Sub-study-A Phase IIIB Multicenter, Randomized, Double-Blind, Double-Dummy Study to Compare the Efficacy and Safety of Abatacept Administered Subcutaneously and Intravenously in Subjects With Rheumatoid Arthritis, Receiving Background Methotrexate, and Experiencing an Inadequate Response to Methotrexate

Number of Participants With Death, Serious Adverse Events (SAEs), Treatment-related SAEs, SAEs Leading to Discontinuation, Adverse Events (AEs), Treatment-related AEs, and AEs Leading to Discontinuation

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to the 1st dose of non-ACP subcutaneous (SC) abatacept, assessed up to 12 months

An AE is any new unfavorable symptom, sign, or disease or worsening of a preexisting condition that does not necessarily have a causal relationship with treatment. An SAE is any unfavorable medical event that at any dose results in death, persistent or significant disability/incapacity, or drug dependency or abuse; is life-threatening, an important medical event, or a congenital anomaly/birth defect; or requires or prolongs hospitalization. Treatment-related=possibly, probably, or certainly related to and of unknown relationship to study treatment.

Number of Participants With AEs of Special Interest in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 56 days post last ACP dose

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).

Number of Participants With Laboratory Test Results in Hematology Meeting the Criteria for Marked Abnormality in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

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.

Number of Participants With Liver Function Laboratories Meeting MA Criteria in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

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

Number of Participants With Electrolyte Laboratories Meeting MA Criteria in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

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 \<LLN

Number of Participants With Other Chemistry and Urinalysis Laboratories Meeting MA Criteria in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

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

Mean Systolic Blood Pressure (SBP) Over Time in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

Mean Diastolic Blood Pressure (DBP) Over Time in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

Mean Heart Rate Over Time in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.

Mean Temperature Over Time in the ACP Device Substudy

Time Frame: ACP substudy Day 1 to last substudy assessment occurring prior to 1st dose of non-ACP SC abatacept (administered once participants switched back to main study). For participants discontinuing both studies: Day 1 of ACP dosing to 7 days post last ACP dose.