A newly identified circulating cell type may be a reliable marker for impending RA flares. The discovery and description of the cells, which bear a “striking” similarity to synovial fibroblasts, provide important clues to the origins of RA and progressive joint inflammation, investigators say.
Dr. Dana E. Orange
By studying longitudinally collected blood samples from four patients with RA over 4 years, Dana E. Orange, MD and colleagues at Rockefeller University, New York, identified a pattern of B-cell activation and expansion of circulating cells that are negative for CD45 and CD31 expression, and positive for PDPN, dubbed preinflammatory mesenchymal or “PRIME” cells.
Expansion of PRIME cells in circulation increased dramatically in the weeks leading up to a flare and decreased during a flare, suggesting the possibility of a serum assay for predicting flares and allowing for early intervention to ameliorate or prevent disabling consequences, the investigators wrote in a study published in the New England Journal of Medicine.
“Our hope is that this will be a diagnostic in the future, but we need to study it in more patients to see how it will perform,” Dr. Orange said in an interview, adding that the cells, if shown to be pathogenic, could also be targets for new therapeutic strategies.
RNA sequencing
Dr. Orange and colleagues discovered the PRIME cells through a novel clinical and technical protocol involving home collection of blood by patients and longitudinal RNA sequencing to study gene expression profiles during times of both disease quiescence and flares, and noticed a distinct pattern of PRIME cell expansion, depletion, and gene expression.
“Looking at their gene expression profiles, they overlapped with fibroblasts that reside in inflamed rheumatoid arthritis synovium, and in an animal model those types of fibroblasts were important for allowing entry of inflammatory infiltrates around the joint,” she said.
PRIME cells may be a precursor of synovial fibroblasts, which have been implicated by some researchers in the spread of RA between joints, Dr. Orange added.
Patients do homework
The investigators began by enrolling four patients, followed for 1-4 years, who met 2010 American College of Rheumatology–European League Against Rheumatism criteria and who were seropositive for anti–cyclic citrullinated peptide antibodies.
They assessed disease activity from patient homes weekly or during escalation of flares up to four times daily, with the Routine Assessment of Patient Index Data 3 (RAPID3) questionnaire, as well as monthly clinic visits. At clinic visits during flares, disease activity was assessed using both the RAPID3 and 28-joint Disease Activity Score.
The patients performed fingerstick blood collection and mailed the samples overnight each week to Rockefeller University, where RNA was extracted and sequenced. The investigators identified gene transcripts that were differentially expressed in blood prior to flares, and compared them with data profiles derived from synovial single-cell RNA sequencing.
To validate the findings, the researchers used flow cytometry and sorted blood-cell RNA sequencing of samples from an additional 19 patients with RA.
They found that a total of 2,613 genes were differentially expressed during a flare, compared with baseline, and that expression of 1,437 of these genes was increased during a flare, with the remaining 1,176 decreased during flares.