A Long-Term Extension Study to Evaluate Continuous Safety and Efficacy of BIIB059 (Litifilimab) in Adults With Active Subacute Cutaneous Lupus Erythematosus (CLE) and/or Chronic CLE With or Without Systemic Manifestations and Refractory and/or Intolerant to Antimalarial Therapy (AMETHYST LTE)

A Long-Term Extension Study to Evaluate Continuous Safety and Efficacy of BIIB059 (Litifilimab) in Adults With Active Subacute Cutaneous Lupus Erythematosus (CLE) and/or Chronic CLE With or Without Systemic Manifestations and Refractory and/or Intolerant to Antimalarial Therapy

A Multicenter, Open-Label, Single-Arm, Phase 3, Long-Term Extension Study to Evaluate Continuous Safety and Efficacy of BIIB059 (Litifilimab) in Adult Participants With Active Subacute Cutaneous Lupus Erythematosus and/or Chronic Cutaneous Lupus Erythematosus With or Without Systemic Manifestations and Refractory and/or Intolerant to Antimalarial Therapy

The primary objective of the study is to evaluate the long-term safety and tolerability BIIB059 (litifilimab) in participants who completed the parent study 230LE301 (NCT05531565) with active subacute CLE and/or chronic CLE with or without systemic manifestations and refractory and/or intolerant to antimalarial therapy. The secondary objectives of the study are to evaluate the long-term effect of litifilimab on disease activity and the effect of litifilimab in preventing disease damage in participants with active subacute CLE and/or chronic CLE with or without systemic manifestations and refractory and/or intolerant to antimalarials; to evaluate the long-term effect of litifilimab on preventing lupus flare in participants with CLE with systemic lupus erythematosus (SLE); to assess long-term use of oral corticosteroid (OCS) in participants receiving litifilimab treatment; to assess the impact of litifilimab on participant-reported health-related quality of life (HRQoL); to evaluate long-term effect of litifilimab on laboratory parameters; to evaluate the immunogenicity and pharmacokinetics (PK) of litifilimab.

Number of Participants With Treatment-Emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs)

Percentage of Participants who Achieve a Cutaneous Lupus Erythematosus Disease Area and Severity Index Activity Score (CLASI)-70 Response, Defined as a 70% Improvement in CLASI-A Score From the Baseline Value (Parent Study [NCT05531565])

Percentage of Participants who Achieve a CLASI-50 Response, Defined as a 50% Improvement in CLASI-A Score From the Baseline Value (Parent Study [NCT05531565])

Percentage of Participants who Achieve a CLASI-90 Response, Defined as a 90% Improvement in CLASI-A Score From the Baseline Value (Parent Study [NCT05531565])

Percentage of Participants who Achieve a Cutaneous Lupus Activity of Physician's Global Assessment-Revised (CLA-IGA-R) Erythema Score of 0 or 1

Percentage of Participants who Achieve a CLA-IGA-R Other Morphologic Characteristics (OMC) Score of 0 or 1

Cumulative Duration of Sustained CLASI-70 Response, Defined as the Number of Weeks With 70% Improvement in CLASI-A Score From the Baseline Value (Parent Study [NCT05531565])

Cumulative Duration of Sustained CLASI-50 Response, Defined as the Number of Weeks With 50% Improvement in CLASI-A Score From the Baseline Value (Parent Study [NCT05531565])

Cumulative Duration of Sustained CLASI-90 Response, Defined as the Number of Weeks With 90% Improvement in CLASI-A Score From the Baseline Value (Parent Study [NCT05531565])

Cumulative Duration of Sustained Efficacy, Defined as the Number of Weeks With CLA-IGA-R Erythema Score of 0 or 1

Cumulative Duration of Sustained Efficacy, Defined as the Number of Weeks With CLA-IGA-R OMC Score of 0 or 1 and Improvement of at Least 1 Point From Baseline Value (Parent Study [NCT05531565])

Cumulative Duration of Sustained Efficacy, Defined as the Number of Weeks With CLA-IGA-R Follicular Activity Score of 0

Percentage of Participants With a CLASI-70 Response Among CLASI-70 Responders at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With a CLASI-50 Response Among CLASI-50 Responders at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With a CLASI-90 Response Among CLASI-90 Responders at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With a CLA-IGA-R Erythema Score of 0 or 1 Among Participants With a CLA-IGA-R Erythema Score of 0 or 1 at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With CLA-IGA-R OMC Score of 0 or 1 and at Least 1 Level of Improvement From Baseline Value(Parent Study) Among Participants With CLA IGA R OMC Score of 0 or 1 and at Least 1 Level Improvement From Baseline Value(Parent Study)

Percentage of Participants With a CLASI-70 Response Among CLASI-50 Responders at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With a CLASI-90 Response Among CLASI-50 Responders at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With a CLASI-90 Response Among CLASI-70 Responders at Week 52 of the Parent Study (NCT05531565)

Percentage of Participants With Loss of Response, Defined as an Increase of ≥ 7 Points in CLASI-A Total Score From Baseline

Percentage of Participants With Loss of Response, Defined as Achieving 2 Points Improvement From Baseline Value(Parent Study) CLA-IGA-R Erythema Score at Beginning of/During LTE Study and Then Relapsing to CLA-IGA-R Erythema Baseline Value(Parent Study)

Percentage of Participants With Loss of Response, Defined as Having at Least 2, 3, and 4 Points Worsening in CLA-IGA-R Erythema Score From Their Minimum Score in Parent Study (NCT05531565)

Absolute Change in Cutaneous Lupus Erythematosus Disease Area and Severity Index Damage (CLASI-D) Score From the Baseline (Parent Study [NCT05531565]) to Week 104

Annualized Mild/Moderate and Severe Safety of Estrogens in Lupus Erythematosus National Assessment-SLE Disease Activity Index Flare Index (SFI) Rates From Baseline Value (Parent Study [NCT05531565]) Through Week 52

Annualized Mild/Moderate and Severe SFI Rates From Baseline Value (Parent Study [NCT05531565]) Through Week 104

Change From Baseline Value (Parent Study [NCT05531565]) in Cutaneous Lupus Erythematosus - Quality of Life (CLE-QoL) at Weeks 52 and 104

Change From Baseline Value (Parent Study [NCT05531565]) in European Quality of Life - 5-Dimensions Questionnaire, 3-Level Version (EQ-5D-3L) at Weeks 52 and 104

Change From Baseline Value (Parent Study [NCT05531565]) in 36-Item Short Form Survey (SF-36) (acute version) at Weeks 52 and 104

Change From Baseline Value (Parent Study [NCT05531565]) in Work Productivity and Activity Impairment (WPAI): Lupus at Weeks 52 and 104

Change From Baseline Value (Parent Study [NCT05531565]) in Patient Health Questionnaire-9 (PHQ-9) at Weeks 52 and 104

Number of Participants With Clinically Relevant Change From Baseline Value (Parent Study [NCT05531565]) in Standard Laboratory Parameters

Number of Participants With Clinically Relevant Change From Baseline Value (Parent Study [NCT05531565]) in ECG Results

Key Inclusion Criteria: Participants who completed the parent study (230LE301 [NCT05531565], Part A or Part B) on study treatment (received treatment through Week 48 and attended the last study assessment visit at Week 52). Ability of the participant to understand the purpose and risks of the study, to provide informed consent, and to authorize the use of confidential health information in accordance with national and local privacy regulations. Key Exclusion Criteria: Early Part A or Part B parent study (230LE301 [NCT05531565]) treatment terminators (participants who discontinued study treatment before Week 48). Early Part A or Part B parent study terminators [participants who withdrew from parent study participation before Week 52 and did not complete the parent study extended treatment period (ETP)]. Participants who have developed any other medical diseases, conditions, or abnormalities, rendering their participation in the long-term extension (LTE) study unsuitable in the opinion of the Investigator. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

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