Abatacept (CTLA4-Ig) – a monoclonal antibody which restricts T cell activation – is an effective treatment for rheumatoid arthritis (RA). Herein, we aimed to investigate for biomarkers of response to abatacept. We performed a detailed immunological profiling of CTLA4-treated RA patients’ peripheral blood (PB) cells and sera using flow cytometry and proteomics analysis, respectively. At 6 months of treatment, 34.5% of patients attained clinical response. Notably, baseline levels of Th1 and myeloid cell populations were significantly elevated in PB of responders compared to non-responders (P-value<0.05). Additionally, proteomics analysis revealed 10 amongst 303 molecules which were associated with clinical responses. Should the present data be confirmed in a larger cohort could be of clinical value.