Biogen’s Litifilimab Demonstrates Rapid and Durable Efficacy in New 52-Week Phase 2 Data from Ongoing Phase 2/3 AMETHYST Study, Reinforcing Its Potential as a First-in-Class Therapy for Cutaneous Lupus Erythematosus

• Continued improvement: An increased response was seen in participants on litifilimab from week 24 through week 52, with more individuals achieving clear or almost clear skin (27.2%; CLA IGA 0-1) and improvements in disease activity (28.8%; CLASI-70) than at week 24 (19.0% and 21.7%, respectively)
• Rapid onset: Participants that switched from placebo to litifilimab experienced improvements in skin disease activity in as early as four weeks -- consistent with results seen in participants who started on litifilimab reported earlier this year
• Consistent safety: Litifilimab's safety profile remained consistent with previous studies, with no new safety signals identified
• Results from the Phase 3 part of AMETHYST are expected in the first half of 2027; in January 2026 the FDA granted Breakthrough Therapy Designation to litifilimab in CLE

CAMBRIDGE, Mass., Oct. 02, 2026 (GLOBE NEWSWIRE) -- Biogen Inc. (Nasdaq: BIIB) today announced 52-week results from the Phase 2 part of the ongoing AMETHYST Phase 2/3 study (Part A) of litifilimab in people living with cutaneous lupus erythematosus (CLE). The updated results, presented at the European Academy of Dermatology and Venereology (EADV) 2026 Congress in Vienna, Austria, represent the longest dataset reported for litifilimab in CLE and further support its potential to achieve rapid and durable improvements in skin disease activity. In the study, participants treated with litifilimab in the double-blind, placebo-controlled period showed continued clinical improvements in skin disease activity through Week 52. Notably, participants who switched from placebo to litifilimab treatment at Week 24 experienced a rapid onset of treatment effect as early as four weeks.  

“Access to 52-week data is critical when evaluating a treatment for a lifelong, chronic disease like cutaneous lupus erythematosus, which can cause permanent scarring and disfigurement that many patients will carry with them forever. That is why achieving clear or almost clear skin, which is rarely seen in CLE, is a truly transformative treatment goal for this disease,” said Joseph F Merola, MD, MMSc, dermatologist, rheumatologist and President of the Rheumatologic Dermatology Society, Lupus Foundation Medical and Scientific Board. “It is highly encouraging to see continued improvement in skin clearance with litifilimab treatment – with over a quarter of participants reaching clear or almost clear skin – and data supporting litifilimab's long-term safety profile.”

Litifilimab is being evaluated as a potential once-monthly, first-in-class treatment designed to reduce inflammation at its source by selectively targeting blood dendritic cell antigen 2 (BDCA2) receptors on plasmacytoid dendritic cells (pDCs), which play a central role early in the inflammatory process in CLE. In January 2026, litifilimab was granted Breakthrough Therapy Designation by the U.S. Food and Drug Administration (FDA) for the treatment of CLE. 

The Phase 2 portion of the ongoing Phase 2/3 AMETHYST study evaluated 93 adults with active skin symptoms for whom standard antimalarial medications were not effective or not tolerable. Over the course of a full year, the study tracked key measures of skin redness, scaling and disease activity to assess how well litifilimab helped participants achieve healthier skin. By Week 52, more than a quarter (27.2%) of participants who received litifilimab from the beginning of the study achieved the clinical endpoint of clear or almost clear skin, as measured by a Cutaneous Lupus Activity Investigators' Global Assessment Revised (CLA-IGA-R) erythema score of 0 or 1, up from 19.0% at Week 24. Similar improvements were seen on the Cutaneous Lupus Erythematosus Disease Area and Severity Index Activity-70 (CLASI-70) measurement with 28.8% of participants receiving litifilimab from the beginning of the study achieving a 70% or greater reduction in CLASI A at Week 52, compared to 21.7% at Week 24. For participants who started the study on placebo and transitioned to litifilimab halfway through the study, the onset of benefit was rapid – as early as four weeks – when skin symptoms began to improve. By Week 52, approximately one in three (33.7%) of these crossover participants reported clear or almost clear skin.

“Living with cutaneous lupus erythematosus carries a heavy physical toll, including dyspigmentation, pain, and scarring, which can be associated with comorbidities like depression and anxiety that can have a profound impact on daily life. These 52-week data reinforce litifilimab's potential to deliver rapid improvement and demonstrate its durable skin clearance effects,” said Daniel Quirk, M.D., Chief Medical Officer at Biogen. “We are encouraged by these results that build on findings in earlier studies as we anticipate the upcoming Phase 3 study results that reflect our commitment to advancing targeted therapies for serious autoimmune conditions.”

Over the course of the 52-week treatment period, litifilimab was generally well tolerated with a safety profile consistent with previously reported Phase 2 studies and no new safety signals identified. The majority of adverse events (AEs) reported were mild or moderate in severity, and serious AEs occurred in 3.4% (3/88) of participants during the extended treatment period. The most common AEs (≥5% during the extended treatment period) were nasopharyngitis, influenza and arthralgia.  

“People living with cutaneous lupus erythematosus face debilitating symptoms, including scarring, hair loss, and extreme sensitivity to light, yet they have long relied on treatments not specifically developed or studied for CLE,” said Albert T Roy, President and CEO of the Lupus Research Alliance. “The new data on litifilimab are encouraging because they point to the potential for both rapid symptom relief and durable improvement for people living with this condition. We look forward to seeing additional data from the Phase 3 study.”

About AMETHYST

AMETHYST is a two-part, Phase 2/3 multicenter, double-blind, placebo controlled, randomized study to evaluate the efficacy and safety of litifilimab compared to placebo. The study aims to assess the efficacy of litifilimab in participants with active subacute cutaneous lupus erythematosus (SCLE) and/or chronic cutaneous lupus erythematosus (CCLE) who are refractory or intolerant to antimalarial therapy. The Phase 2 and Phase 3 parts of the study are each 52 weeks in duration. Participants will be randomized to receive subcutaneous treatment with litifilimab or placebo every four weeks for 20 weeks with an additional dose at Week 2. All participants will receive litifilimab during the 28-week extended treatment period from Weeks 24 to 48. The Phase 3 part of the AMETHYST study remains blinded and is expected to read out in the first half of 2027. More information on the AMETHYST study (NCT05531565) is available at clinicaltrials.gov.

About Litifilimab (BIIB059)

Litifilimab (known as BIIB059) is an investigational first-in-class monoclonal antibody that is the first potential treatment developed by Biogen for lupus and is being evaluated in patients with systemic lupus erythematosus (SLE) and cutaneous lupus erythematosus (CLE). Its targeted mechanism of action acts early in the disease pathway to address the immune dysregulation that drives lupus. Litifilimab selectively targets BDCA2 receptors on plasmacytoid dendritic cells (pDCs) to reduce inflammation. Biogen developed litifilimab over two decades as part of a dedicated lupus discovery and development program.

Litifilimab is an investigational therapeutic candidate that has not yet been approved by any regulatory authority, and its safety and effectiveness have not been established.

Positive results from the CLE portion of the two-part Phase 2 LILAC study were previously published in The New England Journal of Medicine (NEJM) showing litifilimab met the study's primary endpoint by demonstrating superior efficacy to placebo in reducing skin disease activity. In LILAC, litifilimab was generally well tolerated. The AMETHYST (NCT05531565) Phase 3 trial of litifilimab in CLE is currently ongoing.

About Cutaneous Lupus Erythematosus (CLE)

CLE, a type of lupus, is a serious autoimmune skin disease that impacts the daily lives of patients, including their emotional and mental health. It can lead to disfigurement in the form of hair loss, permanent scarring and abnormal skin color. In CLE, the immune system attacks healthy skin, causing rashes, pain, itching and sensitivity to sunlight. Currently, there are no approved targeted therapies for CLE and the last drug was approved in the 1950s.

About Biogen

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