Rheumatoid Arthritis Synovial Tissue Biopsy Study

All patients (n=50) included in this trial will be diagnosed with RA according to the ACR/EULAR 2010 classification criteria. They will be eligible for standard-of-care therapy using TNF blockers, because they have active disease despite previous administration of two conventional DMARDs (including methotrexate) for a period of at least 3 months each. Disease activity at study entry (before initiation of TNF blockade) and at 12 weeks will be assessed using DAS28-CRP (composite score that integrates numbers of tender and swollen joints, serum CRP concentrations, and patient's evaluation of disease activity on a visual analogic scale) and EULAR response criteria. All treatments other than TNF blockade will be stable for at least 4 weeks before study entry, and for the whole duration of the study (4 months after initiation of TNF blockade). All clinical assessments will be performed by the investigators. Efficacy will be assessed according to the ACR/EULAR core set of response (DAS28-CRP, CDAI, SDAI, HAQ) of TNFi and JAKi in period 2 for non-responders to TNFi.