This study is examining the safety and effectiveness of an injection called litifilimab (BIIB059) in adults with systemic lupus erythematosus (SLE). SLE is a disease where the immune system, which normally fights germs, mistakenly attacks the body. Participants with active SLE, already on standard medications like antimalarials and steroids, will be part of this study. The researchers want to see if litifilimab can help reduce SLE symptoms over time.

Participants will be randomly given either a high or low dose of litifilimab or a placebo (a fake treatment), once every 4 weeks for 52 weeks. Nobody, including the researchers, will know if a participant is getting the real medicine or placebo. Participants will continue their regular medications. There will be a follow-up period lasting up to 24 weeks, and participants will attend up to 22 study visits over 80 weeks.

• Study Duration: Up to 80 weeks total.
• Study Visits: Up to 22 visits.
• Treatment: Injections every 4 weeks; may receive a placebo.