Title The role of extracellular vesicles in rheumatoid arthritis development and methotrexate treatment response Background Rheumatoid arthritis (RA) is a chronic inflammatory disease that primarily manifests in synovial joints but it may also lead to systemic alterations. Methotrexate (MTX) is often the initial drug prescribed to RA patients and 53-71% of patients have been reported to respond well to this treatment (1). Still, there is a large fraction of non-responding patients that must undergo consecutive trials to find a treatment that prevents joint degradation, maximize physical function and alleviate pain. This emphasizes the need for diagnostic and prognostic biomarkers. Extracellular vesicles (EVs) are important in cell-cell communication and have received an increased focus for their role in RA pathogenesis, as well as in studies of treatment response (2, 3). EVs are membrane-derived nanoparticles that carry proteins, lipids, DNA, and RNA, and are released by cells into biological fluids and tissues(4). Rationale As a means of cross talk between cells, EVs show great promise as a source of biomarkers in physiological and pathological conditions. We hypothesize that the miRNA content of EVs represent a potential source of disease biomarkers and should be further investigated for their role in RA and MTX treatment response. Details In our study we are currently assessing the miRNA profile of EVs isolated from blood plasma from RA patients stratified based on their response to MTX treatment, and matched healthy controls by next generation sequencing analysis. Based on preliminary data we expect this global analysis to reveal a suggested subset of RA and/or treatment response specific miRNAs. It would be truly beneficial to conduct validation studies of these miRNA by qPCR in a much larger cohort of patients (N=170). Impact of study Since there currently is no cure for RA, patients depend on early diagnosis combined with an efficient therapeutic intervention that gives the best clinical long-lasting outcome. Patients are usually diagnosed based on the 2010 EULAR/ACR during clinical assessment where several parameters are measured (5). Still, universal RA specific biomarkers are lacking. Our studies may reveal candidate biomarkers for RA and/or treatment response contributing to the overall aim of personalized medicine. Furthermore, studying the miRNA profile of EVs in RA will add to the current focus of understanding the importance of EVs in RA and might lead to future studies of the functional role of these miRNAs. References 1. Haavardsholm EA, Aga AB, Olsen IC, Lillegraven S, Hammer HB, Uhlig T, et al. Ultrasound in management of rheumatoid arthritis: ARCTIC randomised controlled strategy trial. BMJ. 2016;354:i4205. 2. Wielinska J, Crossland RE, Lacina P, Swierkot J, Bugaj B, Dickinson AM, et al. Exploring the Extracellular Vesicle MicroRNA Expression Repertoire in Patients with Rheumatoid Arthritis and Ankylosing Spondylitis Treated with TNF Inhibitors. Dis Markers. 2021;2021:2924935. 3. Boilard E, Nigrovic PA, Larabee K, Watts GF, Coblyn JS, Weinblatt ME, et al. Platelets amplify inflammation in arthritis via collagen-dependent microparticle production. Science. 2010;327(5965):580-3. 4. Yanez-Mo M, Siljander PR, Andreu Z, Zavec AB, Borras FE, Buzas EI, et al. Biological properties of extracellular vesicles and their physiological functions. J Extracell Vesicles. 2015;4:27066. 5. Aletaha D, Neogi T, Silman AJ, Funovits J, Felson DT, Bingham CO, 3rd, et al. 2010 Rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis Rheum. 2010;62(9):2569-81.