American College of Rheumatology (ACR) pediatric (PED) 30 response was defined as '≥30% improvement' and '≥3 of the 6 Juvenile Idiopathic Arthritis (JIA) core set' and ≥30% worsening in not more than 1 of the 6 JIA core set variables. JIA core set variables defined as the number of active joints, number of joints with Limit of Motion (LOM), physician's global assessment of disease severity, patient global assessment of overall well being, parent assessment of physical function, and acute phase reactant value. A non-responder imputation was applied.

All Treated Participants: All participants who received at least one dose of study medication

ACR PED 50 response is defined as '≥50% improvement' and '≥3 of the 6 Juvenile Idiopathic Arthritis (JIA) core set' and ≥30% worsening in not more than 1 of the 6 JIA core set variables. ACR PED 70 response is defined as '≥70% improvement' and '≥3 of the 6 JIA core set' and ≥30% worsening in not more than 1 of the 6 JIA core set variables. ACR PED 90 response is defined as '≥90% improvement' and '≥3 of the 6 JIA core set' and ≥30% worsening in not more than 1 of the 6 JIA core set variables. Inactive disease status is defined as no active joints, physician's global assessment of disease severity equal or less than 10mm and C-reactive protein (CRP) within normal limits (0.3 mg/dL). A non-responder imputation is applied. mm=millimeter; mg/dL=milligrams/deciliter

All Treated Participants: All participants who received at least one dose of study medication

Physical function was evaluated using the disability section of the Childhood Health Assessment Questionnaire (CHAQ). The questionnaire was derived from the adult HAQ. The disability section assessed physical functions in 8 domains: dressing and grooming, arising, eating, walking, hygiene, reach, grip and common activities. The questions were 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. A disability index was calculated as the mean of the 8 functional scales. The percentage of Improvement from baseline was calculated using the following equation: (Baseline value - Post-baseline value) / Baseline value x 100.

All Treated Participants: All participants who received at least one dose of study medication

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. SAEs also include hospitalizations for elective surgical procedures. Drug-related=related or missing relationship to study drug. Data includes all events from the date of the first dose of the study drug up to 56 days post the last dose of the study drug in the short-term period or start of the long-term period, whichever occurred first.

All Treated Participants: All participants who received at least one dose of study medication

Cmax was obtained from the serum concentration versus time data after intravenous administration of abatacept. Blood samples were collected at 0 hour (pre-dose) on Days 15 and 29 and at 0 hour (pre-dose) and 0.5 hours (post dose) on Days 57, 85, and 113. A blood sample was also collected on an interim visit that occurred on any day between Day 92 and Day 110. ug/mL=micrograms/milliliter

Pharmacokinetic (PK) Analysis Population: All participants who received at least one dose of study medication and who had at least one adequate PK result reported after start of study medication. The 'n' signifies those participants who received study drug and were evaluated for this measure (each group respectively).

Blood samples were collected at 0 hour (pre-dose) on Days 15 and 29 and at 0 hour (pre-dose) and 0.5 hours (post dose) on Days 57, 85, and 113. A blood sample was also collected on an interim visit that occurred on any day between Day 92 and Day 110. ug/mL=micrograms/milliliter

Pharmacokinetic (PK) Analysis Population: All participants who received at least one dose of study medication and who had at least one adequate PK result reported after start of study medication. The 'n' signifies those participants who received study drug and were evaluated for this measure (each group respectively).

A positive immunogenicity response for 'Cytotoxic T-lymphocyte antigen (CTLA4), Immunoglobulin (Ig)', 'Ig and/or Junction Region', respectively = (1) missing baseline immunogenicity measurement and positive analytical laboratory reported immunogenicity response post-baseline (2) negative baseline immunogenicity response and positive analytical laboratory reported immunogenicity response post-baseline (3) positive baseline immunogenicity response and positive analytical laboratory reported immunogenicity response post-baseline with titer value strictly greater than the baseline titer value. Assessment based on assay cutpoint value. Serum samples were collected prior to study medication at Week 0 (Day 1), Week 8 (Day 57), and Week 16 (Day 113) in the short term period. Participants who early discontinued from the study or complete and did not switch to commercial abatacept had a serum sample collected on final visit or early termination visit, 28, 84 and 168 days after the last dose.

Immunogenicity analysis population: All participants who received at least one dose of study medication and who had at least one immunogenicity result reported after start of study medication