Prevention of allograft rejection by in vitro generated tolerogenic dendritic cells

Quantitative Analysis of OX62-Positive Dendritic Cell Distribution in the Rat Laryngeal Complex

Objectives:

Dendritic cells (DCs) are key instigators of rejection after transplantation. Their distribution has not been systematically characterized in all locations of the larynx and its surrounding tissues.

Methods:

Rat larynges were stained with monoclonal antibodies identifying DCs. These cells were then enumerated by a new combination of techniques including immunofluorescence, confocal microscopy, and imaging software.

Results:

The vast majority of DCs were located in the epithelium and subepithelium of the airway; the mean DC density ranged from 9 cells per square millimeter (0.2% of cells) to 645 cells per square millimeter (10.3% of cells). Their density in the epithelium was 3 to 11 times higher than that in the subepithelium. Non-airway sites (thyroid, parathyroid, muscle, fat) had mean DC densities varying from 3 cells per square millimeter (0.2%) to 57 cells per square millimeter (0.8%). No DCs were detected in cartilage.

Conclusions:

Dendritic cells are concentrated in the laryngotracheal epithelium and subepithelium and represent a much smaller proportion in the other sites studied. A baseline for laryngeal DC population studies has been established, and a computerized model for consistent quantitation using confocal microscopy has been developed. This unique method will serve as a foundation for investigating DC trafficking after rat laryngeal transplantation.

Connexin43 knockdown in bone marrow‑derived dendritic cells by small interfering RNA leads to a diminished T-cell stimulation

Dendritic cells, the most powerful type of antigen‑presenting cells, have the unique ability to induce primary immune responses. Connexin43 expression is upregulated to increase gap junctions when immune cells are exposed to inflammatory factors. The present study applied small‑interfering RNA (siRNA) to decrease connexin43 expression. The results showed that silencing of connexin43 using siRNA resulted in arrest of bone marrow‑derived dendritic cell (BM‑DC) maturation as evidenced by reduced expression of major histocompatibility complex II, CD40, CD80 and CD86. Functionally, connexin43‑silenced BM‑DC showed a markedly decreased capability to induce T-cell stimulation. In conclusion, the present study demonstrated that antigens present on BM‑DCs can be suppressed by connexin43 knockdown in BM‑DCs. The present study therefore presented an effective method to modulate the immunology of BM‑DCs.

Development of lipid nanoparticle formulations of siRNA for hepatocyte gene silencing following subcutaneous administration

Recently developed lipid nanoparticle (LNP) formulations of siRNA have proven to be effective agents for hepatocyte gene silencing following intravenous administration with at least three LNP-siRNA formulations in clinical trials. The aim of this work was to develop LNP-siRNA systems for hepatocyte gene silencing that can be administered subcutaneously (s.c.). Three parameters were investigated, namely LNP size, residence time of the polyethylene glycol (PEG)-lipid coating and the influence of hepatocyte-specific targeting ligands. LNP sizes were varied over the range of 30 to 115 nm in diameter and PEG-lipid that dissociates rapidly (PEG-DMG) and slowly (PEG-DSG) were employed. In mice, results show that large (~80 nm) LNP exhibited limited accumulation in the liver and poor Factor VII (FVII) gene silencing at 1mg siRNA/kg body weight. Conversely, small (~30 nm) LNP systems showed maximal liver accumulation yet still had minimal activity. Interestingly, intermediate size (~45 nm) LNP containing PEG-DSG exhibited nearly equivalent liver accumulation as the smaller systems following s.c. administration but reduced FVII levels by 80% at 1mg siRNA/kg body weight. Smaller systems (~35 nm diameter) containing either PEG-DMG or PEG-DSG were less active; however addition of 0.5 mol.% of a GalNAc-PEG lipid to these smaller systems improved activity to levels similar to that observed for the ~45 nm diameter systems. In summary, this work shows that appropriately designed LNP-siRNA systems can result in effective hepatocyte gene silencing following s.c administration.

Immune tolerance of skin allograft transplantation induced by immature dendritic cells of a third party carrying donor antigens in mice

BACKGROUND

Dendritic cells (DCs) are the most powerful antigen-presenting cells in the body. Immature DCs (imDCs) can induce transplantation tolerance. In this study, using a mouse model of skin transplantation. We explored the antigen uptake by imDCs, changes in phenotype and function after antigen loading, as well as survival of skin grafts.

METHODS

Mononuclear cells from C57BL/6 mice mixed with a tritiated leucine ([(3)H]Leu) antigen supernate were incubated with Kunming mice imDC and mature DCs. We recorded the expressions of surface molecules that were detected using flow cytometry, mixed lymphocyte reactions, mean survival times, and postoperative morphological changes in skin grafts.

RESULTS

After the addition of allogeneic antigen supernate, the counts per minute of imDCs were significantly higher than those of mature DCs. The expression rates of I(A)/I(E) and CD80 significantly increased on the cell surface of imDCs. The counts per minute of imDCs in mixed lymphocyte reactions in the presence of allogeneic antigens was significantly higher than those of controls. Comparing mean survival times with controls, skin grafts were significantly longer in the imDCs groups from donors or from a third party carrying donor antigens.

CONCLUSIONS

ImDCs display a strong antigen uptake, gradually maturing in terms of phenotype and function after loading. Complementary application of cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin blocks the immune response of imDCs. Both imDCs from the third party carrying donor antigens and those from the donor strain can establish antigen-specific immune tolerance to allogeneic skin grafts.

Exosome removal as a therapeutic adjuvant in cancer

Exosome secretion is a notable feature of malignancy owing to the roles of these nanoparticles in cancer growth, immune suppression, tumor angiogenesis and therapeutic resistance. Exosomes are 30-100 nm membrane vesicles released by many cells types during normal physiological processes. Tumors aberrantly secrete large quantities of exosomes that transport oncoproteins and immune suppressive molecules to support tumor growth and metastasis. The role of exosomes in intercellular signaling is exemplified by human epidermal growth factor receptor type 2 (HER2) over-expressing breast cancer, where exosomes with the HER2 oncoprotein stimulate tumor growth and interfere with the activity of the therapeutic antibody Herceptin®. Since numerous observations from experimental model systems point toward an important clinical impact of exosomes in cancer, several pharmacological strategies have been proposed for targeting their malignant activities. We also propose a novel device strategy involving extracorporeal hemofiltration of exosomes from the entire circulatory system using an affinity plasmapheresis platform known as the Aethlon ADAPT™ (adaptive dialysis-like affinity platform technology) system, which would overcome the risks of toxicity and drug interactions posed by pharmacological approaches. This technology allows affinity agents, including exosome-binding lectins and antibodies, to be immobilized in the outer-capillary space of plasma filtration membranes that integrate into existing kidney dialysis systems. Device therapies that evolve from this platform allow rapid extracorporeal capture and selective retention of target particles < 200 nm from the entire circulatory system. This strategy is supported by clinical experience in hepatitis C virus-infected patients using an ADAPT™ device, the Hemopurifier®, to reduce the systemic load of virions having similar sizes and glycosylated surfaces as cancer exosomes. This review discusses the possible therapeutic approaches for targeting immune suppressive exosomes in cancer patients, and the anticipated significance of these strategies for reversing immune dysfunction and improving responses to standard of care treatments.

Influence of cationic lipid composition on gene silencing properties of lipid nanoparticle formulations of siRNA in antigen-presenting cells

Lipid nanoparticles (LNPs) are currently the most effective in vivo delivery systems for silencing target genes in hepatocytes employing small interfering RNA. Antigen-presenting cells (APCs) are also potential targets for LNP siRNA. We examined the uptake, intracellular trafficking, and gene silencing potency in primary bone marrow macrophages (bmMΦ) and dendritic cells of siRNA formulated in LNPs containing four different ionizable cationic lipids namely DLinDAP, DLinDMA, DLinK-DMA, and DLinKC2-DMA. LNPs containing DLinKC2-DMA were the most potent formulations as determined by their ability to inhibit the production of GAPDH target protein. Also, LNPs containing DLinKC2-DMA were the most potent intracellular delivery agents as indicated by confocal studies of endosomal versus cytoplamic siRNA location using fluorescently labeled siRNA. DLinK-DMA and DLinKC2-DMA formulations exhibited improved gene silencing potencies relative to DLinDMA but were less toxic. In vivo results showed that LNP siRNA systems containing DLinKC2-DMA are effective agents for silencing GAPDH in APCs in the spleen and peritoneal cavity following systemic administration. Gene silencing in APCs was RNAi mediated and the use of larger LNPs resulted in substantially reduced hepatocyte silencing, while similar efficacy was maintained in APCs. These results are discussed with regard to the potential of LNP siRNA formulations to treat immunologically mediated diseases.

Dendritic cell apoptosis: regulation of tolerance versus immunity

Dendritic cell (DC) apoptosis is an important event that regulates the balance between tolerance and immunity through multiple pathways, and defects in DC apoptosis can trigger autoimmunity. DC apoptosis is also associated with immunosuppression and has been observed under several pathologies and infections. Recent studies indicate that apoptotic DCs can also play an active role in induction of tolerance. This review discusses the regulatory pathways of DC apoptosis, stimuli inducing DC apoptosis, and the implications of DC apoptosis in the induction of immunosuppression and/or tolerance.

Treatment of autoimmune arthritis using RNA interference-modulated dendritic cells

Dendritic cells (DCs) have a dual ability to either stimulate or suppress immunity, which is primarily associated with the expression of costimulatory molecules. Ag-loaded DCs have shown encouraging clinical results for treating cancer and infectious diseases; however, the use of these cells as a means of suppressing immune responses is only recently being explored. Here, we describe the induction of RNA interference through administering short interfering RNA (siRNA) as a means of specifically generating tolerogenic DCs. Knockdown of CD40, CD80, and CD86, prior to loading DCs with the arthritogenic Ag collagen II, led to a population of cells that could effectively suppress onset of collagen-induced arthritis. Maximum benefits were observed when all three genes were concurrently silenced. Disease suppression was associated with inhibition of collagen II-specific Ab production and suppression of T cell recall responses. Downregulation of IL-2, IFN-gamma, TNF-alpha, and IL-17 and increased FoxP3(+) cells with regulatory activity were observed in collagen-induced arthritis mice treated with siRNA-transfected DCs. Collectively, these data support the use of ex vivo gene manipulation in DCs using siRNA to generate tailor-made tolerogenic vaccines for treating autoimmunity.

Characterization of monocyte-derived dendritic cells from cats infected with feline immunodeficiency virus

Dendritic cells (DCs) are professional antigen presenting cells (APCs) that possess an extraordinary capacity to stimulate naïve T cells and initiate a primary immune response. To develop a DC-based immunotherapy for feline immunodeficiency virus (FIV) infection, we carried out a study to characterize DCs from FIV-infected cats and compared the observations with those obtained from healthy controls. DCs were derived from adherent peripheral blood mononuclear cells that had been cultivated with recombinant feline interleukin 4, granulocyte macrophage colony-stimulating factor and heat-inactivated autologous plasma. Various parameters, such as cell morphology, surface phenotype, endocytosis and mixed leukocyte reaction (MLR), were analyzed to characterize feline DCs. Monocyte-derived DCs from FIV-infected cats as well as those from healthy controls showed a dendritic appearance and expressed an APC-like phenotype (CD1c(+), CD80(+) and MHC class II(+)). However, the expression level of CD1a was variable in the DCs derived from FIV-infected cats, although this was not the case in the DCs derived from the healthy controls. DCs from the FIV-infected cats retained the ability to take up dextran via the mannose receptor and also showed an apparent MLR, indicating that these cells could be useful in immunotherapy. In this study, monocytes obtained from FIV-infected cats could differentiate into functional DCs, suggesting that they might be used in a DC-based immunotherapy against FIV infection.

Adoptive transfer of mFas ligand into dendritic cells influences the spontaneous resorption rate in the CBA/J x DBA/2 mouse model

OBJECTIVE

To investigate the effect of mFasL dendritic cells (DC) on the embryo resorption rate in the CBA/J x DBA/2 abortion mouse model.

DESIGN

Experimental study.

SETTING

University hospital in a major city in China.

ANIMAL(S)

101 CBA/J mice and 50 DBA/2 mice.

INTERVENTION(S)

We constructed the eukaryotic expression vector pcDNA3.1-mFasL, derived the DCs from bone marrow of DBA/2 mice, and transfected the DCs with pcDNA3.1-mFasL. The abortion mouse model were established by mating female CBA/J mice with DBA/2 mice. Via the CBA/J x DBA/2 abortion mouse model, five groups were established: group 1: abortion model without treatment; group 2: abortion mouse model injected with DC culture medium (DCCM); group 3: abortion mouse model injected with DC; group 4: abortion mouse model injected with empty plasmid pcDNA3.1-DC; group 5: abortion model mouse injected with pcDNA3.1-FasL-DC.

MAIN OUTCOME MEASURE(S)

Comparison of difference in the embryo resorption rates of the CBA/J x DBA/2 abortion mouse model treated with either pcDNA3.1-mFasL-DC or different controls observed on gestation days 12 to 14.

RESULT(S)

The embryo resorption rate was statistically significantly decreased in group 3 treated with DC and group 4 with empty plasmid pcDNA3.1-DC when they compared with group 1 (no treatment for abortion mouse model) and group 2 (injected with DC culture medium, DCCM). Furthermore, abortion model group 5 (injected with pcDNA3.1-mFasL-DC) showed a statistically significantly decreased in embryo resorption rate when compared with the other four groups, including groups 1 and 2 and groups 3 and group 4.

CONCLUSION(S)

Adoptive transfer of mFasL-DC can statistically significantly reduce the embryo resorption rate in the CBA/J x DBA/2 abortion mouse model.

Non-expanded adipose stromal vascular fraction cell therapy for multiple sclerosis

The stromal vascular fraction (SVF) of adipose tissue is known to contain mesenchymal stem cells (MSC), T regulatory cells, endothelial precursor cells, preadipocytes, as well as anti-inflammatory M2 macrophages. Safety of autologous adipose tissue implantation is supported by extensive use of this procedure in cosmetic surgery, as well as by ongoing studies using in vitro expanded adipose derived MSC. Equine and canine studies demonstrating anti-inflammatory and regenerative effects of non-expanded SVF cells have yielded promising results. Although non-expanded SVF cells have been used successfully in accelerating healing of Crohn's fistulas, to our knowledge clinical use of these cells for systemic immune modulation has not been reported. In this communication we discuss the rationale for use of autologous SVF in treatment of multiple sclerosis and describe our experiences with three patients. Based on this rationale and initial experiences, we propose controlled trials of autologous SVF in various inflammatory conditions.

Phenotypic and functional differences between wild-type and CCR2-/- dendritic cells: implications for islet transplantation

BACKGROUND

Trafficking of dendritic cells (DC), the primary regulators of alloimmune responses, is controlled by chemokines. Here, we provide evidence that lack of CCR2 could lead to the generation of functionally and phenotypically different DC, which in part could explain the benefits observed in transplanting islets in CCR2 recipients.

METHODS AND RESULTS

We show that, in contrast to the in vitro DC maturation model, in vivo DC maturation is accompanied by an increase in the expression of CCR2. Compared with wild-type (WT), DC generated in vitro from CCR2 mice, and DC extracted from CCR2 naïve mice or from CCR2 recipients of islet allografts, display lesser allostimulatory capacity. Compared with WT DC, CCR2 DC produce more IL-4 and induce more IL-4-producing T cells. CCR2 DC also promote the generation of regulatory T cells that more efficiently suppress T cell proliferative responses by mixed leukocyte reaction. Similarly, the percentage of CD4CD25FoxP3 cells were found to be higher in CCR2 recipients of islet allografts than in WT recipients.

CONCLUSIONS

In summary, lack of CCR2 interferes with the allostimulatory capacity of DC and promotes the generation of regulatory T cells. This is the first demonstration of a mechanistic link between targeting a specific chemokine pathway and the DC-regulatory T cell axis in alloimmunity.

Generation of therapeutic dendritic cells and regulatory T cells for preventing allogeneic cardiac graft rejection

Tolerogenic dendritic cells (Tol-DCs) and regulatory T cells (Treg) are key factors in the induction and maintenance of transplantation tolerance. We previously demonstrated that ex vivo-isolated Tol-DCs promote Treg generation, and vice versa, in an in vitro co-culture system. Here we demonstrate the occurrence of such an immune regulatory feedback loop in vivo. Tol-DC generated in vitro by treatment with LF 15-0195 exhibited features of immature DC and express low levels of MHC class II, CD86 and CD40. These Tol-DCs were capable of augmenting CD4(+)CD25(+)CTLA4(+) and FoxP3(+) Treg cell numbers and activity in cardiac allograft recipients. On the other hand, Tol-DCs possessed an ability to generate Treg cells in vitro. The adoptive transfer of these in vitro-generated Treg cells resulted in an increase of Tol-DC in vivo, suggesting that an immune regulatory feedback loop, between Tol-DC and Treg, exists in vivo. Furthermore, the administration of in vitro-generated Tol-DCs or Treg cells prevented rejection of allografts. Co-administration of Tol-DC and Treg synergized efficacy of promoting allograft survival heart transplantation. The present study highlights the therapeutic potential of preventing allograft rejection using in vitro-generated Tol-DCs and Treg.

Administration of dendritic cells modified by RNA interference prolongs cardiac allograft survival

Systemic administration of immature donor-dendritic cells (DC) that are deficient in co-stimulatory molecules delays the onset of allograft rejection. However, it is not easy to control culture condition and guarantee that the administered DC are in the immature stages, which obviously affects their therapeutic effect. In this study, we attempted to inhibit expression of CD86 on DC using an RNA interference technology. The function of CD86(low) DC was determined by the influence on their capacity to stimulate T cell proliferation and by the effect of DC systemic administration on survival of cardiac allografts. CD86(low) DC stimulated low T cell proliferative responses in vitro and administration of CD86(low) DC prolonged survival of heart allografts in vivo. These results suggest that RNA interference is a useful approach to modify DC function, which has potentials for clinical application.

Modulation of human monocyte-derived dendritic cells maturation by a soluble guanylate cyclase activator, YC-1, in a cyclic nucleotide independent manner

This study evaluated how YC-1, a guanylate cyclase activator, affects the maturation of human monocyte-derived dendritic cells. Maturation markers and intracellular signaling pathways were evaluated. YC-1 inhibited the lipopolysaccharide up-regulation of mature markers, including CD40, CD80 or CD86 in a concentration-dependent manner with IC(50) values of 4.6+/-0.4, 4.9+/-0.6 or 4.5+/-0.5 microM, respectively. YC-1, at a higher concentration, inhibited lipopolysaccharide-induced HLADR expression. These effects of YC-1 were not reversed by ODQ (10 microM), which is a soluble guanylate cyclase inhibitor, nor by KT5823 (1 microM), which is a PKG inhibitor. Additionally, YC-1 did not increase levels of cyclic nucleotides in dendritic cells, supporting the claim that YC-1 affects dendritic cells maturation in a cGMP-independent manner. YC-1, in a cGMP-independent manner, inhibited lipopolysaccharide-induced Akt activation, IkappaBalpha degradation and NF-kappaB translocation, all of which are associated with co-stimulatory molecules expression. YC-1 inhibited the capacity of dendritic cell to activate allogenic T cells with an IC(50) value of 1.2+/-0.3 microM. YC-1-treated dendritic cells have mature phenotypes that exhibit up-regulated CCR7, enhanced IL-10 release and low phagocytosis activity in the presence of lipopolysaccharide. In conclusion, YC-1 inhibited the lipopolysaccharide-induced co-stimulatory molecular expression of dendritic cells by inhibiting Akt activation, IkappaBalpha degradation and NF-kappaB translocation. These inhibitory effects on co-stimulatory molecules suppressed the capacity of dendritic cells to activate allogenic T cells. Additionally, YC-1 treated dendritic cells exhibit the up-regulation of CCR7, enhanced IL-10 release and the down-regulation of phagocytosis in the presence of lipopolysaccharide. Accordingly, YC-1 might be a useful tool for evaluation of dendritic cells on autoimmune or allergic disease.

Immune modulation and tolerance induction by RelB-silenced dendritic cells through RNA interference

Dendritic cells (DC), the most potent APCs, can initiate the immune response or help induce immune tolerance, depending upon their level of maturation. DC maturation is associated with activation of the NF-kappaB pathway, and the primary NF-kappaB protein involved in DC maturation is RelB, which coordinates RelA/p50-mediated DC differentiation. In this study, we show that silencing RelB using small interfering RNA results in arrest of DC maturation with reduced expression of the MHC class II, CD80, and CD86. Functionally, RelB-silenced DC inhibited MLR, and inhibitory effects on alloreactive immune responses were in an Ag-specific fashion. RelB-silenced DC also displayed strong in vivo immune regulation. An inhibited Ag-specific response was seen after immunization with keyhole limpet hemocyanin-pulsed and RelB-silenced DC, due to the expansion of T regulatory cells. Administration of donor-derived RelB-silenced DC significantly prevented allograft rejection in murine heart transplantation. This study demonstrates for the first time that transplant tolerance can be induced by means of RNA interference using in vitro-generated tolerogenic DC.

Predominant immature CD8?+dendritic cells prevent graft-vs.-host disease but do not increase the risk of leukemia recurrence

Graft-vs.-host disease (GVHD) remains the major limitation of allogeneic bone marrow transplantation (BMT) and stem cell transplantation, and leukemia recurrence is another important complication in leukemia treatment. Immature CD8alpha+ dendritic cells (DC) have good potential in GVHD treatment and immunological tolerance studies. To find a new way to prevent GVHD, not increasing the risk of leukemia recurrence, in this study, predominant CD8alpha+ immature DC were induced from murine bone marrow (BM) cells by 5 ng/mL granulocyte-macrophage colony stimulating factor (GM-CSF) plus 20-ng/mL interleukin (IL)-4, 100-ng/mL stem cell factor (SCF) and 25-ng/mL Flt3L, and 97.09 of prepared DC were CD8alpha+ on day 3. These DC were identified as morphologically and phenotypically immature CD8alpha+ DC. The suppressive function was observed in vitro, and then in vivo on allo-BMT leukemia model. The prepared predominant immature CD8alpha+ DC were weak syngeneic lymphocyte stimulators and could suppress mixed leukocyte reaction in vitro. In vivo, they prevented the pathological changes of GVHD and prolonged the surviving time of allo-BMT leukemia mice. The effect showed a dose-effect relationship. 86.7% of allo-BMT plus 1 million predominant CD8alpha+ DC leukemia mice reached long-term survival. Although predominant immature CD8alpha+ DC had the function of GVHD suppression, they did not increase leukemia recurrence. The method and findings may have important potency for GVHD treatment in clinical application.

Effects of RNA interference on CD80 and CD86 expression in bone marrow-derived murine dendritic cells

To investigate whether RNA interference (RNAi) induced by small interfering RNA (siRNA) could suppress CD80 and CD86 expression in bone marrow-derived murine dendritic cells (DC). The bone marrow-derived DC of mice were separated and cultured in vitro, chemically synthesized siRNA were then transferred into the cells by LipofectAMINE 2000, and the siRNA transfection efficacy was assessed by both fluorescence microscope and flow cytometry. The mRNA expression and protein synthesis were analysed by real-time RT-PCR and flow cytometry. The cell viability of transfected DC was determined by annexin V and propidium iodine staining. Transfection of bone marrow-derived murine DC with a non-silencing FITC-labelled control siRNA demonstrated a high (71.86%) transfection efficiency without affecting cellular viability. CD80-1 siRNA was the most effective siRNA to block CD80 expression in three candidates. Similarly, CD86-3 siRNA was extraordinarily effective in repressing the expression of CD86. Cotransfection of siRNA specific to CD80 and CD86 can enhance gene silencing that is not affected by DC activation-inducing signals. CD80 and CD86 siRNA suppressed the expression of CD80 and CD86 to 31.05 +/- 2.41% and 25.43 +/- 0.85%, respectively, of the level in untreated cells (P < 0.05). siRNA is capable of triggering RNAi in bone marrow-derived DC; it can specifically and effectively knock down CD80 and CD86 gene expression. This approach is a useful tool by which costimulatory molecules of DC can be studied as well as a potential therapeutic option for allograft rejection.

Generation of a tissue-engineered thymic organoid

The thymic microenvironment provides essential support for the generation of a functional and diverse population of human T cells. In particular, the three-dimensional (3D) thymic architecture contributes to critical cell-cell interactions. We report that thymic stroma, arrayed on a synthetic 3D matrix, supports the development of functional human T cells from hematopoietic precursor cells. Newly generated T cells contain T-cell receptor excision circles and are both fully mature and functional. The coculture of T-cell progenitors with thymic stroma can thus be used to generate de novo functional and diverse T-cell populations. This novel tissue engineered thymic system has biological applications for the study of T-lymphopoiesis and self-tolerance as well as potential therapeutic applications including the immune reconstitution of immunocompromised patients and the induction of tolerance in individuals receiving tissue or organ transplants.

Maturation-resistant dendritic cells induce hyporesponsiveness in alloreactive CD45RA+ and CD45RO+ T-cell populations

Dendritic cells (DCs) play a crucial role in the induction of antigen-specific immunity and tolerance. Considering in vivo application of DCs prior to human organ transplantation, a protocol to develop tolerogenic DCs that not only induce unresponsiveness in naive (CD45RA+) T cells, but also in alloreactive memory (CD45RO+) T cells is required. The present study shows that dexamethasone (Dex) alters the differentiation of human monocyte-derived DCs. DexDCs cocultured with allogeneic CD4+ T cells induced low proliferating and low IFNgamma producing T cells. This is caused by lack of both costimulation via CD28 and hampered production of a soluble factor, as well as additional active suppression via B7-H1 and IL-10. T cells primed by DexDCs demonstrated hyporesponsiveness upon restimulation with mature DCs seemingly via the induction of anergy, since these cells showed no enhanced apoptosis and only a limited suppressive capacity. Interestingly, not only cocultures of allogeneic CD45RA+, but also of CD45RO+ T cells with DexDCs rendered T-cell populations hyporesponsive to restimulation with mature DCs. The finding that also alloreactive memory T cells can be regulated supports the rationale of cell-based therapies to obtain allograft-specific tolerance in transplant recipients.

A novel method of modifying immune responses by vaccination with lipiodol-siRNA mixtures

The dendritic cell (DC) possesses the ability to stimulate both T helper 1 (Th1) and Th2 responses depending on activation stimuli. Although it is known that chemically or genetically modified DC can be used therapeutically to steer immune responses towards either Th1 or Th2, cellular therapy with ex vivo manipulated DC is clinically difficult. Here we demonstrate a novel method of switching immune responses from Th1 to Th2 through in vivo immune modulation by administration of siRNA. We demonstrate that siRNA targeting of the IL-12p35 gene leads to a Th2 bias in vitro through an IL-10 dependent mechanism. In vivo administration of siRNA admixed with the oil-based contrast agent lipiodol in the presence of antigen and adjuvant induced a deviation in recall response to reduced production of IFN-gamma and augmented IL-4 response using either KLH or ovalbumin. This simple method of in vivo modification of immune response possesses therapeutic potential in Th1-mediated diseases such as multiple sclerosis and autoimmune diabetes.

Inhibition of Human Dendritic Cell Maturation and Function by the Novel Immunosuppressant FK778

BACKGROUND

FK778, a derivative of the active leflunomide-metabolite, A77 1726, has been shown to be a powerful immunosuppressant in several transplantation models, particularly efficient in the prevention of chronic allograft rejection. However, the cellular and molecular mechanisms underlying these effects of FK778 have not been investigated yet in detail. Because dendritic cells (DCs) are the most potent antigen-presenting cells (APCs) and are essential for the initiation of immune responses including acute and chronic allograft rejection, we investigated whether FK778 affects this particular cell type.

METHODS

Allogeneic T cell stimulation by FK778-treated human monocyte-derived DCs was determined by mixed leukocyte cultures. Surface molecule expression was analyzed by flow-cytometric analysis and cytokine production by ELISA from culture supernatants. Activation of NF-kappaB in DCs was assessed by electrophoretic mobility shift assays.

RESULTS

Treatment of DCs with FK778 inhibited their potency to stimulate allogeneic T cells. In line, LPS- and CD40L-induced upregulation of DC surface activation markers and production of IL-12 was significantly inhibited, irrespective of whether cells were treated during or after the monocyte to DC differentiation period. The effects of FK778 on DCs were not reversible by exogenous uridine indicating that FK778 acts independently of its action as an inhibitor of pyrimidine synthesis. On the signaling level, activation of NF-kappaB, the essential transcription factor involved in DC maturation and function, was markedly inhibited by FK778.

CONCLUSIONS

Inhibition of activation and function of DCs as the central APCs may significantly contribute to the immunosuppressive profile of FK778 when applied after allogeneic organ transplantation.

Induction of RNA interference in dendritic cells

Dendritic cells (DC) reside at the center of the immunological universe, possessing the ability both to stimulate and inhibit various types of responses. Tolerogenic/regulatory DC with therapeutic properties can be generated through various means of manipulations in vitro and in vivo. Here we describe several attractive strategies for manipulation of DC using the novel technique of RNA interference (RNAi). Additionally, we overview some of our data regarding yet undescribed characteristics of RNAi in DC such as specific transfection strategies, persistence of gene silencing, and multi-gene silencing. The advantages of using RNAi for DC genetic manipulation gives rise to the promise of generating tailor-made DC that can be used effectively to treat a variety of immunologically mediated diseases.

Prolongation of heart allograft survival by immature dendritic cells generated from recipient type bone marrow progenitors

Recent studies suggest that particular dendritic cells (DC) subpopulations may be tolerogenic. To test the capacity of different DC subpopulations to modulate allograft rejection, we generated two distinct populations of rat bone marrow-derived DCs (BMDC) with low doses of GM-CSF and IL-4. The non-adherent population (nBMDC), which are the 'classical' DCs was able to stimulate naive allogeneic T cells and could be induced to completely mature using various stimuli. In contrast, the adherent population (aBMDC), which displayed an immature phenotype, was unable to stimulate T cells and was more resistant to maturation. We found that syngeneic aBMDCs, injected one day before transplantation, induced significant prolongation of heart allograft survival and decreased anti-donor humoral and cellular responses. Similarly, syngeneic aBMDCs inhibited T-cell responses to KLH in the spleen but not in lymph node in a KLH immunization model without graft. This effect was not antigen specific and could be reversed using an inhibitor of inducible nitric oxide synthase. This compartmentalized inhibition could be in part explained by the fact that the majority of syngeneic adherent cells administered intravenously were found in the spleen with some of them reaching the T-cell areas. These data suggest that syngeneic aBMDCs can modulate immune responses.

Interferon-gamma-modified dendritic cells suppress B cell function and ameliorate the development of experimental autoimmune myasthenia gravis

This study was designed to investigate the therapeutic effects of interferon (IFN)-gamma-modulated dendritic cells (DC) in experimental autoimmune myasthenia gravis (EAMG). We induced EAMG in Lewis rats by immunization with Torpedo nicotinic acetylcholine receptor (nAChR) and adjuvant. On day 33 post-immunization (p.i.), splenic DC were prepared, exposed to IFN-gamma alone (IFN-gamma-DC) or to IFN-gamma in combination with 1-methyl-DL-tryptophan (1-MT), the specific inhibitor of indoleamine 2,3-dioxygenase (IDO) (IFN-gamma + 1-MT-DC), and injected subcutaneously into rats with incipient EAMG on day 5 p.i. A control group of EAMG rats received naive DC on day 5 p.i., while another group received 1-MT every other day, intraperitoneally (p.i.), from days 5 to 41 p.i. The severity of clinical signs of EAMG was reduced dramatically in IFN-gamma-DC-treated rats compared to rats receiving naive DC, IFN-gamma + 1-MT-DC or 1-MT alone. The number of plasma cells secreting nAChR antibodies was reduced and the expression of B cell activation factor (BAFF) on splenic and lymph node mononuclear cells (MNC) was down-regulated in rats treated with IFN-gamma-DC. In vitro co-culture of MNC derived from EAMG rats with IFN-gamma-DC produced relatively few cells secreting nAChR antibodies. Addition of 1-MT to the co-culture significantly increased the number of cells secreting nAChR antibodies. We conclude that IFN-gamma-DC reduced the number of plasma cells secreting nAChR antibodies in an IDO-dependent manner and ameliorated the development of EAMG in Lewis rats.

Fas Ligand as a Tool for Immunosuppression and Generation of Immune Tolerance

The role of Fas ligand (FasL) in physiologically limiting immune responses and maintaining immune-privileged sites has led to a body of research aiming to confer protection to allogeneic grafts by expressing FasL on the allogeneic tissue or by administrating FasL-transduced donor dendritic cells. In addition, several studies have used FasL to abrogate autoimmune responses. This review presents the results of these studies and discusses the problems associated with FasL usage.

Marked prolongation of murine cardiac allograft survival using recipient immature dendritic cells loaded with donor-derived apoptotic cells

We investigated whether recipient dendritic cells (DCs), pretreated with nuclear factor-kappaB oligodeoxyribonucleotide decoy (NF-kappaB ODN decoy) and loaded with ultraviolet B-irradiated donor apoptotic splenocytes (Apo-SCs), were able to induce murine cardiac allograft tolerance. Heterotopic vascularized heart transplantation was performed from BALB/c to C57BL/6 mice, and recipients (C57BL/6) were given one injection of recipient DCs pretreated with NF-kappaB ODN decoy and loaded with donor (BALB/c) apoptotic SCs (decoy Apo-SCs DCs) through the portal vein at 7 days, before heart transplantation in the absence of immunosuppression. The cardiac allograft survival time and the expressive levels of intragraft cytokine genes [interleukin (IL)-2, IL-10, and interferon-gamma] were evaluated. Our results indicated that injection of decoy Apo-SCs DCs significantly prolonged vascularized heart allograft survival and led to skewing of intragraft cytokine expression towards T helper 2 (IL-10). The mechanisms can be useful for therapy of allograft rejection with minimization of systemic immunosuppression.