Rapamycin-treated, alloantigen-pulsed host dendritic cells induce ag-specific T cell regulation and prolong graft survival

The role of regulatory T cells in vitiligo and therapeutic advances: a mini-review

BACKGROUND

Regulatory T cells (Tregs) play vital roles in controlling immune reactions and maintaining immune tolerance in the body. The targeted destruction of epidermal melanocytes by activated CD8+T cells is a key event in the development of vitiligo. However, Tregs may exert immunosuppressive effects on CD8+T cells, which could be beneficial in treating vitiligo.

METHODS

A comprehensive search of PubMed and Web of Science was conducted to gather information on Tregs and vitiligo.

RESULTS

In vitiligo, there is a decrease in Treg numbers and impaired Treg functions, along with potential damage to Treg-related signaling pathways. Increasing Treg numbers and enhancing Treg function could lead to immunosuppressive effects on CD8+T cells. Recent research progress on Tregs in vitiligo has been summarized, highlighting various Treg-related therapies being investigated for clinical use. The current status of Treg-related therapeutic strategies and potential future directions for vitiligo treatment are also discussed.

CONCLUSIONS

A deeper understanding of Tregs will be crucial for advancing Treg-related drug discovery and treatment development in vitiligo.

Negative Vaccination Strategies for Promotion of Transplant Tolerance

Organ transplantation requires the use of immunosuppressive medications that lack antigen specificity, have many adverse side effects, and fail to induce immunological tolerance to the graft. The safe induction of tolerance to allogeneic tissue without compromising host responses to infection or enhancing the risk of malignant disease is a major goal in transplantation. One promising approach to achieve this goal is based on the concept of "negative vaccination." Vaccination (or actively acquired immunity) involves the presentation of both a foreign antigen and immunostimulatory adjuvant to the immune system to induce antigen-specific immunity. By contrast, negative vaccination, in the context of transplantation, involves the delivery of donor antigen before or after transplantation, together with a "negative adjuvant" to selectively inhibit the alloimmune response. This review will explore established and emerging negative vaccination strategies for promotion of organ or pancreatic islet transplant tolerance. These include donor regulatory myeloid cell infusion, which has progressed to early-phase clinical trials, apoptotic donor cell infusion that has advanced to nonhuman primate models, and novel nanoparticle antigen-delivery systems.

Cell therapies and its derivatives as immunomodulators in vascularized composite allotransplantation

The adverse effects of traditional pharmaceutical immunosuppressive regimens have been a major obstacle to successful allograft survival in vascularized composite tissue allotransplantation (VCA) cases. Consequently, there is a pressing need to explore alternative approaches to reduce reliance on conventional immunotherapy. Cell therapy, encompassing immune-cell-based and stem-cell-based regimens, has emerged as a promising avenue of research. Immune cells can be categorized into two main systems: innate immunity and adaptive immunity. Innate immunity comprises tolerogenic dendritic cells, regulatory macrophages, and invariant natural killer T cells, while adaptive immunity includes T regulatory cells and B regulatory cells. Investigations are currently underway to assess the potential of these immune cell populations in inducing immune tolerance. Furthermore, mixed chimerism therapy, involving the transplantation of hematopoietic stem and progenitor cells and mesenchymal stem cells (MSC), shows promise in promoting allograft tolerance. Additionally, extracellular vesicles (EVs) derived from MSCs offer a novel avenue for extending allograft survival. This review provides a comprehensive summary of cutting-edge research on immune cell therapies, mixed chimerism therapies, and MSCs-derived EVs in the context of VCAs. Findings from preclinical and clinical studies demonstrate the tremendous potential of these alternative therapies in optimizing allograft survival in VCAs.

Immunomodulatory potential of rapamycin-loaded mesoporous silica nanoparticles: pore size-dependent drug loading, release, and in vitro cellular responses

Rapamycin is a potent immunosuppressive drug that has been recently proposed for a wide range of applications beyond its current clinical use. For some of these proposed applications, encapsulation in nanoparticles is key to ensure therapeutic efficacy and safety. In this work, we evaluate the effect of pore size on mesoporous silica nanoparticles (MSN) as rapamycin nanocarriers. The successful preparation of MSN with 4 different pore sizes was confirmed by dynamic light scattering, zeta potential, transmission electron microscopy and N2 adsorption. In these materials, rapamycin loading was pore size-dependent, with smaller pore MSN exhibiting greater loading capacity. Release studies showed sustained drug release from all MSN types, with larger pore MSN presenting faster release kinetics. In vitro experiments using the murine dendritic cell (DC) line model DC2.4 showed that pore size influenced the biological performance of MSN. MSN with smaller pore sizes presented larger nanoparticle uptake by DC2.4 cells, but were also associated with slightly larger cytotoxicity. Further evaluation of DC2.4 cells incubated with rapamycin-loaded MSN also demonstrated a significant effect of MSN pore size on their immunological response. Notably, the combination of rapamycin-loaded MSN with an inflammatory stimulus (lipopolysaccharide, LPS) led to changes in the expression of DC activation markers (CD40 and CD83) and in the production of the proinflammatory cytokine TNF-α compared to LPS-treated DC without nanoparticles. Smaller-pored MSN induced more substantial reductions in CD40 expression while eliciting increased CD83 expression, indicating potential immunomodulatory effects. These findings highlight the critical role of MSN pore size in modulating rapamycin loading, release kinetics, cellular uptake, and subsequent immunomodulatory responses.

Tolerogenic Nano-/Microparticle Vaccines for Immunotherapy

Autoimmune diseases, allergies, transplant rejections, generation of antidrug antibodies, and chronic inflammatory diseases have impacted a large group of people across the globe. Conventional treatments and therapies often use systemic or broad immunosuppression with serious efficacy and safety issues. Tolerogenic vaccines represent a concept that has been extended from their traditional immune-modulating function to induction of antigen-specific tolerance through the generation of regulatory T cells. Without impairing immune homeostasis, tolerogenic vaccines dampen inflammation and induce tolerogenic regulation. However, achieving the desired potency of tolerogenic vaccines as preventive and therapeutic modalities calls for precise manipulation of the immune microenvironment and control over the tolerogenic responses against the autoantigens, allergens, and/or alloantigens. Engineered nano-/microparticles possess desirable design features that can bolster targeted immune regulation and enhance the induction of antigen-specific tolerance. Thus, particle-based tolerogenic vaccines hold great promise in clinical translation for future treatment of aforementioned immune disorders. In this review, we highlight the main strategies to employ particles as exciting tolerogenic vaccines, with a focus on the particles' role in facilitating the induction of antigen-specific tolerance. We describe the particle design features that facilitate their usage and discuss the challenges and opportunities for designing next-generation particle-based tolerogenic vaccines with robust efficacy to promote antigen-specific tolerance for immunotherapy.

Transdermally delivered tolerogenic nanoparticles induced effective immune tolerance for asthma treatment

Induction of antigen-specific immune tolerance for the treatment of allergic or autoimmune diseases is an attractive strategy. Herein, we investigated the protective effect of a transdermal microneedle patch against allergic asthma by stimulating allergen-specific immune tolerance. We fabricated biodegradable tolerogenic nanoparticles (tNPs) that are loaded with a model allergen ovalbumin (OVA) and an immunomodulator rapamycin, and filled the tNPs into microneedle tips by centrifugation to form sustained-release microneedles. After intradermal immunization, the microneedles successfully delivered the cargos into the skin and sustainedly released them for over 96 h. Importantly, the microneedles induced allergen-specific regulatory T cells (Treg), decreased the levels of pro-inflammatory cytokines and antibodies while increased anti-inflammation cytokines, finally leading to restored immune homeostasis. The lung tissue analysis illustrated that the sustained-release microneedles significantly reduced the infiltration of eosinophils, decreased the accumulation of mucus and collagen, and significantly relived asthma symptoms. Our results suggested that the sustained-release microneedle-based transdermal delivery system can induce antigen-specific immune tolerance with improved compliance and efficacy, providing a new therapeutic strategy for the treatment of allergic and autoimmune diseases.

Exopolysaccharide-Treated Dendritic Cells Effectively Ameliorate Acute Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a primary and often lethal complication of allogenic hematopoietic stem cell transplantation (HSCT). Prophylactic regimens for GVHD are given as standard pretransplantation therapy; however, up to 50% of these patients develop acute GVHD (aGVHD) and require additional immunosuppressive intervention. Using a mouse GVHD model, we previously showed that injecting mice with exopolysaccharide (EPS) from Bacillus subtilis prior to GVHD induction significantly increased 80-day survival after transplantation of complete allogeneic major histocompatibility complex-mismatched cells. To ask whether EPS might also inhibit GVHD in humans, we used humanized NSG-HLA-A2 mice and induced GVHD by i.v. injection of A2neg human peripheral blood mononuclear cells (PBMCs). Because we could not inject human donors with EPS, we transferred EPS-pretreated dendritic cells (DCs) to inhibit aGVHD. We derived these DCs from CD34+ human cord blood cells, treated them with EPS, and then injected them together with PBMCs into the NSG-HLA-A2 mice. We found that all mice that received untreated DCs were dead by day 35, whereas 25% of mice receiving EPS-treated DCs (EPS-DCs) survived. This DC cell therapy could be readily translatable to humans, because we can generate large numbers of human EPS-DCs and use them as an "off the shelf" treatment for patients undergoing HSCT.

Introducing Molecular Chaperones into the Causality and Prospective Management of Autoimmune Hepatitis

Molecular chaperones influence the immunogenicity of peptides and the activation of effector T cells, and their pathogenic roles in autoimmune hepatitis are unclear. Heat shock proteins are pivotal in the processing and presentation of peptides that activate CD8+ T cells. They can also induce regulatory B and T cells and promote immune tolerance. Tapasin and the transporter associated with antigen processing-binding protein influence the editing and loading of high-affinity peptides for presentation by class I molecules of the major histocompatibility complex. Their over-expression could enhance the autoimmune response, and their deficiency could weaken it. The lysosome-associated membrane protein-2a isoform in conjunction with heat shock cognate 70 supports the importation of cytosolic proteins into lysosomes. Chaperone-mediated autophagy can then process the peptides for activation of CD4+ T cells. Over-expression of autophagy in T cells may also eliminate negative regulators of their activity. The human leukocyte antigen B-associated transcript three facilitates the expression of class II peptide receptors, inhibits T cell apoptosis, prevents T cell exhaustion, and sustains the immune response. Immunization with heat shock proteins has induced immune tolerance in experimental models and humans with autoimmune disease by inducing regulatory T cells. Therapeutic manipulation of other molecular chaperones may promote T cell exhaustion and induce tolerogenic dendritic cells. In conclusion, molecular chaperones constitute an under-evaluated family of ancillary proteins that could affect the occurrence, severity, and outcome of autoimmune hepatitis. Clarification of their contributions to the immune mechanisms and clinical activity of autoimmune hepatitis could have therapeutic implications.

Tolerogenic dendritic cells protect against acute kidney injury

Ischemia reperfusion injury is a common precipitant of acute kidney injury that occurs following disrupted perfusion to the kidney. This includes blood loss and hemodynamic shock, as well as during retrieval for deceased donor kidney transplantation. Acute kidney injury is associated with adverse long-term clinical outcomes and requires effective interventions that can modify the disease process. Immunomodulatory cell therapies such as tolerogenic dendritic cells remain a promising tool, and here we tested the hypothesis that adoptively transferred tolerogenic dendritic cells can limit kidney injury. The phenotypic and genomic signatures of bone marrow-derived syngeneic or allogeneic, Vitamin-D3/IL-10-conditioned tolerogenic dendritic cells were assessed. These cells were characterized by high PD-L1:CD86, elevated IL-10, restricted IL-12p70 secretion and a suppressed transcriptomic inflammatory profile. When infused systemically, these cells successfully abrogated kidney injury without modifying infiltrating inflammatory cell populations. They also provided protection against ischemia reperfusion injury in mice pre-treated with liposomal clodronate, suggesting the process was regulated by live, rather than reprocessed cells. Co-culture experiments and spatial transcriptomic analysis confirmed reduced kidney tubular epithelial cell injury. Thus, our data provide strong evidence that peri-operatively administered tolerogenic dendritic cells have the ability to protect against acute kidney injury and warrants further exploration as a therapeutic option. This technology may provide a clinical advantage for bench-to-bedside translation to affect patient outcomes.

Tolerogenic IL-10-engineered dendritic cell-based therapy to restore antigen-specific tolerance in T cell mediated diseases

Tolerogenic dendritic cells play a critical role in promoting antigen-specific tolerance via dampening of T cell responses, induction of pathogenic T cell exhaustion and antigen-specific regulatory T cells. Here we efficiently generate tolerogenic dendritic cells by genetic engineering of monocytes with lentiviral vectors co-encoding for immunodominant antigen-derived peptides and IL-10. These transduced dendritic cells (designated DC^IL-10/Ag) secrete IL-10 and efficiently downregulate antigen-specific CD4⁺ and CD8⁺ T cell responses from healthy subjects and celiac disease patients in vitro. In addition, DC^IL-10/Ag induce antigen-specific CD49b⁺LAG-3⁺ T cells, which display the T regulatory type 1 (Tr1) cell gene signature. Administration of DC^IL-10/Ag resulted in the induction of antigen-specific Tr1 cells in chimeric transplanted mice and the prevention of type 1 diabetes in pre-clinical disease models. Subsequent transfer of these antigen-specific T cells completely prevented type 1 diabetes development. Collectively these data indicate that DC^IL-10/Ag represent a platform to induce stable antigen-specific tolerance to control T-cell mediated diseases.

Impact of Siglecs on autoimmune diseases

Autoimmune diseases affect tens of millions of people just in the United States alone. Most of the available treatment options are aimed at reducing symptoms but do not lead to cures. Individuals affected with autoimmune diseases suffer from the imbalance between tolerogenic and immunogenic functions of their immune system. Often pathogenesis is mediated by autoreactive B and T cells that escape central tolerance and react against self-antigens attacking healthy tissues in the body. In recent years Siglecs, sialic-acid-binding immunoglobulin (Ig)-like lectins, have gained attention as immune checkpoints for therapeutic interventions to dampen excessive immune responses and to restore immune tolerance in autoimmune diseases. Many Siglecs function as inhibitory receptors suppressing activation signals in various immune cells through binding to sialic acid ligands as signatures of self. In this review, we highlight potential of Siglecs in suppressing immune responses causing autoimmune diseases. In particular, we cover the roles of CD22 and Siglec-G/Siglec-10 in regulating autoreactive B cell responses. We discuss several functions of Siglec-10 in the immune modulation of other immune cells, and the potential of therapeutic strategies for restoring immune tolerance by targeting Siglecs and expanding regulatory T cells. Finally, we briefly review efforts evaluating Siglec-based biomarkers to monitor autoimmune diseases.

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.

Suppression of Autoimmune Rheumatoid Arthritis with Hybrid Nanoparticles That Induce B and T Cell Tolerance to Self-Antigen

Autoimmune diseases affect over 4% of the world's population. Treatments are generally palliative or use broad spectrum immunosuppressants to reduce symptoms and disease progression. In some diseases, antibodies generated to a single autoantigen are the major cause of pathogenic inflammation, suggesting that treatments to induce tolerance to the autoantigen could be therapeutic. Here we report the development of hybrid nanoparticles (NPs) that induce tolerance in both T cells and B cells. The NPs comprise a lipid monolayer encapsulating a PLGA core loaded with rapamycin that promotes development of regulatory T cells (Tregs). The lipid monolayer displays the protein antigen and a ligand of the B cell inhibitory co-receptor CD22 (CD22L) that act together to suppress activation of B cells recognizing the antigen. We demonstrate that the hybrid NPs decorated with ovalbumin (OVA) elicit tolerance to OVA in naı̈ve mice, as judged by low OVA-specific antibody titers after the challenge. In the K/BxN mouse model of rheumatoid arthritis caused by B and T cell-dependent responses to the self-antigen glucose-6-phosphate-isomerase (GPI), we show that GPI hybrid NPs delay development of disease, with some treated mice remaining arthritis-free for 300 days. We provide evidence that the mechanism of rheumatoid arthritis suppression involves induction of B cell tolerance, as measured by low anti-GPI antibodies and decreased plasma cell populations, and T cell tolerance, as measured by increased Tregs. The results show the potential of this versatile NP platform for inducing immune tolerance to a self-antigen and suppressing autoimmune disease.

Activation and regulation of alloreactive T cell immunity in solid organ transplantation

Transplantation is the only curative treatment for patients with kidney failure but it poses unique immunological challenges that must be overcome to prevent allograft rejection and ensure long-term graft survival. Alloreactive T cells are important contributors to graft rejection, and a clearer understanding of the mechanisms by which these cells recognize donor antigens - through direct, indirect or semi-direct pathways - will facilitate their therapeutic targeting. Post-T cell priming rejection responses can also be modified by targeting pathways that regulate T cell trafficking, survival cytokines or innate immune activation. Moreover, the quantity and quality of donor-reactive memory T cells crucially shape alloimmune responses. Of note, many fundamental concepts in transplant immunology have been derived from models of infection. However, the programmed differentiation of allograft-specific T cell responses is probably distinct from that of pathogen-elicited responses, owing to the dearth of pathogen-derived innate immune activation in the transplantation setting. Understanding the fundamental (and potentially unique) immunological pathways that lead to allograft rejection is therefore a prerequisite for the rational development of therapeutics that promote transplantation tolerance.

Tip-concentrated microneedle patch delivering everolimus for therapy of multiple sclerosis

Multiple sclerosis is a chronic progressive demyelinating disease of the central nervous system. At present, systemic drug therapy for multiple sclerosis has limited efficacy and serious side effects. Everolimus, as a new generation of mTOR inhibitors, can effectively alleviate the inflammatory reaction of the central nervous system and offers a promising choice for the treatment of multiple sclerosis. However, due to the low oral bioavailability and narrow response window of oral everolimus, a new delivery system is urgently needed to overcome the above problems. In this study, we constructed a tip-concentrated microneedle patch as a transdermal delivery system of everolimus for the treatment of multiple sclerosis. Here, the drug was concentrated in the needle tips by the rational design, making it delivered completely into the skin. The therapeutic effect of everolimus-loaded microneedles was evaluated using the experimental autoimmune encephalomyelitis (EAE) model and further verified with neurological function scores and the histopathological results of the spinal cord. These results indicated that the tip-concentrated microneedle patch provided an effective, safe and simple method for the transdermal delivery of everolimus, thus providing a new treatment for multiple sclerosis.

CXCR4 blockade reduces the severity of murine heart allograft rejection by plasmacytoid dendritic cell-mediated immune regulation

Allograft-specific regulatory T cells (T_reg cells) are crucial for long-term graft acceptance after transplantation. Although adoptive T_reg cell transfer has been proposed, major challenges include graft-specificity and stability. Thus, there is an unmet need for the direct induction of graft-specific T_reg cells. We hypothesized a synergism of the immunotolerogenic effects of rapamycin (mTOR inhibition) and plerixafor (CXCR4 antagonist) for T_reg cell induction. Thus, we performed fully-mismatched heart transplantations and found combination treatment to result in prolonged allograft survival. Moreover, fibrosis and myocyte lesions were reduced. Although less CD3⁺ T cell infiltrated, higher T_reg cell numbers were observed. Noteworthy, this was accompanied by a plerixafor-dependent plasmacytoid dendritic cells-(pDCs)-mobilization. Furthermore, in vivo pDC-depletion abrogated the plerixafor-mediated T_reg cell number increase and reduced allograft survival. Our pharmacological approach allowed to increase T_reg cell numbers due to pDC-mediated immune regulation. Therefore pDCs can be an attractive immunotherapeutic target in addition to plerixafor treatment.

Cyclosporine A, in Contrast to Rapamycin, Affects the Ability of Dendritic Cells to Induce Immune Tolerance Mechanisms

Following organ transplantation, it is essential that immune tolerance is induced in the graft recipient to reduce the risk of rejection and avoid complications associated with the long-term use of immunosuppressive drugs. Immature dendritic cells (DCs) are considered to promote transplant tolerance and may minimize the risk of graft rejection. The aim of the study was to evaluate the effects of immunosuppressive agents: rapamycin (Rapa) and cyclosporine A (CsA) on generation of human tolerogenic DCs (tolDCs) and also to evaluate the ability of these cells to induce mechanisms of immune tolerance. tolDCs were generated in the environment of Rapa or CsA. Next, we evaluated the effects of these agents on surface phenotypes (CD11c, MHC II, CD40, CD80, CD83, CD86, CCR7, TLR2, TLR4), cytokine production (IL-4, IL-6, IL-10, IL-12p70, TGF-β), phagocytic capacity and resistant to lipopolysaccharide activation of these DCs. Moreover, we assessed ability of such tolDCs to induce T cell activation and apoptosis, Treg differentiation and production of Th1- and Th2-characteristic cytokine profile. Data obtained in this study demonstrate that rapamycin is effective at generating maturation-resistant tolDCs, however, does not change the ability of these cells to induce mechanisms of immune tolerance. In contrast, CsA affects the ability of these cells to induce mechanisms of immune tolerance, but is not efficient at generating maturation-resistant tolDCs.

Modulation of the mTOR pathway plays a central role in dendritic cell functions after Echinococcus granulosus antigen recognition

Immune evasion is a hallmark of persistent echinococcal infection, comprising modulation of innate immune cells and antigen-specific T cell responses. However, recognition of Echinococcus granulosus by dendritic cells (DCs) is a key determinant of the host's response to this parasite. Given that mTOR signaling pathway has been described as a regulator linking metabolism and immune function in DCs, we reported for the first time in these cells, global translation levels, antigen uptake, phenotype, cytokine transcriptional levels, and splenocyte priming activity upon recognition of the hydatid fluid (HF) and the highly glycosylated laminar layer (LL). We found that LL induced a slight up-regulation of CD86 and MHC II in DCs and also stimulated the production of IL-6 and TNF-α. By contrast, HF did not increase the expression of any co-stimulatory molecules, but also down-modulated CD40 and stimulated the expression of the anti-inflammatory cytokine IL-10. Both parasitic antigens promoted protein synthesis through mTOR activation. The use of rapamycin decreased the expression of the cytokines tested, empowered the down-modulation of CD40 and also reduced splenocyte proliferation. Finally, we showed that E. granulosus antigens increase the amounts of LC3-positive structures in DCs which play critical roles in the presentation of these antigens to T cells.

Polymeric nanoparticles containing rapamycin and autoantigen induce antigen-specific immunological tolerance for preventing vitiligo in mice

Vitiligo is an autoimmune disease in which pigment is lost in patches of the skin. CD4⁺ T cells are implicated in vitiligo while regulatory T cells (Tregs) could ameliorate vitiligo. Rapamycin together with autoantigen have been shown to induce immunological tolerance and promote Tregs in multiple autoimmune diseases. In the current study, we synthesized nanoparticles containing rapamycin and autoantigen HEL_46-61 (NP_{HEL46-61/Rapa}) and investigated their effects on vitiligo. We treated bone marrow-derived dendritic cells (BMDCs) from TrpHEL mice with NP_{HEL46-61/Rapa} and monitored the phenotype of BMDCs. We investigated the effects of NP_{HEL46-61/Rapa}-treated BMDCs on CD4⁺ T cell proliferation and differentiation. We administrated NP_{HEL46-61/Rapa} to TCR-TrpHEL mice and investigated the effects on vitiligo. We found that BMDCs can uptake the NP_{HEL46-61/Rapa}, which resulted in decreased expression of costimulation molecules CD80 and CD86 in BMDCs. BMDCs treated with NP_{HEL46-61/Rapa} suppressed antigen-specific CD4⁺ T cell proliferation while promoted the differentiation of these CD4⁺ T cell to Tregs in vitro. Administration of NP_{HEL46-61/Rapa} to TCR-TrpHEL mice ameliorated vitiligo, promoted Treg production, and suppressed IFN-γ and IL-6 production, while induced IL-10 production. Therefore, our study provides experimental evidence that nanoparticles containing rapamycin and autoantigen could induce antigen-specific immunological tolerance and prevent vitiligo.

Localized hydrogel delivery of dendritic cells for attenuation of multiple sclerosis in a murine model

In multiple sclerosis (MS), abnormally activated immune cells responsive to myelin proteins result in widespread damage throughout the central nervous system (CNS) and ultimately irreversible disability. Immunomodulation by delivering dendritic cells (DCs) utilizes a potent and rapid MS disease progression driver therapeutically. Here, we investigated delivering DCs for disease severity attenuation using an experimental autoimmune encephalomyelitis preclinical MS model. DCs treated with interleukin-10 (IL-10) (DC10s) were transplanted using in situ gelling poly(ethylene glycol)-based hydrogel for target site localization. DC delivery increased hydrogel longevity and altered the injection site recruited, endogenous immune cell profile within 2 days postinjection. Furthermore, hydrogel-mediated DC transplantation efficacy depended on the injection-site. DCs delivered to the neck local to MS-associated CNS-draining cervical lymph nodes attenuated paralysis, compared to untreated controls, while delivery to the flank did not alter paralysis severity. This study demonstrates that local delivery of DC10s modulates immune cell recruitment and attenuates disease progression in a preclinical model of MS.

Amelioration of Graft-versus-Host Disease by Exopolysaccharide from a Commensal Bacterium

Acute graft-versus-host disease (aGvHD) is a severe, often lethal, complication of hematopoietic stem cell transplantation, and although prophylactic regimens are given as standard pretransplantation therapy, up to 60% of these patients develop aGvHD, and require additional immunosuppressive intervention. We treated mice with a purified probiotic molecule, exopolysaccharide (EPS) from Bacillus subtilis, shortly before and after induction of aGvHD and found that, whereas only 10% of control mice survived to day 80, 70% of EPS-treated mice survived to 80 d. EPS treatment of donor-only mice resulted in ∼60% survival. Using a biosensor mouse model to assess inflammation in live mice during aGvHD, we found that EPS prevented the activation of alloreactive donor T cells. In vitro, EPS did not affect T cells directly but, instead, induced bone marrow-derived dendritic cells (BMDCs) that displayed characteristics of inhibitory dendritic cells (DCs). Development of these BMDCs required TLR4 signaling through both MyD88 and TRIF pathways. Using BMDCs derived from IDO knockout mice, we showed that T cell inhibition by EPS-treated BMDCs was mediated through the suppressive effects of IDO. These studies describe a bacterial molecule that modulates immune responses by inducing inhibitory DCs in a TLR4-dependent manner, and these cells have the capacity to inhibit T cell activation through IDO. We suggest that EPS or EPS-treated DCs can serve as novel agents for preventing aGvHD.

PD-L1 cellular nanovesicles carrying rapamycin inhibit alloimmune responses in transplantation

Organ transplantation has been employed upon serious injuries, but a T-cell-mediated potent inflammatory immune response often leads to graft rejection. Immunosuppressive drugs such as rapamycin (RAPA) have to be taken after organ transplantation, but long-term use of these drugs causes severe adverse effects. Immune checkpoint pathways such as the programmed death-receptor 1/programmed death-ligand 1 (PD-1/PD-L1) provides an immunosuppressive environment, preventing excessive tissue destruction due to inflammatory immune responses. In this study, we bioengineered cell membrane-derived PD-L1 nanovesicles (PD-L1 NVs) to carry low doses of RAPA. These NVs inhibited T-cell activation and proliferation in vitro, by enhancing the PD-1/PD-L1 immune co-inhibitory signaling axis and inhibiting the mTOR pathway. Importantly, PD-L1 NVs encapsulated with rapamycin exerted stronger effects on inhibiting T-cell proliferation than PD-L1 NVs or rapamycin alone. This can be recapitulated in a mouse skin transplantation model, leading to the weakened alloimmune response and allograft tolerance. We also found that PD-L1/rapamycin vesicles have additional function to induce regulatory T cells in the recipient spleens. Our study highlighted the power of combining low-dose rapamycin and PD-L1 in the nanovesicles as immunosuppressants to promote allograft acceptance.

Detection and Monitoring of Regulatory Immune Cells Following Their Adoptive Transfer in Organ Transplantation

Application of cell-based immunotherapy in organ transplantation to minimize the burden of immunosuppressive medication and promote allograft tolerance has expanded significantly over the past decade. Adoptively transferred regulatory immune cells prolong allograft survival and transplant tolerance in pre-clinical models. Many cell products are currently under investigation in early phase human clinical trials designed to assess feasibility and safety. Despite rapid advances in manufacturing practices, defining the appropriate protocol that will optimize in vivo conditions for tolerance induction remains a major challenge and depends heavily on understanding the fate, biodistribution, functional stability and longevity of the cell product after administration. This review focuses on in vivo detection and monitoring of various regulatory immune cell types administered for allograft tolerance induction in both pre-clinical animal models and early human clinical trials. We discuss the current status of various non-invasive methods for tracking regulatory cell products in the context of organ transplantation and implications for enhanced understanding of the therapeutic potential of cell-based therapy in the broad context of control of immune-mediated inflammatory disorders.

Modulatory effect of rapamycin and tacrolimus on monocyte-derived dendritic cells phenotype and function

BACKGROUND

Immunosuppressive-drugs are needed after solid organ transplantation to prevent allograft rejection but induce severe side effects. Understanding the alloimmune response is critical to modulate it and to achieve graft operational tolerance. The role of regulatory T cells and tolerogenic dendritic cells (Tol-DCs) is undoubtedly essential in tolerance induction. Tacrolimus is considered as the cornerstone of immunosuppression in solid organ transplantation. mTOR inhibitor such as rapamycin are thought to induce tolerance and are used as anticancer drugs in several cancers. The aim of this study was to better understand the effect of these immunosuppressive drugs on the differentiation, maturation and function of human monocyte derived dendritic cells (DCs).

MATERIAL AND METHODS

DCs were differentiated from monocytes of healthy donors with either rapamycin (Rapa-DCs) or tacrolimus (Tac-DCs). The phenotype was evaluated by flow cytometry analysis. The production of pro- and anti-inflammatory cytokines was assessed by ELISA. The mRNA expression level of IDO and PD-L1 was assessed by RTqPCR. Mixed leukocytes reactions were performed to analyse suppressive activity of DCs.

RESULTS

Rapa-DC were characterised by a lower expression of the co-stimulatory molecules and CD83 than control-DCs (CTR-DC) (p < 0.05). In contrast, tacrolimus had no effect on the expression of surface markers compared to CTR-DCs. Rapamycin reduced both IL-12 and IL-10 secretions (p < 0.05). Rapa-DCs had a suppressive effect on CD4⁺ allogenic T cells compared to CTR-DCs (p < 0.05). However, neither Rapa-DCs nor Tac-DCs favoured the emergence of a CD4⁺CD25^highFoxp3⁺ population compared to CTR-DCs. Surprisingly, Rapa-DCs had a reduced expression of IDO and PD-L1 compared to Tac-DCs and CTR-DCs.

CONCLUSION

Rapa-DCs exhibit an incomplete phenotypic tolerogenic profile. To our knowledge this is the first paper showing a reduction of expression of pro-tolerogenic enzyme IDO in DCs. Tacrolimus does not change the phenotypical or functional characteristics of moDCs.

Manipulation of Regulatory Dendritic Cells for Induction Transplantation Tolerance

Current organ transplantation therapy is life-saving but accompanied by well-recognized side effects due to post-transplantation systematic immunosuppressive treatment. Dendritic cells (DCs) are central instigators and regulators of transplantation immunity and are responsible for balancing allograft rejection and tolerance. They are derived from monocyte-macrophage DC progenitors originating in the bone marrow and are classified into different subsets based on their developmental, phenotypical, and functional criteria. Functionally, DCs instigate allograft immunity by presenting donor antigens to alloreactive T cells via direct, indirect, and semidirect recognition pathways and provide essential signaling for alloreactive T cell activation via costimulatory molecules and pro-inflammatory cytokines. Regulatory DCs (DCregs) are characterized by a relatively low expression of major histocompatibility complex, costimulatory molecules, and altered cytokine production and exert their regulatory function through T cell anergy, T cell deletion, and regulatory T cell induction. In rodent transplantation studies, DCreg-based therapy, by in situ targeting or infusion of ex vivo generated DCregs, exhibits promising potential as a natural, well-tolerated, organ-specific therapeutic strategy for promoting lasting organ-specific transplantation tolerance. Recent early-phase studies of DCregs have begun to examine the safety and efficacy of DCreg-induced allograft tolerance in living-donor renal or liver transplantations. The present review summarizes the basic characteristics, function, and translation of DCregs in transplantation tolerance induction.

Triazolopyrimidine derivative NK026680 and donor-specific transfusion induces CD4+CD25+Foxp3+ T cells and ameliorates allograft rejection in an antigen-specific manner

We have previously demonstrated the unique properties of a new triazolopyrimidine derivative, NK026680, which exerts immunosuppressive effects in rat heart transplant model and confers tolerogeneic properties on ex vivo-conditioned dendritic cells in mice. We herein demonstrate that NK026680 promotes the expansion of regulatory T cells (Tregs) with potent immunoregulatory effects when used in combination with donor-specific transfusion (DST). BALB/c (H-2^d) heart graft were transplanted into C57BL/6 (H-2^b) mice following intravenous injection of donor splenocytes (DST) and oral administration of NK026680. The NK026680 plus DST treatment markedly prolonged the survival time of the donor-graft, but not that of the 3rd party-graft (C3H; H-2^k). Treg cells in the recipient spleen on day 0 expanded when stimulated with donor-antigens in vivo and in vitro. After heart transplantation, Treg cells accumulated into the graft and increased in the spleen. NK026680 plus DST also decreased activated CD8⁺ T cells in the spleen and inhibited infiltration of CD8⁺ T cells into the graft. Depletion of CD25⁺ cells inhibited the graft prolonging effect of the NK026680 plus DST treatment. NK026680 administration together with DST induces potent immunoregulatory effects in an antigen-specific manner, likely due to the in vivo generation of donor-specific Tregs.

Correlation between MDSC and Immune Tolerance in Transplantation: Cytokines, Pathways and Cell-cell Interaction

MDSCs play an important role in the induction of immune tolerance. Cytokines and chemokines (GM-CSF, IL-6) contributed to the expansion, accumulation of MDSCs, and MDSCs function through iNOS, arginase and PD-L1. MDSCs are recruited and regulated through JAK/STAT, mTOR and Raf/MEK/ERK signaling pathways. MDSCs' immunosuppressive functions were realized through Tregs-mediated pathways and their direct suppression of immune cells. All of the above contribute to the MDSC-related immune tolerance in transplantation. MDSCs have huge potential in prolonging graft survival and reducing rejection through different ways and many other factors worthy to be further investigated are also introduced.

Response of metastatic mouse invasive lobular carcinoma to mTOR inhibition is partly mediated by the adaptive immune system

Effective treatment of invasive lobular carcinoma (ILC) of the breast is hampered by late detection, invasive growth, distant metastasis, and poor response to chemotherapy. Phosphoinositide 3-kinase (PI3K) signaling, one of the major druggable oncogenic signaling networks, is frequently activated in ILC. We investigated treatment response and resistance to AZD8055, an inhibitor of mammalian target of rapamycin (mTOR), in the K14-cre;Cdh1^Flox/Flox;Trp53^Flox/Flox (KEP) mouse model of metastatic ILC. Inhibition of mTOR signaling blocked the growth of primary KEP tumors as well as the progression of metastatic disease. However, primary tumors and distant metastases eventually acquired resistance after long-term AZD8055 treatment, despite continued effective suppression of mTOR signaling in cancer cells. Interestingly, therapeutic responses were associated with increased expression of genes related to antigen presentation. Consistent with this observation, increased numbers of tumor-infiltrating major histocompatibility complex class II-positive (MHCII+) immune cells were observed in treatment-responsive KEP tumors. Acquisition of treatment resistance was associated with loss of MHCII+ cells and reduced expression of genes related to the adaptive immune system. The therapeutic efficacy of mTOR inhibition was reduced in Rag1^−/- mice lacking mature T and B lymphocytes, compared to immunocompetent mice. Furthermore, therapy responsiveness could be partially rescued by transplanting AZD8055-resistant KEP tumors into treatment-naïve immunocompetent hosts. Collectively, these data indicate that the PI3K signaling pathway is an attractive therapeutic target in invasive lobular carcinoma, and that part of the therapeutic effect of mTOR inhibition is mediated by the adaptive immune system.

Prolongation of rat-to-mouse islets xenograft survival by co-transplantation of autologous IL-10 differentiated murine tolerogenic dendritic cells

BACKGROUND

Tolerogenic dendritic cells (DCs) represent a promising approach to promote transplantation tolerance. In this study, the potential of autologous bone marrow (BM)-derived murine DC to protect rat-to-mouse islets xenografts was analyzed.

METHODS

Tolerogenic DCs were generated by differentiating BM cells in the presence of granulocyte-macrophage colony-stimulating factor and interleukin 10 (IL-10, IL-10 DC). The phenotype of IL-10 DC was characterized in vitro by expression of costimulatory/inhibitory molecules (flow cytometry) and cytokines (Luminex and ELISA), their function by phagocytosis and T-cell stimulation assays. To study transplant tolerance in vivo, rat islets were transplanted alone or in combination with autologous murine IL-10 DC under the kidney capsule of streptozotocin-induced diabetic C57BL/6 mice. Xenograft survival was evaluated by monitoring glycemia, cellular infiltration of xenografts by microscopy and flow cytometry 10 days post-transplantation.

RESULTS

Compared with control DC, IL-10 DC exhibited lower levels of major histocompatibility complex class II, costimulatory molecules (CD40, CD86, CD205), lower production of pro-inflammatory cytokines (IL-12p70, TNF, IL-6), and higher production of IL-10. Phagocytosis of xenogeneic rat splenocytes was not impaired in IL-10 DC, whereas stimulation of T-cell proliferation was reduced in the presence of IL-10 DC. Xenograft survival of rat islets in diabetic mice co-transplanted with autologous murine IL-10 DC was significantly prolonged from 12 to 21 days, without additional immunosuppressive treatment. Overall, infiltration of xenografts by T cells and myeloid cells was not different in IL-10 DC recipient mice, but enriched for CD8⁺ T cells and myeloid cells with suppressor-associated phenotype.

CONCLUSIONS

Autologous IL-10-differentiated DC with tolerogenic properties prolong rat-to-mouse islets xenograft survival, potentially by locally inducing immune regulatory cells, indicating their potential for regulatory immune cell therapy in xenotransplantation.

Effects of Antirejection Drugs on Innate Immune Cells After Kidney Transplantation

Over the last decades, our understanding of adaptive immune responses to solid organ transplantation increased considerably and allowed development of immunosuppressive drugs targeting key alloreactive T cells mechanism. As a result, rates of acute rejection dropped and short-term graft survival improved significantly. However, long-term outcomes are still disappointing. Recently, increasing evidence supports that innate immune responses plays roles in allograft rejection and represents a valuable target to further improve long-term allograft survival. Innate immune cells are activated by molecules with stereotypical motifs produced during injury (i.e., damage-associated molecular patterns, DAMPS) or infection (i.e., pathogen-associated molecular patterns, PAMPs). Activated innate immune cells can exert direct pro- and anti-inflammatory effects, while also priming adaptive immune responses. These cells are activated after transplantation by multiple stimuli, including ischemia-reperfusion injury, rejection, and infections. Data from animal models of graft rejection, show that inhibition of innate immunity promotes development of tolerance. Therefore, understanding mechanisms of innate immunity is important to improve graft outcomes. This review discusses effects of currently used immunosuppressive agents on innate immune responses in kidney transplantation.

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.

Effects of dietary tryptophan levels on antioxidant status and immunity for juvenile blunt snout bream (Megalobrama amblycephala) involved in Nrf2 and TOR signaling pathway

Dietary administration of tryptophan has been proved improving growth performance of fish. An 8-week feeding trial was conducted to investigate the effects of dietary tryptophan level on antioxidant capacity and immune response through Nrf2 and TOR signaling pathway. The results showed that, 0.08% tryptophan level significantly increased plasma aspartate aminotransferase (AST), while immunoglobulin M (IgM) and alkaline phosphatase (ALP) were strikingly increased by 0.40% level. The level of plasma complement component 3 (C3), alanine aminotransferase (ALT) and albumin (ALB) were independent of tryptophan supplementation. Total superoxide dismutase (T-SOD), catalase (CAT), total antioxidant capacity (T-AOC) and glutathione (GSH) activity were increased with increasing dietary tryptophan level until 0.40% and then decreased, while the level of malondialdehyde (MDA) showed a reverse trend. 0.19% and 0.28% tryptophan level significantly improved the glutathione peroxidase 1 (GPx-1) activity. Compared with 0.08% dietary tryptophan level, 0.40% level significantly improved nuclear factor erythroid 2-related factor 2 (Nrf2), GPx, manganese superoxide dismutase (Mn-SOD), CAT and transforming growth factor-β (TGF-β) mRNA level, while Kelch-like ECH-associated protein 1 (Keap1) and interleukin 1β (IL-1β) mRNA level were significantly decreased. The relative expression of copper zinc superoxide dismutase (Cu/Zn-SOD), heme oxygenase-1 (HO-1), target of rapamycin (TOR), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K), protein kinase B (Akt) and interleukin 10 (IL-10) were significantly improved by 0.28% diet, while the mRNA level of tumor necrosis factor-α (TNF-α) and nuclear factor-kappa B (NF-κB) were increased by 0.08% diet. Interleukin 8 (IL-8) mRNA level was not significantly affected by dietary tryptophan. Based on MDA and T-SOD value, the optimal dietary tryptophan level of juvenile blunt snout bream was determined to be 0.33% (1.03% of dietary protein) and 0.36% (1.13% of dietary protein), respectively, using quadratic regression analysis.

mTOR and Aging: An Old Fashioned Dress

Aging is a physiologic/pathologic process characterized by a progressive impairment of cellular functions, supported by the alterations of several molecular pathways, leading to an increased cell susceptibility to injury. This deterioration is the primary risk factor for several major human pathologies. Numerous cellular processes, including genomic instability, telomere erosion, epigenetic alterations, loss of proteostasis, deregulated nutrient-sensing, mitochondrial dysfunction, stem cell exhaustion, and altered intercellular signal transduction represent common denominators of aging in different organisms. Mammalian target of rapamycin (mTOR) is an evolutionarily conserved nutrient sensing protein kinase that regulates growth and metabolism in all eukaryotic cells. Studies in flies, worms, yeast, and mice support the hypothesis that the mTOR signalling network plays a pivotal role in modulating aging. mTOR is emerging as the most robust mediator of the protective effects of various forms of dietary restriction, which has been shown to extend lifespan and slow the onset of age-related diseases across species. Herein we discuss the role of mTor signalling network in the development of classic age-related diseases, focused on cardiovascular system, immune response, and cancer.

Dissecting the Multiplicity of Immune Effects of Immunosuppressive Drugs to Better Predict the Risk of de novo Malignancies in Solid Organ Transplant Patients

De novo malignancies constitute an emerging cause of morbidity after solid organ transplant (SOT), significantly affecting the long-term survival of transplant recipients. Pharmacologic immunosuppression may functionally impair the immunosurveillance in these patients, thereby increasing the risk of cancer development. Nevertheless, the multiplicity and heterogeneity of the immune effects induced by immunosuppressive drugs limit the current possibilities to reliably predict the risk of de novo malignancy in SOT patients. Therefore, there is the pressing need to better characterize the immune dysfunctions induced by the different immunosuppressive regimens administered to prevent allograft rejection to tailor more precisely the therapeutic schedule and decrease the risk of de novo malignancies. We herein highlight the impact exerted by different classes of immunosuppressants on the most relevant immune cells, with a particular focus on the effects on dendritic cells (DCs), the main regulators of the balance between immunosurveillance and tolerance.

Proactively Reducing Anti-Drug Antibodies via Immunomodulatory Bioconjugation

Although PEGylation reduces the immunogenicity of protein drugs to some extent, its limitations for highly immunogenic biotherapeutics have been demonstrated. Herein, a proactive strategy to alleviate the development of anti-drug antibodies (ADAs) against protein drugs by immunomodulatory bioconjugation is reported. Rapamycin was conjugated to a PEGylated protein therapeutic via a cleavable disulfide linker. The conjugated rapamycin can be released from the bioconjugate and prevent immune responses once the bioconjugate is uptaken by antigen-presenting cells. The immunomodulatory bioconjugate significantly reduced the titers of ADAs compared with a PEGylated protein. The inhibition of immune responses was specific to the conjugated antigen, avoiding systemic immune suppression and the risk of increased susceptibility to infections. The reported approach breaks the limitations of PEGylation by the proactive prevention of ADAs.

Rictor deficiency in dendritic cells exacerbates acute kidney injury

Dendritic cells (DCs) are critical initiators of innate immunity in the kidney and orchestrate inflammation following ischemia-reperfusion injury. The role of the mammalian/mechanistic target of rapamycin (mTOR) in the pathophysiology of renal ischemia-reperfusion injury has been characterized. However, the influence of DC-based alterations in mTOR signaling is unknown. To address this, bone marrow-derived mTORC2-deficient (Rictor^-/-) DCs underwent hypoxia-reoxygenation and then analysis by flow cytometry. Adoptive transfer of wild-type or Rictor^-/- DC to C57BL/6 mice followed by unilateral or bilateral renal ischemia-reperfusion injury (20 min ischemia) was used to assess their in vivo migratory capacity and influence on tissue injury. Age-matched male DC-specific Rictor^-/- mice or littermate controls underwent bilateral renal ischemia-reperfusion, followed by assessment of renal function, histopathology, and biomolecular and cell infiltration analysis. Rictor^-/- DCs expressed more costimulatory CD80/CD86 but less coinhibitory programmed death ligand 1 (PDL1), a pattern that was enhanced by hypoxia-reoxygenation. They also demonstrated enhanced migration to the injured kidney and induced greater tissue damage. Following ischemia-reperfusion, Rictor^-/- DC mice developed higher serum creatinine levels, more severe histological damage, and greater proinflammatory cytokine production compared to littermate controls. Additionally, a greater influx of both neutrophils and T cells was seen in Rictor^-/- DC mice, along with CD11c⁺MHCII⁺CD11b^hiF4/80⁺ renal DC, that expressed more CD86 but less PDL1. Thus, DC-targeted elimination of Rictor enhances inflammation and migratory responses to the injured kidney, highlighting the regulatory roles of both DCs and Rictor in the pathophysiology of acute kidney injury.

Generation, Characteristics and Clinical Trials of Ex Vivo Generated Tolerogenic Dendritic Cells

Dendritic cells (DCs) play a key role not only in the initiation of primary immune responses, but also in the development and maintenance of immune tolerance. Numerous protocols have been developed to generate tolerogenic DCs (tolDCs) ex vivo, and the therapeutic efficacy of ex vivo-generated tolDCs has been demonstrated in autoimmune disease animal models. Based on successes in small animal models, several clinical trials have been completed or are on-going in patients with autoimmune diseases such as rheumatoid arthritis, type 1 diabetes, multiple sclerosis, and Crohn's disease. Here we describe the methods used to generate tolDCs ex vivo, and the common features shared by tolDCs. In addition, we overview five completed clinical trials with reported outcomes and summarize the tolDC-based clinical trials that are currently registered with the U.S. National Institutes of Health. Although the number of tolDC-based clinical trials is much smaller than the hundreds of clinical trials using immunogenic DCs, tolDC-based treatment of autoimmune diseases is becoming a reality, and could serve as an innovative cellular therapy in the future.

Myeloid-Derived Suppressor Cells as a Regulator of Immunity in Organ Transplantation

Regulation of allo-immune responses is proposed as a topic for investigation in the current field of organ transplantation. As a regulator, regulatory T cells (Tregs) have received attention due to their ability to control allograft rejection. Concurrently, however, the independent action of Tregs is not enough to achieve tolerance status in many situations. Meanwhile, as a multi-functional regulator, myeloid-derived suppressor cells (MDSCs) can suppress effector T cells as well as induce Tregs or regulatory B cells (Bregs) in certain circumstances. Furthermore, the importance of a crosstalk between MDSCs and natural killer T cells to induce tolerance has been reported. Thus, orchestration between MDSCs, myeloid regulators, T/Bregs and other lymphoid/myeloid regulators can shed light on achieving allogeneic tolerance. Here, we review the current knowledge in terms of immunological regulatory function displayed by MDSCs in the context of organ transplantation. Ideal control of MDSCs would lead to a reduction of allograft rejection and subsequent long-term allograft acceptance.

The impact of metabolic reprogramming on dendritic cell function

Dendritic cells (DCs) are antigen-presenting cells with the ability to activate naïve T cells and direct the adaptive cellular immune response toward a specific profile. This is important, as different pathogens demand specific "profiles" of immune responses for their elimination. Such a goal is achieved depending on the maturation/activation status of DCs by the time of antigen presentation to T cells. Notwithstanding this, recent studies have shown that DCs alter their metabolic program to accommodate the functional changes in gene expression and protein synthesis that follow antigen recognition. In this review, we aim to summarize the data in the literature regarding the metabolic pathways involved with DC phenotypes and their functions.

Murine and Non-Human Primate Dendritic Cell Targeting Nanoparticles for in Vivo Generation of Regulatory T-Cells

Porous silicon nanoparticles (pSiNP), modified to target dendritic cells (DC), provide an alternate strategy for the delivery of immunosuppressive drugs. Here, we aimed to develop a DC-targeting pSiNP displaying c-type lectin, dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), and CD11c monoclonal antibodies. The in vivo tracking of these fluorescent DC-targeting nanoparticles was assessed in both C57BL/6 mice and common marmosets ( Callithrix jacchus) by intravenous injection (20 mg/kg). Rapamycin and ovalbumin (OVA)_323-339 peptide loaded pSiNP were employed to evaluate their ability to generate murine CD4⁺CD25⁺FoxP3⁺ regulatory T-cells in vivo within OVA sensitized mice. In vivo, pSiNP migrated to the liver, kidneys, lungs, and spleen in both mice and marmosets. Flow cytometry confirmed pSiNP uptake by splenic and peripheral blood DC when functionalized with targeting antibodies. C57BL/6 OVA sensitized mice injected with CD11c-pSiNP loaded with rapamycin + OVA_323-339 produced a 5-fold higher number of splenic regulatory T-cells compared to control mice, at 40 days post-pSiNP injection. These results demonstrate the importance of the immobilized targeting antibodies to enhance cellular uptake and enable the in vivo generation of splenic regulatory T-cells.

Upregulation of Heme Oxygenase-1 Endues Immature Dendritic Cells With More Potent and Durable Immunoregulatory Properties and Promotes Engraftment in a Stringent Mouse Cardiac Allotransplant Model

Heme oxygenase-1 (HO-1) is critical for the ability of immature dendritic cells (imDCs) to suppress T-cell responses. Induction of high HO-1 expression may markedly improve the tolerogenic capacity of imDCs. Here, we generated bone marrow-derived DCs (BMDCs) from BALB/c mice with low doses of GM-CSF and IL-4. The adherent BMDCs were obtained as imDCs. Upregulation of HO-1 in imDCs (HO-1^hi-imDCs) was achieved by cobalt protoporphyrin treatment. HO-1^hi-imDCs proved to be more maturation-resistant than conventional imDCs, with an enhanced ability to inhibit allogeneic T-cell proliferation stimulated by anti-CD3/CD28 antibodies. When donor-derived DC adoptive transfer was performed in a stringent mouse cardiac allotransplant model, the extent of graft prolongation observed with HO-1^hi imDCs was superior to that obtained with conventional imDCs. T-cell activation and proliferation in cardiac allograft recipients was more strongly suppressed in the HO-1^hi imDC transfusion group than that in the untreated imDC group. Furthermore, donor HO-1^hi imDCs were able to maintain a status of high HO-1 expression and survived longer in the recipient spleens than did untreated imDCs after adoptive transfer. In vitro-generated HO-1^hi imDCs had an enhanced tolerogenic capacity to modulate alloimmune responses both in vitro and in vivo, and thus may offer a novel antigen-specific and cost-effective strategy to induce transplant tolerance.

Direct modulation of myelin-autoreactive CD4+ and CD8+ T cells in EAE mice by a tolerogenic nanoparticle co-carrying myelin peptide-loaded major histocompatibility complexes, CD47 and multiple regulatory molecules

Purpose

Numerous nanomaterials have been reported in the treatment of multiple sclerosis or experimental autoimmune encephalomyelitis (EAE). But most of these nanoscale therapeutics deliver myelin antigens together with toxins or cytokines and underlay the cellular uptake and induction of tolerogenic antigen-presenting cells by which they indirectly induce T cell tolerance. This study focuses on the on-target and direct modulation of myelin-autoreactive T cells and combined use of multiple regulatory molecules by generating a tolerogenic nanoparticle.

Materials and methods

Poly(lactic-co-glycolic acid) nanoparticles (PLGA-NPs) were fabricated by co-coupling MOG_40–54/H-2D^b-Ig dimer, MOG_35–55/I-A^b multimer, anti-Fas, PD-L1-Fc and CD47-Fc and encapsulating transforming growth factor-β1. The resulting 217 nm tolerogenic nanoparticles (tNPs) were administered intravenously into MOG_35–55 peptide-induced EAE mice, which was followed by the investigation of therapeutic outcomes and the in vivo mechanism.

Results

Four infusions of the tNPs durably ameliorated EAE with a marked reduction of clinical score, neuroinflammation and demyelination. They were distributed in secondary lymphoid tissues, various organs and brain after intravenous injection, with retention over 36 h, and made contacts with CD4⁺ and CD8⁺ T cells. Two injections of the tNPs markedly decreased the MOG_35–55-reactive Th1 and Th17 cells and MOG_40–55-reactive Tc1 and Tc17 cells, increased regulatory T cells, inhibited T cell proliferation and elevated T cell apoptosis in spleen. Transforming growth factor-β1 and interleukin-10 were upregulated in the homogenates of central nervous system and supernatant of spleen cells.

Conclusion

Our data suggest a novel therapeutic nanoparticle to directly modulate autoreactive T cells by surface presentation of multiple ligands and paracrine release of cytokine in the antigen-specific combination immunotherapy for T cell-mediated autoimmune diseases.

Minocycline promotes the generation of dendritic cells with regulatory properties

Minocycline, which has long been used as a broad-spectrum antibiotic, also exhibits non-antibiotic properties such as inhibition of inflammation and angiogenesis. In this study, we show that minocycline significantly enhances the generation of dendritic cells (DCs) from mouse bone marrow (BM) cells when used together with GM-CSF and IL-4. DCs generated from BM cells in the presence of minocycline (Mino-DCs) demonstrate the characteristics of regulatory DCs. Compared with control DCs, Mino-DCs are resistant to subsequent maturation stimuli, impaired in MHC class II-restricted exogenous Ag presentation, and show decreased cytokine secretion. Mino-DCs also show decreased ability to prime allogeneic-specific T cells, while increasing the expansion of CD4⁺CD25⁺Foxp3⁺ T regulatory cells both in vitro and in vivo. In addition, pretreatment with MOG35-55 peptide-pulsed Mino-DCs ameliorates clinical signs of experimental autoimmune encephalitis induced by MOG peptide injection. Our study identifies minocycline as a new pharmacological agent that could be potentially used to increase the production of regulatory DCs for cell therapy to treat autoimmune disorders, allergy, and transplant rejection.

Phosphoproteomics of cAMP signaling of Bordetella adenylate cyclase toxin in mouse dendritic cells

The adenylate cyclase toxin (CyaA) of the whooping cough agent Bordetella pertussis subverts immune functions of host myeloid cells expressing the αMβ2 integrin (CD11b/CD18, CR3 or Mac-1). CyaA delivers into cytosol of cells an extremely catalytically active adenylyl cyclase enzyme, which disrupts the innate and adaptive immune functions of phagocytes through unregulated production of the key signaling molecule cAMP. We have used phosphoproteomics to analyze cAMP signaling of CyaA in murine bone marrow-derived dendritic cells. CyaA action resulted in alterations of phosphorylation state of a number of proteins that regulate actin cytoskeleton homeostasis, including Mena, Talin-1 and VASP. CyaA action repressed mTOR signaling through activation of mTORC1 inhibitors TSC2 and PRAS40 and altered phosphorylation of multiple chromatin remodelers, including the class II histone deacetylase HDAC5. CyaA toxin action further elicited inhibitory phosphorylation of SIK family kinases involved in modulation of immune response and provoked dephosphorylation of the transcriptional coactivator CRTC3, indicating that CyaA-promoted nuclear translocation of CRTC3 may account for CyaA-induced IL-10 production. These findings document the complexity of subversive physiological manipulation of myeloid phagocytes by the CyaA toxin, serving in immune evasion of the pertussis agent.

Manipulating human dendritic cell phenotype and function with targeted porous silicon nanoparticles

Dendritic cells (DC) are the most potent antigen-presenting cells and are fundamental for the establishment of transplant tolerance. The Dendritic Cell-Specific Intracellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN; CD209) receptor provides a target for dendritic cell therapy. Biodegradable and high-surface area porous silicon (pSi) nanoparticles displaying anti-DC-SIGN antibodies and loaded with the immunosuppressant rapamycin (Sirolimus) serve as a fit-for-purpose platform to target and modify DC. Here, we describe the fabrication of rapamycin-loaded DC-SIGN displaying pSi nanoparticles, the uptake efficiency into DC and the extent of nanoparticle-induced modulation of phenotype and function. DC-SIGN antibody displaying pSi nanoparticles favourably targeted and were phagocytosed by monocyte-derived and myeloid DC in whole human blood in a time- and dose-dependent manner. DC preconditioning with rapamycin-loaded nanoparticles, resulted in a maturation resistant phenotype and significantly suppressed allogeneic T-cell proliferation.

The combination of mitomycin-induced blood cells with a temporary treatment of ciclosporin A prolongs allograft survival in vascularized composite allotransplantation

BACKGROUND

Vascularized composite allotransplantation (VCA) is a rapidly expanding field of transplantation and provides a potential treatment for complex tissue defects. Peripheral blood mononuclear cells (PBMCs) shortly incubated with the antibiotic and chemotherapeutic agent mitomycin C (MMC) can suppress allogeneic T cell response and control allograft rejection in various organ transplantation models. MMC-incubated PBMCs (MICs) are currently being tested in a phase I clinical trial in kidney transplant patients. Previous studies with MICs in a complex VCA model showed the immunomodulatory potential of these cells. The aim of this study is to optimize and evaluate the use of MICs in combination with a standard immunosuppressive drug in VCA.

METHODS

Fully mismatched rats were used as hind limb donors [Lewis (RT1¹)] and recipients [Brown-Norway (RT1ⁿ)]. Sixty allogeneic hind limb transplantations were performed in six groups. Group A received donor-derived MICs combined with a temporary ciclosporin A (CsA) treatment. Group B received MICs in combination with a temporarily administered reduced dose of CsA. Group C served as a control and received a standard CsA dose temporarily without an additional administration of MICs, whereas Group D was solely medicated with a reduced CsA dose. Group E received no immunosuppressive therapy, neither CsA nor MICs. Group F was given a continuous standard immunosuppressive regimen consisting of CsA and prednisolone. The endpoint of the study was the onset of allograft rejection which was assessed clinically and histologically.

RESULTS

In group A and B, the rejection-free interval of the allograft was significantly prolonged to an average of 23.1 ± 1.7 and 24.7 ± 1.8 days compared to the corresponding control groups (p < 0.01). Rejection in groups C, D, and E was noted after 14.3 ± 1.1, 7.8 ± 0.7, and 6.9 ± 0.6 days. No rejection occurred in control group F during the follow-up period of 100 days. No adverse events have been noted.

CONCLUSION

The findings of this study show that the combination of MICs with a temporary CsA treatment significantly prolongs the rejection-free interval in a complex VCA model. The combination of MICs with CsA showed no adverse events such as graft-versus-host disease. MICs, which are generated by a simple and reliable in vitro technique, represent a potential therapeutic tool for prolonging allograft survival through immunomodulation.

An antigen-specific semi-therapeutic treatment with local delivery of tolerogenic factors through a dual-sized microparticle system blocks experimental autoimmune encephalomyelitis

Antigen-specific treatments are highly desirable for autoimmune diseases in contrast to treatments which induce systemic immunosuppression. A novel antigen-specific therapy has been developed which, when administered semi-therapeutically, is highly efficacious in the treatment of the mouse model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). The treatment uses dual-sized, polymeric microparticles (dMPs) loaded with specific antigen and tolerizing factors for intra- and extra-cellular delivery, designed to recruit and modulate dendritic cells toward a tolerogenic phenotype without systemic release. This approach demonstrated robust efficacy and provided complete protection against disease. Therapeutic efficacy required encapsulation of the factors in controlled-release microparticles and was antigen-specific. Disease blocking was associated with a reduction of infiltrating CD4⁺ T cells, inflammatory cytokine-producing pathogenic CD4⁺ T cells, and activated macrophages and microglia in the central nervous system. Furthermore, CD4⁺ T cells isolated from dMP-treated mice were anergic in response to disease-specific, antigen-loaded splenocytes. Additionally, the frequency of CD86^hiMHCII^hi dendritic cells in draining lymph nodes of EAE mice treated with Ag-specific dMPs was reduced. Our findings highlight the efficacy of microparticle-based drug delivery platform to mediate antigen-specific tolerance, and suggest that such a multi-factor combinatorial approach can act to block autoimmunity.

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.