The SLE Flare Index categorizes SLE flare as "mild or moderate" or "severe" based on a positive assessment for at least 1 of 5 variables as follows: Change in SELENA SLEDAI score from the most recent assessment to current; Change in signs or symptoms of disease activity; Change in prednisone dosage; Use of new medications for disease activity or hospitalization; Change in Physician's Global Assessment (PGA) score; Hospitalization for SLE activity is an additional category included only for a severe flare. Time to first severe flare is defined as (event date-Day 0 visit date) + 1 for Long-term discontinuation, treatment control groups and holiday phase group. For holiday phase group data censored at last flare assessment by treatment re-start date. Time to first severe flare is defined as (event date-treatment re-start date) + 1 for Re-start treatment holiday group. Median time to first severe SFI flare is reported; estimated using the product-limit method.

Rebound is defined as SELENA SLEDAI score during the first 24 weeks that exceeds the Baseline SELENA SLEDAI score in the participant's respective original parent study. Baseline is defined as the Day 0 visit from the parent study. SELENA SLEDAI assessments consist of 24 individual weighted items in which signs and symptoms, laboratory tests, and physician's assessment for each of 9 organ systems are given a weighted score and summed if present (marked 'Yes') at the time of the visit or in the preceding 10 days. The maximum theoretical score is 105 (all 24 descriptors present simultaneously) with 0 indicating inactive disease (marked 'No'). Any time during the first 24 weeks of this study has been reported.

Immunogenicity assay results were categorized as negative or positive. A persistent positive result was defined as a positive post-Day 0 visit immunogenic response that occurred for at least 2 consecutive assessments or a single result at the final assessment. A transient positive result was defined as a single post-Day 0 visit positive immunogenic response that did not occur at the final assessment. Any time post-Day 0 visit data are reported (or post-Week 24 for Treatment Holiday - Restart phase). Day 0 visit date is defined as Day 0 from present study.

Serum samples were collected at indicated time-points for analysis of immunoglobulins: Immunoglobulin G (IgG), Immunoglobulin A (IgA), and Immunoglobulin M (IgM). Baseline is defined as the Day 0 visit from parent studies. Percentage change from Baseline is equal to 100* (value at specified visit minus Baseline value) divided by Baseline value.

Blood samples were collected at indicated time-points for analysis of autoantibodies like dsDNA. Baseline is defined as the Day 0 visit from parent studies. Percentage change from Baseline is equal to 100* (Value at specified visit minus Baseline value) divided by Baseline value.

Blood samples were collected at indicated time-points for analysis of autoantibodies like ANA. Only participants who had an ANA value measured in INDEX at the parent studies Baseline were included in this analysis. Baseline is defined as the Day 0 visit from parent studies. Percentage change from Baseline is equal to 100* (Value at specified visit minus Baseline value) divided by Baseline value.

Blood samples were collected at indicated time-points for analysis of complement levels like complement 3 (C3) and complement 4 (C4). Baseline is defined as the Day 0 visit from parent studies. Percentage change from Baseline is equal to 100* (Value at specified visit minus Baseline value) divided by Baseline value.

Blood samples were collected at indicated time-points for analysis of Activated B cells subsets like Activated CD19+CD20+CD69+, cluster of differentiation 20+ (CD20+), Memory CD19+CD20+CD27+, Naive CD19+CD20+CD27-, Plasma CD19+CD20-CD138+, Plasmacytoid CD19+CD20+CD138+, and SLE Subset CD19+CD38b+CD27b+Lymph. Baseline is defined as the Day 0 visit from parent studies. Percentage change from Baseline is equal to 100* (Value at specified visit minus Baseline value) divided by Baseline value.

Blood samples were collected at indicated time-points for analysis of Activated B cells subsets like Activated CD19+CD20+CD69+, CD20+, Memory CD19+CD20+CD27+, Naive CD19+CD20+CD27-, Plasma CD19+CD20-CD138+, Plasmacytoid CD19+CD20+CD138+, and SLE Subset CD19+CD38b+CD27b+Lymph. Percentage change from Week 24 of present study was calculated as 100*(value at specified visit - Week 24 value) divided by week 24 value. The data below is only reported for the Treatment Holiday Group (Re-start phase). Participants in this group restarted belimumab therapy one day after Week 24, hence the Baseline for this outcome measure was Week 24 visit. No other groups were measured for this outcome.

SELENA SLEDAI assessments consist of 24 individual weighted items in which signs and symptoms, laboratory tests, and physician's assessment for each of 9 organ systems are given a weighted score and summed if present (marked 'Yes') at the time of the visit or in the preceding 10 days. The maximum theoretical score is 105 (all 24 descriptors present simultaneously) with 0 indicating inactive disease (marked 'No'). Data are reported at the specified time-points from Day 0 (of present study) up to Week 52. Baseline is defined as the Day 0 from parent studies. Change from Baseline is equal to (Value at specified visit minus Baseline value).

All corticosteroids are converted to a prednisone equivalent average daily dose (mg/day). The average daily dose at Day 0 was used to assess the relative change in daily dose on a given day. The average daily dose at Day 0 was calculated as sum of the daily dose across all days from the Screening visit date up to and including Day 0 visit date divided by the number of days in the time period. Data reported are the median number of days on which the specified criteria was met for Day 0 to Week 24, Week 24 to Week 52, Day 0 to Week 52. For treatment holiday group, Day 0 to Week 24 corresponds to holiday phase, Week 24 to Week 52 corresponds to treatment Re-start phase.

All corticosteroids are converted to a prednisone equivalent average daily dose (mg/day). The average daily dose at Day 0 was used to assess the relative change in daily dose on a given day. The average daily dose at Day 0 was calculated as sum of the daily dose across all days from the Screening visit date up to and including Day 0 visit date divided by the number of days in the time period. Data reported are the median number of days on which the specified criteria was met for Day 0 to Week 24, Week 24 to Week 52, Day 0 to Week 52. For treatment holiday group, Day 0 to Week 24 corresponds to holiday phase, Week 24 to Week 52 corresponds to treatment Re-start phase.

Participants in this group continued to receive monthly belimumab 10 mg/kg therapy, in addition to standard of care SLE therapy for 52 weeks. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, then re-started belimumab therapy for further 28 weeks while receiving standard of care SLE therapy. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, Holiday Phase was Day 0 visit to Week 24/Treatment Re-start phase. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. In the event of a severe flare, participants were allowed to enter Maintenance Phase and receive belimumab 10 mg/Kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Following Treatment holiday phase for 24 weeks, participants re-started belimumab therapy for 28 weeks while receiving standard of care SLE therapy for 52 weeks. Re-start Phase started one day after Week 24 up to Week 52. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, Holiday Phase was Day 0 visit to Week 24/Treatment Re-start phase. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. In the event of a severe flare, participants were allowed to enter Maintenance Phase and receive belimumab 10 mg/Kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Following Treatment holiday phase for 24 weeks, participants re-started belimumab therapy for 28 weeks while receiving standard of care SLE therapy for 52 weeks. Re-start Phase started one day after Week 24 up to Week 52. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, then re-started belimumab therapy for further 28 weeks while receiving standard of care SLE therapy. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, Holiday Phase was Day 0 visit to Week 24/Treatment Re-start phase. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. In the event of a severe flare, participants were allowed to enter Maintenance Phase and receive belimumab 10 mg/Kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Following Treatment holiday phase for 24 weeks, participants re-started belimumab therapy for 28 weeks while receiving standard of care SLE therapy for 52 weeks. Re-start Phase started one day after Week 24 up to Week 52. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, Holiday Phase was Day 0 visit to Week 24/Treatment Re-start phase. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. In the event of a severe flare, participants were allowed to enter Maintenance Phase and receive belimumab 10 mg/Kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Following Treatment holiday phase for 24 weeks, participants re-started belimumab therapy for 28 weeks while receiving standard of care SLE therapy for 52 weeks. Re-start Phase started one day after Week 24 up to Week 52. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Participants in the Treatment Holiday Group underwent a 24-week belimumab treatment holiday while remaining on standard of care SLE therapy, Holiday Phase was Day 0 visit to Week 24/Treatment Re-start phase. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. In the event of a severe flare, participants were allowed to enter Maintenance Phase and receive belimumab 10 mg/Kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).

Following Treatment holiday phase for 24 weeks, participants re-started belimumab therapy for 28 weeks while receiving standard of care SLE therapy for 52 weeks. Re-start Phase started one day after Week 24 up to Week 52. Participants from BEL113750 (NCT01345253) and BEL114333 (NCT01597622) were part of this group. Participants had been treated with belimumab for at least 6 months in one of these continuation studies prior to entry into this study. Eligible participants on completion of 52-weeks entered Maintenance period and received belimumab 10 mg/kg every 4 weeks until Week 48 of subsequent years (Maintenance is Year 2, 3, 4).