The objective of this study is to identify a panel of immunological molecular and cellular biomarkers able to predict the success of major dose-reduction or discontinuation of abatacept in rheumatoid arthritis patients

Parameters studied at different time points (before initiation of abatacept if sample is available in our biocollection; prior to dose tapering; prior to discontinuation) ACPA (anti-citrullinated proteins antibodies) repertoire

-IgG (Immunoglobulins G) and/or IgA auto-antibodies repertoire directed against major epitopes of well-known autoantigens

B cell repertoire B cell repertoire and transcriptome of regulatory B lymphocytes, memory B cells and B cells targeting specific autoantigens.

Analysis of type I interferon signature Expression levels of 7 type I interferon (IFN) response genes will be determined to calculate on type I IFN score

Inclusion Criteria:

• Rheumatoid arthritis (RA) patients (> pr = 18 years) fulfilling the 2010 ACR/EULAR criteria
• Associated to high levels (> 3 x upper limit of normal in UA/ml) of ACPA measured by the usual anti-CCP(cyclic citrullinated proteins)2 test at the start of abatacept treatment
• Receiving IV (intravenous) or SC (subcutaneous) abatacept alone or in combination with a conventional Disease Modyfying AntiRheumatic Drugs (cDMARD) (methotrexate, leflunomide, sulfasalasin in monotherapy or in combination) according to the usual scheme or in tapering phase
• Without intra-articular injections of corticosteroids during the last 6 months prior to down-titration of abatacept
• Having discontinued corticosteroids at he time of entrance in the study
• In deep remission (Disease Activity Score (DAS) 28 ESR (or CRP) < 2.6 without clinical synovitis) since at least 1 year
• In sonographic remission at the time of enrollment (absence of PD (Power Doppler)-positive synovitis on 28 joints defined by a score < 2 on a 0-3 semi-quantitative scale for each joint)

Exclusion Criteria:

• Age < 18 years
• RA negative for ACPA (anti-citrullinated proteins antibodies) or not fulfilling ACR/EULAR criteria
• Abatacept discontinuation due to serious adverse event, loss of efficacy or pregnancy project

All ACPA + RA patients from the rheumatology department of Rouen University Hospital receiving IV (intravenous) or SC (subcutaneous) abatacept (according to the usual scheme or having started tapering) and in deep remission (as defined previously) will be included.