A Study to Learn More About the Long-Term Safety of Litifilimab (BIIB059) Injections and it's Effects on Symptoms in Adults With Systemic Lupus Erythematosus (SLE)

Percentage of Participants who Achieved an Systemic Lupus Erythematosus Responder Index (SRI)-4 Response

SRI-4 is a composite endpoint defined as the following: * A reduction from baseline of ≥4 points in Systemic Lupus Erythematosus Disease Activity Index (SLEDAI-2K) score. * No new organ system affected, as defined by no new British Isles Lupus Activity Group-2004 (BILAG-2004 grade A) and no more than 1 new BILAG 2004 grade B versus previous visit. * No worsening from baseline in lupus disease activity as defined by \<0.3-point increase on 3-point Physician's Global Assessment (PGA) visual analog scale (VAS). * No violation of protocol-specified medication rules

Time frame: Up to Week 284

Percentage of Participants With at Least 4 Joints (Both Swollen and Tender) at Baseline who Achieved a Joint-50 Response

Joint-50 response is a 50% reduction in total active joint count from baseline. An active joint is defined as a joint with pain and signs of inflammation (e.g., tenderness, swelling or effusion). A 28-joint assessment will be performed to determine the active joint count, which is defined as the sum of tender and swollen joint counts.

Time frame: Up to Week 284

Percentage of Participants With a Cutaneous Lupus Erythematosus Disease Area and Severity Index - Activity (CLASI-A) Score ≥10 at Baseline who Achieved a CLASI-50, CLASI-70, and CLASI-90 Response

CLASI score is used to evaluate lupus skin manifestations. The activity scale (CLASI-A) includes measurements of erythema, scale and hypertrophy, and mucous membrane disease. Each part of the body is listed separately, from the scalp to the feet, in addition to sections focusing on mucous membrane involvement and alopecia. Points are given for the presence of erythema, scale, mucous membrane lesions, recent hair loss, and inflammatory alopecia. Scores for each area are assigned based on the most severe lesion within the area of interest. CLASI-A scores of 0 to 9, 10 to 20, and 21 to 70 represent disease severity of mild, moderate, and severe, respectively. CLASI-50, CLASI-70, and CLASI-90 responders are defined as ≥ 50%, ≥ 70%, and ≥ 90% improvement in CLASI-A score from baseline at the specified timepoint.

Time frame: Up to Week 284

Percentage of Participants who Achieved a British Isles Lupus Assessment Group based Composite Lupus Assessment (BICLA) Response

BICLA is a composite endpoint defined as the following: * BILAG-2004 improvement, defined as all of BILAG-2004 Grade A at baseline improved to B, C, or D and all of BILAG-2004 Grade B at baseline improved to C or D. * No BILAG-2004 worsening in other BILAG-2004 organ systems such that there are no new BILAG-2004 Grade A or greater than 1 new BILAG-2004 Grade B. * No worsening in the SLEDAI-2K total score compared to baseline. * No worsening from baseline in lupus disease activity as defined by \<0.3-point increase on 3-point PGA VAS. * No violation of protocol-specified medication rules.

Time frame: Up to Week 260

Annualized Severe Safety of Estrogens in Systemic Lupus Erythematosus National Assessment - Systemic Lupus Erythematosus Disease Activity Index Flare Index (SFI) Flare Rate

A severe flare is defined as any of the following: * Change in SLEDAI instrument score to \>12 * New or worse: central nervous system SLE; vasculitis; nephritis; myositis; platelets \<60,000/mL, or hemolytic anemia with hemoglobin \<7 grams per deciliter (g/dL) or decrease in hemoglobin \>3 g/dL and requiring: doubling prednisone dose, increase to \>0.5 milligrams per kilograms per day (mg/kg/day) or hospitalization * Increase in prednisone dose to \>0.5 mg/kg/day * New requirement for cyclophosphamide, azathioprine, methotrexate, or mycophenolate for SLE activity * Hospitalization for SLE activity * Increase in PGA score to \>2.5

Time frame: Up to Week 260

Percentage of Time Spent in Lupus Low Disease Activity State (LLDAS)

LLDAS is a composite endpoint defined as the following: i. SLEDAI-2K score ≤ 4, with no activity in a major organ system (renal, central nervous system, cardiopulmonary, vasculitis, fever); and ii. No new features of lupus disease activity compared with the previous assessment; and iii. SELENA-SLEDAI PGA ≤ 1; and iv. Current prednisone (or equivalent) dose ≤ 7.5 mg/day; and v. Standard maintenance doses of immunosuppressive drugs and approved biological agents. "No new features" is defined as any new SLEDAI-2K component that was not present at the previous assessment. The SELENA-SLEDAI PGA Scale ranges from 0-3, where 0 is no disease activity and 3 is maximum disease activity. "Standard maintenance doses" include drugs limited to those allowed per protocol.

Time frame: Up to Week 284

Percentage of Participants With Sustained LLDAS

LLDAS is a composite endpoint defined as the following: i. SLEDAI-2K score ≤ 4, with no activity in a major organ system (renal, central nervous system, cardiopulmonary, vasculitis, fever); and ii. No new features of lupus disease activity compared with the previous assessment; and iii. SELENA-SLEDAI PGA ≤ 1; and iv. Current prednisone (or equivalent) dose ≤ 7.5 mg/day; and v. Standard maintenance doses of immunosuppressive drugs and approved biological agents. "No new features" is defined as any new SLEDAI-2K component that was not present at the previous assessment. The SELENA-SLEDAI PGA Scale ranges from 0-3, where 0 is no disease activity and 3 is maximum disease activity. "Standard maintenance doses" include drugs limited to those allowed per protocol.

Time frame: Up to Week 284

Duration of Sustained LLDAS as Defined by the Number of Visits in LLDAS

LLDAS is a composite endpoint defined as the following: i. SLEDAI-2K score ≤ 4, with no activity in a major organ system (renal, central nervous system, cardiopulmonary, vasculitis, fever); and ii. No new features of lupus disease activity compared with the previous assessment; and iii. SELENA-SLEDAI PGA ≤ 1; and iv. Current prednisone (or equivalent) dose ≤ 7.5 mg/day; and v. Standard maintenance doses of immunosuppressive drugs and approved biological agents. "No new features" is defined as any new SLEDAI-2K component that was not present at the previous assessment. The SELENA-SLEDAI PGA Scale ranges from 0-3, where 0 is no disease activity and 3 is maximum disease activity. "Standard maintenance doses" include drugs limited to those allowed per protocol.

Time frame: Up to Week 284

Annual Change From Baseline Value From the Parent Phase 3 Studies in Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) Score

SDI score is used to assess the accumulated damage in participants with SLE. It assess 12 organ systems and records damage in participants with lupus, regardless of its cause. Damage could be due to previous disease activity, medication, or intercurrent illness (such as surgery or cancer). To distinguish between active inflammation and damage, an item must be present for at least 6 months. It is assumed that persistent inflammation (for at least 6 months) would result in tissue injury and hence damage. SDI is evaluated on a scale 0-47 with higher score indicating higher damage.

Time frame: Up to Week 260

Cumulative Exposure to OCS Over Time

Time frame: Up to Week 260

Percentage of Participants With OCS ≤7.5 mg

Time frame: Up to Week 260

Percentage of Participants With OCS ≤5 mg

Time frame: Up to Week 260

Change From Baseline in Lupus-Specific Health-Related Quality-Of-Life (LupusQoL) Score

The LupusQoL is a participant-reported, lupus-specific, HRQoL questionnaire consisting of 34 items grouped in 8 domains: physical health, pain, planning, intimate relationships, burden to others, emotional health, body image and fatigue. Participants indicate their responses on a 5-point Likert response format, where 4 = never, 3 = occasionally, 2 = a good bit of the time, 1 = most of the time, and 0 = all the time. A LupusQoL score for each domain will be reported on a 0 to 100 scale, with greater values indicating better HRQoL.

Time frame: Up to Week 260

Change From Baseline in Short Form Health Survey-36 (SF-36) (Acute Version) Score

The SF-36 is a 36-item scale which assesses HRQoL in 8 domains: limitations in physical activities due to health problems, limitations in social activities due to physical or emotional problems, limitations in usual role activities due to physical health problems, bodily pain, general mental health (psychological distress and well-being), limitations in usual role activities due to emotional problems, vitality (energy and fatigue), general health perceptions. The SF-36 (Acute Version) form asks for participants to reply to questions (items) according to how they have felt over a specifically defined period of time. Items 1-4 primarily contribute to the physical component summary (PCS) score of the SF-36. Items 5-8 primarily contribute to the mental component summary (MCS) score of the SF-36 where higher scores indicate best health. Scores on each item are summed and averaged (range: 0=worse health to 100=best possible health).

Time frame: Up to Week 156

Change From Baseline in European Quality of Life 5 Dimensions 3 Level Version (EQ-5D-3L)

The EQ-5D is a standardized generic measure of health status developed by the European Quality of Life Group. This study uses the EQ-5D-3L version of the instrument. This instrument consists of 2 sections. The first section comprises 5 dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. All dimensions are measured on a 3-point scale, 1: No problems; 2: Some problems; 3: Extreme problems. The second section comprises the Visual Analogue Scale, which records the respondent's self-rated health on a vertical scale ranging from 0 to 100, lower scores indicate the worst possible health state.

Time frame: Up to Week 156

Change From Baseline in Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue Score

The FACIT-Fatigue is a participant-administered HRQoL questionnaire that evaluates participant's fatigue in 5 broad categories: physical well-being, social/family well-being, emotional well-being, functional well-being and additional concerns. The level of fatigue is measured by questions assessed on a 5-point scale (0 = not at all; 1 = a little bit; 2 = somewhat; 3 = quite a bit; 4 = very much). The responses for each item are added to obtain a total score which ranges from 0 to 52, with a higher score indicating less fatigue.

Time frame: Up to Week 260

Change From Baseline in Patient Health Questionnaire-9 (PHQ-9) Score

The PHQ-9 is a participant-administered HRQoL questionnaire to screen for the presence and severity of depression. The PHQ-9 is a participant-reported outcome (PRO) that is used to measure depression in adults. It contains 9 questions, with a 2 week recall period. The PHQ-9 yields an overall severity score that can range from 0 to 27 with the following severity scores: 0-4 = none; 5-9 = mild; 10-14 = moderate; 15-19 = moderate-to-severe; and 20-27 = severe.

Time frame: Up to Week 260

Change From Baseline in Work Productivity and Activity Impairment (WPAI):Lupus Score

WPAI questionnaire is a validated instrument to measure impairments in work and activities. The WPAI yields four types of scores: 1. Absenteeism (work time missed) 2. Presenteesism (impairment at work / reduced on-the-job effectiveness) 3. Work productivity loss (overall work impairment / absenteeism plus presenteeism) 4. Activity Impairment. Each score ranges from 0 to 100, with higher numbers indicating greater impairment and less productivity.

Time frame: Up to Week 260

Change from Baseline in Patient Global Assessment (PtGA) Score

The PtGA is participant-administered, single-item question evaluating the impact of health and illness, with responses ranging from very poor to very well on a 100 mm VAS. The participant will consider the previous week when addressing this question.

Time frame: Up to Week 260

Number of Participants with Clinically Relevant Abnormalities in Standard Laboratory Parameters

Standard laboratory parameters will include hematology, blood chemistry, urinalysis, and coagulation.

Time frame: Up to Week 284

Number of Participants with Clinically Relevant Abnormalities in Electrocardiogram (ECG) Results

Time frame: Up to Week 260

Number of Participants with Antibodies to Litifilimab

Time frame: Up to Week 284