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.

Modified Intent to Treat (MIIT) Population: The MITT Population comprised of all the participants enrolled in the study who received at least one dose of IP.

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population

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.

MITT Population. Only those subjects with abnormal (>124 umol/L) creatinine at baseline by year interval.

Serum immunoglobulin G (IgG) was collected at Baseline (BL) (Day 0), at Week 24 and Week 48 in first year, at Week 48 in subsequent years up to 8 years and at follow-up (up to 8 weeks post last infusion). Number of participants with serum immunoglobulins below the lower limit of normal (LLN) (<0.5 nanograms per milliliter [ng/mL]) 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.

MITT Population

The percentage of participants achieving a SLE Responder Index (SRI) response 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) are summarized. The BL 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. Response is defined as:>=4 point reduction from the BL in the safety of estrogen in lupus national assessment (SELENA) SLE disease activity index (SLEDAI) score and no worsening (increase of <0.30 points from the BL) 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 the BL. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MIIT Population

Anti-double stranded deoxyribonucleic acid (anti-dsDNA) levels were assessed 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 in participants who were positive at baseline (anti-dsDNA >=30 International Units/milliliter [IU/mL]). Observed anti-dsDNA levels are summarized. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MITT Population

Anti-dsDNA levels were assessed at Baseline (BL) (Day 0), 24 and 48 in first year, at Week 24 and 48 in subsequent years up to 432 weeks and at exit visit in participants who were positive at baseline (anti-dsDNA ≥30 IU/mL). Median percent change from Baseline in anti-dsDNA levels 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. Percent change from Baseline is calculated as: 100 x ([Post-Dose Visit Value - Baseline] / Baseline). Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MITT Population

Complement C3 and C4 levels were assessed 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 exit visit in participants with low complements at Baseline (C3 <90 milligram per deciliter (mg/dL) and C4 <16 mg/dL). Observed complement C3 and C4 levels are summarized. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MITT Population

Complement C3 and C4 levels were assessed at Baseline (BL) (Day 0), 24 and 48 in first year, at Week 24 and 48 in subsequent years up to 432 weeks and at exit visit in participants with low complements at Baseline (C3 <90 milligrams per decilitre (mg/dL) and C4 <16 mg/dL). Median percent change from Baseline in complement C3 and C4 levels 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. Percent change from Baseline is calculated as: 100 x ([Post-Dose Visit Value - Baseline] / Baseline). Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MITT Population

Trends for reduction in prednisone use in participants receiving belimumab were observed up to 432 weeks. Percentage of participants with daily prednisone dose reduced to <=7.5 mg/day from >7.5 mg/kg at the Baseline 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.

MITT Population

Proteinuria is defined as the presence of an excess of serum proteins in the urine. Trends for reduction in proteinuria in participants receiving belimumab were assessed up to 432 weeks and at Exit visit. Percentage of participants with >= 50% reduction in proteinuria among participants with Baseline proteinuria >0.5 g/24 hour (hr) 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.

MITT Population

B-cell levels were assessed at Baseline (BL) (Day 0), Week (Wk) 24 and 48 in first year, at Week 24 and 48 in subsequent years up to 432 weeks and at exit visit. Observed absolute B cell subsets (CD20+), CD19+/27BRIGHT/38BRIGHT SLE subset, CD19+20-27hi+ short-lived plasma cells (SLPC), CD20+/138+ plasmacytoid, CD20+/27+ memory, CD20+/27- naïve, CD20+/69+activated, CD20-/138+ plasma cells, Total CD19+ B-cells (CD19+) levels are summarized. Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MITT Population

B-cell levels were assessed at Baseline (BL) (Day 0), Week (Wk) 24 and 48 in first year, at Week 24 and 48 in subsequent years up to 432 weeks and at exit visit. Median percent change from Baseline in absolute B cell subsets (CD20+), CD19+/27BRIGHT/38BRIGHT SLE subset, CD19+20-27hi+ short-lived plasma cells (SLPC), CD20+/138+ plasmacytoid, CD20+/27+ memory, CD20+/27- naïve, CD20+/69+activated, CD20-/138+ plasma cells, Total CD19+ B-cells (CD19+) levels 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. Percent change from Baseline is calculated as: 100 x ([Post-Dose Visit Value - Baseline] / Baseline). Only those participants available at the specified time points (represented by n=X in the category titles) were analyzed.

MITT Population

Systemic Lupus International Collaborative Clinics/American College of Rheumatology (SLICC/ACR) Damage Index is a tool used to assess non-reversible organ damage in SLE patients. Damage Index is used to assess 12 systems by 41 items. Score is given as 1 or sometimes 2, if occur more than once, so that that the maximum possible score is 47. Higher damage index scores early in disease are associated with a poor prognosis and with increased mortality. Damage index was assessed at BL (Day 0), Week 48 in first year, at Week 48 in subsequent years up to 8 years. Percentage of participants with worsening in damage index (change >0) are summarized. The BL 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 were analyzed ( n=X).

MITT Population

The SF-36v2 is a participant-reported short form survey to measure functional health and well-being. There are 36 items grouped into eight health domains: Vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning and mental health. SF-36v2 gives a score (0-100) for each of these domains as well as summary score for the physical component score (PCS) and mental component score (MCS) based on the responses by participants. The lower the score the more disability and the higher the score the less disability. The BL 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 BL was calculated as the individual post-BL value minus the BL value. Only those participants available at the specified time points were analyzed ( n=X).

MITT Population

The SF-36v2 is a participant-reported survey to measure functional health and well-being. There are 36 items grouped into eight health domains: Vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning and mental health. SF-36v2 gives a score (0-100) for each of these domains as well as summary score for the physical component score (PCS) and mental component score (MCS) based on the responses by participants. The lower the score the more disability and the higher the score the less disability. The BL 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 BL was calculated as the individual post-BL value minus the BL value. Only those participants available at the specified time points were analyzed ( n=X).

MITT Population

The FACIT-F scale measures the severity and impact of fatigue on functioning and health related quality of life experienced in the past 7 days. FACIT-Fatigue scale total score was assessed at BL (Day 0), Wk 48 in first year, at Wk 48 in subsequent Yrs up to 8 Yrs.The level of fatigue is measured by 13 questions assessed on a four-point scale (0=not at all fatigued; 1=a little bit fatigued; 2=somewhat fatigued; 3=quite a bit fatigued; 4=very much fatigued; possible total score of 0 to 52). Change from BL in FACIT-Fatigue scale total score are summarized. The BL 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 BL was calculated as the individual post-BL value minus the BL value. A negative change from BL represents a worsening condition. Only those participants available at the specified time points were analyzed ( n=X).

MITT Population

The FACIT-F scale measures the severity and impact of fatigue on functioning and health related quality of life experienced in the past 7 days. FACIT-Fatigue scale total score was assessed at BL (Day 0), Week 48 in first year, at Week 48 in subsequent years up to 8 years. The level of fatigue is measured by 13 questions assessed on a four-point scale (0=not at all fatigued; 1=a little bit fatigued; 2=somewhat fatigued; 3=quite a bit fatigued; 4=very much fatigued; possible total score of 0 to 52). Percentage of participants with improvement in FACIT-Fatigue scale score exceeding the minimum clinically important difference (MCID) (>=4 points) are summarized. Only those participants available at the specified time points were analyzed ( n=X).

MITT Population