Superiority of Bone Marrow-Derived Dendritic Cells Over Monocyte-Derived Ones for the Expansion of Regulatory T Cells in the Macaque

Preclinical Assessment of Autologous Tolerogenic Dendritic Cells From End-stage Renal Disease Patients

BACKGROUND

Kidney transplantation is the therapeutic of choice for patients with kidney failure. While immunosuppressive drugs can control graft rejection, their use is associated with increased infections and cancer, and they do not effectively control chronic graft rejection. Cell therapy is an attractive strategy to minimize the use of pharmacological drugs.

METHODS

We recently developed a protocol to generate human monocyte-derived autologous tolerogenic dendritic cells (ATDCs) from healthy volunteers. Herein, we transferred the ATDC manufacturing protocol to a Good Manufacturing Practice (GMP)-compliant facility. Furthermore, we compared the phenotype and in vitro functions of ATDCs generated from patients with end-stage renal disease to those generated from healthy volunteers.

RESULTS

We describe the critical steps for GMP-compliant production of ATDCs and define the quality criteria required to allow release of the cell products. Furthermore, we showed that ATDCs generated from healthy volunteers and patients with kidney failure display the same tolerogenic profile based on their phenotype, resistance to maturation, and ability to modulate T-cell responses.

CONCLUSIONS

Together, these results allowed us to define the production process and the quality criteria for the release of ATDCs before their administration in patients receiving a kidney transplant.

Non-human Primate Regulatory T Cells and Their Assessment as Cellular Therapeutics in Preclinical Transplantation Models

Non-human primates (NHP) are an important resource for addressing key issues regarding the immunobiology of regulatory T cells (Treg), their in vivo manipulation and the translation of adoptive Treg therapy to clinical application. In addition to their phenotypic and functional characterization, particularly in cynomolgus and rhesus macaques, NHP Treg have been isolated and expanded successfully ex vivo. Their numbers can be enhanced in vivo by administration of IL-2 and other cytokines. Both polyclonal and donor antigen (Ag) alloreactive NHP Treg have been expanded ex vivo and their potential to improve long-term outcomes in organ transplantation assessed following their adoptive transfer in combination with various cytoreductive, immunosuppressive and "Treg permissive" agents. In addition, important insights have been gained into the in vivo fate/biodistribution, functional stability, replicative capacity and longevity of adoptively-transferred Treg in monkeys. We discuss current knowledge of NHP Treg immunobiology, methods for their in vivo expansion and functional validation, and results obtained testing their safety and efficacy in organ and pancreatic islet transplantation models. We compare and contrast results obtained in NHP and mice and also consider prospects for future, clinically relevant studies in NHP aimed at improved understanding of Treg biology, and innovative approaches to promote and evaluate their therapeutic potential.

Generation and functional assessment of nonhuman primate regulatory dendritic cells and their therapeutic efficacy in renal transplantation

Nonhuman primates (NHP) are important pre-clinical models for evaluation of the safety and efficacy of the most promising potential therapeutic advances in organ transplantation based on rodent studies. Although rare, dendritic cells (DC) play important roles in preservation of self tolerance and DC with immunoregulatory properties (regulatory DC; DCreg) can promote transplant tolerance in rodents when adoptively transferred to allograft recipients. NHP DCreg can be generated ex vivo from bone marrow precursors or blood monocytes of cynomolgus or rhesus macaques or baboons. NHP DCreg generated in the presence of anti-inflammatory factors that confer stability and resistance to maturation, subvert alloreactive T cell responses. When infused into rhesus renal allograft recipients before transplant, they safely prolong MHC mis-matched graft survival, associated with attenuation of anti-donor immune reactivity. In this concise review we describe the properties of NHP DCreg and discuss their influence on T cell responses, alloimmunity and organ transplant survival.

Role of myeloid regulatory cells (MRCs) in maintaining tissue homeostasis and promoting tolerance in autoimmunity, inflammatory disease and transplantation

Myeloid cells play a pivotal role in regulating innate and adaptive immune responses. In inflammation, autoimmunity, and after transplantation, myeloid cells have contrasting roles: on the one hand they initiate the immune response, promoting activation and expansion of effector T-cells, and on the other, they counter-regulate inflammation, maintain tissue homeostasis, and promote tolerance. The latter activities are mediated by several myeloid cells including polymorphonuclear neutrophils, macrophages, myeloid-derived suppressor cells, and dendritic cells. Since these cells have been associated with immune suppression and tolerance, they will be further referred to as myeloid regulatory cells (MRCs). In recent years, MRCs have emerged as a therapeutic target or have been regarded as a potential cellular therapeutic product for tolerance induction. However, several open questions must be addressed to enable the therapeutic application of MRCs including: how do they function at the site of inflammation, how to best target these cells to modulate their activities, and how to isolate or to generate pure populations for adoptive cell therapies. In this review, we will give an overview of the current knowledge on MRCs in inflammation, autoimmunity, and transplantation. We will discuss current strategies to target MRCs and to exploit their tolerogenic potential as a cell-based therapy.

Renal Allograft Survival in Nonhuman Primates Infused With Donor Antigen-Pulsed Autologous Regulatory Dendritic Cells

Systemic administration of autologous regulatory dendritic cells (DCreg; unpulsed or pulsed with donor antigen [Ag]), prolongs allograft survival and promotes transplant tolerance in rodents. Here, we demonstrate that nonhuman primate (NHP) monocyte-derived DCreg preloaded with cell membrane vesicles from allogeneic peripheral blood mononuclear cells induce T cell hyporesponsiveness to donor alloantigen (alloAg) in vitro. These donor alloAg-pulsed autologous DCreg (1.4-3.6 × 10⁶ /kg) were administered intravenously, 1 day before MHC-mismatched renal transplantation to rhesus monkeys treated with costimulation blockade (cytotoxic T lymphocyte Ag 4 immunoglobulin [CTLA4] Ig) and tapered rapamycin. Prolongation of graft median survival time from 39.5 days (no DCreg infusion; n = 6 historical controls) and 29 days with control unpulsed DCreg (n = 2), to 56 days with donor Ag-pulsed DCreg (n = 5) was associated with evidence of modulated host CD4⁺ and CD8⁺ T cell responses to donor Ag and attenuation of systemic IL-17 production. Circulating anti-donor antibody (Ab) was not detected until CTLA4 Ig withdrawal. One monkey treated with donor Ag-pulsed DCreg rejected its graft in association with progressively elevated anti-donor Ab, 525 days posttransplant (160 days after withdrawal of immunosuppression). These findings indicate a modest but not statistically significant beneficial effect of donor Ag-pulsed autologous DCreg infusion on NHP graft survival when administered with a minimal immunosuppressive drug regimen.

Orchestration of transplantation tolerance by regulatory dendritic cell therapy or in-situ targeting of dendritic cells

PURPOSE OF REVIEW

Extensive research in murine transplant models over the past two decades has convincingly demonstrated the ability of regulatory dendritic cells (DCregs) to promote long-term allograft survival. We review important considerations regarding the source of therapeutic DCregs (donor or recipient) and their mode of action, in-situ targeting of DCregs, and optimal therapeutic regimens to promote DCreg function.

RECENT FINDINGS

Recent studies have defined protocols and mechanisms whereby ex-vivo-generated DCregs of donor or recipient origin subvert allogeneic T-cell responses and promote long-term organ transplant survival. Particular interest has focused on how donor antigen is acquired, processed and presented by autologous dendritic cells, on the stability of DCregs, and on in-situ targeting of dendritic cells to promote their tolerogenic function. New evidence of the therapeutic efficacy of DCregs in a clinically relevant nonhuman primate organ transplant model and production of clinical grade DCregs support early evaluation of DCreg therapy in human graft recipients.

SUMMARY

We discuss strategies currently used to promote dendritic cell tolerogenicity, including DCreg therapy and in-situ targeting of dendritic cells, with a view to improved understanding of underlying mechanisms and identification of the most promising strategies for therapeutic application.

Generation and in vivo evaluation of IL10-treated dendritic cells in a nonhuman primate model of AAV-based gene transfer

Preventing untoward immune responses against a specific antigen is a major challenge in different clinical settings such as gene therapy, transplantation, or autoimmunity. Following intramuscular delivery of recombinant adeno-associated virus (rAAV)-derived vectors, transgene rejection can be a roadblock to successful clinical translation. Specific immunomodulation strategies potentially leading to sustained transgene expression while minimizing pharmacological immunosuppression are desirable. Tolerogenic dendritic cells (TolDC) are potential candidates but have not yet been evaluated in the context of gene therapy, to our knowledge. Following intramuscular delivery of rAAV-derived vectors expressing an immunogenic protein in the nonhuman primate model, we assessed the immunomodulating potential of autologous bone marrow-derived TolDC generated in the presence of IL10 and pulsed with the transgene product. TolDC administered either intradermally or intravenously were safe and well tolerated. While the intravenous route showed a modest ability to modulate host immunity against the transgene product, intradermally delivery resulted in a robust vaccination of the macaques when associated to intramuscular rAAV-derived vectors-based gene transfer. These findings demonstrate the critical role of TolDC mode of injection in modulating host immunity. This study also provides the first evidence of the potential of TolDC-based immunomodulation in gene therapy.

Negative vaccination by tolerogenic dendritic cells in organ transplantation

PURPOSE OF REVIEW

We discussed the use of autologous tolerogenic dendritic cell (Tol-DC) therapy in organ transplantation, with a particular emphasis on illustrating the reasons why it is a clinically relevant approach and interpreting the experimental data that support this strategy.

RECENT FINDINGS

Various parameters are critical for engineering Tol-DCs as a therapeutic tool to manipulate antigen-specific immune responses. Our group has shown that in rats, mice and nonhuman primates, bone marrow progenitors cultured with low doses of granulocyte macrophage colony-stimulating factor can generate Tol-DCs. Injection of autologous Tol-DCs (the same strain as the recipient) is able to significantly prolong allograft survival. Autologous Tol-DCs are more effective than allogeneic Tol-DCs in prolonging allograft survival. Although the reason of this difference remains unclear, it indicates the practical advantages of autologous Tol-DCs as a therapeutic tool in a clinical setting. When autologous Tol-DCs (not pulsed with donor antigens) are administered along with suboptimal immunosuppression treatment, a synergistic effect is achieved, resulting in donor-specific allograft tolerance.

SUMMARY

Autologous Tol-DC therapy is a promising approach to improve long-term allograft survival. This strategy may also help reduce the immunosuppressive load in grafted patients and, therefore, limit the harmful effects of immunosuppressive agents.

Regulatory dendritic cell infusion prolongs kidney allograft survival in nonhuman primates

We examined the influence of regulatory dendritic cells (DCreg), generated from cytokine-mobilized donor blood monocytes in vitamin D3 and IL-10, on renal allograft survival in a clinically relevant rhesus macaque model. DCreg expressed low MHC class II and costimulatory molecules, but comparatively high levels of programmed death ligand-1 (B7-H1), and were resistant to pro-inflammatory cytokine-induced maturation. They were infused intravenously (3.5-10 × 10(6) /kg), together with the B7-CD28 costimulation blocking agent CTLA4Ig, 7 days before renal transplantation. CTLA4Ig was given for up to 8 weeks and rapamycin, started on Day -2, was maintained with tapering of blood levels until full withdrawal at 6 months. Median graft survival time was 39.5 days in control monkeys (no DC infusion; n = 6) and 113.5 days (p < 0.05) in DCreg-treated animals (n = 6). No adverse events were associated with DCreg infusion, and there was no evidence of induction of host sensitization based on circulating donor-specific alloantibody levels. Immunologic monitoring also revealed regulation of donor-reactive memory CD95(+) T cells and reduced memory/regulatory T cell ratios in DCreg-treated monkeys compared with controls. Termination allograft histology showed moderate combined T cell- and Ab-mediated rejection in both groups. These findings justify further preclinical evaluation of DCreg therapy and their therapeutic potential in organ transplantation.

Human tolerogenic DC-10: perspectives for clinical applications

Dendritic cells (DCs) are critically involved in inducing either immunity or tolerance. During the last decades efforts have been devoted to the development of ad hoc methods to manipulate DCs in vitro to enhance or stabilize their tolerogenic properties. Addition of IL-10 during monocyte-derived DC differentiation allows the induction of DC-10, a subset of human tolerogenic DCs characterized by high IL-10/IL-12 ratio and co-expression of high levels of the tolerogenic molecules HLA-G and immunoglobulin-like transcript 4. DC-10 are potent inducers of adaptive type 1 regulatory T cells, well known to promote and maintain peripheral tolerance. In this review we provide an in-depth comparison of the phenotype and mechanisms of suppression mediated by DC-10 and other known regulatory antigen-presenting cells currently under clinical development. We discuss the clinical therapeutic application of DC-10 as inducers of type 1 regulatory T cells for tailoring regulatory T-cell-based cell therapy, and the use of DC-10 as adoptive cell therapy for promoting and restoring tolerance in T-cell-mediated diseases.

Tolerogenic dendritic cells and negative vaccination in transplantation: from rodents to clinical trials

The use of immunosuppressive (IS) drugs to treat transplant recipients has markedly reduced the incidence of acute rejection and early graft loss. However, such treatments have numerous adverse side effects and fail to prevent chronic allograft dysfunction. In this context, therapies based on the adoptive transfer of regulatory cells are promising strategies to induce indefinite transplant survival. The use of tolerogenic dendritic cells (DC) has shown great potential, as preliminary experiments in rodents have demonstrated that administration of tolerogenic DC prolongs graft survival. Recipient DC, Donor DC, or Donor Ag-pulsed recipient DC have been used in preclinical studies and administration of these cells with suboptimal immunosuppression increases their tolerogenic potential. We have demonstrated that autologous unpulsed tolerogenic DC injected in the presence of suboptimal immunosuppression are able to induce Ag-specific allograft tolerance. We derived similar tolerogenic DC in different animal models (mice and non-human primates) and confirmed their protective abilities in vitro and in vivo. The mechanisms involved in the tolerance induced by autologous tolerogenic DC were also investigated. With the aim of using autologous DC in kidney transplant patients, we have developed and characterized tolerogenic monocyte-derived DC in humans. In this review, we will discuss the preclinical studies and describe our recent results from the generation and characterization of tolerogenic monocyte-derived DC in humans for a clinical application. We will also discuss the limits and difficulties in translating preclinical experiments to theclinic.

IL-10 deficiency blocks the ability of LPS to regulate expression of tolerance-related molecules on dendritic cells

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that plays an important role in regulating the local inflammatory immune response, but regulatory mechanisms of this cytokine have not been fully elucidated. Here, we demonstrate that IL-10 deficiency renders LPS treatment ineffective in regulating the expression of CD40, CD80, CD86, B7-H2, and B7-DC on dendritic cells (DCs) and blocks upregulation of IL-27. This inability to respond to LPS was found in both IL-10(-/-) bone marrow derived and splenic DCs. Compared with wild-type DCs, IL-10(-/-) DCs expressed similar levels of TLR4 and CD14, but produced less LPS-binding protein. The deficiency in LPS-binding protein production may explain the failure of IL-10(-/-) DCs to respond normally to LPS. Moreover, lack of IL-10 modulated the proportions of CD11c(+) CD8(+) and CD11c(+) B220(+) DCs, which play an important role in local inflammatory responses and tolerance. IL-10 deficiency also blocked expression of galectin-1, CD205, and CD103, which are necessary for central and peripheral tolerance. While they did not respond to LPS, IL-10(-/-) DCs produced increased levels of IL-6 and CCL4 after TNF-α treatment. Together, our results demonstrate that IL-10 deficiency affects the immune functions of DCs, which may contribute to the increased severity of autoimmune diseases seen in IL-10(-/-) mice.

Therapeutic potential of semi-mature dendritic cells for tolerance induction

Dendritic cells (DCs) are major players in the control of adaptive tolerance and immunity. Therefore, their specific generation and adoptive transfer into patients or their in vivo targeting is attractive for clinical applications. While injections of mature immunogenic DCs are tested in clinical trials, tolerogenic DCs still are awaiting this step. Besides the tolerogenic potential of immature DCs, also semi-mature DCs can show tolerogenic activity but both types also bear unfavorable features. Optimal tolerogenic DCs, their molecular tool bar, and their use for specific diseases still have to be defined. Here, the usefulness of in vitro generated and adoptively transferred semi-mature DCs for tolerance induction is outlined. The in vivo targeting of semi-mature DCs as represented by steady state migratory DCs are discussed for treatment of autoimmune diseases and allergies. First clinical trials with transcutaneous allergen application may point to their therapeutic use in the future.

Non-human primate dendritic cells

Non-human primates (NHP) are essential translational models for biomedical research. Dendritic cells (DC) are a group of antigen presenting cells (APC) that play pivotal roles in the immunobiology of health and disease and are attractive cells for adoptive immunotherapy to stimulate and suppress immunity. DC have been studied extensively in humans and mice but until recently, have not been well characterized in NHP. This review considers the available data about DC across a range of NHP species and summarizes the understanding of in vitro-propagated DC and in vivo-isolated DC, which is now established. It is clear that although NHP DC exist within the paradigm of human DC, there are important functional and phenotypic differences when compared with human DC subsets. These differences need to be taken into account when designing preclinical, translational studies of DC therapy using NHP models.

Non-human primate regulatory T cells: current biology and implications for transplantation

Regulatory T cells (Treg) offer potential for improving long-term outcomes in cell and organ transplantation. The non-human primate model is a valuable resource for addressing issues concerning the transfer of Treg therapy to the clinic. Herein, we discuss the properties of non-human primate Treg and prospects for their evaluation in allotransplantation and xenotransplantation.

Injection of donor-derived OX62+ splenic dendritic cells with anti-CD4 monoclonal antibody generates CD4+CD25+FOXP3+ regulatory T cells that prolong allograft skin survival indefinitely and abrogate production of donor-specific antibodies in a rat model

OBJECTIVE

To examine in a rat model the ability of donor dendritic cells and anti-CD4 monoclonal antibody (mAb) to generate donor-specific CD4+CD25+ regulatory T cells (Tregs) and to evaluate the capacity of these Tregs to prolong skin allograft survival and abrogate the production of donor-specific antibodies after skin grafting.

MATERIALS AND METHODS

OX62+ (nonplasmacytoid) splenic dendritic cells were isolated from Fischer rats using magnetic beads and injected (2 x 10(6)) into Lewis rat recipients with or without treatment with a nondepleting anti-CD4 (W3/25) mAb. After 4 weeks, splenic CD4+CD25+FOXP3+ T cells were harvested using magnetic beads from conditioned animals and injected (1 x 10(6)) into naïve Lewis recipients (day 1) before they received a skin graft from a Fischer (n = 4) or a third-party (Norway; n = 4) donor rat. Donor-specific antibodies were detected in recipient blood using flow cytometric cross-matches with donor lymphocytes from day 0 to day 30 after grafting.

RESULTS

After injection of conditioned CD4+CD25+FOXP3+ T cells, Lewis recipients accepted skin grafts from Fischer donors indefinitely (>100 days) but rejected third-party skin grafts. Donor-specific antibodies were detected at low levels in only 1 recipient receiving conditioned Tregs before grafting. Naive Tregs did not prolong skin graft survival.

CONCLUSION

These preliminary data suggest that splenic dendritic cells in combination with an anti-CD4 mAb induce donor-specific Tregs that indefinitely prolong allogeneic skin graft survival and inhibit donor-specific antibody production. Experiments are under way to determine whether this protocol can inhibit chronic lesions after heart transplantation in this model.

Rhesus monkey immature monocyte-derived dendritic cells generate alloantigen-specific regulatory T cells from circulating CD4+CD127-/lo T cells

BACKGROUND

Generation of non-human primate regulatory T cells (Treg) with alloantigen (alloAg) specificity would allow their testing in preclinical transplant models. Low recovery of Treg from peripheral blood limits their potential utility. In small animals and humans, conventional myeloid dendritic cells (DC) have been shown to select or induce alloAg-specific Treg.

METHODS

We combined enrichment of rhesus macaque blood CD4 Treg based on IL-7Ralpha (CD127) expression with their stimulation in mixed leukocyte cultures with immature, allogeneic control or vitamin (Vit) D3/IL-10-conditioned monocyte-derived DC. After co-culture in IL-2 and IL-15 for up to 14 days, the ability of the resulting T cells to suppress alloreactive effector T-cell proliferation was assessed.

RESULTS

CD4CD127 T cells represented approximately 7% of normal rhesus circulating CD4 T cells and were enriched for forkhead box P3 (Foxp3) cells. When stimulated with control allogeneic DC, they exhibited much inferior proliferative responses compared with bulk CD4 or CD4CD127 cells. This anergic state was reversed by exogenous IL-2 and IL-15. After 10 to 14 days culture of CD4CD127 T cells with immature allogeneic DC, particularly maturation-resistant VitD3/IL-10 DC, the frequency of Foxp3 T cells was increased. The cultured cells markedly inhibited CD4 effector T-cell proliferation in a dose-related and donor alloAg-specific manner.

CONCLUSION

Stimulation of rhesus CD4CD127 T cells with immature and especially maturation-resistant allogeneic DC, generated highly-suppressive, alloAg-specific Treg. Without resorting to a more purified starting population, this approach may have therapeutic utility in clinically relevant transplant models.

Preparation of mouse bone marrow-derived dendritic cells with immunoregulatory properties

Tolerogenic dendritic cells (Tol-DCs) are critical players in physiological tolerance. Moreover, they also play a role in immune regulation both in a pathophysiological context and when used as therapeutic tools in cell therapy strategies. Here, we describe a protocol to differentiate murine Tol-DCs from bone marrow precursors in vitro. Importantly, Tol-DCs actively suppress T cells stimulated with immunogenic allogeneic DCs. Indeed, Tol-DCs generated using this approach can be useful in studying and characterising the immunoregulatory pathways of Tol-DC and in developing Tol-DC-based cell therapy protocols using in vivo models.

Tolerogenic dendritic cell-regulatory T-cell interaction and the promotion of transplant tolerance

Evidence has accumulated that targeting of donor alloantigen to quiescent dendritic cells (DC) in situ or adoptive DC therapy is associated with the expansion or induction of regulatory T cells (Treg) in experimental organ transplantation. These Treg can mediate suppression of antidonor T-effector cell responses and promote allograft tolerance. In addition, Treg can exert reciprocal, inhibitory effects on DC that maintain their tolerogenic properties. Several groups have exploited DC to expand allo-Ag-specific Treg in vitro, followed by adoptive transfer of the Treg to graft recipients, an approach that holds promise for tolerogenic cell therapy in clinical cell and organ transplantation.

Regulation of rat and human T-cell immune response by pharmacologically modified dendritic cells

BACKGROUND

The central function of dendritic cells (DC) in inducing and preventing immune responses makes them ideal therapeutic targets for the induction of immunologic tolerance. In a rat in vivo model, we showed that dexamethasone-treated DC (Dex-DC) induced indirect pathway-mediated regulation and that CD4+CD25+ T cells were involved in the observed effects. The aim of the present study was to investigate the mechanisms underlying the acquired immunoregulatory properties of Dex-DC in the rat and human experimental systems.

METHODS

After treatment with dexamethasone (Dex), the immunogenicity of Dex-DC was analyzed in T-cell proliferation and two-step hyporesponsiveness induction assays. After carboxyfluorescein diacetate succinimidyl ester labeling, CD4+CD25+ regulatory T-cell expansion was analyzed by flow cytometry, and cytokine secretion was measured by ELISA.

RESULTS

In this study, we demonstrate in vitro that rat Dex-DC induced selective expansion of CD4+CD25+ regulatory T cells, which were responsible for alloantigen-specific hyporesponsiveness. The induction of regulatory T-cell division by rat Dex-DC was due to secretion of interleukin (IL)-2 by DC. Similarly, in human studies, monocyte-derived Dex-DC were also poorly immunogenic, were able to induce T-cell anergy in vitro, and expand a population of T cells with regulatory functions. This was accompanied by a change in the cytokine profile in DC and T cells in favor of IL-10.

CONCLUSION

These data suggest that Dex-DC induced tolerance by different mechanisms in the two systems studied. Both rat and human Dex-DC were able to induce and expand regulatory T cells, which occurred in an IL-2 dependent manner in the rat system.