IL-23 past, present, and future: a roadmap to advancing IL-23 science and therapy.

Interleukin (IL)-23, an IL-12 cytokine family member, is a hierarchically dominant regulatory cytokine in a cluster of immune-mediated inflammatory diseases (IMIDs), including psoriasis, psoriatic arthritis, and inflammatory bowel disease. We review IL-23 biology, IL-23 signaling in IMIDs, and the effect of IL-23 inhibition in treating these diseases. We propose studies to advance IL-23 biology and unravel differences in response to anti-IL-23 therapy. Experimental evidence generated from these investigations could establish a novel molecular ontology centered around IL-23-driven diseases, improve upon current approaches to treating IMIDs with IL-23 inhibition, and ultimately facilitate optimal identification of patients and, thereby, outcomes.

Association between enthesitis/dactylitis resolution and patient-reported outcomes in guselkumab-treated patients with psoriatic arthritis.

OBJECTIVES: To evaluate the association between enthesitis resolution (ER) and dactylitis resolution (DR) and meaningful improvements in patient-reported outcomes (PROs) among biologic-naïve patients with PsA receiving guselkumab in the DISCOVER-2 study. METHODS: Enthesitis and dactylitis, characteristic lesions of PsA, were evaluated by independent assessors using the Leeds Enthesitis Index (range, 0-6) and Dactylitis Severity Score (range, 0-60). Proportions of patients with ER or DR (score = 0) among those with score > 0 at baseline were determined at weeks 24, 52, and 100. PROs included: fatigue (Functional Assessment of Chronic Illness Therapy-Fatigue [FACIT-Fatigue]), pain (0-100 visual analog scale), physical function (Health Assessment Questionnaire-Disability Index [HAQ-DI]), and health-related quality of life (36-item Short-Form Health Survey physical/mental component summary [SF-36 PCS/MCS]). Meaningful responses were defined as: improvements of ≥ 4 for FACIT-Fatigue, ≥ 0.35 for HAQ-DI, and ≥ 5 for SF-36 PCS/MCS and absolute scores of ≤ 15 for minimal pain and ≤ 0.5 for normalized HAQ-DI. Associations between ER/DR status and PRO response status were tested using a Chi-square test. RESULTS: Guselkumab-treated patients with ER were more likely than those without ER to achieve minimal pain (p < 0.001), normalized HAQ-DI (p < 0.001), and PCS response (p < 0.05) at weeks 24, 52, and 100. Patients with DR were more likely than those without DR to achieve FACIT-Fatigue response at week 24 and week 52 (both p ≤ 0.01) and minimal pain at week 24 and normalized HAQ-DI at week 52 (both p ≤ 0.03). CONCLUSION: In biologic-naïve patients with active PsA treated with guselkumab, achieving ER or DR was associated with durable improvements in selected PROs, including those of high importance to patients. TRIAL REGISTRATION: ClinicalTrials.gov ( https://clinicaltrials.gov ) NCT03158285; Registered: May 16, 2017. Key Points • At week 100, 65% and 76% of guselkumab-treated patients achieved enthesitis and dactylitis resolution (ER/DR). • Achieving ER was associated with achieving DR and vice versa through the end of study. • Achieving ER or DR was associated with durable and meaningful improvements in selected patient-reported outcomes.

The role of interleukin (IL)-23 in regulating pain in arthritis.

Current understanding of IL-23 biology, with its link to other pro-inflammatory cytokines, for example, IL-17 and granulocyte macrophage-colony stimulating factor (GM-CSF), is primarily focused on T lymphocyte-mediated inflammation/autoimmunity. Pain is a significant symptom associated with many musculoskeletal conditions leading to functional impairment and poor quality of life. While the role of IL-23 in arthritis has been studied in mouse models of adaptive immune-mediated arthritis using targeted approaches (e.g., monoclonal antibody (mAb) neutralization), the literature on IL-23 and arthritis pain is limited. Encouragingly, the anti-IL-23p19 mAb, guselkumab, reduces pain in psoriatic arthritis patients. Recent evidence has suggested a new biology for IL-23, whereby IL-23 is required in models of innate immune-mediated arthritis and its associated pain with its action being linked to a GM-CSF-dependent pathway (the so-called GM-CSF➔CCL17 pathway). This Commentary discusses the current understanding of potential cytokine networks involving IL-23 in arthritis pain and provides a rationale for future clinical studies targeting IL-23p19 in arthritis pain.

Author Correction: Pathogenic stromal cells as therapeutic targets in joint inflammation.

In the originally published version of this article, the acknowledgements and affiliations contained errors. In the acknowledgements, "NIHR Oxford and Birmingham Biomedical Research Centres" and "the Department of Health and Social Care" were incorrectly presented as "NIHR Oxford Biomedical Research Centres" and "the Department of Health". For affiliation 4, "NIHR Birmingham Biomedical Research Centre, University Hospitals Birmingham NHS Foundation Trust and University of Birmingham, Institute of Inflammation and Ageing, Birmingham, UK" was incorrectly presented as "Institute of Inflammation and Ageing, University of Birmingham, Birmingham, UK". For affiliation 3, "Institute" was incorrectly spelt. These errors have now been corrected in the HTML and PDF versions of the manuscript.

Pathogenic stromal cells as therapeutic targets in joint inflammation.

Knowledge of how the joint functions as an integrated unit in health and disease requires an understanding of the stromal cells populating the joint mesenchyme, including fibroblasts, tissue-resident macrophages and endothelial cells. Knowledge of the physiological and pathological mechanisms that involve joint mesenchymal stromal cells has begun to cast new light on why joint inflammation persists. The shared embryological origins of fibroblasts and endothelial cells might shape the behaviour of these cell types in diseased adult tissues. Cells of mesenchymal origin sustain inflammation in the synovial membrane and tendons by various mechanisms, and the important contribution of newly discovered fibroblast subtypes and their associated crosstalk with endothelial cells, tissue-resident macrophages and leukocytes is beginning to emerge. Knowledge of these mechanisms should help to shape the future therapeutic landscape and emphasizes the requirement for new strategies to address the pathogenic stroma and associated crosstalk between leukocytes and cells of mesenchymal origin.

The biology of IL-23 and IL-17 and their therapeutic targeting in rheumatic diseases.

PURPOSE OF REVIEW: Interleukin (IL)-23 and the related cytokine IL-17 play vital roles in immune-mediated inflammatory pathology. In the years since its discovery, IL-23 has been implicated as a central pathogenic factor in multiple rheumatic conditions and has been shown to act via a wide range of immune cells including type 17 T-helper (Th17) cells and innate-like immune cells. We review here the pivotal role of these cytokines and IL-23-responsive cells in both the bona fide autoimmune rheumatic diseases rheumatoid arthritis and systemic lupus erythematosus, as well as the spondyloarthropathies which more closely resemble the auto-inflammatory conditions. RECENT FINDINGS: IL-23 and related cytokines have been found to be up-regulated in rheumatoid arthritis, systemic lupus erythematosus and spondyloarthropathy, and preclinical models suggest that they play important pathological roles in these conditions. SUMMARY: It is anticipated that agents which target the IL-23 pathway will have profound roles in modifying the natural history of these diseases and in preventing the structural damage which occurs secondary to such chronic inflammation. This is especially relevant in the case of spondyloarthropathy in which case prevention of the novel bone formation is a particular challenge. It is also potentially pertinent for patients with rheumatoid arthritis, particularly those who do not respond to other biological therapies.

The critical role of interleukin-23 in spondyloarthropathy.

The spondyloarthropathies represent highly enigmatic conditions and although their clinical features, anatomical distribution of disease and genetic predisposing factors have been known for some time, a unified concept of the basic pathobiology underlying these illnesses has remained undefined. Recently progress has been made because numerous independent studies have converged upon IL-23 as a central cytokine in spondyloarthropathy and the mechanism and sites of action of this cytokine have now become much clearer. These findings enable the rational design of therapeutic strategies which it is hoped will profoundly modify the progression of these diseases. We will review the anatomical sites affected and the evidence for the importance of IL-23 in these conditions, before drawing these lines of investigation together to propose a model for the unified understanding of spondyloarthropathy.

What can rheumatologists learn from translational cancer therapy?

It is well established that an intimate connection exists between inflammation and neoplasia. Indeed, particular chronic infections and autoimmune processes giving rise to prolonged site-specific inflammation are known to increase the probability of the development of specific cancers. Molecular characterisation of these processes has revealed profound similarities in the specific molecules involved in persistence of inflammation and in both the primary induction of neoplastic processes and in specification of the preferred anatomic sites of metastatic spread. The therapeutic importance of these findings is underscored by the remarkable success in the treatment of autoimmune pathology using medications initially developed for use in oncology and this arena is one of considerable therapeutic promise for rheumatologists.

Interleukin-23: a promising therapeutic target in seronegative spondyloarthropathy.

Particular therapeutic challenges are raised by the spondyloarthropathies which represent a key area of unmet medical need. Recent investigations have shown that these conditions are characterised both by altered responsiveness to interleukin(IL)-23 and expansion of IL-23 responsive cells as well as increased production of IL-23. The gut in particular has emerged as a key site of IL-23 production, and gut inflammation is known to be strongly clinically associated with these conditions. Moreover, HLA-B27, which is strongly associated with spondyloarthropathy, has also been shown to stimulate IL-23 production. The view is thus emerging that dysregulation of IL-23 biology is a unifying feature of spondyloarthropathy, suggesting that treatments targeting this cytokine are likely to be highly efficacious.

IL-23 induces spondyloarthropathy by acting on ROR-γt+ CD3+CD4-CD8- entheseal resident T cells.

The spondyloarthropathies are a group of rheumatic diseases that are associated with inflammation at anatomically distal sites, particularly the tendon-bone attachments (entheses) and the aortic root. Serum concentrations of interleukin-23 (IL-23) are elevated and polymorphisms in the IL-23 receptor are associated with ankyosing spondylitis, however, it remains unclear whether IL-23 acts locally at the enthesis or distally on circulating cell populations. We show here that IL-23 is essential in enthesitis and acts on previously unidentified IL-23 receptor (IL-23R)(+), RAR-related orphan receptor γt (ROR-γt)(+)CD3(+)CD4(-)CD8(-), stem cell antigen 1 (Sca1)(+) entheseal resident T cells. These cells allow entheses to respond to IL-23 in vitro-in the absence of further cellular recruitment--and to elaborate inflammatory mediators including IL-6, IL-17, IL-22 and chemokine (C-X-C motif) ligand 1 (CXCL1). Notably, the in vivo expression of IL-23 is sufficient to phenocopy the human disease, with the specific and characteristic development of enthesitis and entheseal new bone formation in the initial complete absence of synovitis. As in the human condition, inflammation also develops in vivo at the aortic root and valve, which are structurally similar to entheses. The presence of these entheseal resident cells and their production of IL-22, which activates signal transducer and activator of transcription 3 (STAT3)-dependent osteoblast-mediated bone remodeling, explains why dysregulation of IL-23 results in inflammation at this precise anatomical site.

A distinct subset of podoplanin (gp38) expressing F4/80+ macrophages mediate phagocytosis and are induced following zymosan peritonitis.

Macrophages are important tissue resident cells that regulate the dynamics of inflammation. However, they are strikingly heterogeneous. During studies looking at podoplanin (gp38) expression on stromal cells in the murine spleen and peritoneal cavity we unexpectedly discovered that podoplanin was expressed on a subset of F4/80(+) macrophages; a subset which we have termed fibroblastic macrophages (FM). These cells function as phagocytes in vitro as measured by bead mediated phagocytosis assays. FM also exist at high frequency in the peritoneal cavity and in zymosan induced peritonitis in vivo. These FM represent a unique subgroup of F4/80(+) macrophages and their presence in the inflamed peritoneum suggests that they play a role in zymosan induced peritonitis.