• Dana E Orange, Vicky Yao, Kirsty Sawicka, John Fak, Mayu O Frank, Salina Parveen, Nathalie E Blachere, Caryn Hale, Fan Zhang, Soumya Raychaudhuri, Olga G Troyanskaya, and Robert B Darnell.
• From the Laboratory of Molecular Neuro-oncology, Rockefeller University (D.E.O., K.S., J.F., M.O.F., S.P., N.E.B., C.H., R.B.D.), the Hospital for Special Surgery (D.E.O.), and the Simons Foundation (O.G.T.) - all in New York; Rice University, Houston (V.Y.); Princeton University, Princeton, NJ (V.Y., O.G.T.); Howard Hughes Medical Institute, Chevy Chase, MD (N.E.B., R.B.D.); and the Divisions of Rheumatology and Genetics, Brigham and Women's Hospital, Harvard Medical School, Boston, and the Broad Institute, Cambridge - both in Massachusetts (F.Z., S.R.).
• N. Engl. J. Med. 2020 Jul 16; 383 (3): 218-228.

BackgroundRheumatoid arthritis, like many inflammatory diseases, is characterized by episodes of quiescence and exacerbation (flares). The molecular events leading to flares are unknown.MethodsWe established a clinical and technical protocol for repeated home collection of blood in patients with rheumatoid arthritis to allow for longitudinal RNA sequencing (RNA-seq). Specimens were obtained from 364 time points during eight flares over a period of 4 years in our index patient, as well as from 235 time points during flares in three additional patients. We identified transcripts that were differentially expressed before flares and compared these with data from synovial single-cell RNA-seq. Flow cytometry and sorted-blood-cell RNA-seq in additional patients were used to validate the findings.ResultsConsistent changes were observed in blood transcriptional profiles 1 to 2 weeks before a rheumatoid arthritis flare. B-cell activation was followed by expansion of circulating CD45-CD31-PDPN+ preinflammatory mesenchymal, or PRIME, cells in the blood from patients with rheumatoid arthritis; these cells shared features of inflammatory synovial fibroblasts. Levels of circulating PRIME cells decreased during flares in all 4 patients, and flow cytometry and sorted-cell RNA-seq confirmed the presence of PRIME cells in 19 additional patients with rheumatoid arthritis.ConclusionsLongitudinal genomic analysis of rheumatoid arthritis flares revealed PRIME cells in the blood during the period before a flare and suggested a model in which these cells become activated by B cells in the weeks before a flare and subsequently migrate out of the blood into the synovium. (Funded by the National Institutes of Health and others.).Copyright © 2020 Massachusetts Medical Society.

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