ELISA is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. For anti-abatacept antibody ELISA, a sample was considered seropositive if it had a titer of 400 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 400. A sample was considered positive in CTLA4-T antibody ELISA if it had a titer of 25 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 25.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses.

DAS28-CRP is a continuous variable which is a composite of 4 variables: the number of tender joint out of 28, the number of swollen joint out of 28, C-reactive protein (CRP) in milligrams/Liter (mg/L) and subject assessment of disease activity measure on a VAS of 100mm. DAS 28 = 0.56 * sqrt(tender28) + 0.28 * sqrt(swollen28) + 0.36 * ln(CRP+1) + 0.014 * VAS + 0.96.

All treated participants included those participants who received at least 1 dose of the study medication (abatacept) in the ST period with baseline and post-baseline values.

ELISA is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. For anti-abatacept antibody ELISA, a sample was considered seropositive if it had a titer of 400 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 400. A sample was considered positive in CTLA4-T antibody ELISA if it had a titer of 25 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 25.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses. n = those participants who were evaluated for this measure at each timepoint, for each group respectively.

The ECL (MSD) assay method is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. It is more sensitive and has a higher drug tolerance than ELISA method. For the anti-abatacept antibody ECL (MSD) assay, a sample was considered seropositive if it had a titer of 10 or greater and if immunodepletion was observed with abatacept, or abatacept and CTLA4-T. Those responses that were not positive in the initial screen or were not confirmed to be positive based on immunodepletion were reported as seronegative and were assigned a value of < 10.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses. n=number of participants who were evaluated for this measure at each timepoint, for each group respectively.

ELISA is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. For anti-abatacept antibody ELISA, a sample was considered seropositive if it had a titer of 400 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 400. A sample was considered positive in CTLA4-T antibody ELISA if it had a titer of 25 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 25.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses. There were no positive Immunoglobulin G (IMG) samples on Day 113, therefore this analysis was not necessary.

The ECL (MSD) assay method is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. It is more sensitive and has a higher drug tolerance than the ELISA method. For anti-abatacept antibody ECL (MSD) assay, a sample was considered seropositive if it had a titer of 10 or greater and if immunodepletion was observed with abatacept, or abatacept and CTLA4-T. Those responses that were not positive in the initial screen or were not confirmed to be positive based on immunodepletion were reported as seronegative and were assigned a value of < 10.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses. There were no positive IMG samples on Day 113, therefore this analysis was not necessary.

ELISA is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. For anti-abatacept antibody ELISA, a sample was considered seropositive if it had a titer of 400 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 400. A sample was considered positive in CTLA4-T antibody ELISA if it had a titer of 25 or greater and if immunodepletion was observed. The responses that were negative in initial screen were reported as seronegative with a value of < 25.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses.The overall percentage of subjects who had at least one positive sample was very low, therefore this analysis was not necessary.

The ECL (MSD) assay method is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum . It is more sensitive and has a higher drug tolerance than the ELISA method. For anti-abatacept antibody ECL(MSD) assay, a sample was considered seropositive if it had a titer of 10 or greater and if immunodepletion was observed with abatacept, or abatacept and CTLA4-T. Those responses that were not positive in the initial screen or were not confirmed to be positive based on immunodepletion were reported as seronegative and were assigned a value of < 10.

Treated participants in the ST period who were evaluable for anti-abatacept or anti-CTLA4-T responses. The overall percentage of subjects who had at least one positive sample was very low, therefore this analysis was not necessary.

A clinically meaningful improvement is defined as a greater than or equal to 1.2 reduction in DAS28-CRP score from baseline.

All treated participants included those participants who received at least 1 dose of the study medication (abatacept) in the ST period with baseline and post-baseline values.

HAQ-DI takes into account participant's use of aids or devices or assistance in scoring algorithm for a disability category. The questionnaire includes 20 questions assessing physical function in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip, and common activities. 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. The score is calculated by summing worst scores in each domain and dividing by the number of domains answered.

All treated participants included those participants who received at least 1 dose of the study medication (abatacept) in the ST period with baseline and post-baseline values.

HAQ-DI takes into account participant's use of aids or devices or assistance in scoring algorithm for a disability category. The questionnaire includes 20 questions assessing physical function in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip, and common activities. 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. The score is calculated by summing worst scores in each domain and dividing by the number of domains answered.

All treated participants included those participants who received at least 1 dose of the study medication (abatacept) in the ST period. n is the number of participants with baseline and post-baseline values.

RF is an autoantibody that is usually present in the serum of people with rheumatoid arthritis. The cut-point value for seroconversion was 15 IU/mL (>= 15 IU/mL resulted in a positive result). Cross-tabulation of frequency of seroconversion of RF at Day 113 with baseline, in the ST period, was provided.

All treated participants included those participants who received at least 1 dose of the study medication (abatacept) in the ST period.

AEs: any new untoward medical occurrences/worsening of pre-existing medical condition, whether or not related to study drug. SAE: any AE that resulted in death; was life threatening; resulted in persistent/significant disability/incapacity; resulted in/prolonged an existing in-patient hospitalization; was a congenital anomaly/birth defect; or was an overdose. Participants who discontinued the study due to any AEs or SAEs were recorded.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period, were included in the safety analyses.

Drug-related AEs are those events with a relationship to the study therapy of certain; probable; possible; or missing. Drug-related SAEs are those events with any relationship to the study therapy.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period, were included in the safety analyses.

An AE was defined as any new untoward medical occurrence or worsening of a pre-existing medical condition (even if not caused by the study drug). For this study, AEs of particular importance were associated with the use of immunomodulatory agents: infections, autoimmune disorders, malignancies, and injection reaction AEs (systemic AEs occurring within 24 hours of SC injection and local injection site reactions) were recorded.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period, were included in the safety analyses.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following hematology MA definitions specify the criteria for the data presented. Hemoglobin: >3 g/dL decrease from pre-treatment (pre Rx); hematocrit: <0.75 * pre-Rx value; platelet count: <0.67 * (LLN -lower limit of normal) (or, if pre-Rx value <LLN, then <0.5 * pre-Rx value and <100,000/mm^3); leukocytes: <0.75 * LLN or >1.25 * ULN (or, if pre-Rx value <LLN, then <0.8 * pre-Rx or >(ULN -upper limit of normal) ; erythrocytes: <0.75 * pre Rx.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following hematology MA definitions specify the criteria for the data presented. Neutrophils + bands (absolute): <1.00 * 10^3cells/microlitre (uL); lymphocytes (absolute): <0.75 * 10^3 cells/uL or >7.50 * 10^3 cells/uL; monocytes (absolute): >2.00 * 10^3 cells/uL; basophils (absolute): >0.40 * 10^3 cells/uL; eosinophils (absolute): >0.75 * 10^3 cells/uL.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept)in the ST period.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following serum chemistry MA definitions specify MA criteria. ALP: >2.0 * ULN (if pre-Rx > ULN, then >3 * pre-Rx); AST, ALT: > 3 * ULN (if pre-Rx > ULN, then > 4 * pre-Rx); bilirubin (total): >2 * ULN, or if pre Rx > ULN then >4 * Pre Rx; BUN : >2 * pre Rx; GGT : >2 * ULN, or if pre Rx > ULN then >3 * pre Rx.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period.

MAs= laboratory measurements marked as abnormal: creatinine: >1.5 * pre-Rx; sodium (serum):<0.95 * LLN or >1.05 * ULN (if pre-Rx < LLN, then <0.95 * pre-Rx or >1.05 * ULN. If pre-Rx > ULN, then >0.95 * pre-Rx or < ULN); potassium (serum):<0.9 * LLN or >1.1 * ULN (if pre-Rx < LLN, then <0.9 * pre-Rx or > ULN; chloride (serum),protein (total):<0.9 * LLN or >1.1 8 ULN (if pre-Rx < LLN, then <0.9 * pre-Rx or > ULN. If pre-Rx > ULN, then >1.1 * pre-Rx or < LLN); calcium (total): <0.8 * LLN or >1.2 * ULN (if pre-Rx < LLN, then <0.9 * pre-Rx or > ULN. If pre-Rx > ULN, then >0.75 * pre-Rx or < ULN).

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following serum chemistry MA definitions specify MA criteria. Glucose (fasting serum): <0.8 * LLN or >1.5 ULN (if pre-Rx <LLN, then <2.0 * pre-Rx or >ULN; albumin: <0.9 * LLN (if pre-Rx < LLN, then <0.75 * pre-Rx); uric acid: >1.5 * ULN (if pre-Rx > ULN, then >2.0 * pre-Rx); phosphorous (inorganic):<0.75 * LLN or >1.25 * ULN (if pre-Rx < ULN, then <0.67 * pre-Rx or < ULN. If pre-Rx > ULN, then >1.33 * re-Rx or < LLN); glucose (serum): <65 mg/dL or >220 mg/dL.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period, n= number of participants evaluated for this measure.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following definitions specify the criteria for MAs in urinalysis: protein, glucose, blood, leukocyte esterase, RBC, WBC: >= 2+ (or, if value >= 4, or if pre-Rx value = 0 or 0.5, then >= 2x or if pre-Rx value =1, then >= 3, or if pre-Rx = 2 or 3, then >= 4).

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period, n= number of participants evaluated for this measure.

ANA status was categorized as negative or positive corresponding to the following dilutions: less than 1:160 and greater than equal to 1:160.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period.

Anti-dsDNA antibody status was categorized as negative or positive based upon assay-specific numeric cut-off values.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period.

Vital signs measurements (including seated blood pressure, heart rate and temperature) were recorded. The investigator used his/her clinical judgment to decide whether or not abnormalities in vital signs/physical examination were clinically meaningful.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period.

Cmin serum abatacept concentration was obtained directly from the concentration-time data.

All treated participants analysis population included all participants who received at least 1 dose of study medication (abatacept) in the ST period. n=those participants who received study drug and were evaluated for this measure at the timepoint for each group respectively.

The Meso-Scale Discovery (MSD) electrochemiluminescence (ECL) assay method is a validated, sensitive assay technique used to analyze presence of abatacept-specific antibodies in serum. It is more sensitive and has a higher drug tolerance than ELISA method. For the anti-abatacept antibody ECL (MSD) assay, a sample was considered seropositive if it had a titer of 10 or greater and if immunodepletion was observed with abatacept, or abatacept and CTLA4-T. Those responses that were not positive in the initial screen or were not confirmed to be positive based on immunodepletion were reported as seronegative and were assigned a value of < 10. Antibody responses included CTLA4 and possibly immune globulin (IG), IG and/or junction region.

Participants who received at least 1 dose of abatacept in the LTE Study and who had values at each specified timepoint, were evaluated.

DAS28-CRP is a continuous variable which is a composite of 4 variables: the number of tender joints out of 28, the number of swollen joints out of 28, C-reactive protein (CRP) in milligrams/Liter (mg/L) and subject assessment of disease activity measure on a VAS of 100mm. DAS 28 = 0.56 * sqrt(tender28) + 0.28 * sqrt(swollen28) + 0.36 * ln(CRP+1) + 0.014 * VAS + 0.96. Baseline was Day 1 of the ST Study; Day 113 was the end of the ST Study.

Participants who received at least 1 dose of abatacept in the LTE Study and who had DAS28-CRP values at Baseline, Day 113 and Day 1345, were evaluated.

A clinically meaningful improvement is defined as a greater than or equal to 1.2 reduction in DAS28-CRP score from baseline. Baseline was Day 1 of the ST Study. Day 113 was the end of the ST Study.

Participants who received at least 1 dose of abatacept in the LTE Study and who had values at Baseline, Day 113 and Day 1345, were evaluated.

DAS28-CRP remission was defined as DAS28-CRP less than 2.6 and LDA was defined as DAS28-CRP less than, equal to 3.2. End of ST Study was Day 113.

Participants who received at least 1 dose of abatacept in the LTE study and who had values at Day 113 and Day 1345, were evaluated.

HAQ-DI takes into account participant's use of aids or devices or assistance in scoring algorithm for a disability category. The questionnaire includes 20 questions assessing physical function in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip, and common activities. 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. The score is calculated by summing worst scores in each domain and dividing by the number of domains answered. Baseline was Day 1 in the ST Study and Day 113 was the last day of the ST Study.

Participants who received at least 1 dose of abatacept in the LTE study and who had values at Baseline, Day 113 and Day 1345, were evaluated.

HAQ response was defined as an improvement of at least 0.3 units from baseline in the HAQ Disability Index (HAQ DI). Baseline was Day 1 of the ST Study and Day 113 was the last day of the ST Study.

Participants who received at least 1 dose of abatacept in the LTE study and who had values at Baseline, Day 113 and Day 1345, were evaluated.

RF is an autoantibody that is usually present in the serum of people with rheumatoid arthritis. The cut-point value for seroconversion was 15 IU/mL (>= 15 IU/mL resulted in a positive result).

Participants who received at least 1 dose of abatacept in the LTE and who had an RF test result up to 7 days post the last dose of abatacept in the LTE study, were evaluated.

Abatacept Monotherapy Subgroup consisted of participants who received SC abatacept and did not receive MTX in the ST and LTE Studies. DAS28-CRP: continuous variable which is a composite of 4 variables:number of tender joints out of 28, number of swollen joints out of 28, C-reactive protein (CRP) in mg/L and self assessment of disease activity measure on a VAS of 100mm. DAS 28 = 0.56 * sqrt(tender28) + 0.28 * sqrt(swollen28) + 0.36 * ln(CRP+1) + 0.014 * VAS + 0.96. HAQ-DI includes 20 questions assessing physical function in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip, and common activities 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. The score sums worst scores in each domain and divides by the number of domains answered. Baseline was Day 1 of Short Term Study. Day 113 was the last day of the Short Term Study.

Participants who received abatacept monotherapy (at least 1 dose of abatacept and no MTX) in the ST and LTE Studies and who had values at Baseline, Day 113, and Day 1345, were evaluated.

Remission was defined as DAS 28-CRP < 2.6 and LDA was defined as DAS 28-CRP <= 3.2. End of ST Study was Day 113. Abatacept Monotherapy Subgroup was defined as those participants who received as at least 1 dose of abatacept and did not receive MTX in the ST and LTE Studies.

Participants who received abatacept monotherapy (at least 1 dose of abatacept and no MTX) in the ST and LTE Studies, and who had values at Day 113 and Day 1345, were evaluated.

AEs: any new untoward medical occurrences/worsening of pre-existing medical condition, whether or not related to study drug. SAE: any AE that resulted in death; was life threatening; resulted in persistent/significant disability/incapacity; resulted in/prolonged an existing in-patient hospitalization; was a congenital anomaly/birth defect; or was an overdose. Drug-related AEs/SAEs are those events with a relationship to the study therapy of certain; probable; possible; or missing.

Participants who received at least 1 dose of abatacept in the LTE Study and who had events up to 56 days post the last dose of abatacept in the LTE period, were evaluated. Includes all deaths reported during the LTE including those that occurred greater than 56 days after the last dose.

An AE was defined as any new untoward medical occurrence or worsening of a pre-existing medical condition (even if not caused by the study drug). For this study, AEs of particular importance were associated with the use of immunomodulatory agents: infections, autoimmune disorders, malignancies, and injection reaction AEs (systemic AEs occurring within 24 hours of SC injection and local injection site reactions) were recorded.

Participants who received at least 1 dose of abatacept in the LTE Study and who had events up to 56 days post the last dose of abatacept in the LTE Study, were evaluated.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following hematology MA definitions specify the criteria for the data presented. Hemoglobin: >3 g/dL decrease from pre-treatment (pre Rx); hematocrit: <0.75 * pre-Rx value; platelet count: <0.67 * (LLN -lower limit of normal) (or, if pre-Rx value <LLN, then <0.5 * pre-Rx value and <100,000/mm^3); leukocytes: <0.75 * LLN or >1.25 * ULN (or, if pre-Rx value <LLN, then <0.8 * pre-Rx or >(ULN -upper limit of normal) ; erythrocytes: <0.75 * pre Rx. Neutrophils + bands (absolute): <1.00 * 10^3cells/microlitre (uL); lymphocytes (absolute): <0.75 * 10^3 cells/uL or >7.50 * 10^3 cells/uL; monocytes (absolute): >2.00 * 10^3 cells/uL; basophils (absolute): >0.40 * 10^3 cells/uL; eosinophils (absolute): >0.75 * 10^3 cells/uL.

Participants who received at least 1 dose of abatacept in the LTE Study and who had specified laboratory values up to 56 days post the last dose of abatacept in the LTE Study, were evaluated. n=number of participants evaluated.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. Alkaline Phosphatase (ALP), Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT), Bilirubin (Total), G-Glutamyl Transferase (G-GT), Blood Urea Nitrogen (BUN) and Creatinine MA criteria: ALP: >2.0 * ULN (if pre-Rx > ULN, then >3 * pre-Rx); AST, ALT: > 3 * ULN (if pre-Rx > ULN, then > 4 * pre-Rx); bilirubin (total): >2 * ULN, or if pre Rx > ULN then >4 * Pre Rx; BUN : >2 * pre Rx; GGT : >2 * ULN, or if pre Rx > ULN then >3 * pre Rx; creatinine: >1.5 * pre-Rx.

Participants who received at least 1 dose of abatacept in the LTE Study and with specified laboratory values up to 56 days post the last dose of abatacept in the LTE Study, were evaluated. n=number of participants evaluated.

Sodium (serum):<0.95 * LLN or >1.05 * ULN (if pre-Rx < LLN, then <0.95 * pre-Rx or >1.05 * ULN. If pre-Rx > ULN, then >0.95 * pre-Rx or < ULN); potassium (serum):<0.9 * LLN or >1.1 * ULN (if pre-Rx < LLN, then <0.9 * pre-Rx or > ULN; chloride (serum),protein (total):<0.9 * LLN or >1.1 8 ULN (if pre-Rx < LLN, then <0.9 * pre-Rx or > ULN. If pre-Rx > ULN, then >1.1 * pre-Rx or < LLN); calcium (total): <0.8 * LLN or >1.2 * ULN (if pre-Rx < LLN, then <0.9 * pre-Rx or > ULN. If pre-Rx > ULN, then >0.75 * pre-Rx or < ULN); phosphorous (inorganic):<0.75 * LLN or >1.25 * ULN (if pre-Rx < ULN, then <0.67 * pre-Rx or < ULN. If pre-Rx > ULN, then >1.33 * re-Rx or <LLN); glucose (serum): <65 mg/dL or >220 mg/dL; Glucose (fasting serum): <0.8 * LLN or >1.5 ULN (if pre-Rx <LLN, then <2.0 * pre-Rx or >ULN; albumin: <0.9 * LLN (if pre-Rx < LLN, then <0.75 * pre-Rx); uric acid: >1.5 * ULN (if pre-Rx > ULN, then >2.0 * pre-Rx).

Participants who received at least 1 dose of abatacept in the LTE Study and who had specified laboratory values up to 56 days post the last dose of abatacept in the LTE study, were summarized. n=number of participants evaluated.

MAs are laboratory measurements marked as abnormal, per pre-defined study criteria, at any study time point. The following definitions specify the criteria for MAs in urinalysis: protein, glucose, blood, leukocyte esterase, RBC, WBC: >= 2+ (or, if value >= 4, or if pre-Rx value = 0 or 0.5, then >= 2x or if pre-Rx value =1, then >= 3, or if pre-Rx = 2 or 3, then >= 4).

Participants who received at least 1 dose of abatacept in the LTE Study and who had specified laboratory values up to 56 days post the last dose of abatacept in the LTE period, were evaluated. n=number of participants evaluated.