Participants received abatacept while also receiving DMARDS over a short term (ST) 12 Week period. To eliminate contribution from the IV loading dose of abatacept during the short term study period, Cmin values were selected from Days 71 to 85, when contribution from IV was negligible. Minimum trough serum concentration of abatacept (Cmin) was measured in micrograms/milliliter (µg/mL). Data are presented by treatment the participant actually received, not by what they were randomized to receive.

50 of the 51 abatacept-treated subjects were included. One subject who discontinued after receiving only Day 1 dosing was not included in this analysis.

Peak serum concentration (Cmax) of abatacept after weekly SC administration was determined between the SC dosing interval from Day 71 to 78. Abatacept in human serum was measured by enzyme-linked immunosorbent assay (ELISA). Lower limit of quantification (LLOQ) was 0.001, Upper limit of quantification (ULOQ) was 0.030. Cmax measured in micrograms per milliliter(µg/mL). Data are presented by treatment the participant actually received, not by what they were randomized to receive.

Pharmacokinetic (PK) analysis set included those participants treated with abatacept and having PK data available

The steady-state pharmacokinetic parameter AUC(TAU) of abatacept after weekly SC administration was determined between the SC dosing interval from Day 71 to 78 (TAU=7 days). Abatacept in human serum was measured by enzyme-linked immunosorbent assay (ELISA). Lower limit of quantification (LLOQ) was 0.001; Upper limit of quantification (ULOQ) was 0.030. AUC(TAU) measured in in micrograms*hours per milliliter (µg*h/mL). Data are presented by treatment the participant actually received, not by what they were randomized to receive.

Pharmacokinetic (PK) analysis set included those participants treated with abatacept and having PK data available.

AEs during variable dose phase of LTE + 56 days post last dose in the variable dose phase or start of the fixed dose phase, which ever came first; includes deaths reported during the variable dose phase including those that occurred greater than 56 days after last dose. Medical Dictionary for Regulatory Activities (MedDRA) version: 15.1. AE=any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that may not have a causal relationship with treatment. SAE=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 (included hospitalizations for elective surgical procedures). Treatment-related=having certain, probable, possible, or missing relationship to study drug. Data presented by treatment the participant was randomized to and not what they actually received.

Participants included those that rolled over into the LTE, receiving variable SC dosing of abatacept in the Variable Dose Period.

Number of Participants with Adverse events (AEs), Serious AEs, discontinuations due to AEs, or Deaths occurring while participant was on treatment from Day 1 (treatment) to Day 85 or early termination from the study. 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 (also included hospitalizations for elective surgical procedures). Data are presented by treatment the participant actually received, not by what they were randomized to receive.

AEs of special interest: infection and/or infestation; neoplasms (benign, malignant, unspecified; autoimmune disorder; infusional AEs (peri-infusional: AEs occurring during first 24 hours (hrs) after start of the IV loading dose; acute infusional: AEs occurring during the first hour after the start of the IV loading dose; injection site AEs: AEs occurring at the site of the SC injection. Data are presented by treatment the participant actually received, not by what they were randomized to receive.

All subjects treated were analyzed for safety.

Serum samples were obtained on Days 1, 8, 15, 29, 57 and day of discharge (Day 85 or earlier) for determination of presence of rheumatoid factor (RF). Baseline was defined as Day 1 to calculate percent change. Lower limit of quantitation (LLQ) was 5 Units/milliliter (U/mL). Values below LLQ were set to 2.5 U/mL. Data are presented by treatment the participant actually received, not by what they were randomized to receive.

Analysis set included all available data from participants who received abatacept or placebo. For RF analysis in Group 1 Day 1/Day 85 number of participants = 7/7; Group 2 = 3/3; Group 3 = 29/29; Group 4 = 6/6; Group 5 = 5/5; Placebo = 17/15 participants.

Blood samples were obtained: At screening, within 24 hours prior to study drug administration on Day 1, on Days 15, 29, 57 and at study discharge. Baseline (BL) defined as Day 1 prior to treatment. Common toxicity criteria (CTC), Version 3 used to assess parameters. lower limit of normal (LLN). ANC=absolute neutrophil count. White blood cells Grade (Gr) 1:\

All participants treated with either abatacept or placebo. Participant counted once in total for each arm but participant could have multiple AEs of different grade. Grade category is number of participants with that Grade of AE (Grades 1, 2, 3, 4)

Screening, BL, Days 15, 29, 57, 85 or discharge. Upper limit of normal (ULN). CTC grade (Gr): Alanine transaminase Gr 1:>ULN to 2.5*ULN; Gr 2: >2.5 to 5.0*ULN; Gr 3: >5.0 to 20.0*ULN; Gr 4: >20.0*ULN. Aspartate aminotransferase Gr 1: >ULN to 2.5*ULN; Gr 2:>2.5 to 5.0*ULN; Gr 3: >5.0 to 20.0*ULN; Gr 4: >20.0*ULN. G-Glutamyl Transferase (U/L) Gr 1:>ULN to 2.5*ULN; Gr 2: >2.5 to 5.0*ULN; Gr 3: >5.0 to 20.0*ULN; Gr 4: >20.0*ULN. Alkaline phosphatase (U/L) Gr 1:>ULN to 2.5*ULN, Gr2:>2.5 to 5.0*ULN, Gr3:>5.0 to 20.0*ULN, Gr4: >20.0*ULN; creatinine (mg/dL) Gr 1: >ULN to 1.5*ULN; Gr 2: >1.5 to 3.0*ULN; Gr 3: >3.0 to 6.0*ULN; Gr 4: >10.0*ULN. Albumin (g/dL) Gr 1:<LLN to 3.0; Gr 2:<3.0 to 2.0; Gr 3: <2.0. Uric Acid (mg/dL)Gr 1: >1.0 x ULN to 10.0; Gr 4: >10.0. Sodium (mEq/L) Gr 1: >ULN to 150; Gr 2: >150 to 155; Gr 3: >155 to 160; Gr 4: > 160. Potassium (mEq/L) Gr 1: >ULN to 5.5; Gr 2: >5.5 to 6.0; Gr 3: >6.0 to 7.0; Gr 4: >7.0. Data presented by treatment participant actually received.

All participants treated with abatacept or placebo in the short term period. Participant is counted once in total but could have multiple AEs of different grade. Grade category is number of participants with that Grade of AE (Grades 1, 2, 3, 4)

Blood pressure (systolic and diastolic) was recorded while the participant was seated during the screening visit, at baseline on Day 1 (prior to administration of IV infusion), prior to administration of all SC injections, and at study discharge (Day 85 or 7 days after the last dose for subjects who terminated early). In addition, blood pressure was recorded at 30 and 60 minutes after the start of the IV infusion on Day 1, and 30 and 60 minutes after all SC injections. Blood pressure was measured in millimeters of mercury (mm Hg). Data are presented by treatment the participant actually received, not by what they were randomized to receive.

All participants who were treated with abatacept or placebo and had vital signs taken were analyzed throughout the 12 weeks. At Day 85 N = 6, 3, 28,6, 5, 17 in groups 1, 2, 3, 4, 5, Placebo, respectively

Pulse rate was taken while participant was seated. Pulse rate was recorded during the screening visit, at baseline on Day 1 (prior to administration of IV infusion), prior to administration of all SC injections, and at study discharge (Day 85 or 7 days after the last dose for subjects who terminated early). In addition, vital signs were recorded at 30 and 60 minutes after the start of the IV infusion on Day 1, and 30 and 60 minutes after all SC injections. Pulse rate measured in beats/min (bpm). Data are presented by treatment the participant actually received, not by what they were randomized to receive.

All participants who were treated with abatacept or placebo and had vital signs taken were analyzed throughout the 12 weeks. At Day 85 N = 6, 3, 28, 6, 5, 17 in groups 1, 2, 3, 4, 5, Placebo, respectively

A 12-lead electrocardiogram (ECG) was recorded at screening and at discharge from the study (Day 85 or 7 days after the last dose of study drug for those subjects who terminated early). If there was no history of known cardiac events, an ECG was performed within 6 months of study entry, and documentation was on file, then the screening ECG was not repeated at screening. QT interval, PR interval and QRW Width were reported in milliseconds (msec). If no ECG issues were found in the 12 weeks of the Short Term Period, ECG was not repeated during LTE. Data are presented by treatment the participant actually received, not by what they were randomized to receive.

A total of 68 participants were treated with abatacept or placebo: 66 had results at screening and 52 had results at Discharge (Day 85) for QT interval and QRS Width; 65 and 51 participants had PR interval results at Screening and Discharge (Day 85), respectively.

LTE period with variable abatacept dosing starting on Day 85 and continuing until Day 533 when LTE fixed dosing started. AEs of special interest: infection and/or infestation; neoplasms (malignant); pre-specified autoimmune disorder; infusional AEs (peri-infusional: pre-specified AEs occurring during first 24 hours (hrs) after start of the IV loading dose; acute infusional: pre-specified AEs occurring during the first hour after the start of the IV loading dose; systemic injection site reactions (SIR): pre-specified AEs for SIR; local injection site reaction: pre-specified AEs for local site reaction. Data are presented by treatment the participant was randomized to and not what they actually received.

All 63 participants who completed the ST period enrolled into the LTE variable dosing period and were analyzed.

A 12-lead electrocardiogram (ECG) was recorded at screening and at discharge from the study (Day 85 or 7 days after the last dose of study drug for those subjects who terminated early). If there was no history of known cardiac events, an ECG was performed within 6 months of study entry, and documentation was on file, then the screening ECG was not repeated at screening. Heart Rate was reported in beats per minute (bpm). In no ECG issues were found in the 12 weeks of the Short Term Period, ECG was not repeated during LTE. Data are presented by treatment the participant actually received, not by what they were randomized to receive.

A total of 68 participants were treated with abatacept or placebo: 65 had results at screening and 53 had results at Discharge (Day 85) for Heart Rate.

On Day 85 participants rolled over into the LTE with variable dose phase first and at Day 533, a fixed dose phase of 125 mg abatacept SC weekly, irrespective of body weight. This summary includes AEs reported during entire LTE treatment plus 56 days post last dose; includes all deaths reported during the LTE including those that occurred greater than 56 days after last dose. MedDRA version: 15.1. 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 (also included hospitalizations for elective surgical procedures). Treatment-related=having certain, probable, possible, or missing relationship to study drug.

total number of participants in the Long Term Extension Period.

Assessment of positive antibody response based upon analysis using a validated enzyme-linked immunosorbent assay (ELISA) with a cut-off value. CTLA4 is a protein receptor that downregulates the immune system. Short Term (ST) period was initial 12 Weeks of the study. Overall LTE includes both the variable and fixed abatacept dosing periods and was from the end of the ST period (Day 85) up to 168 days post last dose (treatment in LTE ranged from 4.4 to 74.2 months. Data in the ST period are summarized by the treatment the participants actually received, while the LT period data are summarized by treatment the participant was randomized to receive.

In the ST period, only subjects treated with abatacept (51) were evaluated for antibodies. In LTE, 61 participants were analyzed for anti-abatacept antibodies, and 62 participants were analyzed for CTLA4-T antibodies. Participants were analyzed during treatment and post-treatment (28, 56, 85, and 168 days post-treatment).