bone marrow transplantation.Nat Med. 2003; 9: 1144-1150Crossref PubMed Scopus (868) Google Scholar To date, 4 phase I trials, 1 phase II trial, and 1 case study in hematopoietic stem cell (HSC) transplant recipients have been reported. In one setting umbilical cord blood−derived Treg cells were expanded before infusion with HSCs from cord blood of a third-party donor. Despite the suboptimal dose and limited survival of the allogeneic Treg cells, the investigators observed a trend of delaying GvHD onset when compared with historical controls.49Brunstein C.G. Miller J.S. McKenna D.H. Hippen K.L. DeFor T.E. Sumstad D. et al.Umbilical cord blood-derived T regulatory cells to prevent GVHD: kinetics, toxicity profile, and clinical effect.Blood. 2016; 127: 1044-1051Crossref PubMed Scopus (92) Google Scholar, 50Brunstein C.G. Miller J.S. Cao Q. McKenna D.H. Hippen K.L. Curtsinger J. et al.Infusion of ex vivo expanded T regulatory cells in adults transplanted with umbilical cord blood: safety profile and detection kinetics.Blood. 2011; 117: 1061-1070Crossref PubMed Scopus (580) Google Scholar, 51Brunstein C.G. Blazar B.R. Miller J.S. Cao Q. Hippen K.L. 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Regulatory T-cell therapy in transplantation: moving to the clinic.Cold Spring Harb Perspect Med. 2013; 3Crossref PubMed Scopus (110) Google Scholar Currently, 2 phase I trials in kidney transplantation have been reported. The first pilot trial treated subclinical inflammation present on 6-month surveillance biopsy with ex vivo–expanded Treg cells. The study showed that it is feasible to expand Treg cells from immunosuppressed patients. Moreover, the pharmacokinetics of the infused Treg cells, which were monitored by using a novel deuterium labeling approach, were similar to those of nonimmunosuppressed patients with type 1 diabetes.56Chandran S. Tang Q. Sarwal M. Laszik Z.G. Putnam A.L. Lee K. et al.Polyclonal regulatory T cell therapy for control of inflammation in kidney transplants.Am J Transplant. 2017; 17: 2945-2954Crossref PubMed Scopus (10) Google Scholar In a separate phase I trial, patients receiving living donor kidney transplants received alemtuzumab induction, followed by infusion of up to 5 × 109 Treg cells 60 days later. A 5- to 20-fold increase in the percentage of Treg cells in all subjects up to 1 year after transplantation was observed.57Mathew J.M. HV J. LeFever A. Konieczna I. Stratton C. He J. et al.A phase I clinical trial with ex vivo expanded recipient regulatory T cells in living donor kidney transplants.Sci Rep. 2018; 8: 7428Crossref PubMed Scopus (0) Google Scholar Liver transplantation offers a clinical setting in which the efficacy of Treg cell therapy can be tested by withdrawing immunosuppressive drugs. A trial in Japan enrolled 10 living donor liver transplant recipients who received an autologous Treg cell–enriched cell preparation 13 days after liver transplantation and cyclophosphamide induction. Seven of the 10 patients were successfully withdrawn from immunosuppression.58Todo S. Yamashita K. Goto R. Zaitsu M. Nagatsu A. Oura T. et al.A pilot study of operational tolerance with a regulatory T-cell-based cell therapy in living donor liver transplantation.Hepatology. 2016; 64: 632-643Crossref PubMed Google Scholar Although the trial was not controlled and the product was a complex mixture of different cell types (including Treg cells), this result strongly suggests efficacy compared with a historic rate of 13% successful cessation of immunosuppression within 2 years of liver transplantation. 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