A Long-Term Extension Study to Learn More About the Safety of Litifilimab (BIIB059) Injections and Whether They Can Improve Symptoms of Adult Participants Who Have Active Cutaneous Lupus Erythematosus (LTE AMETHYST)

In this study, researchers will learn more about a study drug called litifilimab (BIIB059) in participants with cutaneous lupus erythematosus (CLE). The study will focus on participants who have either active subacute CLE or chronic CLE, or both. They may also have systemic lupus erythematosus (SLE). The participants did not respond to antimalarial therapy or had problems with the treatment that made it hard to continue.

The study will enroll only those participants who have completed treatment with litifilimab in the parent study, 230LE301.

The main objective of the study is learning more about the long-term safety of litifilimab.

The main question researchers want to answer is:

- How many participants have adverse events and serious adverse events after taking litifilimab? Adverse events are unwanted medical problems that may or may not be caused by the study drug.

Researchers will also learn more about the effect of litifilimab on CLE. They will do this by measuring the symptoms of CLE over time using a variety of scoring tools. These include the Cutaneous Lupus Erythematosus Disease Area and Severity Index (CLASI), the Cutaneous Lupus Activity of Investigator's Global Assessment-Revised (CLA-IGA-R), and the SELENA-SLEDAI Flare Index (SFI).

Researchers will assess the effect litifilimab and CLE has on the quality of life of participants using a group of questionnaires. They will also study how litifilimab affects laboratory tests and how participants' immune systems respond to litifilimab.

The study will be done as follows:

* The last visit of parent study 230LE301 will be the first visit of study 230LE305.
* All participants will receive litifilimab as an injection under the skin once every 4 weeks. Both researchers and participants will know the dose and identity of the study drug.
* The treatment period will last up to 104 weeks, or 2 years.
* There will be a follow-up safety period that lasts up to 24 weeks.
* In total, participants will have up to 33 study visits.
* The total study duration for participants will be up to 128 weeks.

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 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.

Eligibility Criteria:
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.