Percentage of subjects with a ≥ 4 point reduction from baseline in SELENA SLEDAI score, and no worsening (increase of \< 0.30 points from baseline) in PGA, and no new BILAG A organ domain score or 2 new BILAG B organ domain scores compared with baseline. SELENA SLEDAI is calculated from 24 individual descriptors; 0 indicates inactive disease and the maximum theoretical score is 105; scores \> 20 are rare. PGA is a visual analog scale scored from 0 to 3 (1=mild, 2=moderate, 3=severe). BILAG uses a single score for each of the 8 organ domains; range is from severe to no disease (A to E).

Forced vital capacity is the total amount of air exhaled during the lung function test. Low FVC (mL) reflects more impaired lung function. Absolute Change from Baseline in FVC will be reported.

Percentage of participants with a state of disease control (Independent blinded assessor \[IBA\]) was defined as the percentage of participants with a Systemic Lupus Erythematosus Disease Activity Index 2000(SLEDAI-2K)score less than or equal to(\<=)2 achieved without immunosuppressants and with corticosteroids at a prednisone equivalent dose of \<=5 mg/day at Week 52. SLEDAI-2K was a weighted, cumulative index for measuring systemic lupus erythematosus (SLE) disease activity in previous 10 days,consisting 24 individual items in which signs and symptoms, laboratory tests and physician's assessment for each item within each of 9 organ systems were given a weighted score(1 to 8 with higher score indicating increased activity)and summed if present at the time of visit or in preceding 10 days. The SLEDAI-2K score was sum of all 24 individual items from the SLEDAI-2K, ranges from 0(no symptoms) to 105(presence of all defined symptoms) with higher scores representing increased disease activity.

SFI Flare was defined as a mild/moderate or severe flare according to the modified Safety of Estrogen in Lupus National Assessment Systemic Lupus Erythematosus Disease Activity Index (SELENA SLEDAI) SLE Flare Index (modified excluded severe flares from the SELENA SLEDAI flare assessment that were triggered only by an increase in SELENA SLEDAI score to \>12).Time to first SFI flare is defined as the number of days from Day 0 visit date to the date the participant has a flare (event date - Day 0 visit date + 1) in the 52 Week/Holiday phase; (event date - treatment re-start date + 1) in the Re-start Holiday phase. Day 0 visit date is defined as Day 0 from present study. Median time to first SFI flare is reported; estimated using the product-limit method.

Any untoward medical occurrence in participant, temporally associated with use of medicinal product, whether or not considered related to medicinal product. Any untoward event resulting in death,life threatening,requires hospitalization or prolongation of existing hospitalization,results in disability/incapacity,congenital anomaly/birth defect,medically important were categorized as SAE. Number of participants who had any AE(includes those having non-serious and/or serious AEs) or any SAE are presented.Treatment-emergent AEs are defined as AEs that started on or after first dose of belimumab treatment and for those participants who were randomized to placebo in parent study,ongoing AEs that started before first open-label belimumab dose(in either C1115 open-label extension or BEL114333),worsened (severity,seriousness,relatedness) at any point during the open-label treatment.Timeframe includes exposure in parent study/upto16 weeks post infusion in current study(114333).

SRI response is defined as \>=4 point reduction, from Baseline in safety of estrogen in lupus national assessment (SELENA) systemic lupus erythematosus disease activity index (SLEDAI) score, no worsening (increase of \<0.30 points from Baseline) in physician's global assessment (PGA) and no new British Isles Lupus Assessment Group of SLE clinics (BILAG) A organ domain score or 2 new BILAG B organ domain scores compared with Baseline. Analysis was performed using a logistic regression model for the comparison between belimumab and placebo with covariates treatment group, Baseline SELENA SLEDAI score (\<=9 vs. \>=10), Baseline complement levels (low C3 and/or C4 vs. no low C3 or C4) and race (black vs. other).

SRI response is a composite index, defined as the percent of participants with \>=4 point reduction from Baseline in safety of estrogen in lupus national assessment (SELENA) systemic lupus erythematosus disease activity index (SLEDAI) score and no worsening (increase of \< 0.30 points from Baseline) in physicians global assessment (PGA) and no new British isles lupus assessment group (BILAG) A organ domain score or 2 new BILAG B organ domain scores compared with Baseline at the time of assessment (at Week 52 of the blinded period). A SELENA SLEDAI score of 0 would suggest no lupus activity; while a score of 105 is the maximum calculable if all items were scored as being present from active lupus. PGA ranges from 0 (no activity) to 3 (severe activity). BILAG has no range. The higher thresholds of SELENA SLEDAI improvement (i.e., SRI5, SRI6, and SRI7) indicates a higher response (SRI5 is a 5 point SELENA SLEDAI reduction, SRI6 is a 6 point reduction, and SRI7 is a 7 point reduction).

An AE is defined as any untoward medical occurrence in a participant (par.) temporally associated with the use of a investigational product (IP), whether or not considered related to the IP. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of an IP. An SAE is defined as any untoward medical occurrence that, at any dose, results in death, is life threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity, is a congenital anomaly/birth defect, is an important medical event that jeopardizes the participant or may require medical or surgical intervention to prevent one of the other outcomes listed in the above definition, or is associated with liver injury and impaired liver function. Only those participants available at the specified time points (represented by n=X, in the category titles) were analyzed.

AE rates by SOC adjusting for participant-years on study drug anytime post Baseline are summarized, which included the follow up visits. Only treatment-emergent adverse events (AEs) are summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. The event rate of an AE was calculated as the number of events per 100 participant years: Event Rate = 100\* Number of Events / Participant Years. Participant years were calculated as sum across all participants (\[last visit of interval day - first visit of interval day + 1\]/365). Participant years excluded between study gaps if participant had not started extension study on date of last visit of parent study.

SAE rates by SOC adjusting for participants-years on study drug anytime post Baseline are summarized, which included the follow up visits. Only treatment-emergent SAEs are summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. The event rate of an SAE was calculated as the number of events per 100 participant years: Event Rate = 100\* Number of Events / participants Years. participants years were calculated as = sum across all participants (\[last visit of interval day - first visit of interval day + 1\]/365). participants years excluded between study gaps if participant had not started extension study on date of last visit of parent study.

Hematology parameters were assessed at Baseline (BL) (Day 0), Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in APTT and PT is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Hematology parameters were assessed at Baseline (BL) (Day 0), Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in basophils, eosinophils, lymphocytes, monocytes, neutrophils, neutrophils segmented and platelets is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Hematology parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in erythrocytes is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Hematology parameters were assessed at Baseline (BL) (Day 0), Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in hematocrit is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Hematology parameters were assessed at Baseline (BL) (Day 0), Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in hemoglobin is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Clinical chemistry parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in albumin and protein is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Clinical chemistry parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in blood urea nitrogen, glucose, calcium, carbon dioxide, chloride, magnesium, phosphate, potassium and sodium is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Clinical chemistry parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in urate, creatinine and bilirubin is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Clinical chemistry parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in creatinine clearance is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Clinical chemistry parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Change from Baseline in BUN/creatinine is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Clinical chemistry parameters were assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 432 weeks and at exit visit. Change from Baseline in alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, gamma glutamyl transferase and lactate dehydrogenase is summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post- Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Immunogenic response was assessed by binding confirmatory assay at Baseline (BL) (Day 0), at Week 24 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Number of participants with the indicated immunogenic response are summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Results of binding confirmatory assay were categorized as negative, persistent positive (defined as a positive immunogenic response that occurs at least 2 consecutive assessments or a single result at the final assessment) or transient positive (defined as a single positive immunogenic response that does not occur at the final assessment). Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Systolic blood pressure (SBP) and diastolic blood pressure (DBP) was measured at Baseline (BL) (Day 0), at Week 24 and 48 in first year, at Week 24 and 48 in subsequent years up to 432 weeks and at exit visit. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Serum creatinine was assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Percentage of participants with at least 25% increase from baseline in creatinine are summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Serum creatinine was assessed at Baseline (BL) (Day 0), at Week 4, 12, 24, 36 and 48 in first year, at Week 24 and 48 in subsequent years up to 440 weeks and at follow-up (up to 8 weeks post last infusion). Percentage of participants with at least 25% reduction from baseline in creatinine are summarized. The Baseline is defined as the Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

An adverse event is defined as any unfavorable or unintended sign, symptom, or disease that is temporally associated with the use of a study agent but is not necessarily caused by the study agent. This includes worsening (example: increase in frequency or severity) of preexisting conditions. Participants with incidences of any event at any time post-baseline are presented by yearly interval. Only treatment-emergent AEs are summarized.

An adverse event resulting in death, is life threatening (ie, an immediate threat to life), inpatient hospitalization, prolongation of existing hospitalization, persistent or significant disability/incapacity, congenital anomaly/birth defect or any other situation which is medically important is categorized as SAE. Only treatment-emergent AEs are summarized.

SAE rates by SOC adjusting for participants-years on study drug anytime post Baseline are summarized, which included the follow up visits. Only treatment-emergent SAEs are summarized. The event rate of an SAE was calculated as the number of events per 100 participant years. Participants years were calculated as = sum across all participants (\[last visit of interval day - first visit of interval day + 1\] divided by 365). Participants years excluded between study gaps if participant had not started extension study on date of last visit of parent study.

Hematology parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 hematology parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Plt, Lymp, Leu, Eos, Baso, Mono, Neu, NeuBF, and NueS are summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Hematology parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 hematology parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Hg is summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Hematology parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 hematology parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Erythrocytes is summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Electrolytes parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 electrolytes parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Ca,CO2, Chloride, Mg, Phos, K and Na were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Other chemistries parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 other chemistries parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in BUN/Cr is summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Other chemistries parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 other chemistries parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Alb and Protein were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Other chemistries parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 other chemistries were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in BUN and Glucose were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Other chemistries parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 other chemistries were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Cr and Urate were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Liver function parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 liver function parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in ALT, ALP, AST, GGT and LDH were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.NA indicates standard deviation was not calculable for a single data point.

Liver function parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 liver function parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Bili were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Immunoglobulin (Ig) parameters were assessed at Baseline, Week 4,12,24,36, and 48 during Year 1. From Year 2-9 Ig parameters were assessed at Week 24 and 48 ; Exit visit and at follow-up (up to 8 weeks post infusion). Change from Baseline in Ig G were summarized. The Baseline is defined as For Year 1, Day 0 values for MITT participants who were treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants who were treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed. NA indicates standard deviation was not calculable for a single data point.

Immunogenic response was analyzed using serum samples for anti-belimumab antibody measurements in MITT population. Categories of response are Negative, Transient Positive (+) means single + response that does not occur at the final assessment, and Persistent + means + response that occurs at least 2 consecutive assessments or a single result at the final assessment. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Blood samples were collected to evaluate IgG levels at Baseline and at Weeks 12, 24 and 48 during Year 1. From Year 2-9, IgG was evaluated at Week 24 and 48 ; Exit visit and at follow-up visit (up to 8 weeks post last infusion). Number of participants with IgG immunoglobulin values below the LLN at each one year interval are presented. Baseline includes Extension Year 1 Day 0 values for MITT participants treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants treated with Belimumab in the parent study. If a participant had more than one response within a year, then the last response within the year interval (usually the Week 48 assessment) was summarized. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Participants who had improving SLE disease activity for at least 8 weeks, at the investigator's discretion, the steroid dose was reduced by reduction to 7.5 mg/day. If the participant continued to have stable or improving disease activity after 4 weeks on a reduced dose, then the investigator considered reducing the dose again. Baseline includes extension Year 1 Day 0 values for MITT participants treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants treated with Belimumab in the parent study. Number of participants with shifts from Baseline total daily dose category by visit is summarized.

The SLICC/ACR Damage Index was assessed every 48 weeks and at the exit visit as a measure of disease activity. It was developed to assess the accumulated damage since the onset of the disease. The number of participants with worsening in their SLICC/ACR Damage Index score compared with Baseline have been presented. Worsening was defined as a change in score (post-Baseline visit score - Baseline score) \> 0. Baseline includes extension Year 1 Day 0 values for MITT participants treated with placebo in the parent study, and the last pre-treatment value in the parent study for MITT participants treated with Belimumab in the parent study. For years in which a participant was withdrawn from the study, the exit visit assessment was used in place of the Week 48 assessment for the year. This value was not carried forward through later years. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

Blood samples were collected for measurement of serum concentrations of belimumab. Observed belimumab concentrations at Week 12 is presented.

Blood samples were collected for measurement of serum concentrations of belimumab at steady state. Average concentrations were analyzed and reported for all time-points from Week 1 through Week 60.

Blood samples were collected for measurement of serum concentrations of belimumab at steady state. Cmax was analyzed and reported for all time-points from Week 1 through Week 60.

Blood samples were collected for measurement of serum concentrations of belimumab at steady state. Cmin was analyzed and reported for all time-points from Week 1 through Week 60.

An AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An SAE is any untoward medical occurrence that at any dose results in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity, is a congenital anomaly/birth defect, other situations based on medical or scientific judgment and is associated with liver injury and impaired liver function. Data for number of participants with SAE and non-SAE has been summarized.

An AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. AESIs were Malignant Neoplasms, Post-Administration Systemic Reactions (PASR), All Infections of Special Interest (opportunistic infections, herpes zoster, tuberculosis and sepsis), Depression/suicide/self-injury, Deaths and study specific AESI which includes: severe skin reaction per GlaxoSmithKline (GSK) Adjudication, cardiac disorders, Posterior Reversible Encephalopathy Syndrome (PRES) and Progressive multifocal leukoencephalopathy (PML). Data for number of participants with AESI has been summarized.

The primary objective was to assess the suitability of the auto injector for self-administration of belimumab. An overall assessment of usability and reliability for the device was determined by assessing the rate of successfully complete self-administered injections relative to attempted ones. The assessment for the parameter, drug successfully injected was elicited by a Yes/No response. The participants who were able to administer injections inside and outside of the clinic without assistance were included.

Naive B cell is cell that is not exposed to antigen. Naïve B cell count is CD20+CD27 concentration of cells (conc-cell)/cubic millimeter (cumm). Change from Baseline in naïve B cells was calculated as the value at Week 24 minus the value at Baseline. MITT Population consisted of all participants randomized to treatment, who have had taken at least one dose of study. Participants analyzed included those who had data at Week 24 for naïve B cells count (MITT Population). Baseline value used in the analysis was of Day 0 (Day of transplant). Adjusted mean differences (treatment-placebo) and 95% confidence intervals for differences were obtained from mixed-models repeated-measures (MMRM) model, with fixed categorical effects of treatment, visit, donor type and treatment-by-visit interaction and fixed continuous covariates of Baseline and Baseline-by-visit interaction. A compound symmetry variance structure was used to model the within-participant errors, shared across treatments.

Number of participants with AEs, SAEs and AESI are summarized. The On-treatment (OT) phase started on the day and time of receiving the start of the first infusion and ended on the last dose date plus 28 days. The Post-treatment (PT) phase started 29 days after day of last dose up to 1 year. An AE is any untoward medical occurrence, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. SAE is defined as any untoward medical occurrence that at any dose results in, death, is life threatening, Requires hospitalization or prolongation of existing hospitalization, Results in disability/incapacity, Is a congenital anomaly/birth defect or event that but may jeopardize the subject or may require medical or surgical intervention to prevent one of the other outcomes listed. AESI included malignant neoplasms, infusion/anaphylaxis/hypersensitivity reactions, all infections, depression/suicide/self-injury, deaths.

All infections included: 1. Opportunistic infections per-clinical assessment, 2. Herpes Zoster, a. Recurrent, b. Disseminated, 3. Sepsis. Opportunistic infections were identified using list of preferred terms as per Medical Dictionary for Regulatory Activities (MedDRA) version 18.1. Any events falling under these preferred terms were adjudicated to determine if criteria was met for an opportunistic infection.

Change from Baseline in SBP and DBP were assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value at Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in heart rate was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value at Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in body temperature was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value at Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Number of participants outside the normal range (NR) for SBP and DBP was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Number of participants outside the normal range are summarized by less than (\<) normal range and greater than (\>) normal range categories at Week 24 and Week 52. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Number of participants outside the normal range (NR) for heart rate was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Number of participants outside the normal range are summarized by less than (\<) normal range and greater than (\>) normal range categories at Week 24 and Week 52. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Number of participants outside the normal range (NR) for body temperature was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Number of participants outside the normal range are summarized by less than (\<) normal range and greater than (\>) normal range categories at Week 24 and Week 52. Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Hematology parameters included: basophils (B), eosinophils (E), lymphocytes (L), monocytes (M), total neutrophils (N), platelet count (PC) and white blood cells (WBC). Change from Baseline in haematology parameter was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in hemoglobin was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Endpoint was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in MCH was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in MCV was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in RBC was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in albumin was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Clinical chemistry parameter included alkaline phosphatase (ALP), alanine amino Transferase (ALT) and aspartate amino transferase (AST). Endpoint was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Clinical chemistry parameters included direct bilirubin (DB), total bilirubin (TB) and creatinine (C). Endpoint was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Clinical chemistry parameters included calcium (Ca), carbon dioxide content/bicarbonate (CO2/Bicar), glucose (Gl), potassium (K), sodium (Na), phosphorus inorganic (PhI), urea/blood urine nitrogen (U/BUN). Endpoint was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in GFR was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

Change from Baseline in immunoglobulins IgA, IgG and IgM was assessed at Week 24 (at the end of therapy) and at Week 52 (at study end). Change from Baseline was calculated as the value on Week 24 and Week 52 minus the value at Baseline. Baseline value used in the analysis was of Day 0 (Day of transplant). Only those participants available at the specified time points were analyzed (represented by n=X, X in the category titles).

The QMG is a 13 item ordinal scale which measures ocular, bulbar, extremity fatigue and strength, along with respiratory function. The total QMG score was calculated by adding the score of each of the 13 individual QMG questions. Possible scoring on the QMG range from 0 (normal) to 39 (severe). A lower score indicates a better clinical outcome. The QMG score at Baseline is the average of the screening and Week 0 Baseline scores. Change from Baseline was calculated by subtracting the Baseline value from the post-baseline value. The differences in adjusted least square means were presented (Belimumab 10 mg/kg minus Placebo). A negative treatment difference indicates benefit relative to placebo. The analysis method was Mixed-Model Repeated Measures adjusted for Treatment, Visit, Baseline QMG Score, Treatment by Visit, and Baseline QMG Score by Visit.

SRI response is defined as \>=4 point reduction, from Baseline in safety of estrogen in lupus national assessment (SELENA) systemic lupus erythematosus disease activity index (SLEDAI) score, no worsening (increase of \<0.30 points from Baseline) in physician's global assessment (PGA) and no new British Isles Lupus Assessment Group of SLE clinics (BILAG) A organ domain score or 2 new BILAG B organ domain scores compared with Baseline. Analysis was performed using a logistic regression model for the comparison between belimumab and placebo with covariates treatment group, Baseline SELENA SLEDAI score (\<=12 vs. \>=13). Percentage of participants with SRI response at Week 52 of Part A were reported. Intent-to-Treat Population comprised of all participants who were randomized and treated with at least one dose of study agent in Part A. One participant had missing data at Baseline and therefore, could not be included in the analysis.

Proteinuria based on urinary protein creatinine ratio (PCR) was measured from 2 consecutive 24 hour (h) urine collection pre and post dosing at Baseline and Week 28 and the mean PCR was determined at each time point. Baseline is defined as the mean of the pre and post dosing Day 0 values. The ratio is defined as the Week 28 value divided by the Baseline value. Ratio to Baseline: Estimated value = 0.76, 2-sided 95% confidence interval (CI)=0.57 to 1.01. The geometric mean method was used to calculate the CI. The analysis was performed on Intent-to-treat (ITT) Population which comprised of all eligible participants who received at least one dose of investigational drug. Only those participants available at the indicated time point (Week 28) were analyzed.

PLA2R autoantibody titers in serum were analyzed at Baseline and Week 28 by means of a validated anti- PLA2R enzyme linked immunosorbent assay (ELISA) from EuroImmun. Baseline is defined as the Day 0 value and change from Baseline was calculated as ratio to Baseline by dividing the Week 28 values with the Baseline values. Ratio to Baseline: Estimated value = 0.27, 2-sided 95% CI=0.12 to 0.58. The geometric mean method was used to calculate the CI.

AE rates by SOC adjusting for participant-years on study drug anytime post Baseline are summarized, which included the follow up visits. Only treatmentemergent AEs are summarized. The Baseline is defined as the last available value prior to belimumab start date, for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. The event rate of an AE was calculated as the number of events per 100 participant years: Event Rate=100\* number of events divided by participant years. Participant years were calculated as sum across all participants (\[last visit of interval day minus first visit of interval day plus 1\] divided by 365).

Hematology parameters were assessed at Baseline, Week 8, 16, 24, 32, 40 and 48 during Year 1 to 12; Week 8, 16, 24, 32, and 40 during Year 13; Exit visit and at follow-up (up to 8 weeks and 24 weeks post last infusion). Change from Baseline in basophils, eosinophils, lymphocytes, monocytes, neutrophils segmented and platelets is summarized. The Baseline is defined as the Extension Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value.

Clinical chemistry parameters were assessed at Baseline, Week 8, 16, 24, 32, 40 and 48 during Year 1 to 12; Week 8, 16, 24, 32, and 40 during Year 13; Exit visit and at follow-up (up to 8 weeks and 24 weeks post last infusion). Change from Baseline in BUN, glucose, calcium, carbon dioxide, chloride, magnesium, phosphate, potassium and sodium is summarized. The Baseline is defined as the Extension Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value.

Clinical chemistry parameters were assessed at Baseline, Week 8, 16, 24, 32, 40 and 48 during Year 1 to 12; Week 8, 16, 24, 32, and 40 during Year 13; Exit visit and at follow-up (up to 8 weeks and 24 weeks post last infusion). Change from Baseline in ALT, AP, AST, GGT and LD are summarized. Baseline is defined as the Extension Year 1 Day 0 values for participants treated with placebo in the parent study and last pre-treatment value in the parent study for participants treated with belimumab in the parent study. Change from Baseline is defined as the difference between the post-dose post-Baseline visit value and the Baseline value.

Blood samples were collected at indicated time points for pharmacokinetic (PK) analysis of belimumab. AUCss,0-tau of belimumab for participants weighing \>= 50 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. AUCss,0-tau of belimumab for participants weighing between 30 kg and \< 50 kg has been reported.

Blood samples were collected at indicated time points for PK analysis of belimumab. AUCss,0-tau of belimumab for participants weighing between 15 kg and \< 30 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cavg,ss of belimumab for participants weighing \>= 50 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cavg,ss of belimumab for participants weighing between 30 kg and \< 50 kg has been reported.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cavg,ss of belimumab for participants weighing between 15 kg and \< 30 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cmin,ss of belimumab for participants weighing \>= 50 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cmin,ss of belimumab for participants weighing 30 kg and \< 50 kg has been reported.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cmin,ss of belimumab for participants weighing 15 kg and \< 30 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cmax,ss of belimumab for participants weighing \>= 50 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cmax,ss of belimumab for participants weighing between 30 kg and \< 50 kg has been reported.

Blood samples were collected at indicated time points for PK analysis of belimumab. Cmax,ss of belimumab for participants weighing between 15 kg and \< 30 kg has been reported. As the first dose of belimumab was administered on Day 1, Week 12 post-dose correlates to Day 1 plus 84 days, i.e., Day 85.

Blood samples were collected at indicated time points for measurement of serum concentrations of belimumab following intravenous administration. Pharmacokinetic Population comprised of all safety participants (all randomized participants who received at least one dose of study treatment) for whom at least one evaluable pharmacokinetic sample was obtained and analyzed.

Blood samples were collected at indicated time points for measurement of serum concentrations of belimumab following subcutaneous administration.

Blood samples were collected at the indicated timepoints to calculate Cmax of belimumab.

Blood samples were collected at the indicated timepoints to calculate AUC (0 to t) and AUC (0 to inf) of belimumab.

Blood samples were collected at the indicated time points to calculate t1/2 of belimumab.

Blood samples were collected at the indicated time points to calculate lambda z of belimumab.

Blood samples were collected at the indicated time points to calculate CL of belimumab.

Blood samples were collected at the indicated time points to calculate Vz of belimumab.

AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product. For marketed medicinal products, this also includes failure to produce expected benefits (i.e., lack of efficacy), abuse or misuse. SAE is any untoward medical occurrence that, at any dose results in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity, or is a congenital anomaly/birth defect or is medically significant, or associated with liver injury and impaired liver function.

Blood sample will be collected for estimation of relative bioavailability and assessment of PK parameters including maximum observed concentration; Cmax, area under the concentration-time curve from time 0 to time t; AUC(0-t) and area under the concentration-time curve from time 0 to infinity; AUC(0-inf)