The objective of this study was to identify specific gene expression profiles able to predict the response of rheumatoid arthritis patients treated with methotrexate /abatacept (Aba). Thirty six RA patients were received Abatacept. The drug efficacy was evaluated with the DAS28 score after 6 months of treatment according to the EULAR response criteria. Among 36 Aba RA patients, 17 were responders and 19 were classified as no-responders. A blood sample was carried out in patients just before the first injection of treatment in PaxGene tubes. Two color experiments : patient(Cy5)/Control pool (Cy3).