Daniel R. Getts

Ly6c+ “inflammatory monocytes” are microglial precursors recruited in a pathogenic manner in West Nile virus encephalitis

In a lethal West Nile virus (WNV) model, central nervous system infection triggered a threefold increase in CD45int/CD11b+/CD11c− microglia at days 6–7 postinfection (p.i.). Few microglia were proliferating, suggesting that the increased numbers were derived from a migratory precursor cell. Depletion of “circulating” (Gr1−(Ly6Clo)CX3CR1+) and “inflammatory” (Gr1hi/Ly6Chi/CCR2+) classical monocytes during infection abrogated the increase in microglia. C57BL/6 chimeras reconstituted with cFMS–enhanced green fluorescent protein (EGFP) bone marrow (BM) showed large numbers of peripherally derived (GFP+) microglia expressing GR1+(Ly6C+) at day 7 p.i., suggesting that the inflammatory monocyte is a microglial precursor. This was confirmed by adoptive transfer of labeled BM (Ly6Chi/CD115+) or circulating inflammatory monocytes that trafficked to the WNV-infected brain and expressed a microglial phenotype. CCL2 is a chemokine that is highly expressed during WNV infection and important in inflammatory monocyte trafficking. Neutralization of CCL2 not only reduced the number of GFP+ microglia in the brain during WNV infection but prolonged the life of infected animals. Therefore, CCL2-dependent inflammatory monocyte migration is critical for increases in microglia during WNV infection and may also play a pathogenic role during WNV encephalitis.

Microparticles bearing encephalitogenic peptides induce T-cell tolerance and ameliorate experimental autoimmune encephalomyelitis

Aberrant T-cell activation underlies many autoimmune disorders, yet most attempts to induce T-cell tolerance have failed. Building on previous strategies for tolerance induction that exploited natural mechanisms for clearing apoptotic debris, we show that antigen-decorated microparticles (500-nm diameter) induce long-term T-cell tolerance in mice with relapsing experimental autoimmune encephalomyelitis. Specifically, intravenous infusion of either polystyrene or biodegradable poly(lactide-co-glycolide) microparticles bearing encephalitogenic peptides prevents the onset and modifies the course of the disease. These beneficial effects require microparticle uptake by marginal zone macrophages expressing the scavenger receptor MARCO and are mediated in part by the activity of regulatory T cells, abortive T-cell activation and T-cell anergy. Together these data highlight the potential for using microparticles to target natural apoptotic clearance pathways to inactivate pathogenic T cells and halt the disease process in autoimmunity.

Therapeutic Inflammatory Monocyte Modulation Using Immune-Modifying Microparticles

Negatively charged immune-modifying microparticles bind to the scavenger receptor MARCO on inflammatory monocytes, resulting in their apoptosis and reduced inflammatory damage in a range of diseases. A New Frontier in Immune Modulation Inflammatory monocytes markedly potentiate the immune pathology observed in many diseases, yet no therapy exists that specifically inhibits these cells. The therapeutic accessibility of monocytes in the bloodstream and their inherent propensity to engulf particulate material suggest that highly negatively charged microparticles might provide a readily translatable solution to this problem. These microparticles, referred to as immune-modifying microparticles (IMPs), may be derived from numerous compounds, including the biodegradable polymer poly(lactic-co-glycolic acid) (PLGA-IMP), already used in humans for inter alia dissolvable sutures. Getts et al. now show that upon infusion, IMPs bind to a receptor with a positive domain on inflammatory monocytes, resulting in monocyte sequestration in the spleen and apoptosis through a similar pathway observed for senescing leukocytes. This safe monocyte clearance pathway culminated in substantially reduced inflammatory tissue damage in mouse models of West Nile virus encephalitis, experimental autoimmune encephalomyelitis, peritonitis, colitis, and myocardial infarction. Together, the data suggest that IMPs could transform the treatment of acute inflammation. Indeed, phase 1/2 testing is planned to begin in 2014, with rapid translation supported by the availability of clinical-grade PLGA. Inflammatory monocyte-derived effector cells play an important role in the pathogenesis of numerous inflammatory diseases. However, no treatment option exists that is capable of modulating these cells specifically. We show that infused negatively charged, immune-modifying microparticles (IMPs), derived from polystyrene, microdiamonds, or biodegradable poly(lactic-co-glycolic) acid, were taken up by inflammatory monocytes, in an opsonin-independent fashion, via the macrophage receptor with collagenous structure (MARCO). Subsequently, these monocytes no longer trafficked to sites of inflammation; rather, IMP infusion caused their sequestration in the spleen through apoptotic cell clearance mechanisms and, ultimately, caspase-3–mediated apoptosis. Administration of IMPs in mouse models of myocardial infarction, experimental autoimmune encephalomyelitis, dextran sodium sulfate–induced colitis, thioglycollate-induced peritonitis, and lethal flavivirus encephalitis markedly reduced monocyte accumulation at inflammatory foci, reduced disease symptoms, and promoted tissue repair. Together, these data highlight the intricate interplay between scavenger receptors, the spleen, and inflammatory monocyte function and support the translation of IMPs for therapeutic use in diseases caused or potentiated by inflammatory monocytes.

CXCR3 Signaling Reduces the Severity of Experimental Autoimmune Encephalomyelitis by Controlling the Parenchymal Distribution of Effector and Regulatory T Cells in the Central Nervous System

The chemokine receptor CXCR3 promotes the trafficking of activated T and NK cells in response to three ligands, CXCL9, CXCL10, and CXCL11. Although these chemokines are produced in the CNS in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), their role in the pathogenesis of CNS autoimmunity is unresolved. We examined the function of CXCR3 signaling in EAE using mice that were deficient for CXCR3 (CXCR3−/−). The time to onset and peak disease severity were similar for CXCR3−/− and wild-type (WT) animals; however, CXCR3−/− mice had more severe chronic disease with increased demyelination and axonal damage. The inflammatory lesions in WT mice consisted of well-demarcated perivascular mononuclear cell infiltrates, mainly in the spinal cord and cerebellum. In CXCR3−/− mice, these lesions were more widespread throughout the CNS and were diffused and poorly organized, with T cells and highly activated microglia/macrophages scattered throughout the white matter. Although the number of CD4+ and CD8+ T cells infiltrating the CNS were similar in CXCR3−/− and WT mice, Foxp3+ regulatory T cells were significantly reduced in number and dispersed in CXCR3−/− mice. The expression of various chemokine and cytokine genes in the CNS was similar in CXCR3−/− and WT mice. The genes for the CXCR3 ligands were expressed predominantly in and/or immediately surrounding the mononuclear cell infiltrates. We conclude that in EAE, CXCR3 signaling constrains T cells to the perivascular space in the CNS and augments regulatory T cell recruitment and effector T cell interaction, thus limiting autoimmune-mediated tissue damage.

Immunopathology of flavivirus infections.

With the recent emergence of the flavivirus, West Nile virus (WNV), in particular, the New York strain of Lineage I WNV in North America in 1999, there has been a significant increase in activity in neurotropic flavivirus research. These viruses cause encephalitis that can result in permanent neurological sequelae or death. Attempts to develop vaccines have made progress, but have been variably successful, despite considerable commercial underwriting. Thus, the discovery of ways and means to combat disease is no less urgent. As such, most recent work has been directed towards dissecting and understanding the pathogenesis of disease, as a way of informing possible approaches to abrogation or amelioration of illness. Whether inherent to flaviviruses or because humans are incidental, dead‐end hosts, it is clear that these viruses interact with their human hosts in extremely complex ways. This occurs from the cellular level, at which infection must be established to produce disease, to its interaction with the adaptive immune response, which may result in its eradication, with or without immunopathological and consequent neurological sequelae. As human proximity to and contact with flavivirus insect vectors and amplifying hosts cannot practically be eliminated, our understanding of the pathogenesis of flavivirus‐induced diseases, especially with regard to possible targets for treatment, is imperative.

Coordinated Regulation and Widespread Cellular Expression of Interferon-Stimulated Genes (ISG) ISG-49, ISG-54, and ISG-56 in the Central Nervous System after Infection with Distinct Viruses

ABSTRACT The interferon (IFN)-stimulated genes (ISGs) ISG-49, ISG-54, and ISG-56 are highly responsive to viral infection, yet the regulation and function of these genes in vivo are unknown. We examined the simultaneous regulation of these ISGs in the brains of mice during infection with either lymphocytic choriomeningitis virus (LCMV) or West Nile virus (WNV). Expression of the ISG-49 and ISG-56 genes increased significantly during LCMV infection, being widespread and localized predominantly to common as well as distinct neuronal populations. Expression of the ISG-54 gene also increased but to lower levels and with a more restricted distribution. Although expression of the ISG-49, ISG-54, and ISG-56 genes was increased in the brains of LCMV-infected STAT1 and STAT2 knockout (KO) mice, this was blunted, delayed, and restricted to the choroid plexus, meninges, and endothelium. ISG-56 protein was regulated in parallel with the corresponding RNA transcript in the brain during LCMV infection in wild-type and STAT KO mice. Similar changes in ISG-49, ISG-54, and ISG-56 RNA levels and ISG-56 protein levels were observed in the brains of wild-type mice following infection with WNV. Thus, the ISG-49, ISG-54, and ISG-56 genes are coordinately upregulated in the brain during LCMV and WNV infection; this upregulation, in the case of LCMV, was totally (neurons) or partially (non-neurons) dependent on the IFN-signaling molecules STAT1 and STAT2. These findings suggest a dominant role for the ISG-49, ISG-54, and ISG-56 genes in the host response to different viruses in the central nervous system, where, particularly in neurons, these genes may have nonredundant functions.

ECDI-fixed allogeneic splenocytes induce donor-specific tolerance for long-term survival of islet transplants via two distinct mechanisms

A major challenge for human allogeneic islet transplantation is the development of effective methods to induce donor-specific tolerance to obviate the need for life-long immunosuppression that is toxic to the insulin-producing β cells and detrimental to the host. We developed an efficient donor-specific tolerance therapy that utilizes infusions of ethylene carbodiimide (ECDI)-treated donor splenic antigen-presenting cells that results in indefinite survival of allogeneic islet grafts in the absence of immunosuppression. Furthermore, we show that induction of tolerance is critically dependent on synergistic effects between an intact programmed death 1 receptor–programmed death ligand 1 signaling pathway and CD4+CD25+Foxp3+ regulatory T cells. This highly efficient antigen-specific therapy with a complete avoidance of immunosuppression has significant therapeutic potential in human islet cell transplantation.

A Biodegradable Nanoparticle Platform for the Induction of Antigen-Specific Immune Tolerance for Treatment of Autoimmune Disease

Targeted immune tolerance is a coveted therapy for the treatment of a variety of autoimmune diseases, as current treatment options often involve nonspecific immunosuppression. Intravenous (iv) infusion of apoptotic syngeneic splenocytes linked with peptide or protein autoantigens using ethylene carbodiimide (ECDI) has been demonstrated to be an effective method for inducing peripheral, antigen-specific tolerance for treatment of autoimmune disease. Here, we show the ability of biodegradable poly(lactic-co-glycolic acid) (PLG) nanoparticles to function as a safe, cost-effective, and highly efficient alternative to cellular carriers for the induction of antigen-specific T cell tolerance. We describe the formulation of tolerogenic PLG particles and demonstrate that administration of myelin antigen-coupled particles both prevented and treated relapsing-remitting experimental autoimmune encephalomyelitis (R-EAE), a CD4 T cell-mediated mouse model of multiple sclerosis (MS). PLG particles made on-site with surfactant modifications surpass the efficacy of commercially available particles in their ability to couple peptide and to prevent disease induction. Most importantly, myelin antigen-coupled PLG nanoparticles are able to significantly ameliorate ongoing disease and subsequent relapses when administered at onset or at peak of acute disease, and minimize epitope spreading when administered during disease remission. Therapeutic treatment results in significantly reduced CNS infiltration of encephalitogenic Th1 (IFN-γ) and Th17 (IL-17a) cells as well as inflammatory monocytes/macrophages. Together, these data describe a platform for antigen display that is safe, low-cost, and highly effective at inducing antigen-specific T cell tolerance. The development of such a platform carries broad implications for the treatment of a variety of immune-mediated diseases.

Tolerance Induced by Apoptotic Antigen-Coupled Leukocytes Is Induced by PD-L1+ and IL-10–Producing Splenic Macrophages and Maintained by T Regulatory Cells

Ag-specific tolerance is a highly desired therapy for immune-mediated diseases. Intravenous infusion of protein/peptide Ags linked to syngeneic splenic leukocytes with ethylene carbodiimide (Ag-coupled splenocytes [Ag-SP]) has been demonstrated to be a highly efficient method for inducing peripheral, Ag-specific T cell tolerance for treatment of autoimmune disease. However, little is understood about the mechanisms underlying this therapy. In this study, we show that apoptotic Ag-SP accumulate in the splenic marginal zone, where their uptake by F4/80+ macrophages induces production of IL-10, which upregulates the expression of the immunomodulatory costimulatory molecule PD-L1 that is essential for Ag-SP tolerance induction. Ag-SP infusion also induces T regulatory cells that are dispensable for tolerance induction but required for long-term tolerance maintenance. Collectively, these results indicate that Ag-SP tolerance recapitulates how tolerance is normally maintained in the hematopoietic compartment and highlight the interplay between the innate and adaptive immune systems in the induction of Ag-SP tolerance. To our knowledge, we show for the first time that tolerance results from the synergistic effects of two distinct mechanisms, PD-L1–dependent T cell-intrinsic unresponsiveness and the activation of T regulatory cells. These findings are particularly relevant as this tolerance protocol is currently being tested in a Phase I/IIa clinical trial in new-onset relapsing-remitting multiple sclerosis.

Site-Specific Production of IL-6 in the Central Nervous System Retargets and Enhances the Inflammatory Response in Experimental Autoimmune Encephalomyelitis

IL-6 is crucial for the induction of many murine models of autoimmunity including experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. To establish the role of site-specific production of IL-6 in autoimmunity, we examined myelin oligodendrocyte glycoprotein immunization-induced EAE in transgenic mice (GFAP-IL6) with IL-6 production restricted to the cerebellum. Myelin oligodendrocyte glycoprotein-immunized (Mi-) GFAP-IL6 mice developed severe ataxia but no physical signs of spinal cord involvement, which was in sharp contrast to Mi-wild type (WT) animals that developed classical EAE with ascending paralysis. Immune pathology and demyelination were nearly absent from the spinal cord, but significantly increased in the cerebellum of Mi-GFAP-IL6 mice. Tissue damage in the cerebellum in the Mi-GFAP-IL6 mice was accompanied by increased total numbers of infiltrating leukocytes and increased proportions of both neutrophils and B-cells. With the exception of IL-17 mRNA, which was elevated in both control immunized and Mi-GFAP-IL6 cerebellum, the level of other cytokine and chemokine mRNAs were comparable with Mi-WT cerebellum whereas significantly higher levels of IFN-γ and TNF-α mRNA were found in Mi-WT spinal cord. Thus, site-specific production of IL-6 in the cerebellum redirects trafficking away from the normally preferred antigenic site the spinal cord and acts as a leukocyte “sink” that markedly enhances the inflammatory cell accumulation and disease. The mechanisms underlying this process likely include the induction of specific chemokines, activation of microglia, and activation and loss of integrity of the blood-brain barrier present in the cerebellum of the GFAP-IL6 mice before the induction of EAE.