A CD200FC immunoadhesin prolongs rat islet xenograft survival in mice

The association between expression of CD200 on B lymphocytes and the count of eosinophils and basophils in atopic dermatitis patients with and without dupilumab therapy - Pilot study

BACKGROUND

Eosinophils and basophils are implicated in allergic reactions, and the molecule CD200 on B cells may have regulatory functions. Assessing the associations between the expression of CD200 on B lymphocytes and eosinophils and basophils helps unravel the complex immune interactions in atopic dermatitis, aiding in targeted therapeutic approaches.

OBJECTIVE

The aim of our study is to evaluate the association between the count of eosinophils, basophils, CD16+ eosinophils, CD203+ basophils, the expression of activation marker CD200 on B cells and on their subsets in patients suffering from atopic dermatitis with and without dupilumab and in control group.

MATERIALS AND METHODS

Altogether we examined 75 subjects: 45 patients suffering from atopic dermatitis -32 patients without dupilumab treatment, 13 patients with dupilumab treatment and 30 subjects as a control group. Immunophenotype was examined by flow cytometry in which monoclonal antibodies with fluorescent molecules were used. For statistical analysis we used non-parametric Kruskal-Wallis one-factor analysis of variance with post-hoc by Dunn's test with Bonferroni modification and the Spearman's rank correlation coefficient with calculation of R2 (%, percent of Variation Explained).

RESULTS

In patients with dupilumab therapy we confirmed the association between absolute eosinophils and expression of molecule CD200 on total B lymphocytes (in 23.9 %), non-switched (in 27.2 %), naive (in 25 %) and memory (in 20.3 %) B lymphocytes and between relative eosinophils and expression of CD200 on total B lymphocytes (in 22.8 % %), non-switched (in 29 %), naive (in 21.3 %) and memory (in 22.3 %) B lymphocytes. This association is low in AD patients without dupilumab and even non linear in control healthy subjects.

CONCLUSION

The higher association between eosinophils and expression of CD200 molecule on memory, naive and non switched B lymphocytes in AD patients under dupilumab therapy suggests that activation of B lymphocytes is caused by IL-4, whose production involves eosinophils and the CD200 molecule on B lymphocytes.

Tissue-engineered vascular microphysiological platform to study immune modulation of xenograft rejection

Most of the vascular platforms currently being studied are lab-on-a-chip types that mimic capillary networks and are applied for vascular response analysis in vitro. However, these platforms have a limitation in clearly assessing the physiological phenomena of native blood vessels compared to in vivo evaluation. Here, we developed a simply fabricable tissue-engineered vascular microphysiological platform (TEVMP) with a three-dimensional (3D) vascular structure similar to an artery that can be applied for ex vivo and in vivo evaluation. Furthermore, we applied the TEVMP as ex vivo and in vivo screening systems to evaluate the effect of human CD200 (hCD200) overexpression in porcine endothelial cells (PECs) on vascular xenogeneic immune responses. These screening systems, in contrast to 2D in vitro and cellular xenotransplantation in vivo models, clearly demonstrated that hCD200 overexpression effectively suppressed vascular xenograft rejection. The TEVMP has a high potential as a platform to assess various vascular-related responses.

Pre-transplant CD200 and CD200R1 concentrations are associated with post-transplant events in kidney transplant recipients

CD200 is an immunoglobulin superfamily membrane protein that binds to a myeloid cell-specific receptor and induces inhibitory signaling. The aim of this study was to investigate the role of CD200 and its receptor (CD200R1) on kidney transplant (KTx) outcome. In a collective of 125 kidney recipients (University hospital, Heidelberg, Germany), CD200 and CD200R1 concentrations were evaluated immediately before transplantation. Recipient baseline and clinical characteristics and KTx outcome, including acute rejection (AR), acute tubular necrosis, delayed graft function, cytomegalovirus (CMV) and human polyomaviridae (BK) virus infections, and graft loss were evaluated during the first post-transplant year. The association of CD200 and CD200R1 concentrations and CD200R1/CD200 ratios with the outcome of KTx was investigated for the first time in a clinical setting in a prospective cohort. There was a positive association between pre-transplant CD200R1 concentrations and CMV (re)activation (P = .041). Also, increased CD200R1 concentration was associated with a longer duration of CMV infection (P = .049). Both the frequency of AR and levels of creatinine (3 and 6 months after KTx) were significantly higher in patients with an increased CD200R1/CD200 ratio (median: 126 vs 78, P = .008). Increased pre-transplant CD200R1/CD200 ratios predict immunocompetence and risk of AR, whereas high CD200R1 concentrations predict immunosuppression and high risk of severe CMV (re)activation after KTx.

CD200R1 regulates eosinophilia during pulmonary fungal infection in mice

CD200 receptor 1(CD200R1) signalling limits myeloid cell responses and reduces autoimmunity, alloimmunity and viral‐mediated immunopathology, but has never been examined in the context of eosinophilic inflammation. Susceptibility to lung fungal infection is associated with T‐helper 2 (Th2) cytokine dominated responses and strong eosinophilic pathology. Blockade of CD200R1 enhances type I cytokine responses in many infectious and non‐infectious settings and so may promote a more protective response to fungal infection. By contrast, we demonstrate that, rather than promoting type I cytokine responses, CD200R1 blockade enhanced eosinophilia in a mouse model of Cryptococcus neoformans infection, whereas CD200R1 agonism reduced lung eosinophilia – with neither strategy completely altering fungal burden. Thus, we reveal a surprising disconnect between pulmonary eosinophilia and cryptococcal burden and dissemination. This research has 2 important implications. Firstly, a lack of CD200R1 signalling enhances immune responses regardless of cytokine polarisation, and secondly reducing eosinophils does not allow protective immunity to develop in susceptible fungal system. Therefore, agonists of CD200R1 may be beneficial for eosinophilic pathologies.

Role of Human CD200 Overexpression in Pig-to-Human Xenogeneic Immune Response Compared With Human CD47 Overexpression

BACKGROUND

Macrophages play important roles in xenograft rejection. Here, we investigated whether overexpression of human CD200 or CD47 in porcine endothelial cells (PEC) can suppress macrophages activation in xenogeneic immune responses.

METHODS

PECs and human macrophages were incubated together, harvested, and analyzed for in vitro macrophage phagocytic and cytotoxicity activity, and cytokine release. Next, PECs were injected into renal subcapsular space of humanized mice. On day 10 posttransplantation, we analyzed xenograft survival and perigraft inflammatory cell infiltrations in PEC-to-humanized mouse transplantation.

RESULTS

PECs highly expressing human CD200, CD47, or both CD47/CD200 were established by lentiviral vector transduction. Both CD200 and CD47 suppressed in vitro macrophage phagocytic and cytotoxic activity against PECs; decreased TNF-α, IL-1β, and IL-6 secretion; and increased IL-10 secretion. However, simultaneous overexpression of CD200 and CD47 did not show additive effects. Next, PECs were transplanted into NOD-scid IL-2Rg null mice, and human monocytes and lymphocytes were adoptively transferred 1 day after xenotransplantation. PEC xenograft cell death and apoptosis were decreased in the CD200-PEC and CD47/CD200-PEC groups. Perigraft infiltration of human T cells was suppressed by CD47; CD200 suppressed infiltration of human macrophages to a greater extent than CD47; and the CD47/CD200-PEC group exhibited the lowest level of leukocyte infiltration. In summary, overexpression of CD200 in PECs suppressed xenogeneic activation of human macrophages and improved survival of PEC xenografts in humanized mice; however, coexpression of CD200 and CD47 did not show additive effects.

CONCLUSIONS

Therefore, overexpression of human CD200 in donor pigs could constitute a promising strategy for overcoming xenograft rejection.

Immune Checkpoints as Therapeutic Targets in Autoimmunity

Antibodies that block the immune checkpoint receptors PD1 and CTLA4 have revolutionized the treatment of melanoma and several other cancers, but in the process, a new class of drug side effect has emerged—immune related adverse events. The observation that therapeutic blockade of these inhibitory receptors is sufficient to break self-tolerance, highlights their crucial role in the physiological modulation of immune responses. Here, we discuss the rationale for targeting immune checkpoint receptors with agonistic agents in autoimmunity, to restore tolerance when it is lost. We review progress that has been made to date, using Fc-fusion proteins, monoclonal antibodies or other novel constructs to induce immunosuppressive signaling through these pathways. Finally, we explore potential mechanisms by which these receptors trigger and modulate immune cell function, and how understanding these processes might shape the design of more effective therapeutic agents in future.

A Synthetic Cross-Species CD200R1 Agonist Suppresses Inflammatory Immune Responses In Vivo

Functional aptamers displaying agonistic or antagonistic properties are showing great promise as modulators of immune responses. Here, we report the development of a polyethylene glycol-modified (PEGylated) DNA aptamer as a cross-species (murine and human) CD200R1 agonist that modulates inflammatory responses in vivo. Specifically, DNA aptamers were discovered by performing independent SELEX searches on recombinant murine and human CD200R1. Aptamer motifs identified by next generation sequencing (NGS) were subsequently compared, leading to the discovery of motifs common to both targets. The CD200R1 DNA aptamer CCS13 displayed the highest agonistic activity toward CD200R1 in terms of suppressing the induction of cytotoxic T-lymphocytes (CTLs) in both human and murine allogeneic-mixed lymphocyte cultures (allo-MLCs). A 20-kDa polyethylene glycol (PEG) chain was covalently attached to the 5′ end of this aptamer, and the resulting conjugate was shown to block inflammatory responses in murine models of skin graft rejection and house-dust-mite-induced allergic airway inflammation. Importantly, this agonistic aptamer does not suppress CTL induction in 5-day allo-MLCs with responder cells derived from CD200R1^−/− mice, indicating that its mode of action is directly linked to CD200R1 activation. This study suggests that one can derive agonistic DNA aptamers that can be verified as immuno-modulators in murine models with outcomes potentially translatable to the treatment of human conditions.

Local targeting of the CD200-CD200R axis does not promote corneal graft survival

Corneal graft rejection is primarily a CD4(+) T cell-mediated mechanism in which macrophages may play an important inflammatory role. CD200Fc fusion protein is an artificial agonist of CD200R1, a receptor expressed predominantly on myeloid cells, engagement of which is known to down-regulate macrophage function. We therefore wished to test whether CD200Fc could be used as a therapeutic agent to prolong corneal graft survival. The distribution of CD200R1 and CD200, its natural ligand, was examined by immunohistology in the cornea and conjunctiva of unoperated rats and rats that had received corneal allografts. Mouse CD200Fc was injected subconjunctivally into transplanted rats on six occasions from the day of surgery until day 10 after transplantation. Control groups received injections of mouse IgG or diluent PBS. Allo-transplants were also performed in CD200(-/-) and control mice. The ability of CD200Fc to bind rat macrophages in vitro and to inhibit nitric oxide production was tested. Mean day of rejection in CD200Fc, IgG and PBS-treated rats was 12, 10 and 9 respectively (p=0.24). Mean day of rejection in CD200(-/-) and wild type mice was 17.5 and 16.0 respectively (p=0.07). Mouse CD200Fc bound to rat macrophages in a dose-dependent manner, but was unable to inhibit nitric oxide production. The fact that treatment with CD200Fc did not inhibit graft rejection and the failure of CD200 deficiency to affect graft survival suggests that local targeting of the CD200-CD200R axis to suppress macrophage activation is not a useful therapeutic strategy in corneal graft rejection.

Agonistic CD200R1 DNA Aptamers Are Potent Immunosuppressants That Prolong Allogeneic Skin Graft Survival

CD200R1 expressed on the surface of myeloid and lymphoid cells delivers immune inhibitory signals to modulate inflammation when engaged with its ligand CD200. Signalling through CD200/CD200R1 has been implicated in a number of immune-related diseases including allergy, infection, cancer and transplantation, as well as several autoimmune disorders including arthritis, systemic lupus erythematosus, and multiple sclerosis. We report the development and characterization of DNA aptamers, which bind to murine CD200R1 and act as potent signalling molecules in the absence of exogenous CD200. These agonistic aptamers suppress cytotoxic T-lymphocyte induction in 5-day allogeneic mixed leukocyte culture and induce rapid phosphorylation of the CD200R1 cytoplasmic tail thereby initiating immune inhibitory signalling. PEGylated conjugates of these aptamers show significant in vivo immunosuppression and enhance survival of allogeneic skin grafts as effectively as soluble CD200Fc. As DNA aptamers exhibit inherent advantages over conventional protein-based therapeutics including low immunogenicity, ease of synthesis, low cost, and long shelf life, such CD200R1 agonistic aptamers may emerge as useful and safe nonsteroidal anti-inflammatory therapeutic agents.

CD200:CD200R-Mediated Regulation of Immunity

The type 1 membrane glycoprotein CD200, widely expressed on multiple cells/tissues, uses a structurally similar receptor (CD200R1), whose expression is more restricted to cells of the myeloid and lymphoid lineages, to transmit signals affecting responses in multiple physiological systems. Thus CD200 expression is reported to exert effects on cancer growth, autoimmune and allergic disorders, infection, transplantation, bone development and homeostasis, and reproductive biology. It was initially thought, based on the idea that CD200R1 was mostly expressed on cells of myeloid origin, that CD200:CD200R1 interactions were primarily dedicated to controlling myeloid cell function. However additional members of the CD200R family have now also been identified, although their function(s) remain unclear, and CD200R1 itself is now known to be expressed by subsets of T cells and other cells. Together these observations add layers of complexity to our understanding of CD200-related regulation. In common with a number of physiological systems, the mechanism(s) of CD200-induced signaling seem to fit within a similar framework of opposing actions of kinases and phosphatases. This paper highlights the advances in our knowledge of immunoregulation achieved following CD200:CD200R interaction and the potential clinical applicability of that information.

CD200R1 agonist attenuates mechanisms of chronic disease in a murine model of multiple sclerosis

To assess the effects and mechanisms of a CD200R1 agonist administered during the progressive stage of a multiple sclerosis model, we administered CD200R1 agonist (CD200Fc) or control IgG2a during the chronic phase of disease (days 10-30) in mice with experimental autoimmune encephalomyelitis (EAE), induced using myelin oligodendrocyte glycoprotein peptide 35-55 (MOG35-55) peptide. We found that administration of CD200Fc during the chronic stages of EAE reduced disease severity, demyelination, and axonal damage, through the modulation of several key disease mechanisms. CD200Fc treatment suppressed macrophage and microglial accumulation within the CNS, in part through downregulation of adhesion molecules VLA-4 and LFA-1, which are necessary for macrophage migration. Additionally, expression of activation markers MHC-II and CD80 and production of proinflammatory cytokines IL-6, tumor necrosis factor-alpha, and nitric oxide by CD11b(+) cells were decreased in both the spleen and CNS in CD200Fc-treated animals. Antigen-presenting cell function in the spleen and CNS was suppressed in CD200Fc-treated mice, but there were no significant alterations on T cell activation or phenotype. CD200Fc increased apoptosis of CD11b(+) cells but not astrocytes. In contrast, addition of CD200Fc treatment protected oligodendrocytes from apoptosis in vitro and in vivo. Our results demonstrate that CD200R1 agonists modulate both myeloid- and non-myeloid-related mechanisms of chronic disease in the EAE model and may be effective in the treatment of progressive multiple sclerosis and other neurodegenerative diseases.

Control of viral immunoinflammatory lesions by manipulating CD200:CD200 receptor interaction

Previous investigators have demonstrated that the CD200:Fc that engages CD200 receptors (CD200R) shows promise as an immunosuppressive and anti-inflammatory reagent. In this report, we evaluate the use of CD200:Fc to control a viral induced immunoinflammatory reactions caused by ocular infection with herpes simplex virus (HSV). Our results show that HSV infection causes invasion of the cornea by CD200R(+) cells most of which were CD11b(+) cells. Systemic administration of CD200:Fc, starting at 5 days post infection (p.i.), resulted in diminished incidence and severity of lesions compared to controls. Splenocytes isolated from treated animals showed reduced IL-12 and IFN-gamma responses when stimulated in vitro and ex vivo. Treated animals also had increased frequencies of Foxp3(+) regulatory T cells in both the cornea and draining lymph nodes perhaps contributing also to the control of the corneal immunopathology. Treatment of animals in the chronic phase was minimally effective. Our data are the first to demonstrate the use of CD200R stimulation to control lesion severity in a viral induced inflammatory disease.

Decreased expression of CD200 and CD200 receptor in Alzheimer's disease: a potential mechanism leading to chronic inflammation

Inflammatory activation of microglia in response to neurodegenerative changes in diseases such as Alzheimer's disease (AD) and Parkinson's disease has been extensively described. These observations have suggested that inflammation could be contributing to disease progression. In this paper, the potential role of CD200 and CD200 receptor (CD200R), whose known functions are to activate anti-inflammatory pathways and induce immune tolerance through binding of CD200 to CD200 receptor (CD200R), was studied in AD. Quantitative studies showed a significant decrease in CD200 protein and mRNA in AD hippocampus and inferior temporal gyrus, but not cerebellum. Immunohistochemistry of brain tissue sections of hippocampus, superior frontal gyrus, inferior temporal gyrus and cerebellum from AD and non-demented cases demonstrated a predominant, though heterogeneous, neuronal localization for CD200. Decreased neuronal expression was apparent in brain regions affected by AD pathology. There was also a significant decrease in CD200R mRNA expression in AD hippocampus and inferior temporal gyrus, but not cerebellum. Low expression of CD200R by microglia was confirmed at the mRNA and protein level using cultured human microglia compared to blood-derived macrophages. Treatment of microglia and macrophages with interleukin-4 and interleukin-13 significantly increased expression of CD200R. Expression of these cytokines was not generally detectable in brain. These data indicate that the anti-inflammatory CD200/CD200R system may be deficient in AD brains. Mechanisms aimed at increasing levels of CD200 and CD200R could have therapeutic potential for controlling inflammation in human neurodegenerative diseases.

Elevated neuronal expression of CD200 protects Wlds mice from inflammation-mediated neurodegeneration

Axonal damage secondary to inflammation is likely the substrate of chronic disability in multiple sclerosis and is found in the animal model of experimental autoimmune encephalomyelitis (EAE). Wld(s) mice have a triplication of the fusion gene Ube4b/Nmnat and a phenotype of axon protection. Wld(s) mice develop an attenuated disease course of EAE, with decreased demyelination, reduced axonal pathology, and decreased central nervous system (CNS) macrophage and microglial accumulation. We show that attenuated disease in Wld(s) mice was associated with robust constitutive expression of the nonsignaling CD200 molecule on neurons in the CNS compared with control mice. CD200 interacts with its signaling receptor CD200R, which we found to be expressed on microglia, astrocytes, and oligodendrocytes at similar levels in control and Wld(s) mice. Administration of blocking anti-CD200 antibody to Wld(s) mice abrogated disease attenuation and was associated with increased CNS inflammation and neurodegeneration. In vitro, Wld(s) neuronal cultures were protected from microglial-induced neurotoxicity compared with control cultures, but protection was abrogated by anti-CD200 antibody. The CD200-CD200R pathway plays a critical role in attenuating EAE and reducing inflammation-mediated damage in the CNS. Strategies that up-regulate the expression of CD200 in the CNS or molecules that ligate the CD200R may be relevant as neuroprotective strategies in multiple sclerosis.

Modulation of immunity to respiratory viral infection

Acute respiratory tract infections cause approximately 4 million deaths globally each year. Current strategies to combat these infections include vaccines and antiviral drugs. However, a significant proportion of the pathology and illness induced by respiratory viral infection is attributed to an excessive host immune response, rather than the cytopathic nature of the pathogen. Distinct respiratory viruses elicit common immune mediators and cells, which are subsequently the cause of pathology. Therefore, strategies that seek to attenuate the potency of the host’s immune response may provide generic relief from multiple respiratory infections.

Decreased Alloreactivity Using Donor Cells from Mice Expressing a CD200 Transgene Under Control of a Tetracycline-Inducible Promoter

BACKGROUND

CD200 delivers an immunsuppressive signal that augments allograft survival following interaction with its receptor, CD200R1. We hypothesized that mice overexpressing CD200 as a trangene would also show a diminished alloresponsiveness and decreased allograft rejection.

METHODS

A transgenic mouse on a C57BL/6 background, expressing a murine CD200 cDNA genetically linked to a green fluorescent protein tag (GFP) under control of a tetracycline response element (TRE), was mated with a commercial transgenic mouse carrying the reverse tetracycline regulated transactivator gene under control of a human CMV promoter. F1 mice were examined for induction of alloimmunity in vivo/in vitro, and for their ability to reject skin allografts in vivo.

RESULTS

The F1 hybrid expressed CD200 after exposure to doxycyline (DOX), as assessed both by enhanced GFP expression in multiple organs and CD200-GFP expression. Splenocytes from F1 mice stimulated with LPS or allogeneic cells in vitro in the presence/absence of DOX showed reduced production of TNFalpha, and of allospecific CTL. Splenocytes from F1 mice used as stimulator cells in allogeneic MLCs in the presence of DOX were inefficient at induction of cytokines or CTL in vitro from normal allogeneic responder cells. Skin grafts from transgenic mice were inefficient at induction of CTL in vivo. Transgenic mice receiving DOX showed prolonged acceptance of skin allografts, which was abolished by infusion of anti-CD200 mAb.

CONCLUSIONS

Our data confirmed that overexpression of CD200 in transgenic mice, or in skin grafts from these mice, decreases alloimmunity. This has potential clinical utility in transplantation and other diseases.

Discrete monoclonal antibodies define functionally important epitopes in the CD200 molecule responsible for immunosuppression function

BACKGROUND

Both murine and human CD200 fusion proteins (CD200Fc) act as immunosuppressants after engagement of cell-bound receptors (CD200R). Anti-CD200 monoclonal antibodies (mAbs) augment activity in mixed leukocyte cultures (MLCs) (increased cytotoxic T lymphocyte/cytokine production) after neutralization of endogenous CD200 activity. Previous studies documented critical regions in the N-terminal domains of both CD200 and CD200R1 for ligand:receptor binding and defined a number of synthetic CD200 and CD200R peptides that antagonize that interaction.

METHODS

We used a panel of mAbs to mouse and human CD200Fc to compare the rank activities of antibodies for binding (flow cytometric analysis [FACS] or enzyme-linked immunoadsorbent assay [ELISA]) to CD200 with their abilities to augment immune reactivity in MLCs.

RESULTS

Only mAbs defining epitopes in the N-terminal domain could augment MLC reactivity (or block immunosuppression by soluble CD200Fc), whereas mAbs targeting C-domain epitopes, although reactive in ELISA or FACS (targeting cell surface CD200), were inactive in MLCs.

CONCLUSION

In addition to defining the importance of N-terminal epitopes for CD200 function, rank comparison of mAbs for FACS staining of CD200 expressed on various cell types indicates heterogeneity in expressed CD200.

Long-term graft function of adult rat and human islets encapsulated in novel alginate-based microcapsules after transplantation in immunocompetent diabetic mice

We describe the results of the first study to show that adult rat and human islets can be protected against xenogenic rejection in immunocompetent diabetic mice by encapsulating them in a novel alginate-based microcapsule system with no additional permselective membrane. Nonencapsulated islets lost function within 4-8 days after being transplanted into diabetic Balb/c mice, whereas transplanted encapsulated adult rat or human islets resulted in normoglycemia for >7 months. When rat islet grafts were removed 10 and 36 weeks after transplantation, the mice became immediately hyperglycemic, thus demonstrating the efficacy of the encapsulated islets. The explanted capsules showed only a mild cellular reaction on their surface and a viability of >85%, and responded to a glucose stimulus with a 10-fold increase in insulin secretion. Furthermore, transplanted mice showed a slight decrease in the glucose clearance rate in response to intraperitoneal glucose tolerance tests 3-16 weeks after transplantation; after 16 weeks, the rate remained stable. Similar results were obtained for encapsulated human islets. Thus we provide the first evidence of successful transplantation of microencapsulated human islets. In conclusion, we have developed a novel microcapsule system that enables survival and function of adult rat and human islets in immunocompetent mice without immunosuppression for >7 months.

INDUCTION OF TOLERANCE-INDUCING ANTIGEN-PRESENTING CELLS IN BONE MARROW CULTURES IN VITRO USING MONOCLONAL ANTIBODIES TO CD200R

CD200 to CD200R interactions produce immunoregulation. We investigated whether the expression of CD200R on dendritic cell (DC) precursors affects their developmental fate. C57BL/6 bone marrow (BM) cells were cultured in vitro in the presence of (interleukin-4 + granulocyte-macrophage colony-stimulating activity) to generate allostimulatory DCs, which were in turn used to induce cytotoxic T-lymphocyte and cytokine production after culture with C3H responder spleen cells. Some marrow cultures included anti-CD200R antibodies. The inclusion of monoclonal antibodies in different isoforms of CD200R in the BM culture led to a generation of cells (tolerogenic DCs) that were unable to produce allostimulation in vitro with responder cells. Cells taken from these latter mixed leukocyte cultures (MLCs) now contained CD4(+)CD25(+) cells able to inhibit the antigen-specific MLC response of fresh C3H responder cells to stimulation with C57BL/6 cells, but not stimulation with BALB/c cells. Tolerogenic DCs, infused in vivo into mice receiving C57BL/6 skin grafts, produced antigen-specific decreased rejection of BL/6 allografts, not BALB/c allografts, compared with mice receiving control DCs (generated from BM in the absence of anti-CD200R). The induction of CD4(+)CD25(+) suppressor cells in MLCs using tolerogenic DCs from the initial BM cultures could be overcome by using limiting numbers of tolerogenic DCs and an excess of allostimulatory DCs derived from BM cultures maintained in the absence of anti-CD200R. These data indicate that anti-CD200R biases stem cells in BM toward the development of suppressive antigen-presenting cells, which can induce CD4(+)CD25(+) regulatory T cells. Tolerogenic DCs have the potential to modify graft acceptance in vivo.

Islet transplant: an option for childhood diabetes?

Careful assessment of the safety and efficacy of islet transplantation should guide the selection process of a small number of children with type 1 diabetes who may be eligible for the procedure--some of whom are already receiving immunosuppression because of a previous transplant, others who are scheduled to receive de novo islet alone transplantation because of a life threatening risk of hypoglycemia. The outcomes of these initial investigations are predicted to shape the future boundaries of islet transplantation, diabetes, and transplantation.