Multiple unit pooled umbilical cord blood is a viable source of therapeutic regulatory T cells

The potential for Treg-enhancing therapies in transplantation

Since the discovery of regulatory T cells (Tregs) as crucial regulators of immune tolerance against self-antigens, these cells have become a promising tool for the induction of donor-specific tolerance in transplantation medicine. The therapeutic potential of increasing in vivoTreg numbers for a favorable Treg to Teff cell ratio has already been demonstrated in several sophisticated pre-clinical models and clinical pilot trials. In addition to improving cell quantity, enhancing Treg function utilizing engineering techniques led to encouraging results in models of autoimmunity and transplantation. Here we aim to discuss the most promising approaches for Treg-enhancing therapies, starting with adoptive transfer approaches and ex vivoexpansion cultures (polyclonal vs. antigen specific), followed by selective in vivostimulation methods. Furthermore, we address next generation concepts for Treg function enhancement (CARs, TRUCKs, BARs) as well as the advantages and caveats inherit to each approach. Finally, this review will discuss the clinical experience with Treg therapy in ongoing and already published clinical trials; however, data on long-term results and efficacy are still very limited and many questions that might complicate clinical translation remain open. Here, we discuss the hurdles for clinical translation and elaborate on current Treg-based therapeutic options as well as their potencies for improving long-term graft survival in transplantation.

Benefit of Belatacept in Cord Blood-Derived Regulatory T Cell-Mediated Suppression of Alloimmune Response

The role of Regulatory T cells (Tregs) in tolerance induction post-transplantation is well-established, but Tregs adoptive transfer alone without combined immunosuppressants have failed so far in achieving clinical outcomes. Here we applied a set of well-designed criteria to test the influence of commonly used immunosuppressants (belatacept, tacrolimus, and mycophenolate) on cord blood-derived Tregs (CB-Tregs). Our study shows that while none of these immunosuppressants modulated the stability and expression of homing molecules by CB-Tregs, belatacept met all other selective criteria, shown by its ability to enhance CB-Tregs-mediated in vitro suppression of the allogeneic response without affecting their viability, proliferation, mitochondrial metabolism and expression of functional markers. In contrast, treatment with tacrolimus or mycophenolate led to reduced expression of functional molecule GITR in CB-Tregs, impaired their viability, proliferation and mitochondrial metabolism. These findings indicate that belatacept could be considered as a candidate in Tregs-based clinical immunomodulation regimens to induce transplant tolerance.

Suppressive Characteristics of Umbilical Cord Blood-derived Regulatory T Cells After Ex Vivo Expansion on Autologous and Allogeneic T Effectors and Various Lymphoblastic Cells

The third-party umbilical cord blood (UCB)-derived regulatory T cells (Treg) are an alternative to donor-derived Treg as cellular therapy of graft-versus-host disease following hematopoietic stem cell transplantation. However, their suppressive characteristics against autologous and allogeneic T effector cells (Teff) have rarely been documented. The exact role of UCB-Treg in hematologic malignancies is also uncertain. Here, we investigated the direct effects of UCB-Treg on the proliferation of autologous Teff, as compared with allogeneic Teff, and also determined cellular fates of lymphoblasts after UCB-Treg co-culture. UCB-Treg were isolated from 8 UCB samples using 2-step immunomagnetic bead sorting. After 10-day ex vivo expansion, up to 60-fold increase in cell number with 76.7%±4.9% of CD4CD25CD127FoxP UCB-Treg was obtained. Further characterization showed that ex vivo-expanded UCB-Treg contained a higher proportion of CD95CD45RACCR4Treg-B subpopulation compared with the CD95CD45RACCR4Treg-A subpopulation (13.0%±4.8% vs. 0.8%±0.7%; P<0.05), along with the detecting of substantial amounts of secretory IL-10 (57.7±17.8 pg/mL) and TGF-β1 (196.5±29.7 pg/mL) in culture supernatants. After 4 days co-culture with UCB-Treg (at the ratio of 1:1), the proliferation of autologous and allogeneic Teff was decreased comparably (43.6%±17.5% vs. 37.6±17.7%; P=0.437). Suppression was independent of HLA-A, B, and DRB1 compatibility between UCB-Treg and Teff. UCB-Treg co-culture with various lymphoblasts showed proliferative suppression of Jurkat T lymphoblasts (45.4%±20.5% at the ratio of 1:1), but not Namalwa and Raji B lymphoblasts. All lymphoblasts had no significant cell apoptosis or death after co-culture. In conclusion, the ex vivo-expanded UCB-Treg had no difference in autologous and allogeneic Teff suppression. UCB-Treg therapy in patients with graft-versus-host disease who have a primary disease of T-cell leukemia may have additional benefits in the prevention of relapsed disease.

Isolation of Human Regulatory T Lymphocytes by Fluorescence-Activated Cell Sorting

Regulatory T cells (Tregs) are a population of lymphocytes that exerts suppressive effects upon the immune system. In human peripheral blood, the major population of T lymphocytes with suppressive capacity are defined by expression of the T cell co-receptor CD4 and the interleukin-2 receptor α-chain (CD25), combined with minimal expression of the interleukin-7 receptor α subunit (CD127). We begin by outlining the method for isolating peripheral blood mononuclear cells (PBMCs) from human blood by centrifugation of whole blood overlayed on a hydrophilic polysaccharide, with an additional erythrocyte lysis step. The protocol that follows utilizes Fluorescence-Activated Cell Sorting (FACS) for the isolation of this CD4⁺CD25⁺CD127^lo population of regulatory T cells, with high yield and purity, from immunostained PBMCs. Prior to FACS isolation, this protocol exploits magnetic immunoselection for pre-enrichment of CD25⁺ PBMC, which reduces the duration of the subsequent FACS isolation.

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

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

Selective blockade of CD28 on human T cells facilitates regulation of alloimmune responses

T cells are central to the detrimental alloresponses that develop in autoimmunity and transplantation, with CD28 costimulatory signals being key to T cell activation and proliferation. CTLA4-Ig molecules that bind CD80/86 and inhibit CD28 costimulation offer an alternative immunosuppressive treatment, free from some of the chronic toxicities associated with calcineurin inhibition. However, CD80/86 blockade by CTLA4-Ig also results in the loss of coinhibitory CTLA4 signals that are critical to the regulation of T cell activation. Here, we show that a nonactivating monovalent anti-CD28 that spares CTLA4 signaling is an effective immunosuppressant in a clinically relevant humanized mouse transplant model. We demonstrate that selective CD28 blockade prolongs human skin allograft survival through a mechanism that includes a reduction in the cellular graft infiltrate. Critically, selective CD28 blockade promotes Treg function in vivo and synergizes with adoptive Treg therapy to promote transplant survival. In contrast to CTLA4-Ig treatment, selective CD28 blockade promotes regulation of alloimmune responses and facilitates Treg-based cellular therapy.

Immunotherapy after hematopoietic stem cell transplantation using umbilical cord blood-derived products

Umbilical cord blood (UCB) is being increasingly used as a source of hematopoietic stem cells (HSC) for transplantation. UCB transplantation (UCBT) has some advantages such as less stringent HLA-matching requirements, fast availability of the graft and reduced incidence and severity of graft-versus-host disease. However, UCBT is also associated with a higher incidence of infection, graft failure, slow engraftment and slow immune reconstitution. UCB is mainly used as a source of HSC; however, it is also rich in immune cells that could be used to treat some of the main complications post-UCBT as well as other diseases, thus implicating the use of UCB for immunotherapy. Here, we aim to describe some of the therapies currently developed that use UCB as a cell source, focusing in particular on regulatory T cells and natural killer cells.

The potential role for regulatory T-cell therapy in vascularized composite allograft transplantation

PURPOSE OF REVIEW

Vascularized composite allograft (VCA) transplantation restores defects to a degree not possible by conventional techniques. However, it is limited by the need for long-term immunosuppression and high rates of acute rejection directed against skin. There is therefore a need for a therapy that may shift the risk-benefit ratio in favour of VCA transplantation. Regulatory T cells (Tregs) are a subset of T cells with potent immunoregulatory properties and the potential to promote immunosuppression-free allograft survival. In this review, we consider the evidence for Treg therapy in VCA transplantation.

RECENT FINDINGS

CD4 Tregs are the best-studied immunoregulatory cell type, and a large amount of experimental and clinical data is emerging to endorse their use in VCA transplantation. Data from animal and humanized models are particularly encouraging and demonstrate the potent efficacy of Treg at preventing skin allograft rejection. Moreover, central tolerance induction techniques in VCA transplantation models are demonstrating a dependence on Tregs for graft survival.

SUMMARY

An improvement in outcomes after VCA transplantation has the potential to revolutionize the field. Several effective therapeutic strategies have demonstrated great promise experimentally, and there is now a need to assess their safety and efficacy in a clinical setting.

Treatment of graft-versus-host disease with naturally occurring T regulatory cells

A significant body of evidence suggests that treatment with naturally occurring CD4⁺CD25⁺ T regulatory cells (Tregs) is an appropriate therapy for graft-versus-host disease (GvHD). GvHD is a major complication of bone marrow transplantation in which the transplanted immune system recognizes recipient tissues as a non-self and destroys them. In many cases, this condition significantly deteriorates the quality of life of the affected patients. It is also one of the most important causes of death after bone marrow transplantation. Tregs constitute a population responsible for dominant tolerance to self-tissues in the immune system. These cells prevent autoimmune and allergic reactions and decrease the risk of rejection of allotransplants. For these reasons, Tregs are considered as a cellular drug in GvHD. The results of the first clinical trials with these cells are already available. In this review we present important experimental facts which led to the clinical use of Tregs. We then critically evaluate specific requirements for Treg therapy in GvHD and therapies with Tregs currently under clinical investigation, including our experience and future perspectives on this kind of cellular treatment.

Therapy of type 1 diabetes with CD4(+)CD25(high)CD127-regulatory T cells prolongs survival of pancreatic islets - results of one year follow-up

It is hypothesized that CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) can prevent destruction of pancreatic islets protecting from type 1 diabetes (DM1). Here we present results of one year follow-up of 12 DM1 children treated with autologous expanded ex vivo Tregs. Patients received either a single or double Tregs infusion up to the total dose of 30×10(6)/kg. No severe adverse effects were observed. The treatment did not impair post-immunization antibody responses. Tregs infusion was followed by increase in Tregs number in peripheral blood. Most of the patients responded to the therapy with increase in C-peptide levels (8/12 and 4/6 after the first and the second dose, respectively). Tregs administration resulted also in lower requirement for exogenous insulin (8/12 treated patients versus 2/10 untreated controls in remission) with two children completely insulin independent at one year. Repetitive administration of Tregs is safe and can prolong survival of β-cells in DM1 (registration: ISRCTN06128462).

Harnessing regulatory T cells for clinical use in transplantation: the end of the beginning

Owing to the adverse effects of immunosuppression and an inability to prevent chronic rejection, there is a pressing need for alternative strategies to control alloimmunity. In three decades, regulatory T cells (Tregs) have evolved from a hypothetical mediator of adoptively transferred tolerance to a well-defined population that can be expanded ex vivo and returned safely to patients in clinical trials. Herein, we review the historical developments that have permitted these advances and the current status of clinical trials examining Tregs as a cellular therapy in transplantation. We conclude by discussing the critical unanswered questions that face this field in the coming years.

Novel GMP-compatible protocol employing an allogeneic B cell bank for clonal expansion of allospecific natural regulatory T cells

The adoptive transfer of natural regulatory T cells (nTreg) is a new option to reshape undesired immune reactivity in autoimmunity and transplantation toward "tolerance." The first clinical trials using adoptive transfer of polyclonal nTreg demonstrated safety and hints of efficacy. However, the low frequencies of antigen-specific cells among the pool of polyclonal nTreg and their broad antigen nonspecific suppression are limitations of this approach regarding efficacy and safety. Recently, the isolation and expansion of (allo)antigen-specific nTreg have successfully been achieved by using Treg-specific activation markers but the yield is relatively low. Here, we describe a novel good manufacturing practice (GMP)-compatible expansion protocol of alloantigen-specific nTreg based on the stimulation of nTreg by allogeneic activated B cells. Their functionality and specificity are superior compared to polyclonal nTreg both in vitro and in vivo. Employing an allogeneic B cell bank, designed to cover the majority of HLA types, allows fast GMP-compliant manufacturing for donor-specific nTreg for clinical application in organ and stem cell transplantation. TCR repertoire analyses by next generation sequencing revealed impressive expansion by several log-steps of even very low-abundance alloantigen-specific nTreg clones. This novel method offers a simple approach for expanding antigen-specific nTreg and is characterized by high replicability and easy transferability to full GMP standards.