Human tolerogenic DC-10: perspectives for clinical applications

IL-10-modulated dendritic cells from birch pollen- and hazelnut-allergic patients facilitate Treg-mediated allergen-specific and cross-reactive tolerance

BACKGROUND

Approximately 70% of individuals allergic to birch pollen (Bet v 1.01 [Bet]) develop a secondary food allergy (e.g., hazelnut: Cor a 1.04 [Cor]), due to allergen cross-reactivity. However, standard immunotherapy for type I allergies often does not improve the food allergy sufficiently. We analyzed the allergen-specific and cross-reactive suppressive capacity of primary human regulatory T cells (Treg) induced by autologous IL-10-modulated dendritic cells (IL-10 DC) in vitro and in vivo.

METHODS

CD4+ T cells of patients with birch pollen and associated hazelnut allergies were differentiated into Bet-specific or non-specific induced Treg (iTreg). After Bet- or Cor-specific restimulation the phenotype, proliferation, and suppressive capacity of iTreg subsets were analyzed. iTreg function was further investigated in humanized mouse models of airway and intestinal allergy, generated by engraftment of peripheral blood mononuclear cells from allergic donors into immunodeficient animals.

RESULTS

After IL-10 DC priming and allergen-specific restimulation (Bet or Cor), non-specific control iTreg remained anergic, whereas Bet-specific iTreg proliferated extensively and exhibited a regulatory phenotype (enhanced expression of CTLA-4, PD-1, TNFR2, IL-10). Accordingly, activated Bet-specific iTreg displayed a high capacity to suppress Bet- and Cor-induced responder Th2 cell responses in vitro, indicating induction of both allergen-specific (birch) and cross-reactive tolerance (hazelnut). In vivo, the beneficial effect of Bet-specific iTreg was verified in humanized mouse models of allergic airway and intestinal inflammation, resulting in reduced allergen-induced clinical symptoms, and immune responses.

CONCLUSION

Human IL-10 DC-induced iTreg facilitate allergen-specific and cross-reactive tolerance. Therefore, they are potential candidates for regulatory cell therapy in allergic and autoimmune diseases.

Aryl hydrocarbon receptor activation ameliorates experimental colitis by modulating the tolerogenic dendritic and regulatory T cell formation

Background

Intestinal immune dysfunction is involved in the onset of Crohn’s disease (CD). Dendritic cells (DCs), antigen-presenting cells, play a key role in the maintenance of intestinal immune homeostasis. The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor widely expressed in various immune cells, including DCs. Although AhR plays an important role in immune tolerance, its role in the DCs is unclear. The purpose of this study was to investigate whether the activation of AhR can induce tolerogenic DCs (tolDCs) and the differentiation of regulatory T (Treg) cells, as well as ameliorate experimental colitis.

Results

AhR activation in the DCs resulted in a lower expression of surface markers such as CD80, CD83, CD86, and pro-inflammatory cytokine production, and higher anti-inflammatory production (IL-1β, IL-23, and IL-12) compared to the control DCs. The surface dendrites in DCs were significantly reduced following AhR activation by 6-formylindolo [3,2-b]carbazole (FICZ). Such DCs with FICZ-mediated activation of AhR, namely tolDCs, promoted Treg cell differentiation. Adoptive transfer of tolDCs to a TNBS-induced colitis mouse model significantly alleviated the severity of inflammation by improving the colon length and decreasing the disease activity index (DAI) and histopathological score. Moreover, the transferred tolDCs decreased the frequency of Th17 cells and increased the frequency of Treg cells in the spleen and mesenteric lymph nodes (MLNs) in murine colitis models.

Conclusions

Activation of AhR in the DCs could induce tolDCs, and the transplantation of tolDCs may help in relieving intestinal inflammation and maintaining the Th17/Treg differentiation balance. Thus, our data suggest that AhR may be a potential therapeutic target for CD.

HLA-G 14bp Ins/Del Polymorphism, Plasma Level of Soluble HLA-G, and Association with IL-6/IL-10 Ratio and Survival of Glioma Patients

HLA-G is an immune checkpoint molecule with immunosuppressive and anti-inflammatory activities, and its expression and level of its soluble form (sHLA-G) may play an important role in tumor prognosis. The HLA-G 14bp ins/del polymorphism and the plasma level of soluble HLA-G (sHLA-G) were investigated by a polymerase chain reaction and ELISA, respectively, in 59 glioma patients. A significantly higher proportion of glioma patients had the 14 nt insert in both homozygous and heterozygous states compared to the control group. Glioma patients also had higher plasma levels of sHLA-G. Patients with methylated MGMT promoters had lower levels of sHLA-G than those with unmethylated MGMT promoters. The level of sHLA-G negatively correlated with the overall survival of patients. Glioblastoma patients who survived more than one year after diagnosis had lower levels of sHLA-G than those surviving less than one year. Patients with sHLA-G levels below the cut-off value of 40 U/mL survived significantly longer than patients with sHLA-G levels above 40 U/mL. The levels of sHLA-G were also negatively correlated with the level of IL-6 (p = 0.0004) and positively with IL-10/IL-6 (p = 0.046). Conclusion: The presence of the 14 nt insert in both homozygous and heterozygous states of the HLA-G 14bp ins/del polymorphism is more frequent in glioma patients and the elevated plasma levels of sHLA-G are negatively associated with their survival.

Monocyte Gene and Molecular Expression Profiles Suggest Distinct Effector and Regulatory Functions in Beninese HIV Highly Exposed Seronegative Female Commercial Sex Workers

We have previously reported that the female genital tract (FGT) of Beninese HIV highly-exposed seronegative (HESN) commercial sex workers (CSWs), presented elevated frequencies of a myeloid HLA-DR+CD14+CD11c+ population presenting “tolerogenic” monocyte derived dendritic cells (MoDC) features. In order to assess whether a differential profile of monocytes may be involved in the generation of these genital MoDCs, we have herein characterized the blood monocyte compartment of Beninese HESNs (HIV-uninfected ≥ 10 years CSWs) and relevant controls (HIV-uninfected 2.5–5 years CSWs herein termed “early HESNs”), HIV-infected CSWs, and low-risk HIV-uninfected women from the general population. Transcriptomic analyses by RNA-Seq of total sorted blood monocytes demonstrate that in comparison to the control groups, HESNs present increased expression levels of FCGR2C, FCAR, ITGAX, ITGAM, CR2, CD68, and CD163 genes, associated with effector functions. Moreover, we found increased expression levels of genes associated with protection/control against SHIV/HIV such as CCL3, CCL4, CCL5, BHLHE40, and TNFSF13, as well as with immune regulation such as IL-10, Ahr, CD83, and the orphan nuclear receptor (NR)4A1, NR4A2, and NR4A3. Through multicolor flow cytometry analyses, we noticed that the frequencies of intermediate and non-classical monocyte populations tended to be elevated in the blood of HESNs, and exhibited increased expression levels of effector CD16, CD11c, CD11b, as well as regulatory HLA-G, IL-10, and IFN-α markers when compared to HIV-uninfected women and/or HIV-infected CSWs. This profile is compatible with that previously reported in the FGT of HESNs, and likely confers an enormous advantage in their resistance to HIV infection.

The Importance of Regulation in Natural Immunity to HIV

Worldwide, most Human Immunodeficiency Virus (HIV) infections are acquired through heterosexual intercourse, and in sub-Saharan Africa, 59% of new HIV infections affect women. Vaccines and microbicides hold promise for preventing the acquisition of HIV. To this end, the study of HIV highly exposed seronegative (HESN) female commercial sex workers (CSWs), who constitute a model of natural immunity to HIV, provides an exceptional opportunity to determine important clues for the development of preventive strategies. Studies using both female genital tract (FGT) and peripheral blood samples of HESN CSWs, have allowed identifying distinct features, notably low-inflammatory patterns associated with resistance to infection. How this seemingly regulated response is achieved at the initial site of HIV infection remains unknown. One hypothesis is that populations presenting regulatory profiles contribute to the orchestration of potent anti-viral and low-inflammatory responses at the initial site of HIV transmission. Here, we view to update our knowledge regarding this issue.

Decidualization Process Induces Maternal Monocytes to Tolerogenic IL-10-Producing Dendritic Cells (DC-10)

Decidualization is a process that involves phenotypic and functional changes of endometrial stromal cells to sustain endometrial receptivity and the participation of immunoregulatory factors to maintain immune homeostasis. In this context, tolerogenic dendritic cells (DCs) can induce regulatory T cells, which are essential to manage the pro- to anti-inflammatory transition during embryo implantation. Recently, Myeloid Regulatory Cells (MRCs) were proposed as immunosuppressants and tolerance-inducer cells, including the DC-10 subset. This novel and distinctive subset has the ability to produce IL-10 and to induce type 1 regulatory T cells (Tr1) through an HLA-G pathway. Here we focus on the impact of the decidualization process in conditioning peripheral monocytes to MRCs and the DC-10 subset, and their ability to induce regulatory T cells. An in vitro model of decidualization with the human endometrial stromal cell line (HESC), decidualized by medroxyprogesterone and dibutyryl-cAMP was used. Monocytes isolated from peripheral blood mononuclear cells from healthy women were cultured with rhGM-CSF + rhIL-4 and then, the effect of conditioned media from decidualized (Dec-CM) and non-decidualized cells (Non-dec-CM) was tested on monocyte cultures. We found that Dec-CM inhibited the differentiation to the CD1a⁺CD14^– immature DC profile in a concentration-dependent manner. Dec-CM also significantly increased the frequency of CD83⁺CD86^low and HLA-DR⁺ cells in the monocyte-derived culture. These markers, associated with the increased production of IL-10, are consistent with a MRCs tolerogenic profile. Interestingly, Dec-CM treatment displayed a higher expression of the characteristic markers of the tolerogenic DC-10 subset, HLA-G and ILT2/CD85j; while this modulation was not observed in cultures treated with Non-dec-CM. Moreover, when monocyte cultures with Dec-CM were challenged with LPS, they sustained a higher IL-10 production and prevented the increase of CD83, CD86, IL-12p70, and TNF-α expression. Finally, the DC-10 subset was able to induce a CD4⁺HLA-G⁺ regulatory T cells subset. These results suggest that the decidualization process might induce different subsets of MRCs, like DC-10, able to induce regulatory T cells as a novel CD4⁺HLA-G⁺ subset which might play an immunoregulatory role in embryo implantation.

Cell Therapy in Solid Organ Transplantation

Transplantation is the only cure for end-stage organ failure. Current immunosuppressive drugs have two major limitations: 1) non antigen specificity, which increases the risk of cancer and infection diseases, and 2) chronic toxicity. Cell therapy appears to be an innovative and promising strategy to minimize the use of immunosuppression in transplantation and to improve long-term graft survival. Preclinical studies have shown efficacy and safety of using various suppressor cells, such as regulatory T cells, regulatory B cells and tolerogenic dendritic cells. Recent clinical trials using cellbased therapies in solid organ transplantation also hold out the promise of improving efficacy. In this review, we will briefly go over the rejection process, current immunosuppressive drugs, and the potential therapeutic use of regulatory cells in transplantation.

Development of an In Vitro Assay to Assess Pharmacological Compounds and Reversion of Tumor-Derived Immunosuppression of Dendritic Cells

BACKGROUND

Cancer immunotherapies have achieved much success and have become the forefront treatment of cancers previously associated with poor prognosis. However, a major challenge in cancer immunotherapies remains the heterogeneity of the immunoregulatory capacities of cancers, and not all patients of a given cancer responds to current therapeutic strategies. To address this issue and to facilitate the development of new pharmacological compounds, we here describe an in vitro model of dendritic cell suppression by cancer cells.

METHODS

We treated monocyte-derived dendritic cells with conditioned medium from cancer cell lines and assessed their maturation using ELISA and flow cytometry. In addition, we assessed their ability to induce T cell activation and differentiation.

RESULTS

We found that both the phenotypic and functional maturation of dendritic cells was suppressed by the conditioned medium. The expression of IL-12p70, TNF-α, CD80, CD83, and CD86 was significantly reduced by conditioned medium from the 786-O and HeLa cell lines, and CD4⁺ T cells had a weaker T_H1 phenotype with significantly decreased expression of IFN-γ and T-bet following co-culturing. Furthermore, we use our model to characterize the differential immunoregulatory capacities of primary cancers by using conditioned medium of cultured primary cancer cells.

CONCLUSION

This model can be used to screen pharmacological compounds seeking to alleviate the immunosuppression of the tumor microenvironment and can furthermore be used to investigate the immunoregulatory capacities of primary cancer cells, which could be a helpful prognostic tool following tumor resection.

Activation of immunosuppressive network in the aging process

Chronic low-grade inflammation has a key role in the aging process, a state called inflammaging. It is known that the chronic inflammatory condition generates counteracting immunosuppressive state in many diseases. Inflammaging is also associated with an immune deficiency; generally termed as immunosenescence, although it is not known whether it represents the senescence of immune cells or the active remodeling of immune system. Evidence has accumulated since the 1970's indicating that immunosenescence might be caused by an increased activity of immunosuppressive cells rather than cellular senescence. Immune cells display remarkable plasticity; many of these cells can express both proinflammatory and immunosuppressive phenotypes in a context-dependent manner. The immunosuppressive network involves the regulatory subtypes of T (Treg) and B (Breg) cells as well as regulatory phenotypes of macrophages (Mreg), dendritic (DCreg), natural killer (NKreg), and type II natural killer T (NKT) cells. The immunosuppressive network also includes monocytic (M-MDSC) and polymorphonuclear (PMN-MDSC) myeloid-derived suppressor cells which are immature myeloid cells induced by inflammatory mediators. This co-operative network is stimulated in chronic inflammatory conditions preventing excessive inflammatory responses but at the same time they exert harmful effects on the immune system and tissue homeostasis. Recent studies have revealed that the aging process is associated with the activation of immunosuppressive network, especially the functions of MDSCs, Tregs, and Mregs are increased. I will briefly review the properties of the regulatory phenotypes of immune cells and examine in detail the evidences for an activation of immunosuppressive network with aging.

Effect of seminal plasma on dendritic cell differentiation in vitro depends on the serum source in the culture medium

Dendritic cells (DCs) are key in shaping immune responses and are recruited to the human cervix after coitus by seminal plasma (SP). SP has been shown to skew the differentiation of monocyte-derived DCs towards an anti-inflammatory profile when cultured in medium containing fetal calf serum (FCS). Here, we confirmed that SP skewed DCs cultured in fetal bovine serum (FBS) towards a tolerogenic profile. To create a setting more similar to the in vivo situations in humans, we tested the immune regulatory effect of SP on DCs in cell cultures containing human serum (HS). SP-DCs cultured in HS did show increased CD14 and decreased CD1a, indicating an inhibited maturation phenotype. Gene expression of TGF-β and IL-10 and IL-10 protein expression were elevated in LPS-activated SP-DCs, whereas IL-12p70 protein levels were decreased compared to LPS-activated control DCs. In contrast to FBS culture conditions, in the presence of HS co-cultures of SP-DCs with allogeneic peripheral blood mononuclear cells (PBMCs) did not result in decreased T cell proliferation and inflammatory cytokine production. Thus, under HS culture conditions SP can skew the differentiation of monocyte-derived DCs phenotypically towards alternatively activated DCs, but this immune regulatory phenotype is functionally less pronounced compared to SP-treated DCs cultured in FBS containing medium. These findings highlight the importance of the source of the serum that is used in SP treated cell cultures in vitro.

Induction of Tolerance and Immunity by Dendritic Cells: Mechanisms and Clinical Applications

Dendritic cells (DCs) are key regulators of immune responses that operate at the interface between innate and adaptive immunity, and defects in DC functions contribute to the pathogenesis of a variety of disorders. For instance, cancer evolves in the context of limited DC activity, and some autoimmune diseases are initiated by DC-dependent antigen presentation. Thus, correcting aberrant DC functions stands out as a promising therapeutic paradigm for a variety of diseases, as demonstrated by an abundant preclinical and clinical literature accumulating over the past two decades. However, the therapeutic potential of DC-targeting approaches remains to be fully exploited in the clinic. Here, we discuss the unique features of DCs that underlie the high therapeutic potential of DC-targeting strategies and critically analyze the obstacles that have prevented the full realization of this promising paradigm.

Regulatory T cells induce CD4- NKT cell anergy and suppress NKT cell cytotoxic function

BACKGROUND

Due to the strong tumoricidal activities of activated natural killer T (NKT) cells, invariant NKT cell-based immunotherapy has shown promising clinical efficacy. However, suppressive factors, such as regulatory T cells (Tregs), may be obstacles in the use of NKT cell-based cancer immunotherapy for advanced cancer patients. Here, we investigated the suppressive effects of Tregs on NKT cells and the underlying mechanisms with the aim to improve the antitumor activities of NKT cells.

METHODS

Peripheral blood samples were obtained from healthy donors, patients with benign tumors, and patients with head and neck squamous cell carcinoma (HNSCC). NKT cells, induced with α-galactosylceramide (α-GalCer), and monocyte-derived dendritic cells (DCs) were co-cultured with naïve CD4⁺ T cell-derived Tregs to investigate the mechanism of the Treg suppressive effect on NKT cell cytotoxic function. The functions and phenotypes of NKT cells were evaluated with flow cytometry and cytometric bead array.

RESULTS

Treg suppression on NKT cell function required cell-to-cell contact and was mediated via impaired DC maturation. NKT cells cultured under Treg-enriched conditions showed a decrease in CD4^- NKT cell frequency, which exert strong tumoricidal responsiveness upon α-GalCer stimulation. The same results were observed in HNSCC patients with significantly increased effector Tregs.

CONCLUSION

Tregs exert suppressive effects on NKT cell tumoricidal function by inducing more CD4^- NKT cell anergy and less CD4⁺ NKT cell anergy. Both Treg depletion and NKT cell recovery from the anergy state may be important for improving the clinical efficacy of NKT cell-based immunotherapy in patients with advanced cancers.

European Patent in Immunoncology: From Immunological Principles of Implantation to Cancer Treatment

The granted European patent EP 2 561 890 describes a procedure for an immunological treatment of cancer. It is based on the principles of the HLA-supported communication of implantation and pregnancy. These principles ensure that the embryo is not rejected by the mother. In pregnancy, the placenta, more specifically the trophoblast, creates an “interface” between the embryo/fetus and the maternal immune system. Trophoblasts do not express the “original” HLA identification of the embryo/fetus (HLA-A to -DQ), but instead show the non-classical HLA groups E, F, and G. During interaction with specific receptors of NK cells (e.g., killer-immunoglobulin-like receptors (KIR)) and lymphocytes (lymphocyte-immunoglobulin-like receptors (LIL-R)), the non-classical HLA groups inhibit these immunocompetent cells outside pregnancy. However, tumors are known to be able to express these non-classical HLA groups and thus make use of an immuno-communication as in pregnancies. If this occurs, the prognosis usually worsens. This patent describes, in a first step, the profiling of the non-classical HLA groups in primary tumor tissue as well as metastases and recurrent tumors. The second step comprises tailored antibody therapies, which is the subject of this patent. In this review, we analyze the underlying mechanisms and describe the currently known differences between HLA-supported communication of implantation and that of tumors.

Soluble factors derived from neuroblastoma cell lines suppress dendritic cell differentiation and activation

Dendritic cells (DC) play a key role in the initiation of both antitumor immunity and immunological tolerance. It has been demonstrated that exposure to soluble factors produced by tumor cells modulates DC functions and induces tolerogenic DC differentiation. In this study, we investigated the effects of neuroblastoma cell line-derived soluble factors on DC differentiation. Monocytes isolated from healthy volunteers were incubated with interleukin (IL)-4 and granulocyte-macrophage colony-stimulating factor in the presence of culture supernatants from neuroblastoma cell lines. The culture supernatants from neuroblastoma cell lines, such as NLF and GOTO, partially blocked both downregulation of CD14 and upregulation of CD1a, and dramatically decreased IL-12 and tumor necrosis factor (TNF)-α production from mature DC, while no effect of SH-SY5Y cell supernatant was noted. In addition, IL-6 and IL-10 production from monocytes was increased by the supernatants of NLF and GOTO cells at 24 hours after incubation. Furthermore, we evaluated DC functions through stimulation of invariant natural killer T (iNKT) cells. α-Galactosylceramide-pulsed DC co-cultured with supernatants of NLF cells were unable to sufficiently stimulate iNKT cells. The decreased ability of iNKT cells to produce interferon (IFN)-γ after stimulation with neuroblastoma cell line supernatant-cultured DC was reversed by addition of IL-12. CD40 expression and IL-12 production in NLF-sup-treated DC were increased by addition of exogenous IFN-γ. These results indicate that tolerogenic DC are induced in the neuroblastoma tumor microenvironment and attenuate the antitumor effects of iNKT cells. Interactions between iNKT cells and αGalCer-pulsed DC have the potential to restore the immunosuppression of tolerogenic DC through IFN-γ production.

Natural Immunity to HIV: A Template for Vaccine Strategies

Africa accounts for the majority of global human immunodeficiency virus (HIV) infections, most of which affect women through heterosexual intercourse. Currently, there is no cure for HIV and the development of vaccines and microbicides remains the best solution to eradicate the pandemic. We and others have identified HIV highly-exposed seronegative (HESN) individuals among African female commercial sex workers (CSWs). Analyses of genital samples from HESNs have demonstrated potent innate and anti-inflammatory conditions, HIV-specific CD4⁺ and CD8⁺ T-cells as well as immunoglobulins (Igs), and increased regulatory cell populations, all of which support a delicate balance between strength and control against HIV intrusion. Moreover, we have recently shown that frequencies of innate marginal zone (MZ) B-cells are decreased in the blood of HESNs when compared to HIV-uninfected non-CSW women, suggesting their recruitment to peripheral sites. This coincides with the fact that levels of B lymphocyte stimulator (BLyS/BAFF), known to shape the MZ pool and whose overexpression leads to MZ deregulation in HIV-infected progressors, are significantly lower in the blood of HESNs when compared to both HIV-infected CSWs and HIV-uninfected non-CSW women. Interestingly, MZ B-cells can bind HIV gp120 and produce specific IgG and IgA, and have a propensity for B regulatory potential, which could help both the fight against HIV and maintenance of low inflammatory conditions in HESNs. HESN individuals provide an exceptional opportunity to identify important clues for the development of protective devices, and efforts should aim at soliciting immune responses observed in the context of their natural immunity to HIV.

Interleukin-10-Producing DC-10 Is a Unique Tool to Promote Tolerance Via Antigen-Specific T Regulatory Type 1 Cells

The prominent role of tolerogenic dendritic cells (tolDCs) in promoting immune tolerance and the development of efficient methods to generate clinical grade products allow the application of tolDCs as cell-based approach to dampen antigen (Ag)-specific T cell responses in autoimmunity and transplantation. Interleukin (IL)-10 potently modulates the differentiation and functions of myeloid cells. Our group contributed to the identification of IL-10 as key factor in inducing a subset of human tolDCs, named dendritic cell (DC)-10, endowed with the ability to spontaneously release IL-10 and induce Ag-specific T regulatory type 1 (Tr1) cells. We will provide an overview on the role of IL-10 in modulating myeloid cells and in promoting DC-10. Moreover, we will discuss the clinical application of DC-10 as inducers of Ag-specific Tr1 cells for tailoring Tr1-based cell therapy, and as cell product for promoting and restoring tolerance in T-cell-mediated diseases.

Tolerogenic Dendritic Cells in Solid Organ Transplantation: Where Do We Stand?

Over the past century, solid organ transplantation has been improved both at a surgical and postoperative level. However, despite the improvement in efficiency, safety, and survival, we are still far from obtaining full acceptance of all kinds of allograft in the absence of concomitant treatments. Today, transplanted patients are treated with immunosuppressive drugs (IS) to minimize immunological response in order to prevent graft rejection. Nevertheless, the lack of specificity of IS leads to an increase in the risk of cancer and infections. At this point, cell therapies have been shown as a novel promising resource to minimize the use of IS in transplantation. The main strength of cell therapy is the opportunity to generate allograft-specific tolerance, promoting in this way long-term allograft survival. Among several other regulatory cell types, tolerogenic monocyte-derived dendritic cells (Tol-MoDCs) appear to be an interesting candidate for cell therapy due to their ability to perform specific antigen presentation and to polarize immune response to immunotolerance. In this review, we describe the characteristics and the mechanisms of action of both human Tol-MoDCs and rodent tolerogenic bone marrow-derived DCs (Tol-BMDCs). Furthermore, studies performed in transplantation models in rodents and non-human primates corroborate the potential of Tol-BMDCs for immunoregulation. In consequence, Tol-MoDCs have been recently evaluated in sundry clinical trials in autoimmune diseases and shown to be safe. In addition to autoimmune diseases clinical trials, Tol-MoDC is currently used in the first phase I/II clinical trials in transplantation. Translation of Tol-MoDCs to clinical application in transplantation will also be discussed in this review.

DHRS9 Is a Stable Marker of Human Regulatory Macrophages

Background

The human regulatory macrophage (Mreg) has emerged as a promising cell type for use as a cell-based adjunct immunosuppressive therapy in solid organ transplant recipients. In this brief report, dehydrogenase/reductase 9 (DHRS9) is identified as a robust marker of human Mregs.

Methods

The cognate antigen of a mouse monoclonal antibody raised against human Mregs was identified as DHRS9 by immunoprecipitation and MALDI-MS sequencing. Expression of DHRS9 within a panel of monocyte-derived macrophages was investigated by quantitative PCR, immunoblotting and flow cytometry.

Results

DHRS9 expression discriminated human Mregs from a panel of in vitro derived macrophages in other polarisation states. Likewise, DHRS9 expression distinguished Mregs from a variety of human monocyte-derived tolerogenic antigen-presenting cells in current development as cell-based immunotherapies, including Tol-DC, Rapa-DC, DC-10, and PGE₂-induced myeloid-derived suppressor cells. A subpopulation of DHRS9-expressing human splenic macrophages was identified by immunohistochemistry. Expression of DHRS9 was acquired gradually during in vitro development of human Mregs from CD14⁺ monocytes and was further enhanced by IFN-γ treatment on day 6 of culture. Stimulating Mregs with 100 ng/mL lipopolysaccharide for 24 hours did not extinguish DHRS9 expression. Dhrs9 was not an informative marker of mouse Mregs.

Conclusion

DHRS9 is a specific and stable marker of human Mregs.

A brief definitive report that dehydrogenase/reductase 9 (DHRS9) is a robust marker of human, but not mouse, Mregs.

Clinical Tolerogenic Dendritic Cells: Exploring Therapeutic Impact on Human Autoimmune Disease

Tolerogenic dendritic cell (tDC)-based clinical trials for the treatment of autoimmune diseases are now a reality. Clinical trials are currently exploring the effectiveness of tDC to treat autoimmune diseases of type 1 diabetes mellitus, rheumatoid arthritis, multiple sclerosis (MS), and Crohn's disease. This review will address tDC employed in current clinical trials, focusing on cell characteristics, mechanisms of action, and clinical findings. To date, the publicly reported human trials using tDC indicate that regulatory lymphocytes (largely Foxp3+ T-regulatory cell and, in one trial, B-regulatory cells) are, for the most part, increased in frequency in the circulation. Other than this observation, there are significant differences in the major phenotypes of the tDC. These differences may affect the outcome in efficacy of recently launched and impending phase II trials. Recent efforts to establish a catalog listing where tDC converge and diverge in phenotype and functional outcome are an important first step toward understanding core mechanisms of action and critical "musts" for tDC to be therapeutically successful. In our view, the most critical parameter to efficacy is in vivo stability of the tolerogenic activity over phenotype. As such, methods that generate tDC that can induce and stably maintain immune hyporesponsiveness to allo- or disease-specific autoantigens in the presence of powerful pro-inflammatory signals are those that will fare better in primary endpoints in phase II clinical trials (e.g., disease improvement, preservation of autoimmunity-targeted tissue, allograft survival). We propose that pre-treatment phenotypes of tDC in the absence of functional stability are of secondary value especially as such phenotypes can dramatically change following administration, especially under dynamic changes in the inflammatory state of the patient. Furthermore, understanding the outcomes of different methods of cell delivery and sites of delivery on functional outcomes, as well as quality control variability in the functional outcomes resulting from the various approaches of generating tDC for clinical use, will inform more standardized ex vivo generation methods. An understanding of these similarities and differences, with a reference point the large number of naturally occurring tDC populations with different immune profiles described in the literature, could explain some of the expected and unanticipated outcomes of emerging tDC clinical trials.

MITAP-compliant characterization of human regulatory macrophages

This article provides a transparent description of Mreg_UKR cell products, including manufacture and quality-control processes, using the structure and vocabulary of the 'Minimum Information about Tolerogenic Antigen-presenting Cells' reporting guidelines. This information is intended as a resource for those in the field, as well as a stimulus to develop a new wave of immunoregulatory and tissue-reparative monocyte-derived cell therapies.

NOD1 modulates IL-10 signalling in human dendritic cells

NOD1 belongs to the family of NOD-like receptors, which is a group of well-characterised, cytosolic pattern-recognition receptors. The best-studied function of NOD-like receptors is their role in generating immediate pro-inflammatory and antimicrobial responses by detecting specific bacterial peptidoglycans or by responding to cellular stress and danger-associated molecules. The present study describes a regulatory, peptidoglycan-independent function of NOD1 in anti-inflammatory immune responses. We report that, in human dendritic cells, NOD1 balances IL-10-induced STAT1 and STAT3 activation by a SOCS2-dependent mechanism, thereby suppressing the tolerogenic dendritic cell phenotype. Based on these findings, we propose that NOD1 contributes to inflammation not only by promoting pro-inflammatory processes, but also by suppressing anti-inflammatory pathways.

IL-10-Modulated Human Dendritic Cells for Clinical Use: Identification of a Stable and Migratory Subset with Improved Tolerogenic Activity

Dendritic cells (DCs) are key regulators of protective immune responses and tolerance to (self-)Ags. Therefore, the scientific rationale for the use of tolerogenic DC therapy in the fields of allergies, autoimmunity, and transplantation medicine is strong. In this study, we analyzed the tolerogenic capacity of IL-10-modulated DC (IL-10DC) subpopulations to identify a DC subset that combines potent immunosuppressive activities with valuable immune properties for clinical implementation. IL-10DCs consist of two phenotypically distinct subpopulations: CD83highCCR7+ IL-10DCs and CD83lowCCR7- IL-10DCs. Suppressor assays with activated effector T cells revealed that CD4+ regulatory T cells generated by CD83high IL-10DCs (iTreg+) exhibited a significantly higher suppressive capacity compared with CD4+ regulatory T cells generated by CD83low IL-10DCs (iTreg-). In this context, iTreg+ displayed a more activated phenotype (proliferation, cytokine production) compared with iTreg- In contrast to CD83low IL-10DCs, CD83high IL-10DCs exerted a strong migratory capacity toward the secondary lymphoid organ chemokine CCL21 and retained a functionally stable phenotype under inflammatory conditions. In addition, CD83high IL-10DCs expressed significantly higher levels of surface and soluble CD25. Functional analysis demonstrated that IL-10DC-related soluble CD25 efficiently inhibited the proliferation of activated T cells and that blockade of CD25 function abolished the induction of regulatory T cells by IL-10DCs, indicating a critical role for IL-10DC-related CD25 in shifting the immune response toward an iTreg- controlled tolerance reaction. In conclusion, the selective use of the CD83high IL-10DC subset may result in a higher efficacy of tolerance induction in vivo and may support the development of novel DC vaccination strategies for transplantations, as well as for allergic and autoimmune diseases.

Tr1-Like T Cells - An Enigmatic Regulatory T Cell Lineage

The immune system evolved to respond to foreign invaders and prevent autoimmunity to self-antigens. Several types of regulatory T cells facilitate the latter process. These include a subset of Foxp3⁻ CD4⁺ T cells able to secrete IL-10 in an antigen-specific manner, type 1 regulatory (Tr1) T cells. Although their suppressive function has been confirmed both in vitro and in vivo, their phenotype remains poorly defined. It has been suggested that the surface markers LAG-3 and CD49b are biomarkers for murine and human Tr1 cells. Here, we discuss these findings in the context of our data regarding the expression pattern of inhibitory receptors (IRs) CD49b, TIM-3, PD-1, TIGIT, LAG-3, and ICOS on Tr1-like human T cells generated in vitro from CD4⁺ memory T cells stimulated with αCD3 and αCD28 antibodies. We found that there were no differences in IR expression between IL-10⁺ and IL-10⁻ T cells. However, CD4⁺IL-10⁺ T cells isolated ex vivo, following a short stimulation and cytokine secretion assay, contained significantly higher proportions of TIM-3⁺ and PD-1⁺ cells. They also expressed significantly higher TIGIT mRNA and showed a trend toward increased TIM-3 mRNA levels. These data led us to conclude that large pools of IRs may be stored intracellularly; hence, they may not represent ideal candidates as cell surface biomarkers for Tr1-like T cells.

Minimum information about tolerogenic antigen-presenting cells (MITAP): a first step towards reproducibility and standardisation of cellular therapies

Cellular therapies with tolerogenic antigen-presenting cells (tolAPC) show great promise for the treatment of autoimmune diseases and for the prevention of destructive immune responses after transplantation. The methodologies for generating tolAPC vary greatly between different laboratories, making it difficult to compare data from different studies; thus constituting a major hurdle for the development of standardised tolAPC therapeutic products. Here we describe an initiative by members of the tolAPC field to generate a minimum information model for tolAPC (MITAP), providing a reporting framework that will make differences and similarities between tolAPC products transparent. In this way, MITAP constitutes a first but important step towards the production of standardised and reproducible tolAPC for clinical application.

Induction of CD4(+) Regulatory and Polarized Effector/helper T Cells by Dendritic Cells

Dendritic cells (DCs) are considered to play major roles during the induction of T cell immune responses as well as the maintenance of T cell tolerance. Naive CD4(+) T cells have been shown to respond with high plasticity to signals inducing their polarization into effector/helper or regulatory T cells. Data obtained from in vitro generated bone-marrow (BM)-derived DCs as well as genetic mouse models revealed an important but not exclusive role of DCs in shaping CD4(+) T cell responses. Besides the specialization of some conventional DC subsets for the induction of polarized immunity, also the maturation stage, activation of specialized transcription factors and the cytokine production of DCs have major impact on CD4(+) T cells. Since in vitro generated BM-DCs show a high diversity to shape CD4(+) T cells and their high similarity to monocyte-derived DCs in vivo, this review reports data mainly on BM-DCs in this process and only touches the roles of transcription factors or of DC subsets, which have been discussed elsewhere. Here, recent findings on 1) the conversion of naive into anergic and further into Foxp3(-) regulatory T cells (Treg) by immature DCs, 2) the role of RelB in steady state migratory DCs (ssmDCs) for conversion of naive T cells into Foxp3(+) Treg, 3) the DC maturation signature for polarized Th2 cell induction and 4) the DC source of IL-12 for Th1 induction are discussed.

Elevation of HLA-G-expressing DC-10 cells in patients with gastric cancer

DC-10 is a distinct subset of human tolerogenic dendritic cells (DCs) which express high levels of human leukocyte antigen-G (HLA-G). DC-10 could induce adaptive type 1 regulatory T cells through the IL-10 dependent ILT4/HLA-G signaling pathway. However, the significance of DC-10 in malignancies remains unclear. In this study, the frequency and mean fluorescence intensity (MFI) of HLA-G+ DC-10 in the peripheral blood of 124 patients with gastric cancer (GC) and 130 normal controls was analyzed with flow cytometry. Plasma sHLA-G was analyzed with ELISA. Results showed both the percentages of peripheral HLA-G+ DC-10 (median: 0.13% vs 0.01%; p<0.01) and MFI of HLA-G on these cells (median: 310.0 vs 91.5; p<0.01) were dramatically increased in GC patients than in normal controls. The frequency of HLA-G+ DC-10 in GC patients was strongly relative to the tumor grade (p=0.021). sHLA-G levels in GC patients were significantly higher than in healthy controls (median: 85.80U/ml vs 61.20U/ml; p<0.01). There was no significant correlation between the percentage of DC-10 and plasma sHLA-G (p>0.05). However, the increased HLA-G+ DC-10, HLA-G MFI and plasma sHLA-G in patients with gastric cancer could be a diagnostic factor with the area under the ROC curve with 0.947 (p<0.01), 0.882 (p<0.01) and 0.700 (p<0.01) respectively. Given the immune tolerant function of DC-10 could play, the increased DC-10 might play an important role in immune suppression for patients with gastric cancer, while more studies are necessary to illustrate the clinical relevance of DC-10 in cancer patients.

Clinical Use of Tolerogenic Dendritic Cells-Harmonization Approach in European Collaborative Effort

The number of patients with autoimmune diseases and severe allergies and recipients of transplants increases worldwide. Currently, these patients require lifelong administration of immunomodulatory drugs. Often, these drugs are expensive and show immediate or late-occurring severe side effects. Treatment would be greatly improved by targeting the cause of autoimmunity, that is, loss of tolerance to self-antigens. Accumulating knowledge on immune mechanisms has led to the development of tolerogenic dendritic cells (tolDC), with the specific objective to restrain unwanted immune reactions in the long term. The first clinical trials with tolDC have recently been conducted and more tolDC trials are underway. Although the safety trials have been encouraging, many questions relating to tolDC, for example, cell-manufacturing protocols, administration route, amount and frequency, or mechanism of action, remain to be answered. Aiming to join efforts in translating tolDC and other tolerogenic cellular products (e.g., Tregs and macrophages) to the clinic, a European COST (European Cooperation in Science and Technology) network has been initiated-A FACTT (action to focus and accelerate cell-based tolerance-inducing therapies). A FACTT aims to minimize overlap and maximize comparison of tolDC approaches through establishment of minimum information models and consensus monitoring parameters, ensuring that progress will be in an efficient, safe, and cost-effective way.

Tolerogenic Dendritic Cells for Regulatory T Cell Induction in Man

Dendritic cells (DCs) are highly specialized professional antigen-presenting cells that regulate immune responses, maintaining the balance between tolerance and immunity. Mechanisms via which they can promote central and peripheral tolerance include clonal deletion, the inhibition of memory T cell responses, T cell anergy, and induction of regulatory T cells (Tregs). These properties have led to the analysis of human tolerogenic DCs as a therapeutic strategy for the induction or re-establishment of tolerance. In recent years, numerous protocols for the generation of human tolerogenic DCs have been developed and their tolerogenic mechanisms, including induction of Tregs, are relatively well understood. Phase I trials have been conducted in autoimmune disease, with results that emphasize the feasibility and safety of treatments with tolerogenic DCs. Therefore, the scientific rationale for the use of tolerogenic DCs therapy in the fields of transplantation medicine and allergic and autoimmune diseases is strong. This review will give an overview on efforts and protocols to generate human tolerogenic DCs with focus on IL-10-modulated DCs as inducers of Tregs and discuss their clinical applications and challenges faced in further developing this form of immunotherapy.

Human Leukocyte Antigen-G (HLA-G) Expression in Cancers: Roles in Immune Evasion, Metastasis and Target for Therapy

Aberrant induction of human leukocyte antigen-G (HLA-G) expression has been observed in various malignancies and is strongly associated with tumor immune escape, metastasis and poor prognosis. To date, great achievements have been made in understanding the underlying mechanisms of HLA-G involved in tumor progression. HLA-G could lead to tumor evasion by inhibition of immune cell cytolysis, differentiation and proliferation and inhibition of cytokine production, induction of immune cell apoptosis, generation of regulatory cells and expansion of myeloid-derived suppressive cells and by impairment of chemotaxis. Moreover, HLA-G could arm tumor cells with a higher invasive and metastatic potential with the upregulation of tumor-promoting factor expression such as matrix metalloproteinases (MMPs), indicating that ectopic HLA-G expression could render multiple effects during the progression of malignancies. In this review, we summarized the mechanisms of HLA-G involved in promoting tumor cell immune escaping, metastasis and disease progression. Special attention will be paid to its significance as an attractive therapeutic target in cancers.

Tolerogenic Dendritic Cells on Transplantation: Immunotherapy Based on Second Signal Blockage

Dendritic cells (DCs), the most important professional antigen-presenting cells (APC), play crucial role in both immunity and tolerance. It is well known that DCs are able to mount immune responses against foreign antigens and simultaneously tolerate self-antigens. Since DCs can be modulated depending on the surrounding microenvironment, they can act as a bridge between innate and adaptive immunity. However, the mechanisms that support this dual role are not entirely clear. Recent studies have shown that DCs can be manipulated ex vivo in order to trigger their tolerogenic profile, what can be a tool to be used in clinical trials aiming the treatment of various diseases and the prevention of transplant rejection. In this sense, the blockage of costimulatory molecules on DC, in the attempt of inhibiting the second signal in the immunological synapse, can be considered as one of the main strategies under development. This review brings an update on current therapies using tolerogenic dendritic cells modulated with costimulatory blockers with the aim of reducing transplant rejection. However, although there are current clinical trials using tolerogenic DC to treat allograft rejection, the actual challenge is to modulate these cells in order to maintain a permanent tolerogenic profile.

Flagellin suppresses experimental asthma by generating regulatory dendritic cells and T cells

BACKGROUND

Although the hygiene hypothesis suggests that microbial infections could subvert asthma and thus a microbial product might serve as a therapeutic adjuvant for asthma, the relationship between bacterial components and asthma is complex. Recently, low levels of flagellin, the Toll-like receptor (TLR) 5 ligand, have been reported to promote asthma.

OBJECTIVE

We show that a therapeutic dose of flagellin suppresses asthma and that the effect occurs through generating regulatory dendritic cells (rDCs) and regulatory T (Treg) cells.

METHODS

Ovalbumin (OVA)-induced wild-type and TLR5 knockout asthmatic mice were treated intranasally with a mixture of OVA and 10 μg of a flagellin B (FlaB; of Vibrio vulnificus). OVA/FlaB-treated rDCs were adoptively transferred to mice with OVA-induced asthma. Anti-CD25 mAb was used to deplete Treg cells. A mixture of house dust mite (HDM) and FlaB was used to treat mice with HDM-induced asthma. Blood CD14(+) monocyte-derived dendritic cells from HDM-sensitive asthmatic patients were treated with FlaB and incubated with autologous CD4(+) T cells.

RESULTS

An OVA/FlaB mixture ameliorated OVA-induced asthma by inhibiting TH1/TH2/TH17 responses in a TLR5-dependent manner through generating rDCs and Treg cells. The adoptive transfer of OVA/FlaB-treated dendritic cells inhibited OVA-induced asthma, whereas the depletion of CD25(+) cells eliminated the inhibitory effect. A similar effect of FlaB was observed in mice with HDM-induced asthma. In patients with HDM-sensitive asthma, FlaB-treated rDCs inhibited HDM-stimulated TH1/TH2 responses while enhancing Treg cells in an IL-10-dependent manner.

CONCLUSION

These findings collectively suggest that flagellin could be used as a tolerogenic adjuvant to treat allergic asthma.

[Immunosuppressives to prevent rejection reactions after allogeneic corneal transplantation]

In order to prevent rejection of an allogeneic corneal transplant after perforating (high risk) keratoplasty, active agents from different classes of pharmacological substances are used, as with solid organ transplantation. In addition to glucocorticoids, antiproliferative agents, small molecule inhibitors and antibodies, those belonging to the group of macrolides with their many derivatives represent an interesting class of substances in this context. As a supplement to cyclosporin A (CSA) the most successful macrolide in transplantation medicine, animal experiments are currently being carried out to test newer macrolide derivatives, such as sanglifehrin A (SFA). This overview describes the classes of drugs and modes of action of currently administered standard medications in the clinical routine and new developments are presented.

Now or never? The case for cell-based immunosuppression in kidney transplantation

By exploiting mechanisms of immunological regulation against donor alloantigen, it may be possible to reduce the dependence of kidney transplant recipients upon calcineurin inhibitor-based maintenance immunosuppression. One means to strengthen regulatory responses is treating recipients with preparations of regulatory cells obtained by ex vivo manipulation. This strategy, which is a well-established experimental method, has been developed to the point that early-phase clinical trials in kidney transplantation are now feasible. Cell-based therapies represent a radical departure from conventional treatment, so what grounds are there for this new approach? This article offers a three-part justification for trialing cell-based therapies in kidney transplantation: first, a clinical need for alternatives to standard immunosuppression is identified, based on the inadequacies of calcineurin inhibitor-based regimens in preventing late allograft loss; second, a mechanistic explanation of how cell-based therapies might address this clinical need is given; and third, the possible benefit to patients is weighed against the potential risks of cell-based immunosuppressive therapy. It is concluded that the safety of cell-based immunosuppressive therapy will not be greatly improved by further basic scientific and preclinical development. Only trials in humans can now tell us whether cell-based therapy is likely to benefit kidney transplant recipients, but these should be conservative in design to minimize any potential harm to patients.

Role of the immunogenic and tolerogenic subsets of dendritic cells in multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated disorder in the central nervous system (CNS) characterized by inflammation and demyelination as well as axonal and neuronal degeneration. So far effective therapies to reverse the disease are still lacking; most therapeutic drugs can only ameliorate the symptoms or reduce the frequency of relapse. Dendritic cells (DCs) are professional antigen presenting cells (APCs) that are key players in both mediating immune responses and inducing immune tolerance. Increasing evidence indicates that DCs contribute to the pathogenesis of MS and might provide an avenue for therapeutic intervention. Here, we summarize the immunogenic and tolerogenic roles of DCs in MS and review medicinal drugs that may affect functions of DCs and have been applied in clinic for MS treatment. We also describe potential therapeutic molecules that can target DCs by inducing anti-inflammatory cytokines and inhibiting proinflammatory cytokines in MS.

New insights into HLA-G mediated tolerance

Human Leukocyte Antigen G (HLA-G) is a nonclassical HLA class I molecule with well-characterized immunomodulatory activities. HLA-G was first described as a regulatory molecule that allows the fetus to elude the maternal immune response. In the last decade it has become evident that HLA-G is involved in modulating both innate and adaptive immune responses, in maintaining tolerance in autoimmune and inflammatory diseases and after transplantation, and in promoting immune escape in cancer and infectious diseases. HLA-G exerts its modulatory/regulatory functions directly by interacting with specific inhibitory receptors. The expression of HLA-G is finely tuned by genetic variations in the noncoding region of the locus. The recent discovery of dendritic cells-10 (DC-10) as naturally occurring HLA-G-expressing dendritic cells opens new perspectives in the identification of the molecular and cellular mechanisms underlying HLA-G-mediated tolerance. An overview on the HLA-G-mediated inhibition of innate and adaptive immune cells, on the genetic influence on HLA-G expression, and on HLA-G-expressing DC-10 is presented. Moreover, we discuss the central and critical role of DC-10 in the HLA-G-mediated tolerance.

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

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

In question: the scientific value of preclinical safety pharmacology and toxicology studies with cell-based therapies

A new cell-based medicinal product containing human regulatory macrophages, known as Mreg_UKR, has been developed and conforms to expectations of a therapeutic drug. Here, Mreg_UKR was subjected to pharmacokinetic, safety pharmacology, and toxicological testing, which identified no adverse reactions. These results would normally be interpreted as evidence of the probable clinical safety of Mreg_UKR; however, we contend that, owing to their uncertain biological relevance, our data do not fully support this conclusion. This leads us to question whether there is adequate scientific justification for preclinical safety testing of similar novel cell-based medicinal products using animal models. In earlier work, two patients were treated with regulatory macrophages prior to kidney transplantation. In our opinion, the absence of acute or chronic adverse effects in these cases is the most convincing available evidence of the likely safety of Mreg_UKR in future recipients. On this basis, we consider that safety information from previous clinical investigations of related cell products should carry greater weight than preclinical data when evaluating the safety profile of novel cell-based medicinal products. By extension, we argue that omitting extensive preclinical safety studies before conducting small-scale exploratory clinical investigations of novel cell-based medicinal products data may be justifiable in some instances.

Controlling the Immunological Crosstalk during Conception and Pregnancy: HLA-G in Reproduction

In several years after its discovery in the placenta, the human leukocyte antigen (HLA) class Ib protein, HLA-G, was not given much attention, nor was it assigned great importance. As time has unraveled, HLA-G has proven to have distinctive functions and an unforeseen and possibly important role in reproduction. HLA-G is characterized mainly by its low polymorphism and restricted tissue distribution in non-pathological conditions. In fact, its expression pattern is primarily limited to extravillous cytotrophoblast cells at the maternal-fetal interface during pregnancy. Due to low polymorphism, almost the same protein is expressed by virtually all individuals. It is these unique features that make HLA-G differ from its highly polymorphic HLA class Ia counterparts, the HLA-A, -B, and -C molecules. Its function, seemingly diverse, is typically receptor-mediated, and involves interactions with a wide range of immune cells. As the expression of HLA-G primarily is limited to gestation, this has given rise to the hypothesis that HLA-G plays an important role in the immunological tolerance of the fetus by the mother. In keeping with this, it might not be surprising that polymorphisms in the HLA-G gene, and levels of HLA-G expression, have been linked to reproductive failure and pre-eclampsia. Based on recent studies, we speculate that HLA-G might be involved in mechanisms in reproductive immunology even before conception because HLA-G can be detected in the genital tract and in the blood of non-pregnant women, and is present in seminal fluid from men. In addition, HLA-G expression has been found in the pre-implanted embryo. Therefore, we propose that a combined contribution from the mother, the father, and the embryo/fetus is likely to be important. Furthermore, this review presents important aspects of HLA-G in relation to reproduction: from genetics to physiological effects, from pregnancy and pregnancy complications to a short discussion on future possible means of preventative measures and therapy.

DCs sensitized with mPD-L1-Ig fusion protein improve the effect of heart transplantation in mice by promoting the generation of T-reg cells

PURPOSE

To detect the effects of DCs sensitized by mPD-L1-Ig fusion protein in heart transplantation in mice as well as its mechanisms.

METHOD

The mPD-L1-IgG1 construct was used to build a yeast expression system, and the fusion protein was expressed by secretion after the transfection of the GS115 yeast strain, purified by affinity chromatography and ion exchange chromatography, and assayed by SDS-PAGE and Western blot. The ability of the fusion protein to bind to the acceptor PD-1 was tested by ELISA, and the ability of the fusion protein to inhibit the function of T cells was tested by mixed lymphocyte reaction (MLR).

RESULTS

We used the new PD-L1-IgG1 fusion protein to sensitize imDCs and maintained the immature state of DCs, so as to induce stable and effective immune tolerance to heart transplantation. After the treatment of DCs by mPD-L1-Ig in vitro, the levels of CD80, CD40 and I-Ab expression on DCs are relatively weaker, the ability of DCs to stimulates the proliferation of allogeneic spleen T cells was significantly decreased (P<0.01), and the levels of Th1 (IL-2, IFN-γ) and Th2 (IL-4, IL-10) secreted by induced allogeneic T cells were significantly decreased (P<0.01). An in vivo experiment also revealed that DCs sensitized by mPD-L1-IgG1 could prolong the survival time of a transplanted heart to 17.8±1.12days, and alleviate the pathological change of the cardiac allografts compared with other three groups.

CONCLUSION

DCs sensitized by the yeast-expressed mPD-L1-Ig fusion protein are shown to alleviate the cardiac allograft rejection in mice.

HLA-G expression on blasts and tolerogenic cells in patients affected by acute myeloid leukemia

Human Leukocyte Antigen-G (HLA-G) contributes to cancer cell immune escape from host antitumor responses. The clinical relevance of HLA-G in several malignancies has been reported. However, the role of HLA-G expression and functions in Acute Myeloid Leukemia (AML) is still controversial. Our group identified a subset of tolerogenic dendritic cells, DC-10 that express HLA-G and secrete IL-10. DC-10 are present in the peripheral blood and are essential in promoting and maintaining tolerance via the induction of adaptive T regulatory (Treg) cells. We investigated HLA-G expression on blasts and the presence of HLA-G-expressing DC-10 and CD4⁺ T cells in the peripheral blood of AML patients at diagnosis. Moreover, we explored the possible influence of the 3′ untranslated region (3′UTR) of HLA-G, which has been associated with HLA-G expression, on AML susceptibility. Results showed that HLA-G-expressing DC-10 and CD4⁺ T cells are highly represented in AML patients with HLA-G positive blasts. None of the HLA-G variation sites evaluated was associated with AML susceptibility. This is the first report describing HLA-G-expressing DC-10 and CD4⁺ T cells in AML patients, suggesting that they may represent a strategy by which leukemic cells escape the host's immune system. Further studies on larger populations are required to verify our findings.

Tr1 cells and the counter-regulation of immunity: natural mechanisms and therapeutic applications

T regulatory Type 1 (Tr1) cells are adaptive T regulatory cells characterized by the ability to secrete high levels of IL-10 and minimal amounts of IL-4 and IL-17. Recently, CD49b and LAG-3 have been identified as Tr1-cell-specific biomarkers in mice and humans. Tr1 cells suppress T-cell- and antigen-presenting cell- (APC) responses primarily via the secretion of IL-10 and TGF-β. In addition, Tr1 cells release granzyme B and perforin and kill myeloid cells. Tr1 cells inhibit T cell responses also via cell-contact dependent mechanisms mediated by CTLA-4 or PD-1, and by disrupting the metabolic state of T effector cells via the production of the ectoenzymes CD39 and CD73. Tr1 cells were first described in peripheral blood of patients who developed tolerance after HLA-mismatched fetal liver hematopoietic stem cell transplant. Since their discovery, Tr1 cells have been proven to be important in maintaining immunological homeostasis and preventing T-cell-mediated diseases. Furthermore, the possibility to generate and expand Tr1 cells in vitro has led to their utilization as cellular therapy in humans. In this chapter we summarize the unique and distinctive biological properties of Tr1 cells, the well-known and newly discovered Tr1-cell biomarkers, and the different methods to induce Tr1 cells in vitro and in vivo. We also address the role of Tr1 cells in infectious diseases, autoimmunity, and transplant rejection in different pre-clinical disease models and in patients. Finally, we highlight the pathological settings in which Tr1 cells can be beneficial to prevent or to cure the disease.

Cell therapy as a strategy to minimize maintenance immunosuppression in solid organ transplant recipients

PURPOSE OF REVIEW

This review presents a clinically focussed introduction to cell-based immunotherapy in solid organ transplantation. The potential benefits and risks of cell-based immunotherapeutics are critically discussed.

RECENT FINDINGS

The use of immunoregulatory cells as medicinal agents is very much in its infancy, but the field is expanding rapidly. In principle, this approach permits manipulation of specific immunological functions, opening new possibilities in the field of tolerance-promoting therapies. Several immunoregulatory cell types have reached the point of preclinical and clinical development that should allow them to be tested in early-phase clinical trials. Solid organ transplantation represents an important potential indication for the use of cell-based immunosuppressive agents because promoting immunological regulation towards allografts remains a promising strategy for preventing chronic rejection.

SUMMARY

Remarkable progress is being made in the implementation of novel cell-based immunotherapeutics in solid organ transplantation studies. It is hoped that these new immunoregulatory therapies will afford better long-term transplant outcomes by mitigating chronic graft injury.

Alternative approaches to myeloid suppressor cell therapy in transplantation: comparing regulatory macrophages to tolerogenic DCs and MDSCs

Several types of myeloid suppressor cell are currently being developed as cell-based immunosuppressive agents. Despite detailed knowledge about the molecular and cellular functions of these cell types, expert opinions differ on how to best implement such therapies in solid organ transplantation. Efforts in our laboratory to develop a cell-based medicinal product for promoting tolerance in renal transplant patients have focused on a type of suppressor macrophage, which we call the regulatory macrophage (M reg). Our favoured clinical strategy is to administer donor-derived M regs to recipients one week prior to transplantation. In contrast, many groups working with tolerogenic dendritic cells (DCs) advocate post-transplant administration of recipient-derived cells. A third alternative, using myeloid-derived suppressor cells, presumably demands that cells are given around the time of transplantation, so that they can infiltrate the graft to create a suppressive environment. On present evidence, it is not possible to say which cell type and treatment strategy might be clinically superior. This review seeks to position our basic scientific and early-stage clinical studies of human regulatory macrophages within the broader context of myeloid suppressor cell therapy in transplantation.

Generation of myeloid-derived suppressor cells using prostaglandin E2

Myeloid-derived suppressor cells (MDSCs) are natural immunosuppressive cells and endogenous inhibitors of the immune system. We describe a simple and clinically compatible method of generating large numbers of MDSCs using the cultures of peripheral blood-isolated monocytes supplemented with prostaglandin E₂ (PGE₂). We observed that PGE₂ induces endogenous cyclooxygenase (COX)2 expression in cultured monocytes, blocking their differentiation into CD1a⁺ dendritic cells (DCs) and inducing the expression of indoleamine 2,3-dioxygenase 1, IL-4Rα, nitric oxide synthase 2 and IL-10 - typical MDSC-associated suppressive factors. The establishment of a positive feedback loop between PGE₂ and COX2, the key regulator of PGE₂ synthesis, is both necessary and sufficient to promote the development of CD1a⁺ DCs to CD14⁺CD33⁺CD34⁺ monocytic MDSCs in granulocyte macrophage colony stimulating factor/IL-4-supplemented monocyte cultures, their stability, production of multiple immunosuppressive mediators and cytotoxic T lymphocyte-suppressive function. In addition to PGE₂, selective E-prostanoid receptor (EP)2- and EP4-agonists, but not EP3/1 agonists, also induce the MDSCs development, suggesting that other activators of the EP2/4- and EP2/4-driven signaling pathway (adenylate cyclase/cAMP/PKA/CREB) may be used to promote the development of suppressive cells. Our observations provide a simple method for generating large numbers of MDSCs for the immunotherapy of autoimmune diseases, chronic inflammatory disorders and transplant rejection.

Immunoregulatory properties of rapamycin-conditioned monocyte-derived dendritic cells and their role in transplantation

In efforts to minimize the chronic administration of immunosuppression (IS) drugs in transplantation and autoimmune disease, various cell-based tolerogenic therapies, including the use of regulatory or tolerogenic dendritic cells (tolDC) have been developed. These DC-based therapies aim to harness the inherent immunoregulatory potential of these professional antigen-presenting cells. In this short review, we describe both the demonstrated tolerogenic properties, and current limitations of rapamycin-conditioned DC (RAPA-DC). RAPA-DC are generated through inhibition of the integrative kinase mammalian target of rapamycin (mTOR) by the immunosuppressive macrolide rapamycin during propagation of monocyte-derived DC. Consistent with the characteristics of tolDC, murine RAPA-DC display resistance to phenotypic maturation induced by pro-inflammatory stimuli; exhibit the ability to migrate to secondary lymphoid tissue (important for 'cross-presentation' of antigen to T cells), and enrich for naturally-occurring CD4+ regulatory T cells. In rodent models, delivery of recipient-derived RAPA-DC pulsed with donor antigen prior to organ transplantation can prolong allogeneic heart-graft survival indefinitely, especially when combined with a short course of IS. These encouraging data support ongoing efforts to develop RAPA-DC for clinical testing. When compared to murine RAPA-DC however, human RAPA-DC have proven only partially resistant to maturation triggered by pro-inflammatory cytokines, and display heterogeneity in their impact on effector T-cell expansion and function. In total, the evidence suggests the need for more in-depth studies to better understand the mechanisms by which mTOR controls human DC function. These studies may facilitate the development of RAPA-DC therapy alone or together with agents that preserve/enhance their tolerogenic properties as clinical immunoregulatory vectors.