Obtaining regulatory T cells from uraemic patients awaiting kidney transplantation for use in clinical trials

Multiple infusions of ex vivo-expanded regulatory T cells promote CD163+ myeloid cells and kidney allograft survival in non-lymphodepleted non-human primates

Clinical verification of adoptively transferred regulatory T cell (Treg) efficacy in transplantation remains challenging. Here, we examined the influence of autologous ex vivo-expanded polyclonal Tregs on kidney graft survival in a clinically relevant non-human primate model. Peripheral blood Tregs were isolated and expanded using artificial antigen presenting cells. Immunosuppression was comprised of tapered tacrolimus and CTLA4 immunoglobulin, in five animals each without or with Treg infusions. Escalating Treg doses were administered 6, 10, 13, 16, 20, 23, 27 and 30 days after transplant. Infused Tregs were monitored for Treg signature, anti-apoptotic (Bcl-2) and proliferation (Ki67) marker expression. Treg infusions prolonged median graft survival time significantly from 35 to 70 days. Treg marker (Ki67 and Bcl-2) expression by infused Tregs diminished after their infusion but remained comparable to that of circulating native Tregs. No major changes in circulating donor-reactive T cell responses or total Treg percentages, or in graft-infiltrating T cell subsets were observed with Treg infusion. However, Treg infusion was associated with significant increases in CD163 expression by circulating HLA-DR+ myeloid cells and elevated levels of circulating soluble CD163. Further, graft-infiltrating CD163+ cells were increased with Treg infusion. Thus, multiple Treg infusions were associated with M2-like myeloid cell enhancement that may mediate immunomodulatory, anti-inflammatory and graft reparative effects.

Barriers to Treg therapy in Europe: From production to regulation

There has been an increased interest in cell based therapies for a range of medical conditions in the last decade. This explosion in novel therapeutics research has led to the development of legislation specifically focused on cell and gene based therapies. In Europe, the European medicines agency (EMA) designates any medicines for human use which are based on genes, tissues, or cells as advanced therapy medicinal products or advanced therapy medicinal products (ATMPs). In this article we discuss the hurdles to widespread adoption of ATMPs in Europe, with a focus on regulatory T cells (Tregs). There are numerous barriers which must be overcome before mainstream adoption of Treg therapy becomes a reality. The source of the cells, whether to use autologous or allogenic cells, and the methods through which they are isolated and expanded, must all meet strict good manufacturing practice (GMP) standards to allow use of the products in humans. GMP compliance is costly, with the equipment and reagents providing a significant cost barrier and requiring specialized facilities and personnel. Conforming to the regulations set centrally by the EMA is difficult, and the different interpretations of the regulations across the various member states further complicates the regulatory approval process. The end products then require a complex and robust distribution network to ensure timely delivery of potentially life saving treatments to patients. In a European market whose logistics networks have been hammered by COVID and Brexit, ensuring rapid and reliable delivery systems is a more complex task than ever. In this article we will examine the impact of these barriers on the development and adoption of Tregs in Europe, and potential approaches which could facilitate more widespread use of Tregs, instead of its current concentration in a few very specialized centers.

Ex vivo generation of regulatory T cells from liver transplant recipients using costimulation blockade

The potential of adoptive cell therapy with regulatory T cells (Tregs) to promote transplant tolerance is under active exploration. However, the impact of specific transplant settings and protocols on Treg manufacturing is not well-delineated. Here, we compared the use of peripheral blood mononuclear cells (PBMCs) from patients before or after liver transplantation to the use of healthy control PBMCs to determine their suitability for Treg manufacture using ex vivo costimulatory blockade with belatacept. Despite liver failure or immunosuppressive therapy, the capacity for Treg expansion during the manufacturing process was preserved. These experiments did not identify performance or quality issues that disqualified the use of posttransplant PBMCs-the currently favored protocol design. However, as Treg input correlated with output, significant CD4-lymphopenia in both pre- and posttransplant patients limited Treg yield. We therefore turned to leukapheresis posttransplant to improve absolute yield. To make deceased donor use feasible, we also developed protocols to substitute splenocytes for PBMCs as allostimulators. In addition to demonstrating that this Treg expansion strategy works in a liver transplant context, this preclinical study illustrates how characterizing cellular input populations and their performance can both inform and respond to clinical trial design and Treg manufacturing requirements.

T cell plasticity in renal autoimmune disease

The presence of immune cells is a morphological hallmark of rapidly progressive glomerulonephritis, a disease group that includes anti-glomerular basement membrane glomerulonephritis, lupus nephritis, and anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis. The cellular infiltrates include cells from both the innate and the adaptive immune responses. The latter includes CD4⁺ and CD8⁺ T cells. In the past, CD4⁺ T cell subsets were viewed as terminally differentiated lineages with limited flexibility. However, it is now clear that Th17 cells can in fact have a high degree of plasticity and convert, for example, into pro-inflammatory Th1 cells or anti-inflammatory Tr1 cells. Interestingly, Th17 cells in experimental GN display limited spontaneous plasticity. Here we review the literature of CD4⁺ T cell plasticity focusing on immune-mediated kidney disease. We point out the key findings of the past decade, in particular that targeting pathogenic Th17 cells by anti-CD3 injection can be a tool to modulate the CD4⁺ T cell response. This anti-CD3 treatment can trigger a regulatory phenotype in Th17 cells and transdifferentiation of Th17 cells into immunosuppressive IL-10-expressing Tr1 cells (Tr1exTh17 cells). Thus, targeting Th17 cell plasticity could be envisaged as a new therapeutic approach in patients with glomerulonephritis.

Chimeric antigen receptor-engineered regulatory T lymphocytes: promise for immunotherapy of autoimmune disease

Regulatory T lymphocytes (Tregs) exist as natural ideal immunosuppressors in the immune system. Autologous or allogeneic Treg transfusion therapy has been carried out in animal models and humans as a new strategy for treating autoimmune disease. Recent studies have shown that Tregs can be engineered with chimeric antigen receptors to be antigen-specific, which are more effective than polyclonal Tregs with fewer target limitations and a lack of major histocompatibility complex restriction. This review describes the potential for applying chimeric antigen receptor-engineered regulatory T cells in autoimmune diseases.

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

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

Clinical Grade Regulatory CD4+ T Cells (Tregs): Moving Toward Cellular-Based Immunomodulatory Therapies

Regulatory T cells (Tregs) are CD4⁺ T cells that are key players of immune tolerance. They are powerful suppressor cells, able to impact the function of numerous immune cells, including key effectors of inflammation such as effector T cells. For this reason, Tregs are an ideal candidate for the development of cell therapy approaches to modulate immune responses. Treg therapy has shown promising results so far, providing key knowledge on the conditions in which these cells can provide protection and demonstrating that they could be an alternative to current pharmacological immunosuppressive therapies. However, a more comprehensive understanding of their characteristics, isolation, activation, and expansion is needed to be able design cost effective therapies. Here, we review the practicalities of making Tregs a viable cell therapy, in particular, discussing the challenges faced in isolating and manufacturing Tregs and defining what are the most appropriate applications for this new therapy.

A novel and rapid method to quantify Treg mediated suppression of CD4 T cells

Measuring regulatory T cell suppression provides important insight into T cell dysfunction in autoimmune disease. However, to date, suppression assays are limited by the requirement for freshly isolated cells, and significant cell numbers. Here, we present a novel and rapid in vitro assay using effector T cell surface expression of both CD25 and CD134 as a surrogate marker of regulatory T cell-mediated suppression. This surface marker-based suppression assay works for frozen samples and for samples with limited cell numbers. It is also shorter taking two days to complete compared to the four days required for proliferation-based assays. Furthermore, this assay works with both in vitro expanded and natural Tregs, as well as anti-CD3/anti-CD28 bead-based and APC stimulation conditions. In conclusion, we have developed and validated a new suppression assay for cryopreserved samples with limited cell numbers that may be helpful to investigate T cell regulation in the context of infection or autoimmune diseases.

Ex Vivo Costimulatory Blockade to Generate Regulatory T Cells From Patients Awaiting Kidney Transplantation

Short-term outcomes of kidney transplantation have improved dramatically, but chronic rejection and regimen-related toxicity continue to compromise overall patient outcomes. Development of regulatory T cells (Tregs) as a means to decrease alloresponsiveness and limit the need for pharmacologic immunosuppression is an active area of preclinical and clinical investigation. Nevertheless, the immunomodulatory effects of end-stage renal disease on the efficacy of various strategies to generate and expand recipient Tregs for kidney transplantation are incompletely characterized. In this study, we show that Tregs can be successfully generated from either freshly isolated or previously cryopreserved uremic recipient (responder) and healthy donor (stimulator) peripheral blood mononuclear cells using the strategy of ex vivo costimulatory blockade with belatacept during mixed lymphocyte culture. Moreover, these Tregs maintain a CD3(+) CD4(+) CD25(+) CD127(lo) surface phenotype, high levels of intracellular FOXP3 and significant demethylation of the FOXP3 Treg-specific demethylation region on allorestimulation with donor stimulator cells. These data support evaluation of this simple, brief Treg production strategy in clinical trials of mismatched kidney transplantation.

Hurdles in therapy with regulatory T cells

Improper activation of the immune system contributes to a variety of clinical conditions, including autoimmune and allergic diseases as well as solid organ and bone marrow transplantation. One approach to counteract this activation is through adoptive therapy with regulatory T cells (Tregs). Efforts to manufacture these cells have led to good maunfacturing practice-compliant protocols, and Treg products are entering early clinical trials. Here, we report the stance of the European Union Cooperation in Science and Technology Action BM1305, "Action to Focus and Accelerate Cell-based Tolerance-inducing Therapies-A FACTT," which identifies hurdles hindering Treg clinical applications in Europe and provides possible solutions.

Immunological profiling of haemodialysis patients and young healthy individuals with implications for clinical regulatory T cell sorting

With the increasing interest in clinical trials with regulatory T cells (Tregs), immunological profiling of prospective target groups and standardized procedures for Treg isolation are needed. In this study, flow cytometry was used to assess peripheral blood lymphocyte profiles of young healthy individuals and patients undergoing haemodialysis treatment. Tregs obtained from the former may be used in haematopoietic stem cell transplantation and Tregs from the latter in the prevention of kidney transplant rejection. FOXP3 mRNA expression with accompanying isoform distribution was also assessed by the quantitative reverse transcriptase polymerase chain reaction. Flow-cytometric gating strategies were systematically analysed to optimize the isolation of Tregs. Our findings showed an overall similar immunological profile of both cohorts in spite of great differences in both age and health. Analysis of flow-cytometric gating techniques highlighted the importance of gating for both CD25high and CD127low expression in the isolation of FOXP3-positive cells. This study provides additional insight into the immunological profile of young healthy individuals and uraemic patients as well as in-depth analysis of flow-cytometric gating strategies for Treg isolation, supporting the development of Treg therapy using cells from healthy donors and uraemic patients.

Clinical grade manufacturing of human alloantigen-reactive regulatory T cells for use in transplantation

Regulatory T cell (Treg) therapy has the potential to induce transplantation tolerance so that immunosuppression and associated morbidity can be minimized. Alloantigen-reactive Tregs (arTregs) are more effective at preventing graft rejection than polyclonally expanded Tregs (PolyTregs) in murine models. We have developed a manufacturing process to expand human arTregs in short-term cultures using good manufacturing practice-compliant reagents. This process uses CD40L-activated allogeneic B cells to selectively expand arTregs followed by polyclonal restimulation to increase yield. Tregs expanded 100- to 1600-fold were highly alloantigen reactive and expressed the phenotype of stable Tregs. The alloantigen-expanded Tregs had a diverse TCR repertoire. They were more potent than PolyTregs in vitro and more effective at controlling allograft injuries in vivo in a humanized mouse model.