Marked prolongation of cardiac allograft survival by dendritic cells genetically engineered with NF-kappa B oligodeoxyribonucleotide decoys and adenoviral vectors encoding CTLA4-Ig

Immune modulation in transplant medicine: a comprehensive review of cell therapy applications and future directions

Balancing the immune response after solid organ transplantation (SOT) and vascularized composite allotransplantation (VCA) remains an ongoing clinical challenge. While immunosuppressants can effectively reduce acute rejection rates following transplant surgery, some patients still experience recurrent acute rejection episodes, which in turn may progress to chronic rejection. Furthermore, these immunosuppressive regimens are associated with an increased risk of malignancies and metabolic disorders. Despite significant advancements in the field, these IS related side effects persist as clinical hurdles, emphasizing the need for innovative therapeutic strategies to improve transplant survival and longevity. Cellular therapy, a novel therapeutic approach, has emerged as a potential pathway to promote immune tolerance while minimizing systemic side-effects of standard IS regiments. Various cell types, including chimeric antigen receptor T cells (CAR-T), mesenchymal stromal cells (MSCs), regulatory myeloid cells (RMCs) and regulatory T cells (Tregs), offer unique immunomodulatory properties that may help achieve improved outcomes in transplant patients. This review aims to elucidate the role of cellular therapies, particularly MSCs, T cells, Tregs, RMCs, macrophages, and dendritic cells in SOT and VCA. We explore the immunological features of each cell type, their capacity for immune regulation, and the prospective advantages and obstacles linked to their application in transplant patients. An in-depth outline of the current state of the technology may help SOT and VCA providers refine their perioperative treatment strategies while laying the foundation for further trials that investigate cellular therapeutics in transplantation surgery.

Emerging roles of MITF as a crucial regulator of immunity

Microphthalmia-associated transcription factor (MITF), a basic helix-loop-helix leucine zipper transcription factor (bHLH-Zip), has been identified as a melanocyte-specific transcription factor and plays a critical role in melanocyte survival, differentiation, function, proliferation and pigmentation. Although numerous studies have explained the roles of MITF in melanocytes and in melanoma development, the function of MITF in the hematopoietic or immune system-beyond its function in melanin-producing cells-is not yet fully understood. However, there is convincing and increasing evidence suggesting that MITF may play multiple important roles in immune-related cells. Therefore, this review is focused on recent advances in elucidating novel functions of MITF in cancer progression and immune responses to cancer. In particular, we highlight the role of MITF as a central modulator in the regulation of immune responses, as elucidated in recent studies.

Dendritic cells in liver transplantation immune response

Dendritic cells (DCs) are the most powerful antigen presenting cells (APCs), they are considered one of the key regulatory factors in the liver immune system. There is currently much interest in modulating DC function to improve transplant immune response. In liver transplantation, DCs participate in both the promotion and inhibition of the alloreponse by adopting different phenotypes and function. Thus, in this review, we discussed the origin, maturation, migration and pathological effects of several DC subsets, including the conventional DC (cDC), plasmacytoid DC (pDC) and monocyte-derived DC (Mo-DC) in liver transplantation, and we summarized the roles of these DC subsets in liver transplant rejection and tolerance. In addition, we also outlined the latest progress in DC-based related treatment regimens. Overall, our discussion provides a beneficial resource for better understanding the biology of DCs and their manipulation to improve the immune adaptability of patients in transplant status.

Innate immune cellular therapeutics in transplantation

Successful organ transplantation provides an opportunity to extend the lives of patients with end-stage organ failure. Selectively suppressing the donor-specific alloimmune response, however, remains challenging without the continuous use of non-specific immunosuppressive medications, which have multiple adverse effects including elevated risks of infection, chronic kidney injury, cardiovascular disease, and cancer. Efforts to promote allograft tolerance have focused on manipulating the adaptive immune response, but long-term allograft survival rates remain disappointing. In recent years, the innate immune system has become an attractive therapeutic target for the prevention and treatment of transplant organ rejection. Indeed, contemporary studies demonstrate that innate immune cells participate in both the initial alloimmune response and chronic allograft rejection and undergo non-permanent functional reprogramming in a phenomenon termed "trained immunity." Several types of innate immune cells are currently under investigation as potential therapeutics in transplantation, including myeloid-derived suppressor cells, dendritic cells, regulatory macrophages, natural killer cells, and innate lymphoid cells. In this review, we discuss the features and functions of these cell types, with a focus on their role in the alloimmune response. We examine their potential application as therapeutics to prevent or treat allograft rejection, as well as challenges in their clinical translation and future directions for investigation.

Harnessing the Therapeutic Potential of Decoys in Non-Atherosclerotic Cardiovascular Diseases: State of the Art

Cardiovascular disease (CVD) is the main cause of global death, highlighting the fact that conventional therapeutic approaches for the treatment of CVD patients are insufficient, and there is a need to develop new therapeutic approaches. In recent years, decoy technology, decoy oligodeoxynucleotides (ODN), and decoy peptides show promising results for the future treatment of CVDs. Decoy ODN inhibits transcription by binding to the transcriptional factor, while decoy peptide neutralizes receptors by binding to the ligands. This review focused on studies that have investigated the effects of decoy ODN and decoy peptides on non-atherosclerotic CVD.

Cellular therapies in organ transplantation

Cellular therapy is a promising tool for improving the outcome of organ transplantation. Various cell types with different immunoregulatory and regenerative properties may find application for specific transplant rejection or injury-related indications. The current era is crucial for the development of cellular therapies. Preclinical models have demonstrated the feasibility of efficacious cell therapy in transplantation, early clinical trials have shown safety of several of these therapies, and the first steps towards efficacy studies in humans have been made. In this review, we address the current state of the art of cellular therapies in clinical transplantation and discuss monitoring tools and endpoints for these studies.

DiR-labeled tolerogenic dendritic cells for targeted imaging in collagen- induced arthritis rats

Tolerogenic dendritic cells (tolDCs) are immunosuppressive cells and play an important role in rheumatoid arthritis (RA) as immunotherapeutic tools. We aimed to investigate whether allogeneic tolDCs (allo-tolDCs) and autologous tolDCs (auto-tolDCs) had long-time tolerogenic potential in vivo and improve arthritis in collagen-induced arthritis (CIA) rats. TolDCs were induced by NF-κB Decoy ODN, and loaded with Bovine Type II collagen (CII- loaded tolDCs) and identified by flow cytometry, and labeled with DiR and injected into CIA rats. The biodistribution of DiR-labeled tolDCs was monitored by IVIS imaging at different time points. Major organs were harvested and analyzed by ex-in vivo cell imaging. The tolDCs were successfully constructed, along with expressing low levels of CD80 and CD86 compared to DCs. The fluorescent signals of all DiR (+) groups were observed at least 25 days, and as long as 35 days. DiR (+) CII- loaded allo-and auto-tolDCs at post injection mainly distributed in the chest and abdomen and gradually moved to limb joints over time. The allo- and auto-tolDCs decreased the expression of IFN-γ and IL-2 in CIA rats with different severity compared to CIA rats without tolDCs treatment, while significantly increased the expression of IL-4 and IL-10. Additionally, these tolDCs ameliorated the ankle joints injury in CIA rats with different severity. The both allo- and auto-tolDCs showed long-time tolerogenic potential in vivo and ameliorated arthritis in CIA rats with different severity.

Donor myeloid derived suppressor cells (MDSCs) prolong allogeneic cardiac graft survival through programming of recipient myeloid cells in vivo

Solid organ transplantation is a lifesaving therapy for patients with end-organ disease. Current immunosuppression protocols are not designed to target antigen-specific alloimmunity and are uncapable of preventing chronic allograft injury. As myeloid-derived suppressor cells (MDSCs) are potent immunoregulatory cells, we tested whether donor-derived MDSCs can protect heart transplant allografts in an antigen-specific manner. C57BL/6 (H2K^b, I-A^b) recipients pre-treated with BALB/c MDSCs were transplanted with either donor-type (BALB/c, H2K^d, I-A^d) or third-party (C3H, H2K^k, I-A^k) cardiac grafts. Spleens and allografts from C57BL/6 recipients were harvested for immune phenotyping, transcriptomic profiling and functional assays. Single injection of donor-derived MDSCs significantly prolonged the fully MHC mismatched allogeneic cardiac graft survival in a donor-specific fashion. Transcriptomic analysis of allografts harvested from donor-derived MDSCs treated recipients showed down-regulated proinflammatory cytokines. Immune phenotyping showed that the donor MDSCs administration suppressed effector T cells in recipients. Interestingly, significant increase in recipient endogenous CD11b⁺Gr1⁺ MDSC population was observed in the group treated with donor-derived MDSCs compared to the control groups. Depletion of this endogenous MDSCs with anti-Gr1 antibody reversed donor MDSCs-mediated allograft protection. Furthermore, we observed that the allogeneic mixed lymphocytes reaction was suppressed in the presence of CD11b⁺Gr1⁺ MDSCs in a donor-specific manner. Donor-derived MDSCs prolong cardiac allograft survival in a donor-specific manner via induction of recipient's endogenous MDSCs.

Tolerogenic dendritic cells in organ transplantation

Dendritic cells (DCs) are specialized cells of the innate immune system that are characterized by their ability to take up, process and present antigens (Ag) to effector T cells. They are derived from DC precursors produced in the bone marrow. Different DC subsets have been described according to lineage-specific transcription factors required for their development and function. Functionally, DCs are responsible for inducing Ag-specific immune responses that mediate organ transplant rejection. Consequently, to prevent anti-donor immune responses, therapeutic strategies have been directed toward the inhibition of DC activation. In addition however, an extensive body of preclinical research, using transplant models in rodents and nonhuman primates, has established a central role of DCs in the negative regulation of alloimmune responses. As a result, DCs have been employed as cell-based immunotherapy in early phase I/II clinical trials in organ transplantation. Together with in vivo targeting through use of myeloid cell-specific nanobiologics, DC manipulation represents a promising approach for the induction of transplantation tolerance. In this review, we summarize fundamental characteristics of DCs and their roles in promotion of central and peripheral tolerance. We also discuss their clinical application to promote improved long-term outcomes in organ transplantation.

Regulatory dendritic cells for human organ transplantation

Current immunosuppressive (IS) regimens used to prevent organ allograft rejection have well-recognized side effects, that include enhanced risk of infection and certain types of cancer, metabolic disorders, cardiovascular disease, renal complications and failure to control chronic allograft rejection. The life-long dependency of patients on these IS agents reflects their inability to induce donor-specific tolerance. Extensive studies in rodent and non-human primate models have demonstrated the ability of adoptively-transferred regulatory immune cells (either regulatory myeloid cells or regulatory T cells) to promote transplant tolerance. Consequently, there is considerable interest in the potential of regulatory immune cell therapy to allow safe minimization/complete withdrawal of immunosuppression and the promotion of organ transplant tolerance in the clinic. Here, we review the properties of regulatory dendritic cells (DCreg) with a focus on the approaches being taken to generate human DCreg for clinical testing. We also document the early phase clinical trials that are underway to assess DCreg therapy in clinical organ transplantation as well as in autoimmune disorders.

Amelioration of collagen-induced arthritis using antigen-loaded dendritic cells modified with NF-κB decoy oligodeoxynucleotides

Dendritic cells (DCs) play an important role in the initiation of autoimmunity in rheumatoid arthritis (RA); therefore, the use of DCs needs to be explored to develop new therapeutic approaches for RA. Here, we investigated the therapeutic effect of bovine type II collagen (BIIC)-loaded DCs modified with NF-κB decoy oligodeoxynucleotides (ODNs) on collagen-induced arthritis (CIA) in rats and explored the underlying mechanisms. DCs treated with BIIC and NF-κB decoy ODNs exhibited features of immature DCs with low levels of costimulatory molecule (CD80 and CD86) expression. The development of arthritis in rats with CIA injected with BIIC + NF-κB decoy ODN-propagated DCs (BIIC-decoy DCs) was significantly ameliorated compared to that in rats injected with BIIC-propagated DCs or phosphate-buffered saline. We also found that the BIIC-decoy DCs exerted antiarthritis effects by inhibiting self-lymphocyte proliferative response and suppressing IFN-γ and anti-BIIC antibody production and inducing IL-10 antibody production. Additionally, antihuman serum antibodies were successfully produced in the rats treated with BIIC-decoy DCs but not in those treated with NF-κB decoy ODN-propagated DCs; moreover, the BIIC-decoy DCs did not affect immune function in the normal rats. These findings suggested that NF-κB decoy ODN-modified DCs loaded with a specific antigen might offer a practical method for the treatment of human RA.

iPSC-Derived Regulatory Dendritic Cells Inhibit Allograft Rejection by Generating Alloantigen-Specific Regulatory T Cells

Regulatory dendritic cell (DCregs)-based immunotherapy is a potential therapeutic tool for transplant rejection. We generated DCregs from murine induced pluripotent stem cells (iPSCs), which could remain in a “stable immature stage” even under strong stimulation. Harnessing this characteristic, we hypothesized that iPS-DCregs worked as a negative vaccine to generate regulatory T cells (Tregs), and induced donor-specific allograft acceptance. We immunized naive CBA (H-2K^k) mice with B6 (H-2K^b) iPS-DCregs and found that Tregs (CD4⁺CD25⁺FOXP3⁺) significantly increased in CBA splenocytes. Moreover, immunized CBA recipients permanently accepted B6 cardiac grafts in a donor-specific pattern. We demonstrated mechanistically that donor-type iPS-DCregs triggered transforming growth factor β1 secretion, under which the donor-antigen peptides directed naive CD4⁺ T cells to differentiate into donor-specific FOXP3⁺ Tregs instead of into effector T cells in vivo. These findings highlight the potential of iPS-DCregs as a key cell therapy resource in clinical transplantation.

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iPS-DCregs keep in stable immature stage that makes them a powerful cellular vaccine

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Donor-type iPS-DCregs lead to permanent acceptance of allogeneic cardiac grafts

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iPS-DCregs reduce CTL and downregulate proinflammatory cytokine

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iPS-DCregs enhance Tregs transmigration capability in a TGF-β1-dependent manner

Harnessing the properties of dendritic cells in the pursuit of immunological tolerance

The acquisition of self-perpetuating, immunological tolerance specific for graft alloantigens has long been described as the "holy grail" of clinical transplantation. By removing the need for life-long immunosuppression following engraftment, the adverse consequences of immunosuppressive regimens, including chronic infections and malignancy, may be avoided. Furthermore, autoimmune diseases and allergy are, by definition, driven by aberrant immunological responses to ordinarily innocuous antigens. The re-establishment of permanent tolerance towards instigating antigens may, therefore, provide a cure to these common diseases. Whilst various cell types exhibiting a tolerogenic phenotype have been proposed for such a task, tolerogenic dendritic cells (tol-DCs) are exquisitely adapted for antigen presentation and interact with many facets of the immune system: as such, they are attractive candidates for use in strategies for immune intervention. We review here our current understanding of tol-DC mediated induction and maintenance of immunological tolerance. Additionally, we discuss recent in vitro findings from animal models and clinical trials of tol-DC immunotherapy in the setting of transplantation, autoimmunity and allergy which highlight their promising therapeutic potential, and speculate how tol-DC therapy may be developed in the future.

Effects of Adoptive Transfer of Tolerogenic Dendritic Cells on Allograft Survival in Organ Transplantation Models: An Overview of Systematic Reviews

Objective. To dissect the efficacy of Tol-DC therapy with or without IS in multiple animal models of transplantation. Methods and Results. PubMed, Medline, Embase, and the Cochrane Library were searched for reviews published up to April 2015. Six systematic reviews and a total of 61 articles were finally included. Data were grouped by organ transplantation models and applied to meta-analysis. Our meta-analysis shows that Tol-DC therapy successfully prolonged allograft survival to varying extents in all except the islet transplantation models and with IS drugs further prolonged the survival of heart, skin, and islet allografts in mice, but not of heart allografts in rats. Compared with IS drugs alone, Tol-DC therapy with IS extended islet allograft survival in rats but failed to influence the survival of skin, small intestine, and heart allografts in rats or of heart and skin allografts in mice. Conclusion. Tol-DC therapy significantly prolonged multiple allograft survival and further prolonged survival with IS. However, standardized protocols for modification of Tol-DC should be established before its application in clinic.

Prospective Clinical Testing of Regulatory Dendritic Cells in Organ Transplantation

Dendritic cells (DC) are rare, professional antigen-presenting cells with ability to induce or regulate alloimmune responses. Regulatory DC (DCreg) with potential to down-modulate acute and chronic inflammatory conditions that occur in organ transplantation can be generated in vitro under a variety of conditions. Here, we provide a rationale for evaluation of DCreg therapy in clinical organ transplantation with the goal of promoting sustained, donor-specific hyporesponsiveness, while lowering the incidence and severity of rejection and reducing patients’ dependence on anti-rejection drugs. Generation of donor- or recipient-derived DCreg that suppress T cell responses and prolong transplant survival in rodents or non-human primates has been well-described. Recently, good manufacturing practice (GMP)-grade DCreg have been produced at our Institution for prospective use in human organ transplantation. We briefly review experience of regulatory immune therapy in organ transplantation and describe our experience generating and characterizing human monocyte-derived DCreg. We propose a phase I/II safety study in which the influence of donor-derived DCreg combined with conventional immunosuppression on subclinical and clinical rejection and host alloimmune responses will be examined in detail.

The transcription factor MITF is a critical regulator of GPNMB expression in dendritic cells

BACKGROUND

Dendritic cells (DC) are the most potent antigen-presenting cells (APC) with the unique ability to activate naïve T cells and to initiate and maintain primary immune responses. Immunosuppressive and anti-inflammatory stimuli on DC such as the cytokine IL-10 suppress the activity of the transcription factor NF-κB what results in downregulation of costimulatory molecules, MHC and cytokine production. Glycoprotein NMB (GPNMB) is a transmembrane protein, which acts as a coinhibitory molecule strongly inhibiting T cell responses if present on APC. Interestingly, its expression on human monocyte-derived dendritic cells (moDC) is dramatically upregulated upon treatment with IL-10 but also by the BCR-ABL tyrosine kinase inhibitors (TKI) imatinib, nilotinib or dasatinib used for the treatment of chronic myeloid leukemia (CML). However, the molecular mechanisms responsible for GPNMB overexpression are yet unknown.

RESULTS

The immunosuppressive cytokine IL-10 and the BCR-ABL TKI imatinib or nilotinib, that were examined here, concordantly inhibit the PI3K/Akt signaling pathway, thereby activating the downstream serine/threonine protein kinase GSK3ß, and subsequently the microphthalmia-associated transcription factor (MITF) that is phosphorylated and translocated into the nucleus. Treatment of moDC with a small molecule inhibitor of MITF activity reduced the expression of GPNMB at the level of mRNA and protein, indicating that GPNMB expression is in fact facilitated by MITF activation. In line with these findings, PI3K/Akt inhibition was found to result in GPNMB overexpression accompanied by reduced stimulatory capacity of moDC in mixed lymphocyte reactions (MLR) with allogeneic T cells that could be restored by addition of the GPNMB T cell ligand syndecan-4 (SD-4).

CONCLUSIONS

In summary, imatinib, nilotinib or IL-10 congruently inhibit the PI3K/Akt signaling pathway thereby activating MITF in moDC, resulting in a tolerogenic phenotype. These findings extend current knowledge on the molecular mechanisms balancing activating and inhibitory signals in human DC and may facilitate the targeted manipulation of T cell responses in the context of DC-based immunotherapeutic interventions.

Construction and evaluation of rats' tolerogenic dendritic cells (DC) induced by NF-κB Decoy method

AIMS

To construct and evaluate rats' tolerogenic dendritic cells (DC) through induction by NF-κB Decoy method.

METHODS

GM-CSF and IL-4 were used to transform rats's monocytes into DC, and DC were stimulated with LPS, NF-κB Decoy ODN, and loaded with Bovine Type II Collagen. The following methods were employed to phenotype DC: 1) Observation of cell morphology; 2) Evaluation of cell viability using trypan blue staining; 3) Purity determination of DC through detection of specific markers OX-62; 4) Evaluation of mature state of DC via the determination of the expression of CD80 and CD86; 5) Determination of stimulation capability towards the proliferation of lymphocyte and the secretion of INF-r and IL-10.

RESULTS

The activity of DC was more than 92%, and the expression of OX-62 was more than 70%. Most of DC exhibited the phenotype of CD80(+)/CD86(-). Compared with control group and LPS-stimulation group, the less mature adhered cells and hairlike DC were observed in NF-κB decoy group. Significant reduction (p < 0.05) was observed for the positive expression and extension of CD80 and CD86 in cell surface. After loaded with calf type II collagen, the low expression of CD80 and CD86 remains to be existed. The stimulation capability of DC towards lymphocyte in NF-κB decoy group was lower than that in control group (p<0.05) and LPS stimulation group (p < 0.05).

CONCLUSION

NF-κB Decoy ODN method can be successfully applied for construct rats' tolerogenic dendritic cells (DC) with stable morphology and phenotype. The tolerogenic DC exhibited immature immune phenotype, and low capability to stimulate lymphocytes.

Redefining Strategies to Introduce Tolerance-Inducing Cellular Therapy in Human beings to Combat Autoimmunity and Transplantation Reactions

Clinical translation of tolerance-inducing cell therapies requires a novel approach focused on innovative networks, patient involvement, and, foremost, a fundamental paradigm shift in thinking from both Academia, and Industry and Regulatory Agencies. Tolerance-inducing cell products differ essentially from conventional drugs. They are personalized and target interactive immunological networks to shift the balance toward tolerance. The human cell products are often absent or fundamentally different in animals. This creates important limitations of pre-clinical animal testing for safety and efficacy of these products and calls for novel translational approaches, which require the combined efforts of the different parties involved. Dedicated international and multidisciplinary consortia that focus on clinical translation are of utmost importance. They can help in informing and educating regulatory policy makers on the unique requirements for these cell products, ranging from pre-clinical studies in animals to in vitro human studies. In addition, they can promote reliable immunomonitoring tools. The development of tolerance-inducing cell products requires not only bench-to-bedside but also reverse translation, from bedside back to the bench.

Regulation of activity of transcription factor NF-κB by synthetic oligonucleotides

Eukaryotic dimeric nuclear factor-κB (NF-κB) is one of the main transcription factors that activate expression of genes, products of which play the key role in development of cardiovascular pathologies, carcinogenesis, and inflammatory and viral diseases. In this review, the main attention is given to modulation of the transcription factor NF-κB activity by antisense oligonucleotides and oligonucleotide decoys. Also, current concepts about interactions between NF-κB dimers and DNA and general problems that arise in experimental use of synthetic oligonucleotides in vivo are discussed.

Adoptive transfusion of tolerogenic dendritic cells prolongs the survival of liver allograft: a systematic review

OBJECTIVES

To systematically review the effects of tolerogenic dendritic cells (Tol-DCs) induced by different methods on liver transplantation and their possible mechanisms of action.

METHODS

PubMed and EMbase were searched for relevant articles through 31 December 2013. The effects of Tol-DCs on liver allograft survival were semiquantitatively evaluated, and the possible mechanisms by which Tol-DCs prolong graft survival were analyzed.

RESULTS

Seven articles were included, and classified according to methods of induction, sources, and methods of infusing Tol-DCs. Tol-DCs induced from immature DCs (imDCs), with cytokines, and by gene modification induced liver transplant tolerance for 33.1 ± 32.5 days (2.7-fold vs. control), 26.17 ± 16.20 days (1.8-fold vs. control), and 11.7 ± 1.6 days (2.3-fold vs. control), respectively. DCs derived from recipient bone marrow, donor bone marrow, and donor spleen induced liver transplant tolerance for 51.0 ± 0.0 days (5.9-fold vs. control), 21.4 ± 26.8 days (2.4-fold vs. control), and 15.0 ± 0.0 days (2.3-fold vs. control), respectively. The primary mechanisms by which Tol-DCs induce liver transplant tolerance were the induction of T-cell hyporeactivity and Th2 differentiation.

CONCLUSIONS

Tol-DCs induced by three different methods could extend liver allograft survival, with imDCs showing optimal results. The optimal infusion method was intravenous injection of 1-2 × 10(6) Tol-DC, similar to findings in renal transplantation. Tol-DCs prolonged liver transplant tolerance more than renal transplant tolerance.

Dendritic cell-based approaches for therapeutic immune regulation in solid-organ transplantation

To avoid immune rejection, allograft recipients require drug-based immunosuppression, which has significant toxicity. An emerging approach is adoptive transfer of immunoregulatory cells. While mature dendritic cells (DCs) present donor antigen to the immune system, triggering rejection, regulatory DCs interact with regulatory T cells to promote immune tolerance. Intravenous injection of immature DCs of either donor or host origin at the time of transplantation have prolonged allograft survival in solid-organ transplant models. DCs can be treated with pharmacological agents before injection, which may attenuate their maturation in vivo. Recent data suggest that injected immunosuppressive DCs may inhibit allograft rejection, not by themselves, but through conventional DCs of the host. Genetically engineered DCs have also been tested. Two clinical trials in type-1 diabetes and rheumatoid arthritis have been carried out, and other trials, including one trial in kidney transplantation, are in progress or are imminent.

Apoptotic cell administration enhances pancreatic islet engraftment by induction of regulatory T cells and tolerogenic dendritic cells

Apoptotic cell transfer has been found to be able to facilitate engraftment of allograft. However, the underlying mechanisms remain to be fully understood. Here we demonstrate that intravenous administration of donor apoptotic splenocytes can promote pancreatic islet engraftment by inducing generation of tolerogenic dendritic cells (Tol-DCs) and expansion of CD4(+)Foxp3(+) regulatory T cells (Tregs). In vivo clearance of either dendritic cells (DCs) or Tregs prevented the induction of immune tolerance by apoptotic cell administration. Transient elimination of Tregs using anti-CD25, monoclonal antibody (mAb) abrogated the generation of Tol-DCs after administration of apoptotic splenocytes. Reciprocally, depletion of DCs within CD11c-DTR mice using diphtheria toxin (DT) prevented the generation of Tregs in the recipients with administration of apoptotic splenocytes. Induction of Tregs by Tol-DCs required direct cell contact between the two cell types, and programmed death 1 ligand (PD-L1) played important role in the Tregs expansion. Apoptotic cell administration failed to induce Tol-DCs in IL-10-deficient and Smad3-deficient mice, suggesting that IL-10 and transforming growth factor-β (TGF-β) are needed to maintain DCs in the tolerogenic state. Therefore, we demonstrate that Tol-DCs promote the expansion of Tregs via PD-L1 on their surface and reciprocally Tregs facilitate Tol-DCs to maintain transplantation tolerance induced by apoptotic cells via secreting IL-10 and TGF-β.

Protein kinase C inhibitor generates stable human tolerogenic dendritic cells

Tolerogenic dendritic cells (DCs) are a promising tool for a specific form of cellular therapy whereby immunological tolerance can be induced in the context of transplantation and autoimmunity. From libraries of bioactive lipids, nuclear receptor ligands, and kinase inhibitors, we screened conventional protein kinase C inhibitors (PKCIs) bisindolylmaleimide I, Gö6983, and Ro32-0432 with strong tolerogenic potential. PKCI-treated human DCs were generated by subjecting them to a maturation process after differentiation of immature DCs. The PKCI-treated DCs had a semimature phenotype, showing high production of IL-10, and efficiently induced IL-10-producing T cells and functional Foxp3(+) regulatory T cells from naive CD4(+) T cells, thus eliciting a strong immunosuppressive function. They also showed CCR7 expression and sufficient capacity for migration toward CCR7 ligands. Additionally, PKCI-treated DCs were highly stable when exposed to inflammatory stimuli such as proinflammatory cytokines or LPS. Conventional PKCIs inhibited NF-κB activation of both the canonical and noncanonical pathways of DC maturation, thus suppressing the expression of costimulatory molecules and IL-12 production. High production of IL-10 in PKCI-treated DCs was due to not only an increase of intracellular cAMP, but also a synergistic effect of increased cAMP and NF-κB inhibition. Moreover, PKCI-treated mouse DCs that had properties similar to PKCI-treated human DCs prevented graft-versus-host disease in a murine model of acute graft-versus-host disease. Conventional PKCI-treated DCs may be useful for tolerance-inducing therapy, as they satisfy the required functional characteristics for clinical-grade tolerogenic DCs.

The Immunosuppressant Protosappanin A Promotes Dendritic Cell-Mediated Expansion of Alloantigen-Specific Tregs and Prolongs Allograft Survival in Rats

Protosappanin A (PrA), an immunosuppressive ingredient of the medicinal herb Caesalpinia sappan L, prolongs heart allograft survival in rats, possibly by impairing the function of antigen-presenting cells (APCs). We examined the effects of PrA on the maturation and function of dendritic cells (DCs), a potent class of APCs, and the downstream cell–cell and intracellular signaling pathways mediating the immunosuppressive activity of PrA. PrA inhibited LPS-stimulated maturation of Wistar rat DCs in vitro as reflected by reduced expression of costimulatory molecules (CD80 and CD86) and reduced expression of TLR4 and NF-κB, two critical signaling components for antigen recognition. PrA also enhanced the release of IL-10 and decreased the release of IL-12 from DCs, but had no effect on the production of TGF-ß. In mixed cultures, Wistar DCs pretreated with PrA impaired the proliferation of Sprague Dawley (SD) rat T cells while promoting the expansion of SD rat CD4⁺CD25⁺ regulatory T cells (Tregs). Both oral PrA treatment and infusion of PrA-pretreated Wistar DCs prolonged cardiac allograft survival (Wistar donor, SD recipient) and expanded recipient CD4⁺CD25⁺Foxp3⁺ Tregs. Donor spleen cells, but not spleen cells from a third rat strain (DA), supported the expansion of recipient CD4⁺CD25⁺Foxp3⁺ Tregs and suppressed recipient T cell proliferation. We conclude that PrA triggers a tolerogenic state in DCs that allows for the induction of alloantigen-specific Tregs and the suppression of allograft rejection in vivo.

Dendritic cell therapy for Type 1 diabetes suppression

While dendritic cell-based therapy is a clinical reality for human malignancies, until now, some conceptual concerns have served to delay its consideration to treat human autoimmune diseases, even in light of almost two decades' worth of overwhelmingly supportive preclinical animal studies. This article provides an overview of the development of dendritic cell-based therapy for Type 1 diabetes mellitus, given that this is the best-studied autoimmune disorder and that there is a good understanding of the underlying immunology. This article also highlights data from the authors' pioneering Phase I clinical trial with tolerogenic dendritic cells, which hopes to motivate the clinical translation of other dendritic cell-based approaches, to one or more carefully selected Type 1 diabetic patient populations.

Tolerogenic Donor-Derived Dendritic Cells Risk Sensitization In Vivo owing to Processing and Presentation by Recipient APCs

Modification of allogeneic dendritic cells (DCs) through drug treatment results in DCs with in vitro hallmarks of tolerogenicity. Despite these observations, using murine MHC-mismatched skin and heart transplant models, donor-derived drug-modified DCs not only failed to induce tolerance but also accelerated graft rejection. The latter was inhibited by injecting the recipient with anti-CD8 Ab, which removed both CD8(+) T cells and CD8(+) DCs. The discrepancy between in vitro and in vivo data could be explained, partly, by the presentation of drug-modified donor DC MHC alloantigens by recipient APCs and activation of recipient T cells with indirect allospecificity, leading to the induction of alloantibodies. Furthermore, allogeneic MHC molecules expressed by drug-treated DCs were rapidly processed and presented in peptide form by recipient APCs in vivo within hours of DC injection. Using TCR-transgenic T cells, Ag presentation of injected OVA-pulsed DCs was detectable for ≤ 3 d, whereas indirect presentation of MHC alloantigen by recipient APCs led to activation of T cells within 14 h and was partially inhibited by reducing the numbers of CD8(+) DCs in vivo. In support of this observation when mice lacking CD8(+) DCs were pretreated with drug-modified DCs prior to transplantation, skin graft rejection kinetics were similar to those in non-DC-treated controls. Of interest, when the same mice were treated with anti-CD40L blockade plus drug-modified DCs, skin graft survival was prolonged, suggesting endogenous DCs were responsible for T cell priming. Altogether, these findings highlight the risks and limitations of negative vaccination using alloantigen-bearing "tolerogenic" DCs.

Zinc finger protein A20 inhibits maturation of dendritic cells resident in rat liver allograft

BACKGROUND

In organ transplant field, although viewed traditionally as instigators of organ allograft rejection, donor-derived interstitial dendritic cells (DCs), including those resident in liver, or host DCs have also been implicated in transplant tolerance in experimental models. This functional dichotomy of DC is governed by various factors, the most important of which appears to be their stage of maturation. This study was designed to examine the effect of zinc finger protein A20 on maturation of DCs resident in rat liver allograft.

MATERIALS AND METHODS

Allogeneic (Dark Agouti [DA] rat to Lewis rat) liver transplantation was performed. Adenovirus carrying the full length of A20 was introduced into liver allografts by ex vivo perfusion via the portal vein during preservation (group A20), physiological saline (group PS), and empty Ad vector rAdEasy (group rAdEasy) that served as controls. Acute liver allograft rejection was assessed, and DCs resident in liver allografts were isolated on day 7 after transplantation. Nuclear factor kappa B (NF-κB)-binding activities, surface expression of costimulatory molecules (CD40, CD80, and CD86), expression of interleukin (IL) 12 messenger RNA (mRNA), and allocostimulatory capacity of DCs were measured with electrophoretic mobility shift assay, flow cytometry, reverse transcription-polymerase chain reaction, and mixed lymphocyte reaction (MLR), respectively.

RESULTS

Ex vivo transfer of A20 adenovirus by portal vein infusion resulted in overexpression of A20 protein in liver allograft after transplantation. On day 7 after transplantation, histologic examination revealed a mild rejection in group A20 but a more severe rejection in group PS and group rAdEasy. DCs from group A20 liver allografts exhibited features of immature DC with detectable but very low level of NF-κB activity, IL-12 mRNA expression, and surface expression of costimulatory molecules (CD40, CD80, and CD86), whereas DCs from group rAdEasy and group PS liver allograft displayed features of mature DC with high level of NF-κB activity, IL-12 mRNA expression, and surface expression of costimulatory molecules (CD40, CD80, and CD86). DCs from group PS and group rAdEasy liver allograft were potent inducers of DNA synthesis and interferon γ production in MLR, and DCs from group A20 liver allografts induced only minimal levels of cell proliferation and interferon γ production in MLR.

CONCLUSIONS

These data suggest that A20 overexpression could effectively inhibit maturation of DCs resident in liver allograft and consequently suppress acute liver allograft rejection.

Therapeutic effect of cytotoxic T lymphocyte antigen 4/immunoglobulin on a murine model of primary biliary cirrhosis

Collectively, the data in both humans and murine models of human primary biliary cirrhosis (PBC) suggest that activated T cells, particularly CD8 T cells, play a critical role in biliary cell destruction. Under physiological conditions, T-cell activation involves two critical signals that involve the major histocompatibility complex and a set of costimulatory molecules, which include a receptor on T cells termed cytotoxic T lymphocyte antigen 4 (CTLA-4). Germane to the studies reported herein, signaling by CTLA-4 has the potential to modulate costimulation and induce inhibitory signals. In this study, we have taken advantage of our well-defined murine model of PBC, in which mice are immunized with 2-octynoic acid coupled to bovine serum albumin (2OA-BSA), leading to the production of high-titer antimitochondrial autoantibodies (AMAs) and portal cellular infiltrates. To investigate the potential of CTLA-4-Ig (immunoglobulin) as an immunotherapeutic agent, we treated mice both before and after induction of autoimmune cholangitis. First, we demonstrate that CTLA-4-Ig treatment, begun 1 day before 2OA-BSA immunization, completely inhibits the manifestations of cholangitis, including AMA production, intrahepatic T-cell infiltrates, and bile duct damage. However, and more critically, treatment with CTLA-4-Ig, initiated after the development of autoimmune cholangitis in previously immunized mice, also resulted in significant therapeutic benefit, including reduced intrahepatic T-cell infiltrates and biliary cell damage, although AMA levels were not altered.

CONCLUSION

These data suggest that an optimized regimen with CTLA-4-Ig has the potential to serve as an investigative therapeutic tool in patients with PBC.

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.

Dendritic cell sphingosine 1-phosphate receptor-3 regulates Th1-Th2 polarity in kidney ischemia-reperfusion injury

Dendritic cells (DCs) are central to innate and adaptive immunity of early kidney ischemia-reperfusion injury (IRI), and strategies to alter DC function may provide new therapeutic opportunities. Sphingosine 1-phosphate (S1P) modulates immunity through binding to its receptors (S1P1-5), and protection from kidney IRI occurs in S1P3-deficient mice. Through a series of experiments we determined that this protective effect was owing in part to differences between S1P3-sufficient and -deficient DCs. Mice lacking S1P3 on bone marrow cells were protected from IRI, and S1P3-deficient DCs displayed an immature phenotype. Wild-type (WT) but not S1P3-deficient DCs injected into mice depleted of DCs prior to kidney IR reconstituted injury. Adoptive transfer (i.e., i.v. injection) of glycolipid (Ag)-loaded WT but not S1P3-deficient DCs into WT mice exacerbated IRI, suggesting that WT but not S1P3-deficient DCs activated NKT cells. Whereas WT DC transfers activated the Th1/IFN-γ pathway, S1P3-deficient DCs activated the Th2/IL-4 pathway, and an IL-4-blocking Ab reversed protection from IRI, supporting the concept that IL-4 mediates the protective effect of S1P3-deficient DCs. Administration of S1P3-deficient DCs 7 d prior to or 3 h after IRI protected mice from IRI and suggests their potential use in cell-based therapy. We conclude that absence of DC S1P3 prevents DC maturation and promotes a Th2/IL-4 response. These findings highlight the importance of DC S1P3 in modulating NKT cell function and IRI and support development of selective S1P3 antagonists for tolerizing DCs for cell-based therapy or for systemic administration for the prevention and treatment of IRI and autoimmune diseases.

Adoptive transfusion of tolerance dendritic cells prolongs the survival of cardiac allograft: a systematic review of 44 basic studies in mice

BACKGROUND AND OBJECTIVE

Tolerogenic DCs (Tol-DCs), a group of cells with imDC phenotype, can stably induce T cells low-reactivity and immune tolerance. We systematically reviewed the adoptive transfusion of Tol-DCs induced by different ways to prolong cardiac allograft survival and its possible mechanism.

METHOD

MEDLINE (1966 to March 2011), EMbase (1980 to March 2011), and ISI (inception to March 2011) were searched for identification of relevant studies. We used allogeneic heart graft survival time as endpoint outcome to analyze the effect of adoptive transfusion of Tol-DC on cardiac allograft. By integrating studies' information, we summarized the mechanisms of Tol-DC in prolonging cardiac grafts.

RESULTS

Four methods were used to induce Tol-DC in all of the 44 included studies including gene-modified, drug-intervened, cytokine-induced, and other-derived (liver-derived & spleen-derived) DCs. The results showed that all types of Tol-DC can effectively prolong graft survival, and the average extension of graft survival time for each group was as follows: 22.02 ± 21.9 days (3.2 folds to control group) in the gene modified group, 25.94 ± 16.9 days (4.3 folds) in the drug-intervened groups, 9.00 ± 8.13 days (1.9 folds) in the cytokine-induced group, and 10.69 ± 9.94 days (2.1 folds) in the other-derived group. The main mechanisms of Tol-DCs to prolong graft survival were as follows: (1) induceT-cell hyporeactivity (detected by MLR); (2) reduce the effect of cytotoxic lymphocyte (CTL); (3) promote Th2 differentiation; (4) induce Treg; (5) induce chimerism.

CONCLUSION

For fully MHC mismatched allogeneic heart transplant recipients of inbred mouse, adoptive transfusion of Tol-DC, which can be gene-modified, drug-intervened, cytokine-induced, spleen-derived or liver-derived, can clearly prolong the survival of cardiac allograft or induce immune tolerance. Gene-modified and drug-induced Tol-DC can prolong graft survival most obviously. Having better reliability and stability than drug-induction, gene-modification is the best way to induce Tol-DCs at present. One-time intravenous infusion of 2 × 10(6) Tol-DC is a simple and feasible way to induce long-term graft survival. Multiple infusions will prolong it but increase the risk and cost. Adoptive transfusion of Tol-DC in conjunction with immunosuppressive agents may also prolong the graft survival time.

Dendritic cell therapies in transplantation revisited: deletion of recipient DCs deters the effect of therapeutic DCs

A critical goal in transplantation is the achievement of donor-specific tolerance, minimizing the use of immunosuppressants. Dendritic cells (DCs) are antigen (Ag) presenting cells (APCs) with capability to promote immunity or tolerance. The immune-regulatory properties of DCs have been exploited for generation of tolerogenic/immunosuppressive (IS) DCs that, when transfer systemically, prolong allograft survival in murine models. Surprisingly, the in vivo mechanisms of therapies based on (donor- or recipient-derived) ISDCs in transplantation remain unknown, given that previous studies investigated their effects in vitro, or ex vivo after transplantation. Since once injected, ISDCs are short-lived and transfer Ag to recipient APCs, we assessed the role of recipient DCs by depleting them at the time of ISDC-therapy in a mouse model of cardiac transplantation. The results indicate that, contrary to the accepted paradigm, systemically administered ISDCs reduce the alloresponse and prolong allograft survival, not by themselves, but through conventional DCs (cDCs) of the recipient. These findings raise doubts on the advantages of the currently used ISDC-therapies, since the immune-regulatory properties of the injected ISDC do not seem to be functionally relevant in vivo, and the quiescent/pro-tolerogenic status of cDCs may be compromised in patients with end-stage diseases that require transplantation.

Potential protective effect of nuclear factor-κB decoy oligodeoxynucleotides on endotoxin-induced liver injury

PURPOSE

We sought to study the protective effects of nuclear factor-κB decoy oligodeoxynucleotides (ODNs) on endotoxin-induced liver injury in a rat model.

METHODS

Sixty Sprague-Dawley rats were randomly divided into a control (n=20), a lipopolysaccharide (LPS) (n=20), and an NF-κB decoy ODN group (n=20). Liver and blood serum samples were collected at 24 hours after the operation. NF-κB binding activity was detected by an electrophoretic mobility shift assay, liver histopathology, by light microscopy; and cell apoptosis, by a terminal-deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling assay. The serum of liver enzyme (aspartate transaminase [AST]) levels were measured using an automated biochemical analyzer and tumor necrosis factor (TNF)-α and interleukin (IL)-6 by enzyme-linked immunosorbent assays.

RESULTS

NF-κB was dramatically activated after endotoxin-induced liver injury. Many hepatocytes underwent degeneration and necrosis in the LPS group. The expressions of AST, TNF-α, and IL-6 were significantly increased compared with the control group (P=.0005), However, NF-κB decoy ODNs altered these undesirable changes. On the other hand, IL-6 expression was not significantly decreased by the NF-κB decoy versus the LPS group (P=.0745).

CONCLUSIONS

NF-κB decoy strategy inhibited the binding activity of NF-κB, thus suppressing production of downstream cytokines which play crucial roles in protection from endotoxin-induced injury.

Gene silencing of IL-12 in dendritic cells inhibits autoimmune arthritis

Background

We have previously demonstrated that immune modulation can be accomplished by administration of gene silenced dendritic cells (DC) using siRNA. In this study, we demonstrate the therapeutic utilization of shRNA-modified DC as an antigen-specific tolerogenic vaccine strategy for autoimmune arthritis.

Methods

A shRNA that specifically targets IL-12 p35 was designed and cloned into a plasmid vectors (IL-12 shRNA). Bone marrow-derived DC from DBA/1 mice were transfected with the IL-12 shRNA construct in vitro. Mice with collagen II (CII)-induced arthritis (CIA) were treated with the modified DCs expressing the shRNA. Recall response and disease progression were assessed.

Results

After gene silencing of IL-12 in DC, DC were shown to selectively inhibit T cell proliferation on recall responses and in an MLR. In murine CIA, we demonstrated that administration of IL-12 shRNA-expressing DC that were pulsed with CII inhibited progression of arthritis. The therapeutic effects were evidenced by decreased clinical scores, inhibition of inflammatory cell infiltration in the joint, and suppression of T cell and B cell responses to CII.

Conclusion

We demonstrate a novel tolerance-inducing protocol for the treatment of autoimmune inflammatory joint disease in which the target antigen is known, utilizing DNA-directed RNA interference.

Donor-derived, tolerogenic dendritic cells suppress immune rejection in the indirect allosensitization-dominant setting of corneal transplantation

Significant interest has been focused on the use of ex vivo-manipulated DCs to optimally induce transplant tolerance and promote allograft survival. Although it is understood that donor-derived, tolerogenic DCs suppress the direct pathway of allosensitization, whether such DCs can similarly suppress the indirect pathway remains unclear. We therefore used the murine model of corneal transplantation to address this, as these allografts are rejected in an indirect pathway-dominant manner. Interestingly, recipients administered with donor bone marrow-derived DCregs, generated via culturing with GM-CSF, IL-10, and TGF-β1, significantly prolonged survival of corneal allografts. Correspondingly, these recipients demonstrated a potent reduction in the frequency of indirectly allosensitized T cells, as determined by ELISPOT. Examination of DCregs relative to mDCs or iDCs showed a resistance to up-regulation of MHC-II and costimulatory molecules, as well as an impaired capacity to stimulate MLRs. In vivo, DCreg administration in corneal-allografted recipients led to inhibition of CD4(+)IFN-γ(+) T cell frequencies and an associated increase in Foxp3 expression in the Treg compartment. We conclude that donor-derived, tolerogenic DCs significantly suppress the indirect pathway, thereby identifying a novel regulatory mechanism for these cells in transplantation.

Tolerance-inducing strategies in islet transplantation

Allogeneic islet transplantation is a promising approach for restoring normoglycemia in type 1 diabetic patients. Current use of immunosuppressive therapies for management of islet transplant recipients can be counterintuitive to islet function and can lead to complications in the long term. The induction of donor-specific tolerance eliminates the dependency on immunosuppression and allows recipients to retain responses to foreign antigens. The mechanisms by which tolerance is achieved involve the deletion of donor-reactive T cells, induction of T-cell anergy, immune deviation, and generation of regulatory T cells. This review will outline the various methods used for inducing donor-specific tolerance in islet transplantation and will highlight the previously unforeseen potential of tissue stromal cells in promoting islet engraftment.

IL-10-generated tolerogenic dendritic cells are optimal for functional regulatory T cell induction--a comparative study of human clinical-applicable DC

Tolerogenic dendritic cells (tDC) are a promising tool for specific cellular therapy to induce immunological tolerance in transplantation and autoimmunity. To date, most described tDC methods have not been converted into clinically applicable protocols and systematic comparison of required functional characteristics, i.e. migration and functional regulatory T cell (Treg) induction, is lacking. We compare clinical-grade tDC generated with vitamin D(3), IL-10, dexamethasone, TGFβ or rapamycin. For good migratory capacity and a stable phenotype, additional maturation of tDC was required. Maturation with a cocktail of TNFα, IL-1β and PGE(2) induced optimal migration. Importantly, all tDC showed a stable phenotype under pro-inflammatory conditions. Especially IL-10 DC showed most powerful tolerogenic characteristics with high IL-10 production and low T cell activation. Moreover, in a functional suppression assay only IL-10 DC induced Treg that strongly suppressed T cell reactivity. Thus, clinical-grade IL-10 DC show functional characteristics that make them best suited for tolerance-inducing therapies.

Role of T cell-nuclear factor κB in transplantation

Nuclear factor (NF) κB is a pleiotropic transcription factor that is ubiquitously expressed. After transplantation of solid organs, NF-κB in the graft is activated within a few hours as a consequence of ischemia/reperfusion and then again after a few days in intragraft infiltrating cells during the process of acute allograft rejection. In the present article, we review the components of the NF-κB pathway, their mechanisms of activation, and their role in T cell and antigen-presenting cell activation and differentiation and in solid organ allograft rejection. Targeted inhibition of NF-κB in selected cell types may promote graft survival with fewer adverse effects compared with global immunosuppressive therapies.

Current state of type 1 diabetes immunotherapy: incremental advances, huge leaps, or more of the same?

Thus far, none of the preclinically successful and promising immunomodulatory agents for type 1 diabetes mellitus (T1DM) has conferred stable, long-term insulin independence to diabetic patients. The majority of these immunomodulators are humanised antibodies that target immune cells or cytokines. These as well as fusion proteins and inhibitor proteins all share varying adverse event occurrence and severity. Other approaches have included intact putative autoantigens or autoantigen peptides. Considerable logistical outlays have been deployed to develop and to translate humanised antibodies targeting immune cells, cytokines, and cytokine receptors to the clinic. Very recent phase III trials with the leading agent, a humanised anti-CD3 antibody, call into question whether further development of these biologics represents a step forward or more of the same. Combination therapies of one or more of these humanised antibodies are also being considered, and they face identical, if not more serious, impediments and safety issues. This paper will highlight the preclinical successes and the excitement generated by phase II trials while offering alternative possibilities and new translational avenues that can be explored given the very recent disappointment in leading agents in more advanced clinical trials.

RNA interference for improving the outcome of islet transplantation

Islet transplantation has the potential to cure type 1 diabetes. Despite recent therapeutic success, it is still not common because a large number of transplanted islets get damaged by multiple challenges including instant blood mediated inflammatory reaction, hypoxia/reperfusion injury, inflammatory cytokines, and immune rejection. RNA interference (RNAi) is a novel strategy to selectively degrade target mRNA. The use of RNAi technologies to downregulate the expression of harmful genes has the potential to improve the outcome of islet transplantation. The aim of this review is to gain a thorough understanding of biological obstacles to islet transplantation and discuss how to overcome these barriers using different RNAi technologies. This eventually will help improve islet survival and function post transplantation. Chemically synthesized small interferring RNA (siRNA), vector based short hairpin RNA (shRNA), and their critical design elements (such as sequences, promoters, and backbone) are discussed. The application of combinatorial RNAi in islet transplantation is also discussed. Last but not the least, several delivery strategies for enhanced gene silencing are discussed, including chemical modification of siRNA, complex formation, bioconjugation, and viral vectors.

Induction of pathogenic cytotoxic T lymphocyte tolerance by dendritic cells: a novel therapeutic target

IMPORTANCE OF THE FIELD

Dendritic cells (DCs) have an important role, both direct and indirect, in controlling the expansion and function of T cells. Of the different subsets of T cells, cytotoxic T lymphocytes (CTLs/CD8(+) T cells) have been implicated in the pathogenesis and development of many diseases, including various forms of autoimmunity and transplant rejection. It may therefore be of therapeutic benefit to control the function of CTL in order to modulate disease processes and to ameliorate disease symptoms. Currently, pharmacological approaches have been employed to either directly or indirectly modulate the function of T cells. However, these treatment strategies have many limitations. Many experimental data have suggested that it is possible to alter CTL activity through manipulation of DC.

AREAS COVERED IN THIS REVIEW

Novel strategies that condition DCs to influence disease outcome through manipulation of CTL activity, both directly and indirectly. This includes the modulation of co-stimulation, negative co-stimulation, as well as manipulation of the cytokine milieu during CTL generation. Furthermore, DCs may also impact CTL activity through effects on effector and regulatory cells, along with manipulation of bioenergetic regulation, apoptotic-cell mediated tolerance and through the generation of exosomes. The implications of related interventions in the clinical arena are in turn considered.

WHAT THE READER WILL GAIN

Insight into such indirect methods of controlling CTL activity allows for an understanding of how disease-specific T cells may be regulated, while also sparing other aspects of adaptive immunity for normal physiological function. Such an approach towards the treatment of disease represents an innovative therapeutic target in the clinical arena.

TAKE HOME MESSAGE

There are numerous innovative methods for using DCs to control CTL responses. Manipulation of this interaction is thus an attractive avenue for the treatment of disease, particularly those of immune dysregulation, such as seen in autoimmunity and transplantation. With the number of studies moving into clinical stages constantly increasing, further advances and successes in this area are inevitable.

Endogenous dendritic cells mediate the effects of intravenously injected therapeutic immunosuppressive dendritic cells in transplantation

The prevailing idea regarding the mechanism(s) by which therapeutic immunosuppressive dendritic cells (DCs) restrain alloimmunity is based on the concept that they interact directly with antidonor T cells, inducing anergy, deletion, and/or regulation. However, this idea has not been tested in vivo. Using prototypic in vitro-generated maturation-resistant (MR) DCs, we demonstrate that once MR-DCs carrying donor antigen (Ag) are administered intravenously, they decrease the direct and indirect pathway T-cell responses and prolong heart allograft survival but fail to directly regulate T cells in vivo. Rather, injected MR-DCs are short-lived and reprocessed by recipient DCs for presentation to indirect pathway CD4(+) T cells, resulting in abortive activation and deletion without detrimental effect on the number of indirect CD4(+) FoxP3(+) T cells, thus increasing the regulatory to effector T cell relative percentage. The effect on the antidonor response was independent of the method used to generate therapeutic DCs or their viability; and in accordance with the idea that recipient Ag-presenting cells mediate the effects of therapeutic DCs in transplantation, prolongation of allograft survival was achieved using donor apoptotic MR-DCs or those lacking surface major histocompatibility complex molecules. We therefore conclude that therapeutic DCs function as Ag-transporting cells rather than Ag-presenting cells to prolong allograft survival.

Dendritic cell-based therapy in Type 1 diabetes mellitus

Dendritic cell (DC) immunotherapy is a clinical reality. Despite two decades of considerable data demonstrating the feasibility of using DCs to prolong transplant allograft survival and to prevent autoimmunity, only now are these cells entering clinical trials in humans. Type 1 diabetes is the first autoimmune disorder to be targeted for treatment in humans using autologous-engineered DCs. This review will highlight the role of DCs in autoimmunity and the manner in which they have been engineered to treat these disorders in rodent models, either via the induction of immune hyporesponsiveness, which may be cell- and/or antigen-specific, or indirectly by upregulation of other immune cell networks.

Dendritic cells and regulation of alloimmune responses: relevance to outcome and therapy of organ transplantation

Dendritic cells are uniquely well-equipped for antigen capture, processing and presentation. They are highly-efficient antigen-presenting cells that induce and regulate T-cell reactivity. Due to their inherent tolerogenicity, immature dendritic cells offer considerable potential as candidate cellular vaccines for negative regulation of immune reactivity/promotion of tolerance. Both classic myeloid and, more recently, characterized plasmacytoid dendritic cells, exhibit tolerogenic properties. Manipulation of dendritic cells differentiation/ maturation in the laboratory using cytokines, pharmacologic agents or genetic engineering approaches can render stably immature dendritic cells that promote organ transplant tolerance in rodents. There are also indications from human studies of the ability of dendritic cells to promote T-cell tolerance and induce T-regulatory cells, with potential for therapeutic application in organ transplantation. In addition, recent clinical observations suggest that modulation of dendritic cell function (e.g., by immunosuppressive drugs) affects the outcome of transplantation. The challenge confronting applied dendritic cell biology is the identification of optimal strategies and therapeutic regimens to allow the potential of these powerful immune regulatory cells to be realized in the clinic.

Regulation of human dendritic cells by a novel specific nuclear factor-kappaB inhibitor, dehydroxymethylepoxyquinomicin

Regulation of antigen-presenting cells (APC) is crucial in controlling allograft rejection. Dendritic cells (DC) are the most potent APC and must mature to present antigens to T-cell receptors. During DC maturation, nuclear factor-kappaB (NF-kappaB) is a key transcriptional factor. We synthesized dehydroxymethylepoxyquinomicin (DHMEQ), which specifically inhibits the final step of nuclear translocation of activated NF-kappaB proteins and examined its immunoregulatory effects on human monocyte-derived DC (Mo-DC). Regulatory Mo-DC were generated by pretreatment with DHMEQ before LPS stimulation, which were termed dl-DC. DHMEQ pretreatment (5 microg/ml) completely inhibited nuclear translocation of activated NF-kappaB. DHMEQ significantly inhibited DC production of proinflammatory cytokines (IL-6, TNF-alpha, and IL-12 p70) in a dose-dependent manner. IL-12 was most potently inhibited. However, IL-10 production by dl-DC was only moderately affected by DHMEQ. Although CD40 and the expression of HLA-DR (HLA-DR) expression on dl-DC was downregulated, CD80 and CD86 expression was moderately upregulated. Induction of T helper 1 cell responses was efficiently impaired by dl-DC. This confirmed that DHMEQ-treated Mo-DC exhibited immunoregulatory effects. These findings suggest that DHMEQ has potential as an immunosuppressive drug for human immune cells.

Endoplasmic reticulum stress-mediated apoptosis involved in indirect recognition pathway blockade induces long-term heart allograft survival

Implementation of dendritic cell- (DC-) based therapies in organ transplantation can reduce dependency on nonspecific immunosuppression. Despite extensive research, mechanisms of equipped DCs inducing transplant tolerance remain incomplete. Here, we applied RNA interference technique to inhibit CD80 and CD86 expression in host bone marrow-derived DCs. This approach could specifically and effectively knock down CD80 and CD86 expression. T cells primed by these DCs inhibited allogeneic responses. Administration of recipient DCs loaded with alloantigen after CD80 and CD86 blockade prolonged cardiac allograft survival. We also found a higher percentage of apoptotic T cells in lymph tissues and grafts than that detected in control group. In addition, these T cells expressed high expression of GRP78 than controls, indicating activation of unfolded protein responses. Upregulation of CHOP expression among these cells suggested that the endoplasmic reticulum stress (ERS) response switched to a proapoptotic response. Our results indicated that ERS-induced apoptosis may be involved in allogeneic T-cell apoptosis, and the ERS-mediated apoptosis pathway may be a novel target in clinical prevention and therapy of allograft rejection.

Development of dendritic cell-based immunotherapy for autoimmunity

Dendritic cells are professional antigen-presenting cells that maintain immune tolerance to self-antigens by deleting or controlling the pathogenicity of auto-reactive T-cells. Dendritic cell-based immunotherapies show great promise for the restoration of tolerance in autoimmune disease. Dendritic cells can be modified ex vivo to induce stable tolerogenic function and be used as cellular 'vaccines' or they can be targeted in vivo with sophisticated antigen delivery systems. Tolerogenic dendritic cells induce antigen-specific T-cell tolerance in vivo and have therapeutic effects in animal models of autoimmunity. The current challenge is to bring tolerogenic dendritic cell therapy to the clinic.