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

Adoptive T Regulatory Cell Therapy for Tolerance Induction

There is a clear need to develop strategies to induce tolerance without the need of chronic immunosuppression in transplant recipient and in patients with autoimmunity. Adoptive T regulatory cell (T_reg) therapy offers the potential of long-lasting protection. However, based on results of clinical trials so far with ex vivo expanded autologous T_regs in type 1 diabetic (T1D) patients, it seems unlikely that single immunotherapy with T_reg infusion without immunomodulation regimens that promote stable donor T_reg engraftment and persistence would afford truly significant clinical benefit. Combination therapies could provide improved outcomes with consideration of the fundamental factors required for T_reg generation, homeostasis, and function to promote long-term donor T_reg persistence to provoke beneficial therapeutic outcomes.

From immunosuppression to tolerance

The past three decades have seen liver transplantation becoming a major therapeutic approach in the management of end-stage liver diseases. This is due to the dramatic improvement in survival after liver transplantation as a consequence of the improvement of surgical and anaesthetic techniques, of post-transplant medico-surgical management and of prevention of disease recurrence and other post-transplant complications. Improved use of post-transplant immunosuppression to prevent acute and chronic rejection is a major factor in these improved results. The liver has been shown to be more tolerogenic than other organs, and matching of donor and recipients is mainly limited to ABO blood group compatibility. However, long-term immunosuppression is required to avoid severe acute and chronic rejection and graft loss. With the current immunosuppression protocols, the risk of acute rejection requiring additional therapy is 10-40% and the risk of chronic rejection is below 5%. However, the development of histological lesions in the graft in long-term survivors suggest atypical forms of graft rejection may develop as a consequence of under-immunosuppression. The backbone of immunosuppression remains calcineurin inhibitors (CNI) mostly in association with steroids in the short-term and mycophenolate mofetil or mTOR inhibitors (everolimus). The occurrence of post-transplant complications related to the immunosuppressive therapy has led to the development of new protocols aimed at protecting renal function and preventing the development of de novo cancer and of dysmetabolic syndrome. However, there is no new class of immunosuppressive drugs in the pipeline able to replace current protocols in the near future. The aim of a full immune tolerance of the graft is rarely achieved since only 20% of selected patients can be weaned successfully off immunosuppression. In the future, immunosuppression will probably be more case oriented aiming to protect the graft from rejection and at reducing the risk of disease recurrence and complications related to immunosuppressive therapy. Such approaches will include strategies aiming to promote stable long-term immunological tolerance of the liver graft.

Now or never? The case for cell-based immunosuppression in kidney transplantation

By exploiting mechanisms of immunological regulation against donor alloantigen, it may be possible to reduce the dependence of kidney transplant recipients upon calcineurin inhibitor-based maintenance immunosuppression. One means to strengthen regulatory responses is treating recipients with preparations of regulatory cells obtained by ex vivo manipulation. This strategy, which is a well-established experimental method, has been developed to the point that early-phase clinical trials in kidney transplantation are now feasible. Cell-based therapies represent a radical departure from conventional treatment, so what grounds are there for this new approach? This article offers a three-part justification for trialing cell-based therapies in kidney transplantation: first, a clinical need for alternatives to standard immunosuppression is identified, based on the inadequacies of calcineurin inhibitor-based regimens in preventing late allograft loss; second, a mechanistic explanation of how cell-based therapies might address this clinical need is given; and third, the possible benefit to patients is weighed against the potential risks of cell-based immunosuppressive therapy. It is concluded that the safety of cell-based immunosuppressive therapy will not be greatly improved by further basic scientific and preclinical development. Only trials in humans can now tell us whether cell-based therapy is likely to benefit kidney transplant recipients, but these should be conservative in design to minimize any potential harm to patients.

Restimulation After Cryopreservation and Thawing Preserves the Phenotype and Function of Expanded Baboon Regulatory T Cells

BACKGROUND

Regulatory T cells (Treg) are being explored for their tolerance-inducing capabilities. Freezing and banking Treg for future use makes this strategy more clinically applicable. We aimed to devise an improved method of expanding and cryopreserving Treg to maximize yield, purity, and function for use in xenotransplantation.

METHODS

Baboon peripheral blood mononuclear cells (PBMC) were isolated from whole blood. CD4+/CD25^hi cells were isolated by flow cytometric sorting and expanded for 26 days in culture with IL-2, anti-CD3 antibody, artificial APCs transfected with human CD58, CD32, and CD80, and rapamycin with weekly restimulations. Expanded Treg were frozen for 2 months then thawed and cultured for 48 hours in medium plus 1) no additives, 2) IL-2, 3) anti-CD3 antibody, 4) IL-2 + anti-CD3 antibody, and 5) IL-2 + anti-CD3 antibody + L cells. Phenotype and suppression were assessed after expansion, immediately after thawing, and after culturing.

RESULTS

We expanded purified baboon Treg more than 10,000-fold. Expanded Treg exhibited excellent suppression in functional assays. Cryopreservation decreased suppressive function without changing phenotype, but increasing amounts of reactivation after thawing produced significantly better viability and suppressive function with a trend towards greater Treg purity.

CONCLUSIONS

We produced numbers of expanded Tregs consistent with clinical use. In contrast to some previous reports, both Treg phenotype and suppressive function were preserved or even enhanced by increasing amounts of restimulation after thawing. Thus, banking of expanded recipient Tregs for in vivo infusion should be possible.

Human monocyte-derived suppressor cells control graft-versus-host disease by inducing regulatory forkhead box protein 3-positive CD8+ T lymphocytes

BACKGROUND

Adoptive transfer of immunosuppressive cells has emerged as a promising strategy for the treatment of immune-mediated disorders. However, only a limited number of such cells can be isolated from in vivo specimens. Therefore efficient ex vivo differentiation and expansion procedures are critically needed to produce a clinically relevant amount of these suppressive cells.

OBJECTIVE

We sought to develop a novel, clinically relevant, and feasible approach to generate ex vivo a subpopulation of human suppressor cells of monocytic origin, referred to as human monocyte-derived suppressive cells (HuMoSCs), which can be used as an efficient therapeutic tool to treat inflammatory disorders.

METHODS

HuMoSCs were generated from human monocytes cultured for 7 days with GM-CSF and IL-6. The immune-regulatory properties of HuMoSCs were investigated in vitro and in vivo. The therapeutic efficacy of HuMoSCs was evaluated by using a graft-versus-host disease (GvHD) model of humanized mice (NOD/SCID/IL-2Rγc(-/-) [NSG] mice).

RESULTS

CD33+ HuMoSCs are highly potent at inhibiting the proliferation and activation of autologous and allogeneic effector T lymphocytes in vitro and in vivo. The suppressive activity of these cells depends on signal transducer and activator of transcription 3 activation. Of therapeutic relevance, HuMoSCs induce long-lasting memory forkhead box protein 3-positive CD8+ regulatory T lymphocytes and significantly reduce GvHD induced with human PBMCs in NSG mice.

CONCLUSION

Ex vivo-generated HuMoSCs inhibit effector T lymphocytes, promote the expansion of immunosuppressive forkhead box protein 3-positive CD8+ regulatory T cells, and can be used as an efficient therapeutic tool to prevent GvHD.

Administration of low doses of IL-2 combined to rapamycin promotes allogeneic skin graft survival in mice

Human CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) prevent allogeneic graft rejection by inhibiting T cell activation, as has been shown in mouse models. Recently, low-dose IL-2 administration was shown to specifically activate Tregs but not pathogenic conventional T cells, leading to resolution of type 1 diabetes in nonobese diabetic mice. We therefore tested the ability of low-dose IL-2 to prevent allogeneic skin graft rejection. We found that while IL-2 alone was inefficient in preventing rejection, combined with rapamycin, IL-2 treatment promoted skin graft survival both in minor disparate and semi-allogeneic skin graft combinations. Tregs are activated by this combined treatment while conventional CD4(+) cell expansion and activation are markedly inhibited. Co-administration of anti-CD25 antibodies dramatically reduces the effect of the IL-2/rapamycin treatment, strongly supporting a central role for Treg activation. Thus, we provide the first preclinical data showing that low-dose IL-2 combined with rapamycin can significantly delay transplant rejection in mice. These findings may form the rational for clinical evaluation of this novel approach for the prevention of transplant rejection.

Potential limitations of IL-2 administration for the treatment of experimental acute graft-versus-host disease

Low-dose IL-2 administration can control autoimmunity by specifically activating CD4(+) Foxp3(+) regulatory T cells (Tregs). Here, we studied IL-2-based immunotherapy in experimental graft-versus-host disease (GVHD). IL-2 administration to donor mice induced a dose-dependent expansion of Tregs in the graft but was insufficient to control GVHD. IL-2 administration to allogeneic-grafted recipient mice activated T-conventional cells (Tcons) and did not prevent GVHD. This loss of IL-2 selectivity toward Tregs was explained by an IL-2-induced increase in the IL-2 receptor α-chain expression on Tcons. Finally, in xeno-GVHD generated by human PBMCs transplanted into immunodeficient mice, low-dose IL-2 increased Treg frequencies but did neither control pro-inflammatory cytokine production by pathogenic Tcons, nor prevented GVHD. Furthermore, combination of low-dose IL-2 with rapamycin was ineffective in this model. Our results indicate that limitations on the use of IL-2 during acute GVHD are likely due to the massive activation of the allogeneic T cells unique to this setting.

Potential and limitations of regulatory T-cell therapy in solid organ transplantation

Over the past few years, the therapeutic potential of Treg has been highlighted in the field of autoimmune diseases and after allogeneic transplantation. The first hurdle for the therapeutic use of Treg is their insufficient numbers in non-manipulated individuals, in particular when facing strong immune activation and expanding effector cells, such as in response to an allograft. Here we review current approaches being explored for Treg expansion in the perspective of clinical therapeutic protocols. We describe different Treg subsets that could be suitable for clinical application, as well as discuss factors such as the required dose of Treg, their antigen-specificity and in vivo stability, that have to be considered for optimal Treg-based immunotherapy in transplantation. Since Treg may not be sufficient as stand-alone therapy for solid organ transplantation in humans, we draw attention to possible hurdles and combination therapy with immunomodulatory drugs that could possibly improve the in vivo efficacy of Treg.

Organ-specific and memory treg cells: specificity, development, function, and maintenance

Foxp3⁺ regulatory T cells (Treg cells) are essential for establishing and maintaining self-tolerance, and also inhibit immune responses to innocuous environmental antigens. Imbalances and dysfunction in Treg cells lead to a variety of immune-mediated diseases, as deficits in Treg cell function contribute to the development autoimmune disease and pathological tissue damage, whereas overabundance of Treg cells can promote chronic infection and tumorigenesis. Recent studies have highlighted the fact that Treg cells themselves are a diverse collection of phenotypically and functionally specialized populations, with distinct developmental origins, antigen-specificities, tissue-tropisms, and homeostatic requirements. The signals directing the differentiation of these populations, their specificities and the mechanisms by which they combine to promote organ-specific and systemic tolerance, and how they embody the emerging property of regulatory memory are the focus of this review.

Regulatory T cells and their roles in immune dysregulation and allergy

The main function of the immune system is to fight off potential infections, but also to maintain its activity below a level that would trigger self-reactivity. Regulatory T cells (Tregs) such as forkhead box P3(+) (FOXP3) Tregs and type 1 regulatory T cells (Tr1) play an essential role in this active process, using several distinct suppressive mechanisms. A wide range of pathologies have been associated with altered Treg cell function. This is best exemplified by the impact of mutations of genes essential for Treg function and the associated autoimmune syndromes. This review summarizes the main features of different subtypes of Tregs and focuses on the clinical implications of their altered function in human studies. More specifically, we discuss abnormalities affecting FOXP3(+) Tregs and Tr1 cells that will lead to autoimmune manifestations and/or allergic reactions, and the potential therapeutic use of Tregs.

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.

Harnessing FOXP3+ regulatory T cells for transplantation tolerance

Early demonstrations that mice could be tolerized to transplanted tissues with short courses of immunosuppressive therapy and that with regard to tolerance to self, CD4+FOXP3+ regulatory T cells (Tregs) appeared to play a critical role, have catalyzed strategies to harness FOXP3-dependent processes to control rejection in human transplantation. This review seeks to examine the scientific underpinning for this new approach to finesse immunosuppression.

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.

Ex Vivo Expanded Autologous Polyclonal Regulatory T Cells Suppress Inhibitor Formation in Hemophilia

Adoptive cell therapy utilizing ex vivo expanded polyclonal CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Treg) is in use in clinical trials for the treatment of type 1 diabetes and prevention of graft vs host disease in bone marrow transplantation. Here we seek to evaluate this approach in the treatment of inherited protein deficiencies, i.e. hemophilia, which is often complicated by antibody formation against the therapeutic protein. Treg from mice that express GFP-marked FoxP3 were highly purified by two-step magnetic/flow sorting and ex vivo expanded 50- to 80-fold over a 2-week culture period upon stimulation with antibody-coated microbeads. FoxP3 expression was maintained in >80% of expanded Treg, which also expressed high levels of CD62L and CTLA-4. Transplanted Treg suppressed inhibitory antibody formation against coagulation factors VIII and IX in protein and gene therapies in strain-matched hemophilia A and B mice, including in mice with pre-existing antibodies. Although transplanted Treg became undetectable within two weeks, suppression persisted for >2 months. Additional studies suggested that antigen-specific suppression emerged due to induction of endogenous Treg. The outcomes of these studies support the concept that cell therapy with ex vivo expanded autologous Treg can be used successfully to minimize immune responses in gene and protein replacement therapies.

Regulatory T-cell therapy in transplantation: moving to the clinic

Regulatory T cells (Tregs) are essential to transplantation tolerance and their therapeutic efficacy is well documented in animal models. Moreover, human Tregs can be identified, isolated, and expanded in short-term ex vivo cultures so that a therapeutic product can be manufactured at relevant doses. Treg therapy is being planned at multiple transplant centers around the world. In this article, we review topics critical to effective implementation of Treg therapy in transplantation. We will address issues such as Treg dose, antigen specificity, and adjunct therapies required for transplant tolerance induction. We will summarize technical advances in Treg manufacturing and provide guidelines for identity and purity assurance of Treg products. Clinical trial designs and Treg manufacturing plans that incorporate the most up-to-date scientific understanding in Treg biology will be essential for harnessing the tolerogenic potential of Treg therapy in transplantation.