Marked abnormality criteria: Alkaline phosphatase (ALP): >2* ULN, or if BL>ULN then use >3* BL; aspartate aminotransferase (AST): >3* ULN, or if BL>ULN then use >4* BL; alanine aminotransferase (ALT): >3* ULN, or if BL>ULN then use >4* BL; G-Glutamyl transferase (GGT): >2* ULN, or if BL>ULN then use >3* BL; Bilirubin: >2* ULN, or if BL>ULN then use >4* BL; blood urea nitrogen (BUN): >2* BL; creatinine: >1.5* BL

Marked abnormality criteria: Sodium (Na): <0.95*LLN/ >1.05*ULN, or if BL<LLN then use <0.95* BL or >ULN, or if BL>ULN then use>1.05* BL or <LLN; potassium (K): <0.9* LLN/>1.1*ULN, or if BL<LLN then use <0.9* BL or >ULN, or if BL>ULN then use>1.1* BL or <LLN; (Cl): <0.9* LLN/>1.1* ULN, or if BL<LLN then use <0.9* BL or >ULN, or if BL>ULN then use>1.1* BL or <LLN; calcium (Ca): <0.8* LLN/>1.2* ULN, or if BL<LLN then use <0.75* BL or >ULN, or if BL>ULN then use>1.25* BL or <LLN; phosphorous (P): <0.75* LLN/ >1.25* ULN, or if BL<LLN then use 0.67* BL or >ULN, or if BL>ULN then use>1.33* BL or \

MA criteria: serum glucose (Glu): <65 mg/dL/>220 mg/dL;fasting serum Glu: <0.8* LLN/>1.5*ULN,or if BL<LLN then use 0.8*BL or >ULN,or if BL>ULN then use >2.0*BL or <LLN;total protein: <0.9*LLN/>1.1*ULN,or if BL<LLN then use <0.9*BL or >UNL,or if BL>UNL then use >1.1*BL or <LLN; albumin: <0.9*LLN,or if BL<LLN then use <0.75 BL;uric acid: >1.5*ULN,or if BL>ULN then use >2*BL. Urinalysis (Urine protein,urine Glu,urine blood,leukocyte esterase,Red Blood Cells [RBCs], White Blood Cells [WBCs]):Use ≥2 when BL value missing or when pre-dose=0 or 0.5; use ≥3 when pre-dose=1, use ≥4 when pre-dose=2 or 3

Serum samples from all treated adult participants with active rheumatoid arthritis were screened for the presence of drug-specific antibodies using ELISA. Immunogenicity was defined as the presence of a positive anti-abatacept or anti-CTLA4 antibody.

An electrochemiluminescence immunoassay screened sera for drug-specific antibodies; immunocompetition was used to identify specific anti-Abatacept reactivity. CTLA4 and Possibly immunoglobulin (Ig) category=reactivity against extracellular domain of human CTLA4, constant regions of human IgG1, or both (CTLA4Ig; Abatacept molecule). Ig and/or Junction (JNCT)category=reactivity against constant regions and/or hinge region of human IgG1. Drug-induced seropositivity defined as a post-baseline titer higher than Baseline, or any post-baseline positivity if Baseline value was missing. TRT=treatment

Tender joints are an indicator of rheumatoid arthritis. The number of tender joints in a standard 68 joint count was evaluated. The number of tender joints ranges from 0 to 68, where an increased number of tender joints indicates increasing level of disease severity.

Swollen joints are an indicator of rheumatoid arthritis. The number of swollen joints in a standard 66 joint count was evaluated. The number of swollen joints ranges from 0 swollen joints to 66, where an increased number of swollen joints indicates increasing level of disease severity.

The participant self-reported pain assessment is a core component of the American College of Rheumatology (ACR)scoring system, where increasing score indicates increasing level of severity as indicated on a 100 mm Visual Analog Scale, with 0 mm representing no pain and 100 mm representing the most pain possible.

The disability section of the full HAQ includes 20 questions that assess physical functions in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip, and other 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=greater dysfunction. A disability index was calculated by summing the worst scores in each domain and dividing by the number of domains answered.

Participant self-reported global rheumatoid arthritis assessment core component of the ACR scoring system, where increasing score indicates increasing level of severity as indicated on a 100 mm Visual Analog Scale, with 0 mm representing no pain and 100 mm representing the most pain possible.

Physician global rheumatoid arthritis assessment core component of the ACR scoring system, where increasing score indicates increasing level of severity as indicated on a 100 mm Visual Analog Scale, with 0 mm representing no pain and 100 mm representing the most pain possible.

hs-CRP is an acute phase reactant protein that is a clinical marker for rheumatoid arthritis. Levels of hs-CRP can be used to determine the disease activity score.

The DAS28 is a continuous disease measure that is a composite of 4 variables: the 28 tender joint count, the 28 swollen joint count, CRP levels, and participant assessment of disease activity measure on a visual analogue scale. The DAS28 has numeric thresholds that define high disease activity (>5.1), low disease activity (<3.2) and remission (<2.6). A clinically significant response=decrease in DAS28 score of >1.2 from baseline.

RF is an autoantibody (antibody directed against an organism's own tissues) most relevant in rheumatoid arthritis. It is an antibody against the Fc portion of Immunoglobulin (Ig)G, which is itself an antibody. RF and IgG join to form immune complexes that contribute to the disease process. A positive value for RF was >20 IU/mL; a negative value for RF was ≤20 IU/mL.

Participants from the long-term period of the IM101-174 main study who enrolled in the ACP substudy switched to administration of SC abatacept via the ACP for the duration of the substudy. Abatacept was administered using the ACP by the participant or caregiver on Substudy SC on Day 1 and at weekly intervals thereafter. The ACP was a prefilled liquid product device delivering 125 mg abatacept/device (125 mg/mL).

Trough levels of abatacept were evaluated based upon serum samples. Day 1 pharmacokinetics were based on exposure to the pre-filled syringes and did not reflect abatacept exposure via the ACP device.

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP. Trough concentrations in participants who discontinued from the substudy were not summarized descriptively, but were included in the concentration listings.

AE=any new untoward medical occurrence or worsening of a preexisting medical condition which does not necessarily have a causal relationship with this treatment. AEs of special interest are those AEs that may be associated with the use of immunomodulatory drugs including all infections, local injection reactions (prespecified), and systemic injection reactions (within 24 hours of dosing).

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of subcutaneous abatacept administered via the ACP.

BL=baseline; LLN lower limit of normal; ULN=upper limit of normal. Marked abnormality criteria: Hemoglobin: >3 g/dL decrease from BL; Hematocrit: <0.75*BL; Erythrocytes: <0.75*BL; Platelets: <0.67*LLN/>1.5*ULN, or if BL <LLN, use 0.5*BL/<100,000 mm^3; Leukocytes: <0.75*LLN/ >1.25*ULN, or if BL<LLN, use <0.8*BL/>ULN, or if BL>ULN, use >1.2*BL/<LLN; neutrophils+bands: <1.0*10^3 c/uL; eosinophils: >0.750*10^3 c/uL; basophils: >400 mm^3; monocytes: >2000 mm^3; lymphocytes: <0.750*10^3 c/uL/ >7.50*10^3 c/uL.

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

Marked abnormality criteria: Alkaline phosphatase (ALP): >2* ULN, or if BL>ULN then use >3* BL; aspartate aminotransferase (AST): >3* ULN, or if BL>ULN then use >4* BL; alanine aminotransferase (ALT): >3* ULN, or if BL>ULN then use >4* BL; G-Glutamyl transferase (GGT): >2* ULN, or if BL>ULN then use >3* BL; Bilirubin: >2* ULN, or if BL>ULN then use >4* BL; blood urea nitrogen (BUN): >2* BL; creatinine: >1.5* BL

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

Marked abnormality criteria: Sodium (Na): <0.95*LLN/ >1.05*ULN, or if BL<LLN then use <0.95* BL or >ULN, or if BL>ULN then use>1.05* BL or <LLN; potassium (K): <0.9* LLN/>1.1*ULN, or if BL<LLN then use <0.9* BL or >ULN, or if BL>ULN then use>1.1* BL or <LLN; (Cl): <0.9* LLN/>1.1* ULN, or if BL<LLN then use <0.9* BL or >ULN, or if BL>ULN then use>1.1* BL or <LLN; calcium (Ca): <0.8* LLN/>1.2* ULN, or if BL<LLN then use <0.75* BL or >ULN, or if BL>ULN then use>1.25* BL or <LLN; phosphorous (P): <0.75* LLN/ >1.25* ULN, or if BL<LLN then use 0.67* BL or >ULN, or if BL>ULN then use>1.33* BL or \

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

MA criteria: serum glucose (Glu): <65 mg/dL/>220 mg/dL;fasting serum Glu: <0.8* LLN/>1.5*ULN,or if BL<LLN then use 0.8*BL or >ULN,or if BL>ULN then use >2.0*BL or <LLN;total protein: <0.9*LLN/>1.1*ULN,or if BL<LLN then use <0.9*BL or >UNL,or if BL>UNL then use >1.1*BL or <LLN; albumin: <0.9*LLN,or if BL<LLN then use <0.75 BL;uric acid: >1.5*ULN,or if BL>ULN then use >2*BL. Urinalysis (Urine protein,urine Glu,urine blood,leukocyte esterase,Red Blood Cells [RBCs], White Blood Cells [WBCs]):Use ≥2 when BL value missing or when pre-dose=0 or 0.5; use ≥3 when pre-dose=1, use ≥4 when pre-dose=2 or 3

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

As-Treated Population, defined as all participants enrolled in ACP substudy who received at least 1 dose of SC abatacept administered via the ACP.

Serum samples from all treated adult participants with active rheumatoid arthritis were screened for the presence of drug-specific antibodies using ELISA. Immunogenicity was defined as the presence of a positive anti-abatacept or anti-CTLA4 antibody.

Immunogenicity Population, defined as all participants who received at least 1 dose of abatacept administered with the ACP who had at least one post Substudy Day 1 immunogenicity result available.

An electrochemiluminescence immunoassay screened sera for drug-specific antibodies; immunocompetition was used to identify specific anti-Abatacept reactivity. CTLA4 and Possibly immunoglobulin (Ig) category=reactivity against extracellular domain of human CTLA4, constant regions of human IgG1, or both (CTLA4Ig; Abatacept molecule). Ig and/or Junction (JNCT)category=reactivity against constant regions and/or hinge region of human IgG1. Drug-induced seropositivity defined as a post-baseline titer higher than Baseline, or any post-baseline positivity if Baseline value was missing. TRT=treatment

Immunogenicity Population, defined as all participants who received at least 1 dose of abatacept administered with the ACP who had at least one post Substudy Day 1 immunogenicity result available.