The ACR 50 definition of improvement is a 50% improvement over baseline in tender and swollen joint counts (#1 and #2) and a 50% improvement in 3 of the 5 remaining core data set measures (Participant global assessment of pain, participant global assessment of disease activity, physician global assessment of disease activity, participant assessment of physical function, and acute phase reactant value). Baseline value is the last assessment taken prior to first dose of single-blind study medication.

Simple Disease Activity Index (SDAI) is calculated using the following formula: TJC + SJC + PGA + MDGA + CRP (TJC = number of painful joints from 28 joints, SJC = number of swollen joints from 28 joints, PGA = patient global assessment on a visual analog scale 0-10 cm, MDGA = physician global assessment on a visual analog scale 0-10 cm, and CRP = c-reactive protein in mg/dL) SDAI Remission is defined as SDAI \<= 3.3. Using a logistic regression model that includes treatment arm, randomization stratification factor, and baseline SDAI as continuous variable and point estimate of adjusted ORs, corresponding 95% CI and p-value was provided. SDAI total score range: 0 to 86. SDAI \<= 3.3 indicates disease remission and SDAI \>26 = high disease activity.

Abatacept SC was self-administered with a prefilled syringe every 7 days for the first 4 weeks until Day 29; Blood samples for PK were taken pre-dose (0 hour) on Days 29 and 113. Serum concentrations of abatacept were analyzed using a validated enzyme-linked immunosorbent assay (ELISA). Steady-state trough observed concentration in serum (Cminss) was measured in micrograms/milliliter (μg/mL). Adjusted geometric mean and 90% confidence interval (CI) are presented.

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.)

Proportion(%)=number of participants meeting criteria (n) divided by number of participants who received drug (N). The ACR score indicates degree of improvement in a patient's rheumatoid arthritis (RA), based on guidelines set forth by the ACR and represents a percentage. To qualify a ACR20 score, patient must have \>=20% fewer tender joints and \>=20% fewer swollen joints and show 20% improvement from baseline in at least 3 of: patient overall assessment of his/her RA, physician global assessment of the patient's RA, patient self-assessment of pain, patient self-assessment of physical functioning, and results of an erythrocyte sedimentation rate or C-reactive protein (CRP) test (to assess inflammation). Baseline was Day 1. Randomization was stratified using screening Disease Activity Score-28 (DAS28) CRP, a composite of 4 variables: number of tender joints/28, number of swollen joints/28, CRP in mg/L and participant assessment of disease activity with visual analogue scale.

LOCF=last observation carried forward. PDUS assessed the degree of synovial inflammation of the MCP joints (2nd to 5th) of both hands and was performed at approximately the same time of day for each participant. Total PDUS scores are independent of the presence and grade of joint effusion and are evaluated as follows: Grade 0 or normal=normal joint (no synovial hypertrophy, no Doppler signal); Grade 1 or minimal=minimal synovitis (minimal synovial hypertrophy, with ≤Grade 1 Doppler signal); Grade 2 or moderate=moderate synovitis (moderate synovial hypertrophy with ≤Grade 2 Doppler signal or minimal synovial hypertrophy and Grade 2 Doppler signal; Grade 3 or severe=severe synovitis (severe synovial hypertrophy with ≤Grade 3 Doppler signal or minimal or moderate synovial hypertrophy and Grade 3 Doppler signal). Each joint is rated 1 to 3, for a total possible score ranging from 8 to 24 (8\*1, 8\*3) for 2 hands. Higher grade/score=more severe disease. Change=score Day x - baseline score.

MCP=metacarpophalangeal; PDUS=power Doppler ultrasonography. Time point at which early signs of Global PDUS improvement were observed=earliest time point for which 0 was not included in the 95% confidence interval for the mean changes from baseline in Global PDUS (MCP 2-5) score at that and all later time points. Total PDUS scores are independent of the presence and grade of joint effusion: Grade (Gr) 0 or normal=normal joint (no synovial hypertrophy \[SH\], no Doppler signal); Gr 1 or minimal=minimal synovitis (minimal SH, with ≤Gr 1 Doppler signal); Gr 2 or moderate=moderate synovitis (moderate SH, with ≤Gr 2 Doppler signal or minimal SH and grade 2 Doppler signal); Gr 3 or severe=severe synovitis (severe SH with ≤Gr 3 Doppler signal or minimal or moderate SH and Gr 3 Doppler signal). Each joint is rated 1 to 3, for a total possible score ranging from 8 to 24 (8\*1, 8\*3) for the 2 hands. Higher Gr/score=more severe disease.

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

Serum samples from Abatacept-treated adult participants with active RA 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.

The ACR 20 is based on 20% improvement (compared with baseline values) in tender and swollen joint counts and on 20% improvement in 3 of the remaining 5 core set measures (participant global assessment of pain, participant global assessment of disease activity, physician global assessment of disease activity, participant assessment of physical function) and 1 acute phase reactant value.

AE=any new untoward medical occurrence or worsening of a preexisting medical condition which does not necessarily have a causal relationship with this treatment. Related AE=relationship of certain, probable, possible, or missing. SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in the development of drug dependency or drug abuse, is an important medical event.

An event of disease relapse was defined as additional Disease-modifying antirheumatic drug (DMARD) therapy given, or 2 or more courses of high steroids given, or return to abatacept 10 mg/kg (rescue medication given), or DAS28 C-reactive protein (CRP) score \>=3.2 at 2 consecutive visits. Time to disease relapse was evaluated using life tables (Kaplan-Meier Cumulative Percentage of Events of Disease Relapse).

AE is defined as any new untoward medical occurrence or worsening of a pre-existing medical condition. SAE is any untoward medical occurrence that at any dose results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a cancer, is a congenital anomaly/birth defect, results in the development of drug dependency or drug abuse, is an important medical event. Both subjective and objective AEs and SAEs are included.

The laboratory tests were analyses included enzyme, gastrointestinal, hematology, hepatobiliary, lipid, metabolic, nutritional, blood gas, microbiology, serology, protein, chemistry, renal, urinary tract, urinalyses, water, electrolyte and mineral investigations.

Number of participants who achieved remission at Month 12 of treatment, as defined by a Disease Activity Score (DAS) 28-CRP score of \<2.6. DAS 28-CRP is a continuous measure, a composite of 4 variables: number of tender joints out of 28 joints, number of swollen joints out of 28 joints, CRP (in mg/L), and subject assessment of disease activity measure on a Visual Analogue Scale (VAS) of 100 millimeters (mm). The DAS28 scale=0 (best) to 10 (worst), indicating the current activity of the rheumatoid arthritis. A DAS28 \>5.1 = high disease activity; \<=3.2 = low disease activity; \<2.6 = remission.

To assess joint damage progression, the Genant-modified Sharp scoring method was used to evaluate radiographs of hands/wrists and feet for erosions and joint space narrowing (JSN). The total Genant-modified Sharp score ranges from 0 (no radiographic damage) to 290 (worst possible radiographic damage) and is the sum of the erosion score (range 0-145) and the joint space narrowing score (range 0-145). Higher scores indicated more damage.

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition in a subject administered an investigational product and that does not necessarily have a causal relationship with this treatment. Related AE/SAE=Certain, Probable, Possible, or Missing. SAE=any untoward medical occurrence that results in death, is life-threatening, requires or prolongs inpatient hospitalization (including elective surgery), results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, or is an important medical event.

SAE=any untoward medical occurrence that results in death, is life-threatening, requires or prolongs inpatient hospitalization (including elective surgery), results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, or is an important medical event.

Any untoward medical occurrence (SAE) that resulted in death

The incidence rates of autoimmune disorders are defined as the (number of patients experiencing the event/exposure within the period)\*100 and are expressed in 100 person-years. Subjects experiencing the event had their exposure censored at the time of the 1st event.

The incidence rates of infections and infestations are defined as the (number of patients experiencing the event /exposure within the period)\*100 and are expressed in 100 person-years. Subjects experiencing the event had their exposure censored at the time of the 1st event.

The incidence rates of malignant neoplasms are defined as the (number of patients experiencing the event /exposure within the period)\*100 and are expressed in 100 person-years. Subjects experiencing the event had their exposure censored at the time of the 1st event.

There were 107 Prespecified, acute-infusional SAEs (occurring within 1 hour after the start of study drug infusion) pre-specified in the protocol; anaphylactic shock was the only one occuring in this study.

Number of subjects with high liver function and kinedy tests: alkaline phosphatase (ALP) \>2x upper limit of normal (ULN) or if pretreatment (PRE-RX) \>ULN then \>3x PRE-RX; aspartate aminotransferase (AST) \>3x ULN or if PRE-RX \>ULN then \>4x PRE-RX; alanine aminotransferase (ALT) \>3x ULN or if PRE-RX \>ULN then \>4x PRE-RX; g-glutamyl transferase (GGT)\>2x ULN or if PRE-RX \>ULN then \>3x PRE-RX; total bilirubin \>2x ULN or if PRE-RX \>ULN then \>4x PRE-RX; blood urea nitrogen \>2x PRE-RX; creatinine \>1.5x PRE-RX.

Marked abnormalities in hemoglobin \>3 g/dL decrease from PRE-RX; hematocrit \<0.75x PRE-RX; erythrocytes \<0.75x PRE-RX; platelet count \<0.67x lower limit of normal (LLN) or \>1.5x ULN or if PRE-RX \<LLN then \<0.5x PRE-RX and \<100,000/mm3; leukocytes \<0.75x LLN or \>1.25x ULN or if PRE-RX \<LLN then \<0.8x PRE-RX or \>ULN if PRE-RX \>ULN then \>1.2x PRE-RX or \<LLN; neutrophils if value \<1.00 x10\^3 c/uL; lymphocytes if value \<.750 x10\^3 c/uL or if value \>7.50 x10\^3 c/uL; monocytes if value \>2000/MM3; basophils if value \>400/mm3; eosinophils if value \>.750 x10\^3 c/uL

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with treatment.SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event.Related AE/SAE=Certain,Probable,Possible,or Missing relationship to Drug

AE=any new untoward medical occurrence or worsening of a pre-existing 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, serious infections, and opportunistic infections; autoimmune disorders; neoplasms; acute infusional AEs (pre-specified AEs occurring within 1 hour of start of infusion) and peri-infusional AEs (pre-specified AEs occurring within 24 hours of the start of infusion).

Upper Normal Limit (ULN), Lower Normal Limit (LLN), Baseline (BL). Marked abnormality criteria are: Hemoglobin (HGB): \>3 g/dL decrease from BL; Hematocrit: \<0.75 \* BL; Erythrocytes: \<0.75 \* BL; Platelets (PLT): \<0.67 \* LLN/\>1.5 \* ULN, or if BL \< LLN then use 0.5 \* BL/\<100,000 mm\^3; Leukocytes: \<0.75 \* LLN/ \>1.25 \* ULN, or if BL\<LLN then use \<0.8 \* BL/\>ULN, or if BL\>ULN then 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.

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; chloride: \<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

Marked abnormality 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; 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 value ≥4,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 (RA) 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.

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with treatment.SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event.Related AE/SAE=Certain,Probable,Possible,or Missing relationship to Drug

AE=any new untoward medical occurrence or worsening of a pre-existing 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, serious infections, and opportunistic infections; autoimmune disorders; neoplasms; acute infusional AEs (pre-specified AEs occurring within 1 hour of start of infusion) and peri-infusional AEs (pre-specified AEs occurring within 24 hours of the start of infusion).

ULN=upper limit of normal; LLN=lower limit of normal; BL=baseline. 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.

Marked abnormality criteria: Alkaline phosphatase (ALP): \>2\*ULN, or if BL\>ULN, use \>3\*BL; aspartate aminotransferase (AST): \>3\*ULN, or if BL\>ULN,use \>4\*BL; alanine aminotransferase (ALT): \>3\*ULN, or if BL\>ULN, use \>4\*BL; G-Glutamyl transferase (GGT): \>2\*ULN, or if BL\>ULN, use \>3\*BL; bilirubin: \>2\*ULN, or if BL\>ULN, 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; chloride: \<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

Marked abnormality 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; 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 value ≥4,or when pre-dose=0 or 0.5. Use ≥3 when pre-dose=1. Use ≥4 when pre-dose=2 or 3

HGB normal range (NR)=11.6 - 16.2 g/dL, marked abnormality (MA) is \>3 g/dL decrease from BL. Total protein NR=6.0 - 8.4 g/dL, MA is \<0.9\* LLN/\>1.1\* ULN; Albumin NR=3.5 - 5.3 g/dL, MA is \<0.9\* LLN, or if BL\<LLN then use \<0.75 BL

The hematocrit value refers to the percentage of blood volume that is occupied by red blood cells. Hematocrit values for participants were expressed as percentages and were averaged to yield a group mean value (percentage) at a particular time point. The mean change from baseline in hematocrit value (expressed as a percent)= mean post-baseline value (expressed as a percent) - mean baseline value (expressed as a percent).

Erythrocytes NR= 3.80 - 5.50 \*10\^6 c/uL, MA is \<0.75 \* BL

Erythrocytes NR= 3.80 - 5.50 \*10\^6 c/uL, MA is \<0.75 \* BL

Leukocytes NR=4.1 - 12.3\*10\^3 c/uL, MA is \<0.75 \* LLN/ \>1.25 \* ULN, or if BL\<LLN then use \<0.8 \* BL/\>ULN, or if BL\>ULN then use \>1.2 \* BL/\<LLN. Neutrophils+bands MA is \<1.0 \* 10\^3 c/uL. Eosinophils MA is \>0.750 \* 10\^3 c/uL. Basophils MA is \> 400 mm\^3. Monocytes MA is \>2000 mm\^3. Lymphocytes MA is \<0.750 \* 10\^3 c/uL/ \>7.50 \* 10\^3 c/uL

HGB normal range (NR)=11.6 - 16.2 g/dL, marked abnormality (MA) is \>3 g/dL decrease from BL. Total protein NR=6.0 - 8.4 g/dL, MA is \<0.9\* LLN/\>1.1\* ULN; Albumin NR=3.5 - 5.3 g/dL, MA is \<0.9\* LLN, or if BL\<LLN then use \<0.75 BL

Bilirubin NR=0.2-1.2 mg/dL, MA: \>2\* ULN, or if BL\>ULN then use \>4\* BL. BUN NR=4.0-24.0 mg/dL, MA: \>2\*BL. Creatinine NR=0.4-1.2 mg/dL, MA: \>1.5\*BL. Ca NR=8.8-10.2 mg/dL, MA: \<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. P NR=2.8-4.0 mg/dL, MA: \<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. Glu MA: \<65 mg/dL/ \>220 mg/dL. Uric acid MA: \>1.5\*ULN, or if BL\>ULN then use \>2\*BL.

Na NR=132 - 147 mEq/L, MA is 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. K NR=3.3 - 5.5 mEq/L, MA is \<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 NR=94 - 111 mEq/L, MA is \<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

Measurements were taken in a seated position before and after abatacept infusion.

Measurements were taken in a seated position before and after abatacept infusion.

ACR 20 response requires a participant to have a 20% reduction in the number of swollen and tender joints, and a reduction of 20% in three of the following five parameters: physician global assessment of disease, participant global assessment of disease, participant assessment of pain, C-reactive protein or erythrocyte sedimentation rate, and degree of disability in Health Assessment Questionnaire (HAQ) score. A participant achieved a sustained ACR 20 response if the participant had ACR 20 observed for at least 2 consecutive study visits.

The disability section of the full HAQ includes 20 questions to assess physical functions in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip and 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. Clinically meaningful HAQ response=an improvement of at least 0.3 units from baseline in HAQ disability Index.

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with treatment. SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event.Related AE/SAE=Certain,Probable,Possible,or Missing relationship to Drug

AE=any new untoward medical occurrence or worsening of a pre-existing 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, serious infections, and opportunistic infections; autoimmune disorders; neoplasms; acute infusional AEs (pre-specified AEs occurring within 1 hour of start of infusion) and peri-infusional AEs (pre-specified AEs occurring within 24 hours of the start of infusion).

Upper Normal Limit (ULN), Lower Normal Limit (LLN), Baseline (BL). Marked abnormality criteria are: Hemoglobin (HGB): \>3 g/dL decrease from BL; Hematocrit: \<0.75 \* BL; Erythrocytes: \<0.75 \* BL; Platelets (PLT): \<0.67 \* LLN/\>1.5 \* ULN, or if BL \< LLN then use 0.5 \* BL/\<100,000 mm\^3; Leukocytes: \<0.75 \* LLN/ \>1.25 \* ULN, or if BL\<LLN then use \<0.8 \* BL/\>ULN, or if BL\>ULN then 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.

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

Serum samples collected from participants were used to determine serum levels of IgA, IgM, and IgG. Time-matched baseline values were presented by visit and represented the mean baseline value for only that cohort of participants with serum samples available at that visit.

Serum samples collected from participants were used to determine serum levels of IgA, IgM, and IgG. Time-matched mean change from baseline = Post-baseline value - time-matched baseline value, where the time-matched baseline value represents the mean baseline value for only that cohort of participants with serum samples available at that visit.

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with this treatment. SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event. Related SAE/AE = possibly, probably, or certainly related to study drug

AE=any new untoward medical occurrence or worsening of a pre-existing 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, serious infections, and opportunistic infections; autoimmune disorders; neoplasms; acute infusional AEs (pre-specified AEs occurring within 1 hour of start of infusion) and peri-infusional AEs (pre-specified AEs occurring within 24 hours of the start of infusion).

Upper Normal Limit (ULN), Lower Normal Limit (LLN), Baseline (BL). Marked abnormality criteria are: Hemoglobin (HGB): \>3 g/dL decrease from BL; Hematocrit: \<0.75 \* BL; Erythrocytes: \<0.75 \* BL; Platelets (PLT): \<0.67 \* LLN/\>1.5 \* ULN, or if BL \< LLN then use \<0.5 \* BL and \<100,000 mm\^3; Leukocytes: \<0.75 \* LLN/ \>1.25 \* ULN, or if BL\<LLN then use \<0.8 \* BL or \>ULN, or if BL\>ULN then use \>1.2 \* BL or \<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.

ULN=upper level of normal; BL=baseline.Marked abnormality criteria: High alkaline phosphatase (ALP): \>2\* ULN, or if BL\>ULN then use \>3\* BL; high aspartate aminotransferase (AST): \>3\* ULN (80 U/L), or if BL\>ULN then use \>4\* BL; high alanine aminotransferase (ALT): \>3\* ULN (34-47 U/L), or if BL\>ULN then use \>4\* BL; high G-Glutamyl transferase (GGT): \>2\* ULN, or if BL\>ULN then use \>3\* BL; high bilirubin: \>2\* ULN, or if BL\>ULN then use \>4\* BL; high blood urea nitrogen (BUN): \>2\* BL; high creatinine: \>1.5\* BL (ULN 14.6 pg/mg. AST ULN=80 U/L; ALT ULN=34-47 U/L;creatinine ULN=14.6 pg/mg.

Physical examinations were performed at the discretion of the investigator and included breast examinations for female participants. Vital sign measurements were performed for participants before and after infusion of study medication at each visit and included seated systolic blood pressure, seated diastolic blood pressure, temperature, and heart rate. Abnormalities were determined to be clinically significant by the investigator.

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with this treatment. SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event. Related SAE/AE = possibly, probably, or certainly related to study drug

AE=any new untoward medical occurrence or worsening of a pre-existing 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, serious infections, and opportunistic infections; autoimmune disorders; neoplasms; acute infusional AEs (pre-specified AEs occurring within 1 hour of start of infusion) and peri-infusional AEs (pre-specified AEs occurring within 24 hours of the start of infusion).

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 \<LLN

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

Physical examinations were performed at the discretion of the investigator and included breast examinations for female participants. Vital sign measurements were performed for participants before and after infusion of study medication at each visit and included seated systolic blood pressure, seated diastolic blood pressure, temperature, and heart rate. Abnormalities were determined to be clinically significant by the investigator.

ACR 20 response requires a patient to have a 20% reduction in the number of swollen and tender joints, and a reduction of 20% in three of the following five parameters: physician global assessment of disease, patient global assessment of disease, patient assessment of pain, C-reactive protein or erythrocyte sedimentation rate, and degree of disability in Health Assessment Questionnaire (HAQ) score. A participant achieved a sustained ACR 20 response if the participant had ACR 20 observed for at least 2 consecutive study visits.

The HAQ-DI includes 20 questions to assess physical function in 8 domains: dressing, arising, eating, walking, hygiene, reach, grip, and common activities. The domain questions are evaluated on a 4-point scale: 0=without any difficulty, 1=with some difficulty, 2=with much difficulty, 3=unable to do. HAQ-DI=sum of worst scores in each domain dividied by the number of domains answered. HAQ-DI ranges from 0 to a maximum overall score of 3.0. Clinically meaningful HAQ response was defined as an improvement of at least 0.3 units from baseline in HAQ DI.

To assess joint damage progression, the Genant-modified Sharp scoring method was used to evaluate radiographs of hands/wrists and feet for erosions. The erosion score range is 0 (no radiographic damage) to 145 (worst possible radiographic damage). Change from baseline = Post-baseline - Baseline value

AE was defined as any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with this treatment. SAE was defined as any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event.

Marked abnormality criteria are: Hemoglobin (HGB): \>3 g/dL decrease from BL; Hematocrit: \<0.75 \* BL; Erythrocytes: \<0.75 \* BL; Platelets (PLT): \<0.67 \* LLN/\>1.5 \* ULN, or if BL \< LLN then use \<0.5 \* BL and \<100,000 mm\^3; Leukocytes: \<0.75 \* LLN/ \>1.25 \* ULN, or if BL\<LLN then use \<0.8 \* BL or \>ULN, or if BL\>ULN then use \>1.2 \* BL or \<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.

Marked abnormality criteria are: Hemoglobin (HGB): \>3 g/dL decrease from BL; Hematocrit: \<0.75 \* BL; Erythrocytes: \<0.75 \* BL; Platelets (PLT): \<0.67 \* LLN/\>1.5 \* ULN, or if BL \< LLN then use \<0.5 \* BL and \<100,000 mm\^3; Leukocytes: \<0.75 \* LLN/ \>1.25 \* ULN, or if BL\<LLN then use \<0.8 \* BL or \>ULN, or if BL\>ULN then use \>1.2 \* BL or \<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.

Sodium \< 0.9 \* LLN or \> 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: \< 0.9 \* LLN or \> 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; Chloride: \< 0.9 \* LLN or \> 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 \<0.8 \* LLN or \> 1.2 \* ULN or if BL \< LLN then use \<0.67 \* BL or \> ULN or if BL \> ULN then use \> 1.3 \* BL or \< LLN.

Glucose: \< 65 mg/dL or \> 220 mg/dL; Fasting Glucose: \<0.8 \* LLN or \> 1.5 \* ULN or if BL \< LLN then use \< 0.8 \* BL or \> ULN or if BL \> ULN then use 1.1 \* BL or \< LLN; Total protein: \< 0.9 \* LLN or 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; Albumin: \< 0.9 \* LLN or if BL \< LLN then use 0.75 \* BL; Uric acid: \> 1.5 \* ULN or if BL \> ULN then use \> 2.0 \* BL. All urinalysis abnormalities were defined as: if missing BL then use \>= 2 or if value \>=4, or if BL = 0 or 0.5 then use \>= 2, or if BL = 1.0 then use \>= 3, or if BL = 2.0 then use \>=4.

Mean baseline values are those that are reported for each cohort at each time point on Day 365, Day 729, and Day 1,093.

Participants with titers to abatacept in the DB and OL periods. Serum samples from abatacept-treated adult participants with active Rheumatoid Arthritis (RA) were screened for the presence of drug-specific antibodies using two validated direct-format enzyme-linked immunosorbent assays (ELISAs) to determine the presence of antibodies to abatacept and or CTLA4-T.

Vital signs included body temperature, heart rate, and seated blood pressure. Clinically significant changes were defined as those that were not within the normal range for the participant.

AEs were defined as any new untoward medical occurrence or worsening of a pre- existing medical condition which does not necessarily have a causal relationship with this treatment. AEs of special interest have been identified to be those which may be associated with the use of immunomodulatory agents or infusion of therapeutic proteins. Acute infusional AEs were defined as those that occurred within 1 hour after the start of the infusion.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Mean baseline values are those that are reported for each cohort at each time point on Day 365 to Day 2,185.

All changes in participant laboratory parameters were monitored on each day of study drug administration.

Assess inhibition \& progression of structural damage in MTX inadequate responders with moderate to severe active RA on SC Abatacept plus MTX, utilizing eMRI and X-ray at baseline, eMRI at Week 12, and eMRI and X-ray final assessment at week 24.

The ACR score of 20 indicates the degree of improvement in a patient's rheumatoid arthritis (RA), based on ACR guidelines (ACR20). The ACR score represents a percentage. To qualify for an ACR20 score, the patient must have \>=20% fewer tender joints and \>=20% fewer swollen joints and show 20% improvement in at least 3 of: patient overall assessment of his/her RA, physician global assessment of the patient's RA, patient self-assessment of pain, patient self-assessment of physical functioning, and results of an erythrocyte sedimentation rate or C-reactive protein test (to assess inflammation). Percentage is calculated n/N with n=number of participants with ACR score of 20 and N= all randomized participants who received at least one dose of study drug.

The ACR score indicates the degree of improvement in a patient's rheumatoid arthritis (RA), based on ACR guidelines. The ACR score= a percentage. To qualify for a score of 20, 50 or 70 (ACR20, ACR50 or ACR70), the patient must have \>=20%, \>=50% or \>=70%, respectively, fewer tender joints and \>=20%, \>=50% or \>=70%, respectively, fewer swollen joints and show 20%, 50% or 70%, respectively, improvement in at least 3 of the following: patient overall assessment of his/her RA, physician global assessment of the patient's RA, patient self-assessment of pain, patient self-assessment of physical functioning, and results of an erythrocyte sedimentation rate or C-reactive protein test (to assess inflammation). Treatment groups represent treatment received in the short term period. Percentage calculated as n/m with n=number of paticipants with sustained ACR response at Day 533; m= long term participants who received at least one dose of drug and were ACR responders in the short term period.

Adjusted mean. The Health Assessment Questionnaire Disability Index (HAQ-DI) assesses patients' functional ability by rating their abilities over the previous week. At least 2 questions are asked 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. Treatment groups represent treatment received in the short term period. Baseline is Day 1 of the study or last non-missing pre-treatment value.

The Health Assessment Questionnaire (HAQ) disability index assesses patients' functional ability by rating their abilities over the previous week. At least 2 questions are asked 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 higher the number the worse the outcome. 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. HAQ response=reduction of at least 0.30 units in HAQ score from baseline. The percentage of participants with a reduction of at least 0.30 units in their HAQ score from baseline is presented. Baseline is Day 1 of the study or last non-missing pre-treatment value. Treatment groups represent treatment received in the short term period.

The Disease Activity Score 28 using C-Reactive Protein (DAS28-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). An overall DAS \>5.1 implies active disease; \<3.2, well controlled disease; and \<2.6, remission.). Treatment groups represent treatment received in the short term period. Baseline is Day 1 of the study or last non-missing pre-treatment value.

ACR 20 response requires a participant to have a 20% reduction in the number of swollen and tender joints, and a reduction of 20% in three of the following five parameters: physician global assessment of disease, participant global assessment of disease, participant assessment of pain, C-reactive protein or erythrocyte sedimentation rate, and degree of disability in Health Assessment Questionnaire score. A participant achieved a sustained ACR 20 response if the participant had ACR 20 observed for at least 2 consecutive study visits.

The number of participants receiving concomitant rheumatoid arthritis treatment with disease modifying rheumatic drugs and/or biologics.

AE=any new untoward medical occurrence or worsening of a pre-existing medical condition which does not necessarily have a causal relationship with treatment.SAE=any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or causes prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, results in development of drug dependency or drug abuse, is an important medical event. Related AE/SAE=Certain,Probable,Possible,or Missing relationship to drug.

AEs were defined as any new untoward medical occurrence or worsening of a pre- existing medical condition which does not necessarily have a causal relationship with this treatment. AEs of special interest were those which may be associated with the use of immunomodulatory agents or infusion of therapeutic proteins. Acute infusional AEs were defined as those that occurred within 1 hour after the start of the infusion. Peri-Infusional AEs were defined as those that occurred within 24 hours after the start of the infusion.

Time-matched baseline (Day 0) values and post-baseline values were presented for each post-baseline visit and represent only that cohort of participants with measurements available at that post-baseline assessment. Mean Change from Baseline data for these cohorts are presented in Outcome Measure 6.

Blood samples for immunoglobulin assessments were obtained to determine change from baseline in serum IgA. Baseline data for these time-matched cohorts are presented in Outcome Measure 5.

Time-matched baseline (Day 0) values and post-baseline vales were presented for each post-baseline visit and represent only that cohort of participants with measurements available at that post-baseline assessment. Mean Change from Baseline data for these cohorts are presented in Outcome Measure 8.

Blood samples for immunoglobulin assessments were obtained to determine change from baseline in serum IgG. Baseline data for these cohorts are presented in Outcome Measure 7.

Time-matched baseline (Day 0) values and post-baseline values were presented for each post-baseline visit and represent only that cohort of participants with measurements available at that post-baseline assessment. Mean Change from Baseline data for these cohorts are presented in Outcome Measure 10.

Blood samples for immunoglobulin assessments were obtained to determine change from baseline in serum IgM. Baseline data for these time-matched cohorts are presented in Outcome Measure 9.

Maximum Observed Serum Concentration

Area under the serum concentration-time curve from time zero extrapolated to infinity

Serum concentrations of abatacept were analyzed using a validated enzyme-linked immunosorbent assay (ELISA). Cmax was measured in micrograms per milliliter (μg/mL). Blood samples for pharmacokinetic (PK) parameters were collected at Day 1 pre-dose at 0 hour (h), 1, 2, and 8 h post dose, and on subsequent Days, 2 (24 h post dose), 3 (48 h), 5 (96 h), 8 (168 h), 15 (336 h), 29 (672 h) , 43 (1008 h), 57 (1344 h) and 71 (1680 h) following the single administration of abatacept SC.

Serum concentrations of abatacept were analyzed using ELISA. AUC (0-T) was measured in μg\*h/mL. Blood samples were collected at Day 1 pre-dose at 0 h, 1, 2, and 8 h post dose, and on subsequent Days, 2 (24 h post dose), 3 (48 h), 5 (96 h), 8 (168 h), 15 (336 h), 29 (672 h) , 43 (1008 h), 57 (1344 h) and 71 (1680 h) following the single administration of abatacept SC.

Serum concentrations of abatacept were analyzed using ELISA. Blood samples were collected at Day 1 pre-dose at 0 hour (h), 1, 2, and 8 h post dose, and on subsequent Days, 2 (24 h post dose), 3 (48 h), 5 (96 h), 8 (168 h), 15 (336 h), 29 (672 h) , 43 (1008 h), 57 (1344 h) and 71 (1680 h) following the single administration of abatacept SC. AUC (INF) was measured in μg\*h/mL

Cmax was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). Cmax was measured in micro grams per milliliter (µg/mL).

Tmax was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). Tmax was measured in hours (h).

AUC (0 - 28) was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). AUC (0 - 28) was measured in micro grams\*hours per milliliter (µg\*h/mL).

AUC (0 - T) was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). AUC (0 - T) was measured in micro grams\*hour per milliliter (µg\*h/mL).

AUC (0 - INF) was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). AUC (0 - INF) was measured in µg\*h/mL.

T-HALF was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). T-HALF was measured in hours (h).

CLT was the volume of abatacept cleared by the system, normalized by baseline body weight. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). CLT was measured in milliliters per hours per kilogram of body weight (mL/h/kg).

Vss was derived from serum concentration versus time data. Serum samples were analyzed for abatacept by a validated enzyme-linked immunosorbent assay (ELISA) and were obtained at: predose (0 hours), 0.25 hours (h), 0.5, 1, 2, 6, 12, 24, 72, 168, 336, 504, 672, 1008, 1344, and 1688 h post dose (Days 1 to 71). The results were summarized. The lower limit of assay quantitation (LLOQ) was 1.00 nanograms per milliliter (ng/mL). Vss was measured in liters per kg body weight (L/kg).

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.

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.

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.

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.