Mycophenolate mofetil impairs the maturation and function of murine dendritic cells

Tolerogenic dendritic cells in autoimmune diseases: crucial players in induction and prevention of autoimmunity

The immune system has evolved to coordinate responses against numerous invading pathogens and simultaneously remain silent facing self-antigens and those derived from commensal organisms. But, if both processes are not maintained in strict balance, a potential threat can emerge due to the risk of chronic inflammation and/or autoimmunity development. Therefore, there is a negative immune regulation where tolerogenic dendritic cells (tDCs) participate actively. Under steady-state conditions, tDC are notably involved in the elimination of autoreactive T cells at the thymus, and in the control of T cells specific to self and harmless antigens in the periphery. But in the presence of foreign antigens in an inflammatory milieu, dendritic cells (DCs) mature and induce T cells activation and their migration to B cell areas to assist in antibody production. Additionally, there are other factors such as infections, anti tumoral immune responses, trauma-mediated disruption, etc. that may induce alterations in the balance between tolerogenic and immunogenic functions of DCs and instigate the development of autoimmune diseases (ADs). Therefore, in recent years, DCs have emerged as therapeutic targets to control of ADs. Diverse strategies in vitro and/or in animal models of ADs have explored the tolerogenic functions of DCs and demonstrated their feasibility to prevent or control an autoimmune process, but still leaving a void in their application in clinical assays. The purpose of this paper is to give a general overview of the current literature on the significance of tDCs in tolerance maintenance to self and innocuous antigens, the most relevant alterations involved in the pathophysiology of ADs, the cellular and molecular mechanisms involved in their tolerogenic function and the current strategies used to exploit their tolerogenic potential.

Dendritic cell-based therapy in Type 1 diabetes mellitus

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

Dendritic cells in immunotoxicity testing

Dendritic cells (DCs) are now recognized to play the key role in the development of adaptive immunity by promoting activation of naïve T cells. Herein, we describe the methodologies to investigate how DCs can be modified by an environmental toxicant and subsequently influence immunity. The prototypic toxicant used as an example for altering DC development and functional influences on T cell development is lead (Pb). It has been reported that the environmental exposure to Pb enhances IgE production in children, which leads to an increase in the incidence of asthma. This effect has been suggested to be due to the preferential enhancement of helper T cell type 2 (Th2) cell responses by Pb. The predominant promotion of Th2 cell development is posited to be due to the altered characteristics of the bone marrow (BM)-DCs from Pb-treated mice (Pb-DCs) when compared to those of the BM-DCs that develop from progenitors in the absence of Pb. The Pb-DCs have a different immunophenotype as well as different cytokine expression after activation. In vitro and in vivo studies confirm that Pb-DCs have the ability to promote antigen-specific T cells to Th2 cells, favoring type-2-related humoral (HI) and cell mediated (CMI) immunity, which may be extracellular signal-regulated kinase (Erk)/mitogen-activated protein (MAP) kinase pathway dependent.

Dendritic cells in intestinal homeostasis and disease

DCs are specialized APCs that orchestrate innate and adaptive immune responses. The intestinal mucosa contains numerous DCs, which induce either protective immunity to infectious agents or tolerance to innocuous antigens, including food and commensal bacteria. Several subsets of mucosal DCs have been described that display unique functions, dictated in part by the local microenvironment. In this review, we summarize the distinct subtypes of DCs and their distribution in the gut; examine how DC dysfunction contributes to intestinal disease development, including inflammatory bowel disease and celiac disease; and discuss manipulation of DCs for therapy.

Mycophenolic acid inhibits maturation and function of human dendritic cells and B cells

Mycophenolic acid (MPA) is considered an immunosuppressive compound mainly because of its inhibitory effects on lymphocyte proliferation. Here we studied specifically the effects of MPA on the ability of dendritic cells (DCs) to activate T cells via the indirect pathway and on the maturation and function of B-lineage cells. We demonstrated that DC cell-surface receptors, associated with antigen uptake and antigen processing and presentation (CD83 and CD205), were differentially downregulated in the presence of MPA, translating into a decreased uptake of alloantigens and reduced stimulation of T cells with decreased cytokine secretion (interleukin (IL)-1Ra and transforming growth factor (TGF)-alpha). Similarly, MPA significantly inhibited B-cell differentiation into memory and plasma cells in vitro and decreased secretion of TNF-alpha, IL-1Ra, and IL-10. We further demonstrated for the first time that not only the amount of antibody secretion was significantly lowered in the presence of MPA but also the total number of antibody-producing cells was reduced. Importantly, we provide direct evidence that HLA-specific antibody secretion was also affected using a newly developed HLA antibody-specific B-cell enzyme-linked immunospot assay. Our data indicate additional pathways by which MPA downregulates the immune system. This in turn may lead to improved conditions for allograft tolerance and control of allograft rejection.

Mycophenolate in dermatology

Originally used to treat psoriasis nearly three decades ago, mycophenolic acid, reformulated as mycophenolate mofetil (MMF), has been rediscovered by the world of dermatology. As a relatively well-tolerated immunosuppressive used in organ transplant recipients, MMF has recently been reported to show promise for several dermatologic conditions, including psoriasis, pemphigus vulgaris, pyoderma gangrenosum, bullous lichen planus, and even connective tissue diseases such as lupus erythematosus and dermatomyositis. Although not intended to be exhaustive, this review discusses MMF with regard to its basic pharmacology, its side effects, and its reported efficacy in a variety of dermatologic indications. Relevant literature was retrieved by a Medline search combining the terms "mycophenolate" or "mycophenolic acid" and "skin" or "skin disease" or a number of specific conditions ("psoriasis", "dermatitis", "eczema", "pemphigoid", "pemphigus", "vasculitis", "pyoderma gangrenosum", "Crohn's disease", "graft-versus-host disease", "lichen planus"). As MMF has only been recently re-introduced for dermatologic application, the nature of much of the literature is admittedly that of case reports or case series. Nevertheless, the results are sufficiently promising to warrant further larger, control studies.

Function and dysfunction of dendritic cells in autoimmune rheumatic diseases

Dendritic cells (DC) have been implicated both in initiation of immunity and in immune tolerance. The mechanisms whereby tolerogenic DC may induce and maintain peripheral tolerance include the generation or expansion of regulatory T cells (Treg) and the promotion of T-cell anergy or deletion. A wide spectrum of hematopoietic growth factors and cytokines are endowed with the ability to differentiate tolerogenic DC both in vitro and in vivo. Based on this knowledge, therapeutic vaccination with cytokine-modulated tolerogenic DC has been applied to animal models of autoimmune disorders. This article will review the current experimental evidence underpinning DC dysfunction in rheumatic autoimmune diseases and will discuss how the manipulation of DC and Treg number and function may control undesired T-cell responses.

Dendritic cell tolerogenicity: a key mechanism in immunomodulation by vitamin D receptor agonists

Dendritic cells (DC) induce or tolerize T cells, and tolerogenic DCs can promote the development of regulatory T cells (Treg) with suppressive activity. Thus, the possibility of manipulating DCs and enhancing their tolerogenic properties using different pharmacologic or biologic agents could be exploited to control a variety of chronic immuno-mediated inflammatory conditions. Among agents able to promote induction of tolerogenic DCs, vitamin D receptor (VDR) agonists have attracted considerable attention, also because of their potential in clinical translation. DCs are key targets for the immunomodulatory effects of VDR agonists, which shape DC phenotype and function, enhancing their tolerogenicity in adaptive immune responses. Tolerogenic DCs induced by a short treatment with VDR agonists promote CD4+CD25+Foxp3+ Treg cells that are able to mediate transplantation tolerance and to arrest the development of autoimmune diseases. VDR agonists not only favor induction of CD4+CD25+ Treg cells, but can also enhance their recruitment at inflammatory sites. The tolerogenic properties induced by VDR agonists in DCs, leading to enhanced Treg cell development, likely contribute to the beneficial activity of these hormone-like molecules in autoimmune disease and graft rejection models, highlighting their applicability to the treatment of chronic inflammatory conditions sustained by autoreactive or alloreactive immune responses.

Mycophenolate mofetil: effects on cellular immune subsets, infectious complications, and antimicrobial activity

Mycophenolate mofetil (MMF) is one of the most frequently used immunosuppressive drugs in solid organ transplant recipients. MMF is an inhibitor of inosine-5'-monophosphate, and is able to preferentially inhibit B-cell and T-cell function. The immunosuppressive abilities of MMF have made it one of the most successful anti-rejection drugs in transplant patients, but patients also appear to have increased susceptibility to infections, specifically cytomegalovirus and BK virus. Despite its association with an increased risk of infection, MMF has also exhibited antimicrobial activity against pathogens including hepatitis C, Pneumocystis jirovecii, and human immunodeficiency virus. A thorough understanding of the functions of MMF on the immune system and interaction with infectious pathogens could be helpful in implementing preventative strategies against opportunistic infections in transplant patients.

T-cell reactivity during tapering of immunosuppression to low-dose monotherapy prednisolone in HLA-identical living-related renal transplant recipients

BACKGROUND

In many transplant centers, human leukocyte antigen (HLA)-identical living-related (LR) renal transplant recipients receive standard maintenance immunosuppression from 1 year after transplantation. We questioned whether discontinuation of azathioprine (AZA) or mycophenolate mofetil (MMF) influenced T-cell reactivity, circulating dendritic cell (DC) subsets numbers and their maturation status.

METHODS

Twenty-nine HLA-identical LR renal transplant recipients were withdrawn from AZA or MMF. Thereafter, the patients received only prednisolone. T-cell reactivity was determined by interferon-gamma (n=23), interleukin (IL)-10 (n=16), and granzyme B (n=10) Elispot assays. Circulating DC subset numbers and their maturation status determined by CCR2, CCR5, CCR7, and CD83 expression were measured by flow cytometry (n=12).

RESULTS

The number of donor, third-party, and tetanus toxoid-reactive interferon-gamma and granzyme-B producing cells was not affected after withdrawal of immunosuppression. Discontinuation of AZA or MMF resulted in significant increased numbers of third-party (P=0.003) and tetanus toxoid-reactive (P=0.008) IL-10 producing cells, and a trend in higher numbers of donor-reactive IL-10 producing cells (P=0.06). No effect was found on the number of circulating DC subsets, but DC was shifted toward a more mature phenotype.

CONCLUSIONS

In HLA-identical LR renal transplant recipients, therapy with AZA and MMF suppress the IL-10 production and the maturation of DC. This suggests that these immunosuppressants may hinder suppression of immune responses in general, including allogeneic responses.

Immunoregulatory profiles in liver transplant recipients on different immunosuppressive agents

We compared peripheral blood immunophenotyping in 31 adult liver transplant recipients on differing long-term immunosuppressive (IS) monotherapy with and without peri-transplantation alemtuzumab (AL) induction. All patients had been stable on monotherapy with either sirolimus (SRL) (n = 10) or without SRL (tacrolimus (TAC) (n = 10), mycophenolate mofetil (MMF) (n = 11)) for more than 6 months. Five-color flow cytometry for putative "regulatory" T and dendritic cells as well as serum assays for soluble HLA-G (sHLA-G) were performed. The SRL monotherapy group had significantly higher percentages of CD4+CD25(high+)Foxp3+ T cells (1.3 +/- 1.0) compared with the non-SRL group (0.7 +/- 0.6) (p = 0.04). The SRL effect was even higher in a subset with prior AL induction and no prior hepatitis C or rejection (1.7 +/- 0.2) compared with all other subgroups (0.7 +/- 0.6) (p = 0.02). TAC patients showed significantly higher "regulatory" DC2:DC1 ratios (10 +/- 7.6) compared with non-TAC patients (4.1 +/- 2.3) (p = 0.04). Although sHLA-G levels appeared higher in TAC patients, the differences were not statistically significant. In conclusion, IS monotherapy provides an opportunity to investigate regulatory roles of individual agents. SRL maintenance and prior AL induction in subsets of patients appeared to show a regulatory T cell immunophenotype. However, TAC patients may have other regulatory characteristics, supporting the need for larger, prospective studies to clarify differences.

Induction of tolerogenic dendritic cells by vitamin D receptor agonists

Dendritic cells induce and regulate T cell responses, and tolerogenic dendritic cells (DCs) can promote the development of regulatory T cells with suppressive activity. Thus, the possibility to manipulate DCs using different pharmacological or biological agents enables them to exert tolerogenic activities, could be exploited to better control a variety of chronic inflammatory conditions, from autoimmune diseases to allograft rejection. A variety of both biological and pharmacological agents can induce tolerogenic DCs, and several in vitro studies have demonstrated that human regulatory T cells can be induced by DCs manipulated to acquire and/or enhance tolerogenic properties, with in vivo data also accumulating. Within this context, we have explored the immunoregulatory activities of vitamin D receptor (VDR) agonists, secosteroid hormones able to induce tolerogenic DCs and regulatory T cells. Tolerogenic DCs induced by a short treatment with VDR agonists promote CD4(+) CD25(+) Foxp3(+) suppressor T cells that are able to mediate transplantation tolerance and to arrest the development of autoimmune diseases. VDR agonists not only favour the induction of CD4(+) CD25(+) regulatory T cells, but can also enhance their recruitment to inflammatory sites. VDR agonists have been proven effective and safe drugs in a variety of autoimmune disease and graft rejection models, highlighting their potential applicability to chronic inflammatory conditions sustained by autoreactive or alloreactive immune responses. In addition to the topical treatment of psoriasis, a Th1-mediated autoimmune disease of the skin where VDR agonists are the most used topical drugs; these agents might eventually find a broader application in the treatment of inflammatory conditions, where their modulatory effects on DCs enhancing T cells with regulatory functions could turn out to be quite beneficial.

Mesenchymal stem cells can induce long-term acceptance of solid organ allografts in synergy with low-dose mycophenolate

The induction of tolerance towards allogeneic solid organ grafts is one of the major goals in transplantation medicine. Mesenchymal stem cells (MSC) inhibit the immune response in vitro, and thus are promising candidate cells to promote acceptance of transplanted organs in vivo. Such novel approaches of tolerance induction are needed since, to date, graft acceptance can only be maintained through life-long treatment with unspecific immunosuppressants that are associated with toxic injury, opportunistic infections and malignancies. We demonstrate that donor-derived MSC induce long-term allograft acceptance in a rat heart transplantation model, when concurrently applied with a short course of low-dose mycophenolate. This tolerogenic effect of MSC is at least partially mediated by the expression of indoleamine 2,3-dioxygenase (IDO), demonstrated by the fact that blocking of IDO with 1-methyl tryptophan (1-MT) abrogates graft acceptance. Moreover we hypothesize that MSC interact with dendritic cells (DC) in vivo, because allogeneic MSC are rejected in the long-term but DC acquire a tolerogenic phenotype after applying MSC. In summary, we demonstrate that MSC constitute a promising tool for induction of non-responsiveness in solid organ transplantation that warrants further investigation in clinical trials.

After discontinuation of calcineurin inhibitors, tapering of mycophenolate mofetil further impairs donor-directed cytotoxicity

BACKGROUND

Recently, we described a significant decrease in donor-specific cytotoxic T-lymphocyte precursor frequency (CTLpf) after discontinuation of calcineurin inhibitors (CNI), while the proliferative capacity in mixed lymphocyte culture (MLC), and the number of interferon-gamma (IFN-gamma) producing cells (pc) in Elispot remained unchanged.

METHODS

We tested T-cell reactivity in CNI free patients with stable renal graft function, on mycophenolate mofetil (MMF) or azathioprine (AZA) plus prednisone, who were tapered to 50% of their MMF or AZA dose.

RESULTS

Furthermore, tapering of the MMF or AZA dose resulted in a decrease of donor-reactive CTLpf in all patients with detectable CTLpf. Detectable numbers decreased from a median of 32 to 8 CTLp/10(6) peripheral blood mononuclear cell (PBMC). No effect on third-party reactive CTLpf was found, while the T-cell reactivity to donor and third-party cells as tested in MLC and in IFN-gamma Elispot was not affected either by tapering of immunosuppression. Third-party reactivity was significantly higher than donor-specific reactivity in all tests. A control group showed no changes in any of the in vitro assays.

CONCLUSION

Both withdrawal of CNI and tapering of MMF or AZA dose decreases the donor-specific CTLpf. Our data suggest that reduction of immunosuppression results in a specific decrease of donor-directed cytotoxic capacity of immunocompetent cells, while their proliferation and cytokine production capacity remained unchanged. Immunosuppression hinders development of cytotoxic non-responsiveness.

Niflumic acid renders dendritic cells tolerogenic and up-regulates inhibitory molecules ILT3 and ILT4

Niflumic acid is a member of non-steroidal anti-inflammatory agents, from which aspirin was recently shown to inhibit maturation of human-monocyte derived dendritic cells (DCs). DCs are crucial regulators of the immune response, capable of inducing immunity as well as tolerance. In our in vitro study we showed a tolerogenic effect of NFA on phenotype and function of LPS-matured monocyte-derived DCs. Different drug concentrations dose-dependently down-regulated the expression of co-stimulatory molecules, particularly CD80 and lowered the expression of dendritic cell marker CD1a. Opposingly, the expressions of two inhibitory surface molecules, associated with tolerogenic DCs, immunoglobulin-like transcripts (ILT)3 and ILT4 were induced in treated DCs. The levels of TNFalpha production by NFA-treated DCs did not change significantly compared to controls, whereas the IL-12p70 and IL-10 production was completely abrogated at higher drug concentrations. However, at lower drug concentrations, the production of IL-12p70 was increased. There were no significant differences in the uptake of FITC labeled dextran by treated DCs compared to untreated cells. In allogeneic cultures with whole CD4+ T cells, dendritic cells differentiated in the presence of NFA appeared poor stimulators of CD4+ T-cell proliferation, even compared to immature DCs (iDCs). These results indicate the immunosuppressive properties of NFA, which may be therapeutically useful in controlling chronic immune and/or inflammatory diseases, by modulating DC characteristics towards tolerogenic DCs.

Use of dendritic cells in drug selection, development and therapy

BACKGROUND

Dendritic cells (DC) have the unique ability to induce immunity against tumors and various pathogens or to promote tolerance in autoimmunity and transplantation. Hence, they are central to the regulation of immune responses.

OBJECTIVE/METHODS

Due to the unique tolerogenic ability of DC, understanding some of the key molecules that regulate DC function may help with targeting the relevant signals in DC as therapeutic options for many disease conditions. DC are also targets of drugs, and many of the anti-inflammatory and pharmaceutical agents used to prevent autoimmunity or inhibit graft rejection interfere with DC function.

RESULTS/CONCLUSION

The drug-induced changes in DC may provide information for the selection of drugs and further drug discovery along with the use of DC as adjuvant in the treatment of autoimmunity and prevention of graft rejection in transplantation.

DC homeostasis in hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation is an important experimental tool and therapeutic modality. Its efficacy and toxicity are both linked to a GvH reaction that is initiated by donor T cells recognizing recipient APC, of which DC are the most potent. In most tissues recipient DC are replaced after transplantation because they turnover rapidly from BM-derived precursors. However, in a number of sites, notably the skin, recipient DC may persist and even self-renew for many months after transplantation. Understanding the homeostasis of different APC populations and how they are related to the induction of alloreactivity may help to improve the therapeutic benefit of transplantation.

GMCSF in the absence of other cytokines sustains human dendritic cell precursors with T cell regulatory activity and capacity to differentiate into functional dendritic cells

Dendritic cell precursors, from human peripheral blood, express epitopes reactive with monoclonal antibodies specific for the empty conformation of HLA-DR1. Expression is substantially up-regulated during GMCSF-induced differentiation to immature dendritic cells, but is strongly down-regulated by IL-4. In the conventional protocol for in vitro generation of human dendritic cells from monocyte precursors, both GMCSF and IL-4 are used together, with IL-4 thought to have an effect on preventing macrophage outgrowth but not substantially altering the dendritic cell maturation pathway, whereas conventional protocols for generation of murine dendritic cells use GMCSF alone. We characterized human monocytes cultured in the presence of GMCSF and in the absence of IL-4, and found that the resultant cultures are stable for long periods in vitro, and have T cell stimulatory and immunodulatory activity characteristic of immature dendritic cells. Their response to maturation stimuli is weak in the absence of IL-4 but these cells retain the ability to differentiate into fully functional mature dendritic cells upon IL-4 treatment. We suggest that these cells may provide a useful model to investigate tolerogenic function as a developmental feature of DC and to understand molecular events involved in IL-4 priming for maturation.

Calcitriol started in the donor, expands the population of CD4+CD25+ T cells in renal transplant recipients

OBJECTIVES

Alloreactive T cells recognize antigens via direct and indirect pathways. The competency of costimulatory molecules on antigen-presenting cells (APC) is important. An active form of vitamin D (1,25(OH)(2)D(3), calcitriol) inhibits APC cell maturation and expression of costimulatory molecules. Herein we studied the immunosuppressive effects of calcitriol, which was started in the donors and continued in the kidney recipients.

METHODS

In this prospective study, candidates for living donor renal transplantation were randomly assigned into two groups: the treatment group were prescribed calcitriol (0.5 microg/day) started in the donor 6 days before donation and continued in recipient side for 6 months after transplantation. The control group received the conventional immunosuppressive regimen, namely, cyclosporine/mycophenolate mofetil and prednisolone. In each group, a recipient blood sample was obtained before and 6 months after transplantation. Diagnostic study of the T-cell markers-CD3, CD4, and CD25-were performed with a flow cytometry technique.

RESULTS

The mean values of CD3(+)CD4(+)CD25(+) T cells in the treatment group (four women and five men; 40.8 +/- 8.5 years) and the control group (four women and six men; 37.2 +/- 10 years) were at 14.2 +/- 4.2% and 15.4 +/- 4.5% of total peripheral lymphocytes. Six months after transplantation, these percentages increased to 29 +/- 6.3% in the treatment group and decreased to 12.1 +/- 4.5% in the controls (P<.0001). No clinical rejection was detected in either group during the study period.

CONCLUSION

Calcitriol started in the donors and continued in the kidney allograft recipients lead to expansion of CD4(+)CD25(+) regulatory T cells in recipients. We speculated that costimulatory deficient APC for both direct and in-direct pathways may play a role.

Dendritic cells and the immunopathogenesis of systemic lupus erythematosus

Over the last decade, the role of dendritic cells (DCs) in the immunopathogenesis of systemic lupus erythematosus (SLE) has become apparent. As unique mediators of both tolerance and immunity, aberrant myeloid and plasmacytoid DC function can promote autoimmune responses via a number of mechanisms and proinflammatory pathways. This review provides an overview of DC function, the potential role of DCs in promoting autoimmune responses in SLE, and how other abnormalities in lupus can lead to an enhanced engagement of DCs in immune responses. How medications used to treat SLE and other autoimmune conditions may exert effects on DCs is also explored.

Immunoregulatory dendritic cells to prevent and reverse new-onset Type 1 diabetes mellitus

Herein, the authors provide an overview of where dendritic cells lie in the immunopathology of autoimmune Type 1 diabetes mellitus and how dendritic cell-based therapy may be usefully translated to treat and reverse the disease. The immunopathology of Type 1 diabetes mellitus offers a number of windows at which immunotherapy can be applied to delay, stop and even reverse the autoimmune processes, especially in light of the recent antibody-based accomplishment of improvement in residual beta-cell mass function. As in almost all cell-specific inflammatory processes, dendritic cells are central regulators of diabetes onset and progression. This realisation, along with accumulating data confirming a role for dendritic cells in maintaining and inducing tolerance in multiple therapeutic settings, has prompted a line of investigation to identify the most effective embodiments of dendritic cells for diabetes immunotherapy.

Lead effects on development and function of bone marrow-derived dendritic cells promote Th2 immune responses

Although lead (Pb) has significant effects on the development and function of macrophages, B cells, and T cells and has been suggested to promote allergic asthma in mice and humans, Pb modulation of bone marrow (BM)-derived dendritic cells (DCs) and the resultant DC effects on Th1 and Th2 development have not been examined. Accordingly, we cultured BM cells with murine granulocyte macrophage-colony stimulating factor (mGM-CSF)+/-PbCl(2). At day 10, culture supernatant (SN) and non-adherent cells were harvested for analysis. Additionally, day 10 non-adherent BM-DCs were harvested and recultured with mGM-CSF+LPS+/-Pb for 2 days. The day 10 Pb exposure significantly inhibited BM-DC generation, based on CD11c expression. Although fewer DCs were generated with Pb, the existing Pb-exposed DCs had significantly greater MHC-II expression than did the non-Pb-exposed DCs. However, these differences diminished upon LPS stimulation. After LPS stimulation, CD80, CD86, CD40, CD54, and MHC-II were all up-regulated on both Pb-DCs and DCs, but Pb-DCs expressed significantly less CD80 than did DCs. The CD86:CD80 ratio suggests a Pb-DC potential for Th2 cell development. After LPS stimulation, IL-6, IL-10, IL-12 (p70), and TNF-alpha levels significantly increased with both Pb-DCs and DCs, but Pb-DCs produced significantly less cytokines than did DCs, except for IL-10, which further supports Pb-DC preferential skewing toward type-2 immunity. In vitro studies confirm that Pb-DCs have the ability to polarize antigen-specific T cells to Th2 cells. Pb-DCs also enhanced allogeneic and autologous T cell proliferation in vitro, and in vivo studies suggested that Pb-DCs inhibited Th1 effects on humoral and cell-mediated immunity. The Pb effect was mainly on DCs, rather than on T cells, and Pb's modification of DC function appears to be the main cause of Pb's promotion of type-2-related immunity, which may relate to Pb's enhanced activation of the Erk/MAP kinase pathway.

Sanglifehrin a blocks key dendritic cell functions in vivo and promotes long-term allograft survival together with low-dose CsA

Sanglifehrin A (SFA) is a novel compound with unsurpassed cyclophilin-binding affinity, but relatively low direct antilymphocytic activity. Here, we report the capacity of SFA to selectively inhibit key dendritic cell (DC) functions in vivo and to suppress acute and chronic heart allograft rejection. We show that in vivo, SFA profoundly decreases DC receptor-mediated endocytosis and macropinocytosis and DC-T-cell allostimulatory activity. Furthermore, SFA abrogates >90% of IL-12p70 production in vivo while having no significant effect on IL-10 and TNF-alpha production. In a rat vascularized heart transplant model, SFA alone did not prevent graft rejection and rejection occurred within 23 days after low-dose CsA, whereas addition of SFA to low-dose CsA promoted long-term graft survival (median survival time >100 days; p = 0.0007). With respect to chronic rejection, SFA + CsA almost completely prevented graft arteriosclerosis compared to animals treated with CsA alone and controls. We propose that SFA represents a novel class of immunophilin-binding immunosuppressants with high activity against DCs and the development of graft vasculopathy in CsA-treated recipients.

The role of antigen-presenting cells in triggering graft-versus-host disease and graft-versus-leukemia

After allogeneic blood or bone marrow transplantation, donor T cells interact with a distorted antigen-presenting cell (APC) environment in which some, but not all, host APCs are replaced by APCs from the donor. Significantly, host APCs are required for the priming of acute graft-versus-host disease (GVHD). Donor APCs play a lesser role in the induction of acute GVHD despite their predicted capacity to cross-present host antigens. In contrast, donor APCs may play a role in perpetuating the tissue injury observed in chronic GVHD. Host APCs are also required for maximal graft-versus-leukemia responses. Recent studies have suggested potential strategies by which the continued presence of host APCs can be exploited to prime strong donor immunity to tumors without the induction of GVHD.

Src homology 2 domain-containing protein tyrosine phosphatase substrate 1 regulates the induction of Langerhans cell maturation

Recently, we reported that Src homology 2 domain-containing protein tyrosine phosphatase substrate 1 (SHPS-1) plays an important role in the migration of Langerhans cells (LC). Here, we show that SHPS-1 is involved in the maturation of LC. Immunofluorescence analysis on epidermal sheets for I-A or CD86 revealed that LC maturation induced by 2,4-dinitro-1-fluorobenzene (DNFB) or by TNF-alpha was inhibited by pretreatment with an anti-SHPS-1 monoclonal antibody (mAb) or with CD47-Fc fusion protein, a ligand for SHPS-1. Further, FACS analysis demonstrated that I-A(+) LC that had emigrated from skin explants expressed CD80 or CD86, whereas CD47-Fc protein reduced CD80(high+) or CD86(high+) cells. CD47-Fc protein also reduced the up-regulation of surface CD80 or CD86 by LC remaining in the skin explants. In SHPS-1 mutant mice, we observed that the up-regulation of surface CD86 and CCR7 by LC induced by DNFB as well as that of surface CD80 and CD86 by LC in skin explants was attenuated. Finally, contact hypersensitivity (CHS) response was suppressed in SHPS-1 mutant mice and in wild-type mice treated with an anti-SHPS-1 mAb. These observations indicate that SHPS-1 plays an important role in the maturation of LC ex vivo and in vivo, and that SHPS-1-CD47 interaction may negatively regulate CHS.

Impairment of Circulating Myeloid Dendritic Cells in Immunosuppressed Renal/Pancreas Transplant Recipients

BACKGROUND

Immunosuppressive drugs used after organ transplantation are known to impair lymphocyte function, resulting in an increased incidence of viral associated malignancies. In vitro data indicate that immunosuppressive drugs also target dendritic cells (DCs). Our study aimed to investigate the phenotype and function of circulating myeloid DCs (mDCs) from renal/pancreas transplant recipients receiving immunosuppressive drugs. In addition, we analyzed the potential of patient monocytes to differentiate into mature DCs (MoDCs) in vitro.

METHODS

Phenotype of mDCs was analyzed by fluorescence-activated cell sorter (FACS) analysis. The ability of mDCs to undergo activation was determined using cytokine bead array and FACS analysis. Allostimulatory capacity was determined by mixed leukocyte reaction. MoDCs were generated using a defined cytokine cocktail and analyzed for maturity of phenotype and function. The ability of patient-MoDCs to expand antigen-specific T cells was analyzed by tetramer staining and interferon (IFN)-gamma ELISPOT assay.

RESULTS

We observed a reduced expression of CD54 (P=0.001), CD86 (P=0.032), HLA-DR (P=0.013), and CD38 (P=0.006) on patient mDCs. Upon stimulation, the expression of HLA-ABC, HLA-DR and CD86 was upregulated on patient mDCs to the same level as on control mDCs. MoDCs were equivalent to control-MoDCs regarding phenotype and function. Co-culture of peptide-pulsed patient-MoDCs with T cells resulted in significant expansion of autologous Epstein-Barr virus-specific, IFN-gamma secreting T cells.

CONCLUSIONS

Our data support the notion that immunosuppressive drugs target DCs and induce a maturation defect in circulating mDCs. However, ex vivo stimulated mDCs as well as MoDCs do not show a significant impairment, suggesting that MoDCs from immunosuppressed patients can be used for immunotherapeutic strategies.

Combination effect of mycophenolate mofetil with mizoribine on cell proliferation assays and in a mouse heart transplantation model

BACKGROUND

Mycophenolate mofetil (MMF) is a highly potent immunosuppressant that suppresses the proliferation of T and B cells by the uncompetitive inhibition of inosine monophosphate dehydrogenase (IMPDH). Consequently, under MMF immunosuppression, good graft survival has been achieved in clinical organ transplantation, although MMF shows adverse gastrointestinal effects. Mizoribine (MZ) also inhibits IMPDH in a competitive manner and is used clinically for organ transplantation in Japan as an immunosuppressant with fewer adverse gastrointestinal effects. Therefore, in this study we investigated the synergistic effects on in vitro and in vivo assays of mice of a combination of MMF with MZ immunosuppression.

METHODS

Mixed lymphocyte reaction (MLR) assay and a mouse heart transplantation model were used to evaluate the immunosuppressive effect of MMF with MZ. The median-effect principle and a combination index (CI) were employed to determine synergism, an additive effect, or antagonism.

RESULTS

Combination of MMF with MZ resulted in mild synergistic effects in the inhibition of MLR (CI = 0.854-1.143). In the mouse heart transplantation model, C57BL/6 recipients who received a BALB/c heart under the combination of MMF and MZ at 40 + 40 or 80 + 80 mg/kg/day showed a strong synergistic prolongation of graft survival with 19.7 +/- 18.9 (P = 0.0012, CI = 0.438) and 78.4 +/- 36.9 days (P = 0.0002, CI = 0.317), respectively, compared with recipients treated with MMF or MZ monotherapy. CONCLUSIONS.: The combination of MMF and MZ showed mild synergistic effects in the inhibition of MLR and strong synergistic effects in a mouse heart transplantation model.

Peripheral CD4+ CD25+ Treg cell expansion in lung transplant recipients is not affected by calcineurin inhibitors

CD4+CD25+ regulatory T (Treg) cells have been shown to play a role in allograft tolerance and their peripheral counts vary according to the degree of graft acceptance in lung transplant recipients (LTR). Recent studies demonstrate that certain drugs might modulate generation, expansion and activity of Treg cells. Aim of this study was to evaluate the effect of therapeutic regimens used in our institution on peripheral CD4+CD25(high)CD69- Treg cell numbers in a group of 51 LTR with stable clinical conditions. They were treated with standard immunosuppression: calcineurin inhibitor (CNI)+azathioprine (AZA)+steroids (n=28) or with CNI+mycophenolate mofetil (MMF)+steroids (n=11) or with CNI+steroids (n=12). These stable LTR were compared with age-matched healthy controls (n=35) and with 19 LTR who developed bronchiolitis obliterans syndrome (BOS) and were treated analogously. Stable LTR showed higher peripheral Treg cell counts with respect to age-matched healthy controls (59.9+/-31.8/mul versus 42.1+/-16.9/mul, respectively; p<0.05). This increase was detectable in all patients treated with CNI either in association with AZA or MMF. During these treatments a significant expansion of Treg cell counts was detectable during acute rejection (AR) episodes (86.03+/-26.6/mul during AR versus 36.34+/-7.6 before AR; p<0,05). Moreover, the development of BOS was associated to a significant decrease of Treg cell counts irrespective to the immunosuppressive regimen used. In conclusion, therapeutic regimens based on CNI seem to allow a certain degree of peripheral Treg cell expansion in stable LTR.

Dendritic cells as promoters of transplant tolerance

Dendritic cells (DCs) play a crucial role during the initiation of immune responses against non-self antigens. Following organ transplantation, activated donor- and recipient-derived DCs participate actively in graft rejection by sensitising recipient T cells via the direct or indirect pathways of allorecognition, respectively. There is increasing evidence that immature/semi-mature DCs induce antigen-specific unresponsiveness or tolerance to self antigens, both in central lymphoid tissue and in the periphery, through a variety of mechanisms (deletion, anergy and regulation). In the past few years, DC-based therapy of experimental allograft rejection has focused on ex vivo biological, pharmacological and genetic engineering of DCs to mimic/enhance their natural tolerogenicity. Successful outcomes in rodent models have built the case that DC-based therapy may provide a novel approach to transplant tolerance. Ongoing research into the role that DCs play in the induction of tolerance should allow for its clinical application in the near future.

Mycophenolic Acid Upregulates B7-DC Expression on Dendritic Cells, Which Is Associated With Impaired Allostimulatory Capacity of Dendritic Cells

In addition to its effects on lymphocytes, mycophenolic acid (MPA) may inhibit the allostimulatory capacity of dendritic cells (DC) via unknown mechanisms. B7-H1 and B7-DC surface markers on DC negatively regulate T-cell responses via the receptor PD-1. In this study, we sought to investigate whether B7-H1 and B7-DC are responsible for the inhibitory functions of MPA on DC. Mouse bone marrow-derived DC were cultured with recombinant granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4 in the presence or absence of MPA (0.01 micromol and 0.1 micromol). The DC phenotype was assessed by flow cytometry, their immunostimulatory capacity measured by mixed lymphocyte reaction (MLR), and cytokine production by ELISA. The results showed that MPA not only inhibited the expression of major histocompatibility complex (MHC) class II and costimulatory molecules CD80 and CD86 but upregulated B7-DC expression on mature DC induced by LPS. These findings were associated with a reduced allostimulatory ability and an altered cytokine secretion pattern of DC. Thus, we suggest that MPA upregulates B7-DC expression during DC maturation induced by LPS in vitro, an effect that may be responsible for MPA-mediated inhibitory effects on the allostimulatory capacity of DC.

Revisiting the immunomodulators tacrolimus, methotrexate, and mycophenolate mofetil: their mechanisms of action and role in the treatment of IBD

Inflammatory bowel diseases (IBDs) are thought to result from unopposed immune responses to normal gut flora in a genetically susceptible host. A variety of immunomodulating therapies are applied for the treatment of patients with IBDs. The first-line treatment for IBDs consists of 5-aminosalicylate and/or budesonide. However, these first-line therapies are often not suitable for continuous treatment or do not suffice for the treatment of severe IBD. Recently, efforts have been made to generate novel selective drugs that are more effective and have fewer side effects. Despite promising results, most of these novel drugs are still in a developmental stage and unavailable for clinical application. Yet, another class of established immunomodulators exists that is successful in the treatment of inflammatory bowel diseases. While waiting for emerging novel therapies, the use of these more established drugs should be considered. Furthermore, one of the advantages of using established immunomodulators is the well-documented knowledge on the long-term side effects and on the mechanisms of action. In this review, the authors discuss 3 well-known immunomodulators that are being applied with increased frequency for the treatment of IBD: tacrolimus, methotrexate, and mycophenolate mofetil. These agents have been used for many years as treatment modalities for immunosuppression after organ transplantation, for the treatment of cancer, and for immunomodulation in several other immune-mediated diseases. First, this review discusses the potential targets for immunomodulating therapies in IBDs. Second, the immunomodulating mechanisms and effects of the 3 immunomodulators are discussed in relationship to these treatment targets.

Inhibition of CD4+CD25+ regulatory T-cell function by calcineurin-dependent interleukin-2 production

CD4+CD25+ regulatory T (Treg) cells control immunologic tolerance and antitumor immune responses. Therefore, in vivo modification of Treg function by immunosuppressant drugs has broad implications for transplantation biology, autoimmunity, and vaccination strategies. In vivo bioluminescence imaging demonstrated reduced early proliferation of donor-derived luciferase-labeled conventional T cells in animals treated with Treg cells after major histocompatibility complex mismatch bone marrow transplantation. Combining Treg cells with cyclosporine A (CSA), but not rapamycin (RAPA) or mycophenolate mofetil (MMF), suppressed Treg function assessed by increased T-cell proliferation, graft-versus-host disease (GVHD) severity, and reduced survival. Expansion of Treg and FoxP3 expression within this population was lowest in conjunction with CSA, suggesting that calcineurin-dependent interleukin 2 (IL-2) production is critically required for Treg cells in vivo. The functional defect of Treg cells after CSA exposure could be reversed by exogenous IL-2. Further, the Treg plus RAPA combination preserved graft-versus-tumor (GVT) effector function against leukemia cells. Our data indicate that RAPA and MMF rather than CSA preserve function of Treg cells in pathologic immune responses such as GVHD without weakening the GVT effect.

Immunomodulatory strategies for celiac disease

Celiac disease (CD) is the most common food-sensitive enteropathy in humans and is caused by the lack of immune tolerance (oral tolerance) to gluten. The identification of gluten-specific T cells in the lamina propria of celiacs and the strong association with HLA-DQ2 and -DQ8 genes support a central role of CD4(+) T cells in CD pathogenesis. Studies focused on the modulation of autoimmunity in different experimental models highlighted possible immune therapeutic protocols useful also for the management of CD. On the basis of these observations, a series of strategies have been designed: some of them are based on the identification of immunogenic epitopes and their suppression via enzymatic treatment or by using peptide analogues; others rely on the delivery of unmodified antigen through the nasal route or coadministered with downregulatory cytokines. studies are generally early stage but encouraging in paving a way for an alternative treatment for celiac disease.

Renal transplantation reverses functional deficiencies in circulating dendritic cell subsets in chronic renal failure patients

BACKGROUND

Dendritic cell (DC) subsets play critical roles in regulation of innate and adaptive immune responses. These important antigen-presenting cells have not been extensively analyzed in chronic renal failure (CRF), during dialysis, or before and after renal transplantation.

METHODS

The incidence of circulating precursor (pre)-DC subsets relative to total peripheral blood mononuclear cells was analyzed in healthy controls, haemodialysis patients, peritoneal dialysis patients, CRF patients, and renal transplant (RT) recipients. DC subsets were identified and characterized phenotypically by multicolour flow cytometric analysis and purified by immunomagnetic bead isolation respectively. Cytokine production and circulating DC mobilizing cytokines were determined by ELISA.

RESULTS

The incidence of circulating prePDC was reduced in all patients, but the incidence of circulating preMDC was comparable in RT and dialysis patients compared to healthy controls. CRF patients exhibited the lowest incidence of circulating preMDC and prePDC. Immunomagnetic bead-isolated preMDC and prePDC from haemodialysis patients were functionally impaired (reduced expression of surface costimulatory molecules and interleukin-12p70 production following bacterial lipopolysaccharide stimulation, and reduced interferon-alpha production following herpes simplex virus stimulation respectively, compared to healthy controls and RT recipients. Glomerular filtration rate correlated significantly with the incidence of circulating preMDC, but not prePDC.

CONCLUSIONS

Deficiencies in the incidence and function of precursor DC can be reversed with successful renal transplantation achieving normal renal function. However, the finding of reduced incidence of circulating prePDC in the peripheral blood in RT recipients may be of significance in the pathogenesis of infections and malignancies.

Mechanisms of action of mycophenolate mofetil in preventing acute and chronic allograft rejection

Mycophenolate mofetil (MMF), a prodrug of mycophenolic acid (MPA), an inhibitor of inosine-5'-monophosphate dehydrogenase, has several immunosuppressant actions. MPA depletes guanosine and deoxyguanosine nucleotides preferentially in T and B lymphocytes, inhibiting proliferation and suppressing cell-mediated immune responses and antibody formation, major factors in acute and chronic rejection. MPA also can induce T-lymphocyte apoptosis. MPA suppresses dendritic cell maturation and can induce human monocyte-macrophage cell line differentiation, decreasing the expression of interleukin (IL)-1 and enhancing expression of the IL-1 receptor antagonist. In addition, MPA inhibits adhesion molecule glycosylation and expression and lymphocyte and monocyte recruitment. Activated macrophages produce nitric oxide (NO) and superoxide, which combine to generate tissue-damaging peroxynitrite. MPA depletes tetrahydrobiopterin and decreases NO production by inducible NO synthase without affecting constitutive NO synthase activity. By these mechanisms, MMF exerts anti-inflammatory activity, which could attenuate both acute and chronic rejection. Unlike calcineurin inhibitors, MMF is nonnephrotoxic and does not induce transforming growth factor-beta production, which is fibrogenic. MMF inhibits arterial smooth muscle cell proliferation, a contributor to graft proliferative arteriopathy, and does not increase blood pressure, cholesterol, or triglyceride levels. By decreasing high-density lipoprotein oxidation and macrophage recruitment, MMF also may delay onset/progression of graft atherosclerosis. Thus, MMF may prevent chronic rejection by several mechanisms. MMF activity is synergistic with that of other agents such as valganciclovir for treating cytomegalovirus infection. MMF also has synergistic activity with angiotensin-converting enzyme inhibitors or angiotensin II receptor antagonists in the treatment of some nephropathies in experimental animals. This combination may prevent progression toward end-stage renal disease in humans with chronic allograft, lupus, and diabetic nephropathies.

Dendritic cells: key cells for the induction of regulatory T cells?

Even though dendritic cells (DCs) are well known for their capacity to induce immune responses, recent results show that they are also involved in the induction of tolerance. These two contrary effects of otherwise homologous DCs on a developing immune response maybe explainedby different DC developmental stages, i.e., different subsets of DCs may exist and/or different spatial distribution of DCs in the body might influence their function. However, independently from the subtype(s), it is obvious that the ability of DCs to act in a tolerogenic fashion depends on the maturation status, since immature DCs are prone to induce regulatory T cells and hence promote tolerance, whereas mature DCs stimulate effector T cells, facilitating immunity. The means by which DCs convey tolerance are not entirely clear yet, but secretion of suppressive cytokines such as IL-10 and induction of regulatory lymphocytes are involved. In this review we focus on the interaction between DCs and T cells and highlight some mechanisms in the decision-making process of whether immunity or tolerance is induced.

Dendritic cells in allogeneic hematopoietic stem cell transplantation

In allogeneic hematopoietic stem cell transplantation (SCT), dendritic cells (DCs) as the most potent antigen-presenting cells play a central role in the development of acute and chronic graft-vs-host disease (GVHD), in graft-vs-leukemia or -malignancy reactions and in fighting infectious complications. Functional maturity and distribution of DC sub-types (DC1 and DC2) differ between the different stem cell sources used (bone marrow, granulocyte colony-stimulating factor-mobilised peripheral blood and cord blood) resulting in various rates of graft-vs-host disease and graft-vs-leukemia activity. Although DC recovery following stem cell transplantation is prompt, graft-vs-host disease and the use of immunosuppressive drugs result in qualitative and quantitative disturbances in DC homeostasis and have been observed for up to 1 year after transplantation. Complete donor DC chimerism seems to be a pre-requisite for the development of chronic GVHD and for graft-vs-leukemia activity, at least following reduced-intensity transplants, although in the early phase of acute graft-vs-host disease the presence of host antigen-presenting cells is essential. Preliminary data show promising results with DC-based immunotherapy for treatment of viral and fungal infections and of leukemic relapse following allogeneic stem cell transplantation. More information on the mechanisms and interactions between dendritic cells and regulatory T cells is needed for DC vaccination concepts for modulation of graft-vs-host disease.

Dendritic cell deficiency in the blood of kidney transplant patients on long-term immunosuppression: results of a prospective matched-cohort study

Evidence from in vitro studies suggests that immunosuppressive drugs interfere with key functions of dendritic cells (DCs), but the in vivo relevance of these findings is elusive. We prospectively analyzed the major DC precursor subsets in the blood of kidney transplant recipients on long-term immunosuppression (> or =1 year). A total of 87 patients were compared to 87 age- and sex-matched controls. Total DC numbers and the precursor subsets, myeloid type 1 DCs, myeloid type 2 DCs (mDC1, mDC2) and plasmacytoid DCs (pDCs) were identified by four color flow cytometry. Long-term immunosuppression was associated with significant reduction of all major DC subsets in comparison to healthy controls (mDC1 p < 0.001; mDC2 p < 0.0001; two-tailed Mann-Whitney U-test) with the strongest negative impact on pDCs (p < 0.00001). In contrast, total leukocyte numbers were not significantly affected. Analysis of the relative impact of different agents revealed a significant impact of prednisolone on pDCs (p = 0.009) and mDCs2 (p = 0.006). The functional relevance of pDC deficiency was confirmed independently by Interferon-alpha analysis after Toll-like receptor 7 (p < or = 0.001) and 9 (p < 0.05) stimulation. These results indicate for the first time a profound negative impact of long-term immunosuppression on major DC subsets in kidney transplant recipients. DC deficiency may have important implications with respect to viral infections and tumor development.

Regulation of the interaction of inosine monophosphate dehydrogenase with mycophenolic Acid by GTP

Inosine monophosphate dehydrogenase (IMPDH), a rate-limiting enzyme in the de novo synthesis of guanine nucleotides, is a major therapeutic target. A prototypic uncompetitive inhibitor of IMPDH, mycophenolic acid (MPA), is the active form of mycophenolate mofeteil (CellCept), a widely used immunosuppressive drug. We have found that MPA interacts with intracellular IMPDH in vivo to alter its mobility on SDS-polyacrylamide gels. MPA also induces a striking conformational change in IMPDH protein in intact cells, resulting in the formation of annular aggregates of protein with concomitant inhibition of IMPDH activity. These aggregates are not associated with any known intracellular organelles and are reversible by incubating cells with guanosine, which repletes intracellular GTP, or with GTPgammaS. GTP also restores IMPDH activity. Treatment of highly purified IMPDH with MPA also results in the formation of large aggregates of protein, a process that is both prevented and reversed by the addition of GTP. Finally, GTP binds to IMPDH at physiologic concentrations, induces the formation of linear arrays of tetrameric protein, and prevents the aggregation of protein induced by MPA. We conclude that intracellular GTP acts as an antagonist to MPA by directly binding to IMPDH and reversing the conformational changes in the protein.

Empiric therapy of autoimmune hepatitis with mycophenolate mofetil: comparison with conventional treatment for refractory disease

GOAL

To assess the outcomes of empiric therapy with mycophenolate mofetil in patients with autoimmune hepatitis.

BACKGROUND

Mycophenolate mofetil is a purine antagonist that selectively inhibits immunocyte proliferation, and its empiric use in autoimmune hepatitis has been stimulated by small clinical experiences.

STUDY

Eight patients received mycophenolate mofetil (0.5-3 g daily) for 19 +/- 7 months as frontline therapy or after adverse responses to conventional corticosteroid treatment. Seventeen patients who had been treated with high-dose corticosteroid regimens after treatment failure constituted a historical comparison population.

RESULTS

Five of the 8 patients receiving mycophenolate mofetil and all 17 patients who had been treated with the conventional corticosteroid regimens for treatment failure responded to therapy. The frequency of response (62% vs. 100%, P = 0.02) was lower during longer intervals of treatment (19 +/- 7 months vs. 6 +/- 1 months, P = 0.02) in the patients receiving mycophenolate mofetil. None receiving mycophenolate mofetil resolved their laboratory abnormalities, whereas 6 patients in the comparison group improved to normal tests (0% vs. 35%, P = 0.1). Histologic resolution did not occur in 4 patients sampled during treatment, and successive specimens in 2 patients showed progressive fibrosis. Corticosteroids could not be withdrawn in the patients treated with mycophenolate mofetil, whereas discontinuation was possible in 7 patients in the comparison group (0% vs. 41%, P = 0.06).

CONCLUSIONS

Mycophenolate mofetil did not induce laboratory resolution, prevent progressive fibrosis, or allow corticosteroid withdrawal. Clinical trials are needed to evaluate its role and target population.

Inosine 5'-monophosphate dehydrogenase inhibition by mycophenolic acid impairs maturation and function of dendritic cells

BACKGROUND

The mechanism of action of mycophenolic acid (MPA) has been described as a blockade of inosine 5'-monophosphate dehydrogenase (IMPDH) and is thought to selectively influence T- and B-lymphocytes due to their strong dependency on guanine nucleotides synthesized via the de novo purine synthesis pathway. Recent evidence suggests MPA to affect antigen-presenting cells.

METHODS

Using CD14+ derived human dendritic cells (DC) we have investigated the effects of MPA on differentiation, maturation and function and studied intracellular nucleotide content and IMPDH activity.

RESULTS

GTP content and IMPDH activities of DC were strongly and dose-dependently decreased when MPA was present during the entire culture period or was added after the fifth (immature DC) or the seventh (mature DC) day of culture. Concurrent to low GTP levels, a dose-dependent reduction in the expression of CD80, CD86, CD40, CD54 and CD83 was seen which was accompanied by a decreased capacity of DC to stimulate T-cells. Our data for the first time shows a direct effect of MPA on the maturation and function of human CD14+ derived DC, indicates a role of IMPDH and a dependency on the de novo purine synthesis pathway.

The effects of renal transplantation on circulating dendritic cells

The effects of immunosuppressive agents on T cell function have been well characterized but virtually nothing is known about the effects of renal transplantation on human dendritic cells (DCs). With the use of flow cytometry, we studied the kinetics of myeloid and plasmacytoid DCs in peripheral blood of 24 kidney allograft recipients before and after transplantation, and in 23 donors before and after kidney donation. All patients were treated with tacrolimus, mycophenolate mofetil and prednisone. Surgery resulted in a strong decline in the number of myeloid and plasmacytoid DCs, both in kidney donors and in their recipients. However, in donors this effect was transient, as the numbers of both DC subsets had normalized completely by the third postoperative month. In contrast, the recovery of myeloid DC counts in kidney transplant recipients was only incomplete at the end of the 3-month follow-up, despite tapering of immunosuppression. The seven patients who required additional immunosuppressive treatment because of acute rejection experienced an even more marked decrease in DC counts in the early postoperative period compared with patients who remained rejection-free. Surgical procedures markedly affect the numbers of circulating myeloid and plasmacytoid DCs. Immunosuppressive drugs have important additional in vivo effects on this cell type and impair the reconstitution of the myeloid DC subset in peripheral blood after renal transplantation.

Topical Immunotherapy: What's New

Further understanding of the pathogenesis of dermatologic conditions at a molecular level has led to targeted therapies. The topical immune response modifiers have contributed significantly to the treatment of cutaneous diseases. New topical remedies, particularly the Toll-like receptor agonists and calcineurin inhibitors, have added to the clinical armamentarium and have further advanced clinicians' ability to treat a wide variety of benign, premalignant, and malignant conditions. Furthermore, these agents have contributed to the understanding of the disease process. The next decade will witness even greater advances in targeted immunotherapies for dermatologic disease.