Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken on Days 1 and 22 at 0 hour (predose), Day 24 at 48 hour (h) post dose, Day 25 at 72 h post dose, Day 26 at 96 h post dose and Day 29 at 0 h (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy; Blood samples for PK were taken on Day 108 at 48 h post dose, Day 109 at 72 h post dose, Day 110 at 96 h post dose and at Day 113 0h (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. Tmax was measured in hours (h).

Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken on Days 1 and 22 at 0 hour (predose), Day 24 at 48 hour (h) post dose, Day 25 at 72 h post dose, Day 26 at 96 h post dose and Day 29 at 0 h (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy; Blood samples for PK were taken on Day 106 at 0 h (predose), Day 108 at 48 h post dose, Day 109 at 72 h post dose, Day 110 at 96 h post dose and at Day 113 0h (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. AUC(TAU) where TAU = 168 hours was calculated in µg*h/mL

Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken at 0 hour (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy. Blood samples for PK were taken at 0 hour (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. Steady-state trough observed concentration in serum (Cminss) was measured in micrograms/milliliter (μg/mL).

Serum samples for immunogenicity were evaluated for presence of anti-abatacept antibodies using a validated bridging ECL on Day 29 and Day 113. The ECL assay differentiated between 2 antibody specificities: the immunoglobulin (Ig) G and/or junction region and cytotoxic leukocyte antigen 4 (CTLA4) and possibly Ig. A positive immunogenicity response relative to baseline was defined as: A missing baseline immunogenicity measurement and a positive analytical laboratory reported immunogenicity response post-baseline; A negative baseline immunogenicity response and a positive analytical laboratory reported immunogenicity response post-baseline; A positive baseline immunogenicity response and a positive analytical laboratory reported immunogenicity response post-baseline that has a titer value strictly greater than the baseline titer value.

Substudy baseline=Day 1 of Substudy. MTX dose is measured in milligrams per week (mg/wk).

125 mg Abatacept SC was self-administered with an autoinjector starting on Day 29. Participants continued to self-administer abatacept with the autoinjector every 7 days for 3 months.

Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken on Days 1 and 22 at 0 hour (predose), Day 24 at 48 hour (h) post dose, Day 25 at 72 h post dose, Day 26 at 96 h post dose and Day 29 at 0 h (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy; Blood samples for PK were taken on Day 108 at 48 h post dose, Day 109 at 72 h post dose, Day 110 at 96 h post dose and at Day 113 0h (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. Cmax was measured in μg/mL.

PK population: A subset of the treated population with at least 1 PK sample collected/assessed for serum concentration after start of autoinjector. Participants did not miss either 0-hour or 168-hour samples and not missed 2 or more time points in the PK profile.

Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken on Days 1 and 22 at 0 hour (predose), Day 24 at 48 hour (h) post dose, Day 25 at 72 h post dose, Day 26 at 96 h post dose and Day 29 at 0 h (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy; Blood samples for PK were taken on Day 108 at 48 h post dose, Day 109 at 72 h post dose, Day 110 at 96 h post dose and at Day 113 0h (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. Tmax was measured in hours (h).

PK population: A subset of the treated population with at least 1 PK sample collected/assessed for serum concentration after start of autoinjector. Participants did not miss either 0-hour or 168-hour samples and not missed 2 or more time points in the PK profile.

Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken on Days 1 and 22 at 0 hour (predose), Day 24 at 48 hour (h) post dose, Day 25 at 72 h post dose, Day 26 at 96 h post dose and Day 29 at 0 h (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy; Blood samples for PK were taken on Day 106 at 0 h (predose), Day 108 at 48 h post dose, Day 109 at 72 h post dose, Day 110 at 96 h post dose and at Day 113 0h (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. AUC(TAU) where TAU = 168 hours was calculated in µg*h/mL

PK population: A subset of the treated population with at least 1 PK sample collected/assessed for serum concentration after start of autoinjector. Participants did not miss either 0-hour or 168-hour samples and not missed 2 or more time points in the PK profile.

Abatacept SC was self-administered with a BD Hypak™ Physiolis prefilled syringe every 7 days for the first 4 weeks of the substudy until Day 29; Blood samples for PK were taken at 0 hour (predose). On substudy Day 29, participants were switched from the prefilled syringe to the autoinjector. Participants continued to self-administer abatacept with the autoinjector every 7 days following Day 29 for the remaining 3 months of the substudy. Blood samples for PK were taken at 0 hour (predose). Serum concentrations of abatacept were analyzed using a validated ELISA. Steady-state trough observed concentration in serum (Cminss) was measured in micrograms/milliliter (μg/mL).

PK population: A subset of the treated population with at least 1 PK sample collected/assessed for serum concentration after start of autoinjector and with Cmin obtained appropriately (7 days + or -3 days after the previous dose).

Serum samples for immunogenicity were evaluated for presence of anti-abatacept antibodies using a validated bridging ECL on Day 29 and Day 113. The ECL assay differentiated between 2 antibody specificities: the immunoglobulin (Ig) G and/or junction region and cytotoxic leukocyte antigen 4 (CTLA4) and possibly Ig. A positive immunogenicity response relative to baseline was defined as: A missing baseline immunogenicity measurement and a positive analytical laboratory reported immunogenicity response post-baseline; A negative baseline immunogenicity response and a positive analytical laboratory reported immunogenicity response post-baseline; A positive baseline immunogenicity response and a positive analytical laboratory reported immunogenicity response post-baseline that has a titer value strictly greater than the baseline titer value.

A subset of the treated analysis population for whom at least 1 immunogenicity sample was collected and assessed for serum anti-abatacept antibodies, were summarized.

125 mg SC abatacept was self administered weekly via pre-filled syringes from Day 1 up to Day 29 when the participant was switched to self administering 125 mg SC abatacept via the autoinjector device for 3 months.