Wei, Slowikowski, Fonseka, Rao et al A single cell map of the RA joint Abstract 78 To define the cell populations in rheumatoid arthritis (RA) driving joint inflammation, we applied 79 single-cell RNA-seq (scRNA-seq), mass cytometry, bulk RNA-seq, and flow cytometry to sorted 80 T cells, B cells, monocytes, and fibroblasts from 51 synovial tissue RA and osteoarthritis (OA) 81 patient samples. Utilizing an integrated computational strategy based on canonical correlation 82 analysis to 5,452 scRNA-seq profiles, we identified 18 unique cell populations. Combining mass 83 cytometry and transcriptomics together revealed cell states expanded in RA synovia: 84 THY1 + HLA high sublining fibroblasts (OR=33.8), IL1B + pro-inflammatory monocytes (OR=7.8), 85 CD11c + T-bet + autoimmune-associated B cells (OR=5.7), and PD-1 + Tph/Tfh (OR=3.0). We also 86 defined CD8 + T cell subsets characterized by GZMK + , GZMB + , and GNLY + expression. Using 87 bulk and single-cell data, we mapped inflammatory mediators to source cell populations, for 88 example attributing IL6 production to THY1 + HLA high fibroblasts and naïve B cells, and IL1B to 89 pro-inflammatory monocytes. These populations are potentially key mediators of RA 90 pathogenesis. 91 92 93 94 95 96 97 98 99 100

Background Heterogeneity is a major obstacle to developing effective treatments for patients with primary Sjögren's syndrome. We aimed to develop a robust method for stratification, exploiting heterogeneity in patient-reported symptoms, and to relate these differences to pathobiology and therapeutic response. MethodsWe did hierarchical cluster analysis using five common symptoms associated with primary Sjögren's syndrome (pain, fatigue, dryness, anxiety, and depression), followed by multinomial logistic regression to identify subgroups in the UK Primary Sjögren's Syndrome Registry (UKPSSR). We assessed clinical and biological differences between these subgroups, including transcriptional differences in peripheral blood. Patients from two independent validation cohorts in Norway and France were used to confirm patient stratification. Data from two phase 3 clinical trials were similarly stratified to assess the differences between subgroups in treatment response to hydroxychloroquine and rituximab. FindingsIn the UKPSSR cohort (n=608), we identified four subgroups: Low symptom burden (LSB), high symptom burden (HSB), dryness dominant with fatigue (DDF), and pain dominant with fatigue (PDF). Significant differences in peripheral blood lymphocyte counts, anti-SSA and anti-SSB antibody positivity, as well as serum IgG, κ-free light chain, β2-microglobulin, and CXCL13 concentrations were observed between these subgroups, along with differentially expressed transcriptomic modules in peripheral blood. Similar findings were observed in the independent validation cohorts (n=396). Reanalysis of trial data stratifying patients into these subgroups suggested a treatment effect with hydroxychloroquine in the HSB subgroup and with rituximab in the DDF subgroup compared with placebo.Interpretation Stratification on the basis of patient-reported symptoms of patients with primary Sjögren's syndrome revealed distinct pathobiological endotypes with distinct responses to immunomodulatory treatments. Our data have important implications for clinical management, trial design, and therapeutic development. Similar stratification approaches might be useful for patients with other chronic immune-mediated diseases.

The development of biological therapies has improved management of rheumatoid arthritis. However, costs and unresponsiveness to therapy in a sizeable proportion of patients limit their use, making it imperative to identify new targets for drug development programs. Here we investigated the melanocortin‐receptor type 3 (MC3) pathway. Gene‐deficient mice were subjected to a model of serum‐transfer‐induced arthritis and joints analyzed for gene expression (cytokines, MCs) and morphology. Pharmacological analyses were also conducted in this model. Osteoclastogenesis was studied from bone marrow cells. Mc3–/– mice displayed an exacerbated inflammatory arthritis, associated with prominent bone erosion and higher articular expression of Rankl. Osteoclastogenesis studied from Mc3–/– bone marrow cells revealed a higher degree of responsiveness to Rankl, linked to prolonged NF‐κB activation compared to wild types. Up‐regulation of a discrete set of inflammatory genes, including Il‐6, and Nos2, was measured in Mc3–/– mice, and a marked up‐regulation of joint Mc3 accompanied arthritis resolution in wild‐type mice. Administration of an MC3 agonist, D[Trp8]‐γ‐MSH, attenuated disease incidence and severity in wild‐type but not Mc3–/– mice. Overall, these findings identify MC3‐mediated signaling as a beneficial pathway in experimental arthritis;hence this receptor is a novel target for the development of therapeutics for arthritis.—Patel, H. B., Bombardieri, M., Sampaio, A. L. F., D’Acquisto, F., Gray, M., Grieco, P., Getting, S. J., Pitzalis, C., Perretti, M. Anti‐inflammatory and antiosteoclastogenesis properties of endogenous melanocortin receptor type 3 in experimental arthritis. FASEB J. 24, 4835–4843 (2010). http://www.fasebj.org