DAS28-CRP remission defined as <2.6; TP=treatment phase; WP=withdrawal phase. The DAS 28-CRP is a measure of disease activity in rheumatoid arthritis (RA) that assesses the 28 joints RA commonly affects; the score includes the number of tender and swollen joints (out of 28), CRP level (a measure of inflammation in the blood), and the patient's global assessment of health (ranging from very good to very bad). These measures are then fed into a complex mathematical formula to produce the overall DAS (a score greater than 5.1 implies active disease; less than 3.2, well controlled disease; and less than 2.6, remission.)

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. Percentage calculated as a/b, where a=number of patients who achieved remission at Month 12 and at both Months 12 and 18, and b=number of patients in the analysis. n=number evaluable

TP=treatment period; WP=withdrawal period. Remission defined as DAS28-CRP<2.6. The DAS 28-CRP is a measure of disease activity in rheumatoid arthritis (RA) that assesses the 28 joints RA commonly affects; the score includes the number of tender and swollen joints (out of 28), CRP level (a measure of inflammation in the blood), and the patient's global assessment of health (ranging from very good to very bad). DAS-CRP scores range from 0 to 10, with higher values indicating greater disease activity. Individual measures are fed into a complex mathematical formula to produce the overall DAS (a score greater than 5.1 implies active disease; less than 3.2, well controlled disease; and less than 2.6, remission.)

All randomized participants who received at least 1 dose of double-blind monotherapy in the Treatment Period. Percentage calculated as a/b, where a=number of patients who achieved remission at Month 12 and at both Months 12 and 18, and b=number of patients in the analysis. n=number evaluable

TP=treatment period; WP=withdrawal period. Remission defined as DAS28-CRP<2.6. The DAS 28-CRP is a measure of disease activity in rheumatoid arthritis (RA) and assesses the 28 joints RA commonly affects; the score includes the number of tender and swollen joints (out of 28), CRP level (a measure of inflammation in the blood), and the patient's global assessment of health (ranging from very good to very bad). DAS-CRP scores range from 0 to 10, with higher values indicating greater disease activity. Individual measures are fed into a complex mathematical formula to produce the overall DAS (a score greater than 5.1 implies active disease; less than 3.2, well controlled disease; and less than 2.6, remission.)

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. Percentage calculated as a/b, where a=number of patients who achieved remission at Day x, and b=number of patients in the analysis (intent to treat).

TP=treatment period; WP=withdrawal period. The DAS 28-CRP is a measure of disease activity in rheumatoid arthritis (RA) that assesses the 28 joints RA commonly affects; the score includes the number of tender and swollen joints (out of 28), CRP level (a measure of inflammation in the blood), and the patient's global assessment of health (ranging from very good to very bad). DAS-CRP scores range from 0 to 10, with higher values indicating greater disease activity. Individual measures are fed into a complex mathematical formula to produce the overall DAS (a score greater than 5.1 implies active disease; less than 3.2, well controlled disease; and less than 2.6, remission.)

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. n=number evaluable

TP=treatment period; WP=withdrawal period. SDAI-defined remission= ≤3.3. The SDAI is the simple linear sum of 5 outcome parameters: tender joint count (TJC) and swollen joint count (SJC) (based on a 28-joint assessment); patient's and physician's global assessments of disease activity (assessed on 0-10 cm visual analog scale, on which higher scores=greater affection due to disease activity); and C-reactive protein level (mg/dL). SDAI total score=0-86. SDAI <=3.3 indicates disease remission, >3.4 to 11=low disease activity, >11 to 26=moderate disease activity, and >26=high disease activity. TJC is assessed and recorded at each visit, with no swelling=0, swelling=1. SJC is assessed through identification of joints that are painful under pressure or to passive motion. TJC is recorded on the joint assessment form at each visit, with no tenderness =0, tenderness = 1. Higher score indicates greater affection due to disease activity.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. Percentage calculated as a/b, where a=number of patients who achieved remission at Months 12 and 18, and b=number of patients in the analysis.

TP=treatment period; WP=withdrawal period. The SDAI is the simple linear sum of 5 outcome parameters: swollen joint count (SJC) and tender joint count (TJC) (based on a 28-joint assessment); patient's and physician's global assessments of disease activity (assessed on 0-10 cm visual analog scale, on which higher scores=greater affection due to disease activity); and C-reactive protein level (mg/dL). SDAI total score=0-86. SJC is assessed and recorded at each visit, with no swelling=0, swelling=1 (higher score indicates greater swelling). TJC is assessed at each visit through identification of joints that are painful under pressure or to passive motion, with no tenderness=0, tenderness=1 (higher score indicates greater affection due to disease activity)..

Intent to Treat (ITT) population. n= number of participants with both post baseline and baseline measurements.

HAQ response defined as a reduction of at least 0.3 units from baseline in score on the Health Assessment Questionnaire Disability Index (HAQ-DI), which assesses patients' functional ability by rating their abilities over the previous week. The HAQ-DI includes at least 2 questions from each of 8 categories: dressing and grooming, hygiene, arising, reach, eating, grip, walking, and common daily activities. Patients rate difficulty performing specific tasks: 0=without difficulty, 1=with some difficulty, 2=with much difficulty, and 3=unable to do. The sum of the categories score (the highest scored item in the category) is divided by the number of categories answered, yielding a score from 0-3. When aids, devices, or help is indicated by the patient, the score for the category item is raised from a 0 or a 1 to a 2, but if the patient's highest score for a subcategory is a 3, it stays a 3.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. Percentage calculated as a/b, where a=number of patients who achieved remission at Day x, and b=number of patients in the analysis.

The Health Assessment Questionnaire Disability Index (HAQ-DI) assesses patients' functional ability by rating their abilities over the previous week. The HAQ-DI includes at least 2 questions from each of 8 categories: dressing and grooming, hygiene, arising, reach, eating, grip, walking, and common daily activities. Patients rate difficulty performing specific tasks: 0=without difficulty, 1=with some difficulty, 2=with much difficulty, and 3=unable to do. The sum of the categories score (the highest scored item in the category) is divided by the number of categories answered, yielding a score from 0-3. When aids, devices, or help is indicated by the patient, the score for the category item is raised from a 0 or a 1 to a 2, but if the patient's highest score for a subcategory is a 3, it stays a 3.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. n=number evaluable

TP=treatment period; WP=withdrawal period. The SF-36 is a 36-item self-administered questionnaire developed to assess health-related quality of life (QOL) and comprises 8 domains, including 4 physical (physical health, bodily pain, physical functioning and physical role limitations) and 4 mental (mental health, vitality, social functioning, and emotional role limitation) subscales. Responses are used to derive physical and mental component summary scores, ranging from 0 to 100, with higher scores indicating better QOL (0=Poorest Health; 100=Best Health). Mean change from baseline=postbaseline value-baseline value; a higher value signifies improvement.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. n=number evaluable

TP=treatment period; WP=withdrawal period. Change from Baseline=Postbaseline-baseline value. MRI was used to assess joint damage progression at Months 6, 12, and 18. If >20% of joints with a missing score for a parameter (erosion, osteitis, and synovitis), the MRI score of each parameter was considered missing. If ≤20% of joints had a missing score for a parameter, the MRI score for that parameter from the missing joints was carried forward from the previous MRI assessment, or carried backward from the next MRI assessment, if missing score occurred at baseline. MRI total score ranged from 0 (best outcome) to 4 (worst outcome). A gadolinium-enhanced MRI of the dominant hand-wrist was performed on all randomized patients at 5 points. The hand/wrist assessed to have more synovitis was selected initially and used for all subsequent evaluations. The MRI examination was standardized to ensure sufficient image quality for the evaluation of radiographic progression of rheumatoid arthritis.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. n=the number of patients with both baseline and postbaseline measurements.

AE=any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that may not have a causal relationship with treatment. SAE=a medical event that at any dose results in death, persistent or significant disability/incapacity, or drug dependency/abuse; is life-threatening, an important medical event, or a congenital anomaly/birth defect; or requires or prolongs hospitalization. Related=having certain, probable, possible, or unknown relationship to study drug.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period

AE=any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that may not have a causal relationship with treatment. SAE=a medical event that at any dose results in death, persistent or significant disability/incapacity, or drug dependency/abuse; is life-threatening, an important medical event, or a congenital anomaly/birth defect; or requires or prolongs hospitalization. Related=having certain, probable, possible, or unknown relationship to study drug. AEs of special interest are events potentially associated with the drug or disease under study.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period

Lower limit of normal (LLN); Upper limit of normal (ULN); Pretreatment (preRX). Criteria for marked abnormality: Platelet count (*10^9 c/µL) <0.67*LLN or >1.5*ULN, or if preRX<LLN, use 0.5*preRX and <100,000/mm^3; potassium, serum (mEq) <0.9*LLN or >1.1*ULN, or if preRX <LLN, use <0.9*preRX or >ULN if preRX>ULN, use >1.1*preRX or <LLN; blood urea nitrogen (mg/dL) >2*preRX; creatinine (mg/dL) >1.5*preRX; ALT (U/L) >3*ULN, or if preRX>ULN, use >4*preRX; AST (U/L) >3*ULN, or if preRX>ULN, use >4*preRX; ALP (U/L) >2*ULN, or if preRX>ULN, use >3*preRX; G-glutamyl transferase U/L) >2*ULN, or if preRX>ULN, use >3*preRX; glucose, fasting (mg/dL) <0.8*LLN or >1.5*ULN, or if preRX<LLN use <0.8*preRX or >ULN if preRX >ULN, use >2.0*preRX or OR <LLN; glucose, serum (mg/dL) <65 or >220; uric acid (mg/dL)>1.5*ULN, or if preRX, use >2*preRX; albumin (g/dL) <0.9*LLN, or if preRX<LLN, use <0.75*preRX; hemoglobin (g/dL)>3 decrease from preRX; hematocrit (%) < 0.75*preRX.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. n=number evaluable

WP=withdrawal period. Remission defined as DAS28-CRP<2.6. The DAS 28-CRP is a measure of disease activity in rheumatoid arthritis (RA) and assesses the 28 joints RA commonly affects; the score includes the number of tender and swollen joints (out of 28), CRP level (a measure of inflammation in the blood), and the patient's global assessment of health (ranging from very good to very bad). DAS-CRP scores range from 0 to 10, with higher values indicating greater disease activity. Individual measures are fed into a complex mathematical formula to produce the overall DAS (a score greater than 5.1 implies active disease; less than 3.2, well controlled disease; and less than 2.6, remission.). Percentage= number of participants with remission divided by number of participants who were analyzed (all treated participants who were in remission at end of treatment period and entered the Withdrawal Period)

Treated participants who were in remission at Month 12 (DAS28-CRP<2.6) and entered the Withdrawal Period were analyzed.( N=number of participants analyzed).

TP=treatment period; WP=withdrawal period. SDAI-defined remission= ≤3.3. The SDAI is the simple linear sum of 5 outcome parameters: tender joint count (TJC) and swollen joint count (SJC) (based on a 28-joint assessment); patient's and physician's global assessments of disease activity (assessed on 0-10 cm visual analog scale, on which higher scores=greater affection due to disease activity); and C-reactive protein level (mg/dL). SDAI total score=0-86. SDAI <=3.3 indicates disease remission, >3.4 to 11=low disease activity, >11 to 26=moderate disease activity, and >26=high disease activity. TJC is assessed and recorded at each visit, with no swelling=0, swelling=1. SJC is assessed through identification of joints that are painful under pressure or to passive motion. TJC is recorded on the joint assessment form at each visit, with no tenderness =0, tenderness = 1. Higher score indicates greater affection due to disease activity. Percent=number with remission/number evaluated (ITT)

ITT analysis population: Included all randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period. Participants were grouped according to the treatment regimen to which they were randomized.N= number evaluated.

AE=any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that may not have a causal relationship with treatment. SAE=a medical event that at any dose results in death, persistent or significant disability/incapacity, or drug dependency/abuse; is life-threatening, an important medical event, or a congenital anomaly/birth defect; or requires or prolongs hospitalization. Includes data up to last active dose date +56 days if the participant discontinued the Treatment Period or did not enter the Withdrawal Period, up to the day of discontinuation in the Withdrawal Period for participants discontinuing the Withdrawal Period without entering the Re-exposure Period (RP), up to Day 729 visit (Month 24) for participants who complete the Withdrawal Period, and up to 56 days post last active dose in Re-exposure Period for participants entering the Re-exposure Period.

All randomized participants who received at least 1 dose of study medication were analyzed.

AE=any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that may not have a causal relationship with treatment. SAE=a medical event that at any dose results in death, persistent or significant disability/incapacity, or drug dependency/abuse; is life-threatening, an important medical event, or a congenital anomaly/birth defect; or requires or prolongs hospitalization. AEs of special interest are events potentially associated with the drug or disease under study. Includes events with an onset date on or after 57 days post last dosing day (active abatacept or active MTX whichever is the later) in the Treatment Period and up to end of Withdrawal Period. Treatment groups represent treatment received during the Treatment Period.

All randomized participants who received at least 1 dose of double-blind study medication in the Treatment Period and entered the Withdrawal Period. Treatment groups represent treatment during the TP.

AE=any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that may not have a causal relationship with treatment. SAE=a medical event that at any dose results in death, persistent or significant disability/incapacity, or drug dependency/abuse; is life-threatening, an important medical event, or a congenital anomaly/birth defect; or requires or prolongs hospitalization. AEs of special interest are events potentially associated with the drug or disease under study. Includes data up to 56 days post the last dosing day (active abatacept or active MTX, whichever is the later) in the Re-exposure Period. Treatment groups represent Treatment received during Treatment Period.

Includes data up to 56 days post the last dosing day (active abatacept or active MTX, whichever is the later) in the Re-exposure Period. Treatment groups represent Treatment received during Treatment Period.

LLN=lower limit of normal; ULN=upper limit of normal; preRX=pretreatment. Criteria for marked abnormality on laboratory test results: Platelet count (*10^9 c/µL) <0.67*LLN or >1.5*ULN, or if preRX<LLN, use 0.5*preRX and <100,000/mm^3; potassium, serum (mEq) <0.9*LLN or >1.1*ULN, or if preRX <LLN, use <0.9*preRX or >ULN if preRX>ULN, use >1.1*preRX or <LLN; blood urea nitrogen (mg/dL) >2*preRX; creatinine (mg/dL) >1.5*preRX; ALT (U/L) >3*ULN, or if preRX>ULN, use >4*preRX; AST (U/L) >3*ULN, or if preRX>ULN, use >4*preRX; ALP (U/L) >2*ULN, or if preRX>ULN, use >3*preRX; G-glutamyl transferase (GGT) (U/L) >2*ULN, or if preRX>ULN, use >3*preRX; glucose, fasting (mg/dL) <0.8*LLN or >1.5*ULN, or if preRX<LLN use <0.8*preRX or >ULN if preRX >ULN, use >2.0*preRX or OR <LLN; glucose, serum (mg/dL) <65 or >220; uric acid (mg/dL)>1.5*ULN, or if preRX, use >2*preRX; albumin (g/dL) <0.9*LLN, or if preRX<LLN, use <0.75*preRX; hemoglobin (g/dL)>3 decrease from preRX; hematocrit (%) < 0.75*preRX.

All randomized participants who received at least 1 dose of study drug in the Treatment Period, entered the Withdrawal Period, and had values available. n=number evaluable

LLN=lower limit of normal; ULN=upper limit of normal; preRX=pretreatment. Criteria for marked abnormality on laboratory test results: Platelet count (*10^9 c/µL) <0.67*LLN or >1.5*ULN, or if preRX<LLN, use 0.5*preRX and <100,000/mm^3; potassium, serum (mEq) <0.9*LLN or >1.1*ULN, or if preRX <LLN, use <0.9*preRX or >ULN if preRX>ULN, use >1.1*preRX or <LLN; blood urea nitrogen (mg/dL) >2*preRX; creatinine (mg/dL) >1.5*preRX; ALT (U/L) >3*ULN, or if preRX>ULN, use >4*preRX; AST (U/L) >3*ULN, or if preRX>ULN, use >4*preRX; ALP (U/L) >2*ULN, or if preRX>ULN, use >3*preRX; G-glutamyl transferase U/L) >2*ULN, or if preRX>ULN, use >3*preRX; glucose, fasting (mg/dL) <0.8*LLN or >1.5*ULN, or if preRX<LLN use <0.8*preRX or >ULN if preRX >ULN, use >2.0*preRX or OR <LLN; glucose, serum (mg/dL) <65 or >220; uric acid (mg/dL)>1.5*ULN, or if preRX, use >2*preRX; albumin (g/dL) <0.9*LLN, or if preRX<LLN, use <0.75*preRX; hemoglobin (g/dL)>3 decrease from preRX; hematocrit (%) < 0.75*preRX.

All treated participants entering the Re-exposure Period and having measurements available were analyzed. n=evaluable. Treatment groups represent Treatment received during Treatment Period.