A longitudinal cohort study uncovers plasma protein biomarkers predating clinical onset and treatment response of rheumatoid arthritis.

Rheumatoid arthritis (RA) is a systemic inflammatory condition posing challenges in identifying biomarkers for onset, severity and treatment responses. Here we investigate the plasma proteome in a longitudinal cohort of 278 RA patients, alongside 60 at-risk individuals and 99 healthy controls. We observe distinct proteome signatures in at-risk individuals and RA patients, with protein levels alterations correlating with disease activity, notably at DAS28-CRP thresholds of 3.1, 3.8 and 5.0. The combination of methotrexate (MTX) and leflunomide (LEF) modulates proinflammatory pathways, whereas MTX plus hydroxychloroquine (HCQ) impact energy metabolism. A machine-learning model is trained for predicting responses, and achieves average receiver operating characteristic (ROC) scores of 0.88 (MTX + LEF) and 0.82 (MTX + HCQ) in the testing sets. The efficiency of these models is further validated in independent cohorts using enzyme-linked immunosorbent assay data. Overall, our study unveils distinct plasma proteome signatures across various stages and subtypes of RA, providing valuable biomarkers for predicting disease onset and treatment responses.