ARA criteria is a 7-item tool for RA classification purposes; a patient is said to have RA (meeting endpoint) if he or she has satisfied at least 4 of the 7 criteria. If a participant discontinued due to lack of efficacy, he/she was regarded as meeting primary endpoint also.

Randomized and treated participants were included in analysis if they were RA positive and/or were discontinued due to lack of efficacy. (Those who discontinued due to reasons other than lack of efficacy in 1-year window were excluded from the analysis). 1 participant in Placebo group was excluded due to presence of RA at baseline.

ARA criteria is a 7-item tool for classification purposes; a patient is said to have RA (meeting endpoint) if he or she has satisfied at least 4 of the 7 criteria. If a participant discontinued due to lack of efficacy, he/she was regarded as meeting endpoint also.

Randomized and treated participants were included in analysis if they were RA positive and/or were discontinued due to lack of efficacy. (Those who discontinued due to reasons other than lack of efficacy in 2-year window were excluded from the analysis). 1 subject in the Placebo group is excluded due to presence of RA at baseline.

Clinical diagnosis of other rheumatic diseases at 12 and 24 months. If a participant discontinued due to lack of efficacy, he/she was regarded as meeting endpoint also.

n=Randomized and treated participants who were RA positive and/or were discontinued due to lack of efficacy. (Those who discontinued due to reasons other than lack of efficacy in the 1- or 2-year window were excluded from the analysis).1 participant in Placebo group was excluded due to the presence of RA at baseline.

Mean change from baseline using the Genant-Modified Sharp Score. Erosion score=assessment of 14 sites in each hand and wrist + 6 joints in each foot, using an 8-point scale from 0 (no erosions) to 3.5 (erosions of 100% or articular surfaces). Joint score= assessment of 13 sites in each wrist and hand + 6 sites in each foot using a 9-point scale from 0 (normal) to 4.0 (definite ankylosis). As-observed data. Change from Baseline=postbaseline score at timepoint (6 or 12 or 24 months) minus baseline score; a lower value signifies improvement.

n=participants with a score at baseline and at timepoint

Mean change from baseline. Degree of synovitis and structural joint damage (erosion, edema) of the carpal and metacarpophalangeal joints, as measured by magnetic resonance imaging (MRI) scores using the European League Against Rheumatism (EULAR)-Outcome Measures in Rheumatology Clinical Trials (OMERACT) assessment. Edema scale=0 (no bone involved) to 3 (67% to 100% of bone involved). Synovitis scale=0 (normal) and 1-3 (mild, moderate, severe. Bone erosion scale=0 (0% of bone involved) to 10 (91% to 100% of bone involved). Change from baseline=postbaseline score at timepoint - baseline score.

All randomized and treated participants (n=number of participants with baseline and postbaseline measurements). MRIs were done only in participants at European Union sites.

Synovitis, assessed by clinical signs and symptoms

All randomized and treated participants (n=number of participants with assessment at baseline and timepoint)

SF-36, a 36-item instrument that covers 8 quality of life domains, which were used to derive the physical and mental component summary scores, which ranged from 0 to 100, with higher scores indicating a better quality of life. Change from baseline=postbaseline - baseline value; a higher value signifies improvement.

All randomized and treated participants (n=number of participants with baseline and postbaseline measurements)

To assess pharmacodynamic effect of abatacept on serum levels of autoantibodies, mean change from baseline in cytokines (interleukin-6 [IL-6], interleukin-1B [IL-1B], tumor necrosis factor Alpha [TNF-Alpha], Matrix Metalloproteinase 3T [MMP3T], and anti-CCP2), as measured by standard laboratory investigations, were assessed. Change from baseline=postbaseline value at timepoint (6 or 12 or 24 months) minus baseline value; a lower value signifies improvement.

All randomized and treated participants (n=number of participants with baseline and postbaseline measurements).

To assess the pharmacodynamic effect of abatacept on serum levels of autoantibodies, number of participants with Anti-CCP2 Positive of Rheumatoid Factor (RF) positive

All randomized and treated participants (n=number of participants with measure at timepoint).

To assess the pharmacodynamic effect of abatacept on serum levels of autoantibodies, a blood sample was obtained for HLA typing to determine the presence or absence of alleles associated with RA susceptibility and severity (shared epitope alleles HLA-DRB10401 and HLA-DRB10404).

All randomized and treated participants

The DAS 28 (CRP) is a composite of 4 variables: 28 tender joint count, 28 swollen joint count, CRP, and subject assessment of disease activity measure on a VAS of 100 mm. Change from Baseline=postbaseline score-baseline score; a lower value signifies improvement.

All randomized and treated participants (n=the number of participants with baseline and postbaseline measurements).

The DAS 28 (CRP) is a composite of 4 variables: tender joint count, swollen joint count, CRP, and subject assessment of disease activity measure on a VAS of 100 mm. Scores for disease activity are defined as low (≤ 3.2) and in remission (< 2.6).

All randomized and treated participants (n=the number of participants with baseline and postbaseline measurements).

This questionnaire includes 20 questions assessing physical function in 8 domains. The questions are evaluated on a 4-point scale: 0=without any difficulty, 1=with some difficulty, 2=with much difficulty and 3=unable to do. Higher scores indicate greater dysfunction. HAQ response =improvement of at least 0.3 units from baseline.

All randomized and treated participants (n=the number of participants with baseline and postbaseline measurements).

AEs were monitored at all scheduled visits of the study drug treatment and observation periods and at the follow-up visits performed 28, 56, and 85 days after the last infusion of study medication for participants who were withdrawn prematurely

All subjects who received at least 1 dose of study medication

Immunogenicity, as measured by the number of positive repsonses for serum levels of abatacept-specific antibodies measured by enzyme-linked immunosorbent assays (ELISA). Postive response for whole molecule assessment was a value of > 400 and for tip assessment was ≥25.