Discovery of the Clinical Candidate IDOR-1117-2520: A Potent and Selective Antagonist of CCR6 for Autoimmune Diseases.

Migration of immune cells to sites of inflammation is a critical step in the body's response to infections but also during autoimmune flares. Chemokine receptors, members of the GPCR receptors, are instrumental in directing specific cell types to their target organs. Herein, we describe a highly potent small molecule antagonist of the chemokine receptor CCR6, which came out of fine-tuned structural elaborations from a proprietary HTS hit. Three main issues in the parent chemical series-cytotoxicity, phototoxicity, and hERG, were successfully solved. Biological characterization demonstrated that compound 45 (IDOR-1117-2520) is a selective and insurmountable antagonist of CCR6. In vivo proof-of-mechanism studies in a mouse lung inflammation model using a representative compound from the chemical class of 45 confirmed that the targeted CCR6+ cells were efficiently inhibited from migrating into the bronchoalveoli. Finally, ADMET and physicochemical properties were well balanced and the preclinical package warranted progress in the clinic.

CD4+ T-cell-derived IL-10 promotes CNS inflammation in mice by sustaining effector T cell survival.

Interleukin (IL)-10 is considered a prototypical anti-inflammatory cytokine, significantly contributing to the maintenance and reestablishment of immune homeostasis. Accordingly, it has been shown in the intestine that IL-10 produced by Tregs can act on effector T cells, thereby limiting inflammation. Herein, we investigate whether this role also applies to IL-10 produced by T cells during central nervous system (CNS) inflammation. During neuroinflammation, both CNS-resident and -infiltrating cells produce IL-10; yet, as IL-10 has a pleotropic function, the exact contribution of the different cellular sources is not fully understood. We find that T-cell-derived IL-10, but not other relevant IL-10 sources, can promote inflammation in experimental autoimmune encephalomyelitis. Furthermore, in the CNS, T-cell-derived IL-10 acts on effector T cells, promoting their survival and thereby enhancing inflammation and CNS autoimmunity. Our data indicate a pro-inflammatory role of T-cell-derived IL-10 in the CNS.

Single-cell sequencing reveals clonal expansions of pro-inflammatory synovial CD8 T cells expressing tissue-homing receptors in psoriatic arthritis.

Psoriatic arthritis (PsA) is a debilitating immune-mediated inflammatory arthritis of unknown pathogenesis commonly affecting patients with skin psoriasis. Here we use complementary single-cell approaches to study leukocytes from PsA joints. Mass cytometry demonstrates a 3-fold expansion of memory CD8 T cells in the joints of PsA patients compared to peripheral blood. Meanwhile, droplet-based and plate-based single-cell RNA sequencing of paired T cell receptor alpha and beta chain sequences show pronounced CD8 T cell clonal expansions within the joints. Transcriptome analyses find these expanded synovial CD8 T cells to express cycling, activation, tissue-homing and tissue residency markers. T cell receptor sequence comparison between patients identifies clonal convergence. Finally, chemokine receptor CXCR3 is upregulated in the expanded synovial CD8 T cells, while two CXCR3 ligands, CXCL9 and CXCL10, are elevated in PsA synovial fluid. Our data thus provide a quantitative molecular insight into the cellular immune landscape of psoriatic arthritis.

Microglial Homeostasis Requires Balanced CSF-1/CSF-2 Receptor Signaling.

CSF-1R haploinsufficiency causes adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). Previous studies in the Csf1r+/- mouse model of ALSP hypothesized a central role of elevated cerebral Csf2 expression. Here, we show that monoallelic deletion of Csf2 rescues most behavioral deficits and histopathological changes in Csf1r+/- mice by preventing microgliosis and eliminating most microglial transcriptomic alterations, including those indicative of oxidative stress and demyelination. We also show elevation of Csf2 transcripts and of several CSF-2 downstream targets in the brains of ALSP patients, demonstrating that the mechanisms identified in the mouse model are functional in humans. Our data provide insights into the mechanisms underlying ALSP. Because increased CSF2 levels and decreased microglial Csf1r expression have also been reported in Alzheimer's disease and multiple sclerosis, we suggest that the unbalanced CSF-1R/CSF-2 signaling we describe in the present study may contribute to the pathogenesis of other neurodegenerative conditions.

Plaque-associated myeloid cells derive from resident microglia in an Alzheimer's disease model.

Alzheimer's disease (AD) is accompanied by a robust inflammatory response mediated by plaque-associated myeloid cells of the brain. These cells exhibit altered gene expression profiles and serve as a barrier, preventing neuritic dystrophy. The origin of these cells has been controversial and is of therapeutic importance. Here, we genetically labeled different myeloid populations and unequivocally demonstrated that plaque-associated myeloid cells in the AD brain are derived exclusively from resident microglia, with no contribution from circulating peripheral monocytes.

Impact of high-altitude therapy on type-2 immune responses in asthma patients.

BACKGROUND: Asthma patients present with distinct immunological profiles, with a predominance of type 2 endotype. The aim of this study was to investigate the impact of high-altitude treatment on the clinical and immunological response in asthma. METHODS: Twenty-six hospitalized asthma patients (nine eosinophilic allergic; EA, nine noneosinophilic allergic; NEA and eight noneosinophilic nonallergic; NN) and nine healthy controls in high altitude for 21 days were enrolled in the study. We assessed eosinophils, T cells, Tregs, and innate lymphoid cells (ILC) from peripheral blood using flow cytometry. RESULTS: The number of eosinophils (both resting and activated) and chemoattractant receptor homolog expressed on Th2 cells (CRTH2)-expressing CD4+ and CD8+ T cells decreased significantly in EA patients after altitude treatment. The frequency of CRTH2+ Tregs as decreased significantly in all the asthma phenotypes as well as the frequency of ILC2 was significantly reduced in EA after altitude treatment. After 21 days of altitude therapy, CRTH2-expressing ILC2, CD4+ and CD8+ T cells and Treg cells showed attenuated responses to exogenous PGD2. Furthermore, PGD2 signaling via CRTH2 was found to diminish the suppressive function of CRTH2+ Tregs which partially normalized during high-altitude treatment. Improved asthma control was particularly evident in allergic asthma patients and correlated with decreased frequencies of CRTH2+ Treg cells in EA patients. Serum IL-5 and IL-13 decreased during climate treatment in asthma patients with high baseline levels. CONCLUSIONS: Asthma treatment in high altitude reduced the type 2 immune response, corrected the increased CRTH2 expression and its dysregulated functions.

EBI2 Is Highly Expressed in Multiple Sclerosis Lesions and Promotes Early CNS Migration of Encephalitogenic CD4 T Cells.

Arrival of encephalitogenic T cells at inflammatory foci represents a critical step in development of experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. EBI2 and its ligand, 7α,25-OHC, direct immune cell localization in secondary lymphoid organs. CH25H and CYP7B1 hydroxylate cholesterol to 7α,25-OHC. During EAE, we found increased expression of CH25H by microglia and CYP7B1 by CNS-infiltrating immune cells elevating the ligand concentration in the CNS. Two critical pro-inflammatory cytokines, interleukin-23 (IL-23) and interleukin-1 beta (IL-1ß), maintained expression of EBI2 in differentiating Th17 cells. In line with this, EBI2 enhanced early migration of encephalitogenic T cells into the CNS in a transfer EAE model. Nonetheless, EBI2 was dispensable in active EAE. Human Th17 cells do also express EBI2, and EBI2 expressing cells are abundant within multiple sclerosis (MS) white matter lesions. These findings implicate EBI2 as a mediator of CNS autoimmunity and describe mechanistically its contribution to the migration of autoreactive T cells into inflamed organs.

Trans-presentation of IL-6 by dendritic cells is required for the priming of pathogenic TH17 cells.

The cellular sources of interleukin 6 (IL-6) that are relevant for differentiation of the TH17 subset of helper T cells remain unclear. Here we used a novel strategy for the conditional deletion of distinct IL-6-producing cell types to show that dendritic cells (DCs) positive for the signaling regulator Sirpα were essential for the generation of pathogenic TH17 cells. Using their IL-6 receptor α-chain (IL-6Rα), Sirpα+ DCs trans-presented IL-6 to T cells during the process of cognate interaction. While ambient IL-6 was sufficient to suppress the induction of expression of the transcription factor Foxp3 in T cells, trans-presentation of IL-6 by DC-bound IL-6Rα (called 'IL-6 cluster signaling' here) was needed to prevent premature induction of interferon-γ (IFN-γ) expression in T cells and to generate pathogenic TH17 cells in vivo. Our findings should guide therapeutic approaches for the treatment of TH17-cell-mediated autoimmune diseases.

BAFF-secreting neutrophils drive plasma cell responses during emergency granulopoiesis.

Prolonged infections or adjuvant usage can trigger emergency granulopoiesis (EG), leading to dysregulation in neutrophil blood counts. However, the impact of EG on T and B cell function remains largely unknown. In this study, to address this question, we used a mouse model of neutropenia and studied immune activation after adjuvant administration. The initial neutropenic state fostered an environment of increased dendritic cell activation and T cell-derived IL-17 production. Interestingly, neutropenic lysozyme 2-diphtheria toxin A mice exhibited striking EG and amplified neutrophil recruitment to the lymph nodes (LNs) that was dependent on IL-17-induced prostaglandin activity. The recruited neutrophils secreted a B cell-activating factor that highly accelerated plasma cell generation and antigen-specific antibody production. Reduction of neutrophil functions via granulocyte colony-stimulating factor neutralization significantly diminished plasma cell formation, directly linking EG with the humoral immune response. We conclude that neutrophils are capable of directly regulating T cell-dependent B cell responses in the LN.

Chronic skin inflammation leads to bone loss by IL-17-mediated inhibition of Wnt signaling in osteoblasts.

Inflammation has important roles in tissue regeneration, autoimmunity, and cancer. Different inflammatory stimuli can lead to bone loss by mechanisms that are not well understood. We show that skin inflammation induces bone loss in mice and humans. In psoriasis, one of the prototypic IL-17A-mediated inflammatory human skin diseases, low bone formation and bone loss correlated with increased serum IL-17A levels. Similarly, in two mouse models with chronic IL-17A-mediated skin inflammation,K14-IL17A(ind)andJunB(Δep), strong inhibition of bone formation was observed, different from classical inflammatory bone loss where osteoclast activation leads to bone degradation. We show that under inflammatory conditions, skin-resident cells such as keratinocytes, γδ T cells, and innate lymphoid cells were able to express IL-17A, which acted systemically to inhibit osteoblast and osteocyte function by a mechanism involving Wnt signaling. IL-17A led to decreased Wnt signaling in vitro, and importantly, pharmacological blockade of IL-17A rescued Wnt target gene expression and bone formation in vivo. These data provide a mechanism where IL-17A affects bone formation by regulating Wnt signaling in osteoblasts and osteocytes. This study suggests that using IL-17A blocking agents in psoriasis could be beneficial against bone loss in these patients.

Externalized decondensed neutrophil chromatin occludes pancreatic ducts and drives pancreatitis.

Ductal occlusion has been postulated to precipitate focal pancreatic inflammation, while the nature of the primary occluding agents has remained elusive. Neutrophils make use of histone citrullination by peptidyl arginine deiminase-4 (PADI4) in contact to particulate agents to extrude decondensed chromatin as neutrophil extracellular traps (NETs). In high cellular density, NETs form macroscopically visible aggregates. Here we show that such aggregates form inside pancreatic ducts in humans and mice occluding pancreatic ducts and thereby driving pancreatic inflammation. Experimental models indicate that PADI4 is critical for intraductal aggregate formation and that PADI4-deficiency abrogates disease progression. Mechanistically, we identify the pancreatic juice as a strong instigator of neutrophil chromatin extrusion. Characteristic single components of pancreatic juice, such as bicarbonate ions and calcium carbonate crystals, induce aggregated NET formation. Ductal occlusion by aggregated NETs emerges as a pathomechanism with relevance in a plethora of inflammatory conditions involving secretory ducts.

IL17A-Mediated Endothelial Breach Promotes Metastasis Formation.

The role of the IL23/IL17A axis in tumor-immune interactions is a matter of controversy. Although some suggest that IL17A-producing T cells (TH17) can suppress tumor growth, others report that IL17A and IL23 accelerate tumor growth. Here, we systematically assessed the impact of IL17A-secreting lymphocytes in several murine models of tumor lung metastasis. Genetic fate mapping revealed that IL17A was secreted within lung metastases predominantly by γδ T cells, whereas TH17 cells were virtually absent. Using different tumor models, we found Il17a(-/-) mice to consistently develop fewer pulmonary tumor colonies. IL17A specifically increased blood vessel permeability and the expression of E-selectin and VCAM-1 by lung endothelial cells in vivo. In transgenic mice, specific targeting of IL17A to the endothelium increased the number of tumor foci. Moreover, the direct impact of IL17A on lung endothelial cells resulted in impaired endothelial barrier integrity, showing that IL17A promotes the formation of lung metastases through tumor-endothelial transmigration.

GM-CSF in Neuroinflammation: Licensing Myeloid Cells for Tissue Damage.

Multiple sclerosis (MS) is the prototypical inflammatory disease of the central nervous system (CNS). MS lesions harbor different immune cells, but the contribution of individual cell types to disease etiology and progression is not well understood. In experimental autoimmune encephalomyelitis (EAE), auto-reactive helper T (Th) cells instigate CNS inflammation by acting on myeloid cells via the production of granulocyte-macrophage colony-stimulating factor (GM-CSF). Recent reports have implicated myeloid cells in both the inflammatory process and as executers of tissue damage in the CNS. We review these findings here, and integrate them into a model wherein GM-CSF produced by Th cells coordinates monocyte recruitment to the CNS, and differentiation into pathogenic effectors. We discuss the implications of this model to current therapies for MS, and outline important areas of further inquiry.

The Cytokine GM-CSF Drives the Inflammatory Signature of CCR2+ Monocytes and Licenses Autoimmunity.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has emerged as a crucial cytokine produced by auto-reactive T helper (Th) cells that initiate tissue inflammation. Multiple cell types can sense GM-CSF, but the identity of the pathogenic GM-CSF-responsive cells is unclear. By using conditional gene targeting, we systematically deleted the GM-CSF receptor (Csf2rb) in specific subpopulations throughout the myeloid lineages. Experimental autoimmune encephalomyelitis (EAE) progressed normally when either classical dendritic cells (cDCs) or neutrophils lacked GM-CSF responsiveness. The development of tissue-invading monocyte-derived dendritic cells (moDCs) was also unperturbed upon Csf2rb deletion. Instead, deletion of Csf2rb in CCR2(+)Ly6C(hi) monocytes phenocopied the EAE resistance seen in complete Csf2rb-deficient mice. High-dimensional analysis of tissue-infiltrating moDCs revealed that GM-CSF initiates a combination of inflammatory mechanisms. These results indicate that GM-CSF signaling controls a pathogenic expression signature in CCR2(+)Ly6C(hi) monocytes and their progeny, which was essential for tissue damage.

Dermal IL-17-producing γδ T cells establish long-lived memory in the skin.

Conventional αß T cells have the ability to form a long-lasting resident memory T-cell (TRM ) population in nonlymphoid tissues after encountering foreign antigen. Conversely, the concept of 'innate memory', where the ability of nonadaptive branches of the immune system to deliver a rapid, strengthened immune response upon reinfection or rechallenge, is just emerging. Using the αß T-cell-independent Aldara psoriasis mouse model in combination with genetic fate-mapping and reporter systems, we identified a subset of γδ T cells in mice that is capable of establishing a long-lived memory population in the skin. IL-17A/F-producing Vγ4(+) Vδ4(+) T cells populate and persist in the dermis for long periods of time after initial stimulation with Aldara. Experienced Vγ4(+) Vδ4(+) cells show enhanced effector functions and mediate an exacerbated secondary inflammatory response. In addition to identifying a unique feature of γδ T cells during inflammation, our results have direct relevance to the human disease as this quasi-innate memory provides a mechanistic insight into relapses and chronification of psoriasis.

Interleukin 17 drives vascular inflammation, endothelial dysfunction, and arterial hypertension in psoriasis-like skin disease.

OBJECTIVE: Interleukin (IL)-17A is regarded as an important cytokine to drive psoriasis, an inflammatory skin disease marked by increased cardiovascular mortality. We aimed to test the hypothesis that overproduction of IL-17A in the skin leading to dermal inflammation may systemically cause vascular dysfunction in psoriasis-like skin disease. APPROACH AND RESULTS: Conditional overexpression of IL-17A in keratinocytes caused severe psoriasis-like skin inflammation in mice (K14-IL-17A(ind/+) mice), associated with increased reactive oxygen species formation and circulating CD11b(+) inflammatory leukocytes in blood, with endothelial dysfunction, increased systolic blood pressure, left ventricular hypertrophy, and reduced survival compared with controls. In K14-IL-17A(ind/+) mice, immunohistochemistry and flow cytometry revealed increased vascular production of the nitric oxide/superoxide reaction product peroxynitrite and infiltration of the vasculature with myeloperoxidase(+)CD11b(+)GR1(+)F4/80(-) cells accompanied by increased expression of the inducible nitric oxide synthase and the nicotinamide dinucleotide phosphate (NADPH) oxidase, nox2. Neutrophil depletion by anti-GR-1 antibody injections reduced oxidative stress in blood and vessels. Neutralization of tumor necrosis factor-α and IL-6 (both downstream of IL-17A) reduced skin lesions, attenuated oxidative stress in heart and blood, and partially improved endothelial dysfunction in K14-IL-17A(ind/+) mice. CONCLUSIONS: Dermal overexpression of IL-17A induces systemic endothelial dysfunction, vascular oxidative stress, arterial hypertension, and increases mortality mainly driven by myeloperoxidase(+)CD11b(+)GR1(+)F4/80(-) inflammatory cells. Depletion of the GR-1(+) immune cells or neutralization of IL-17A downstream cytokines by biologicals attenuates the vascular phenotype in K14-IL-17A(ind/+) mice.

IL-12-and IL-23 in health and disease.

Interleukin (IL)-12 and IL-23 play important roles in the development of experimental autoimmune disease models and numerous afflictions affecting humans. Preclinical data over the last 20 years combined with successful clinical trials has identified a clear relationship between IL-12, IL-23 and the generation of pathogenic T helper cells capable of orchestrating tissue inflammation. Observations made in the clinic have shown that IL-12p40, a common subunit shared by IL-12 and IL-23, is critical to pathologies associated with psoriasis, inflammatory bowel disease (IBD) and tumor growth. These advancements have set in motion the development of a number of potential therapeutics aimed at manipulating IL-12/23 signaling pathways in both mice and humans. This review will discuss a brief history of the understanding and expansion of the IL-12 cytokine family, some difficulties associated with preclinical data interpretation and finally the medicinal interventions that have been developed to combat IL-12/23-driven autoimmune disorders.

IL-6 regulates neutrophil microabscess formation in IL-17A-driven psoriasiform lesions.

The lack of a generally accepted animal model for human psoriasis has hindered progress with respect to understanding the pathogenesis of the disease. Here we present a model in which transgenic IL-17A expression is targeted to the skin in mice, achievable after crossing our IL-17A(ind) allele to the K14-Cre strain. K14-IL-17A(ind/+) mice invariably develop an overt skin inflammation bearing many hallmark characteristics of human psoriasis including dermal infiltration of effector T cells, formation of neutrophil microabscesses, and hyperkeratosis. IL-17A expression in the skin results in upregulated granulopoiesis and migration of IL-6R-expressing neutrophils into the skin. Neutralization of IL-6 signaling efficiently reduces the observed pathogenesis in skin of IL-17A-overexpressing mice, with marked reductions in epidermal neutrophil abscess formation and epidermal thickening. Thus, IL-6 functions downstream of IL-17A to exacerbate neutrophil microabscess development in psoriasiform lesions.

Does dietary salt induce autoimmunity?

Two recent publications suggest that dietary salt may polarize TH17 cells and therefore increase the risk of developing autoimmune disease. Where low salt diets can readily be tested for their therapeutic effects in autoimmune disease, more work is needed to connect dietary salts with the development of immunopathology.