Part A is a randomized, double-blind, placebo-controlled, multi-center Proof-of-Concept (POC) Trial in subjects with severe Alopecia Areata. All participants in Part A have completed participation.

Part B is a multicenter, open-label study to assess the efficacy, safety, and tolerability of bempikibart (ADX-914) in participants with severe Alopecia Areata.

Part A is a Phase IIa, Randomized, Double-blind, Placebo-controlled, multi-center Proof-of-Concept (POC) study in adult subjects with severe Alopecia Areata (AA). Bempikibart (ADX-914) or matching placebo is administered subcutaneously in the clinic setting every 2 weeks for 24 weeks, with follow-up for 12 weeks. Subjects will be randomized 3:1 to drug vs placebo. All participants in Part A have completed participation.

Part B is a multicenter, open-label study comprised of a screening period of up to 4 weeks, a treatment period of 36 weeks, and a follow-up period of 16 weeks, for a total study duration of up to 56 weeks.

Part A Open Label Extension Cohort is a multicenter, open-label extension to assess the long-term efficacy, safety, and tolerability of bempikibart (ADX-914) in participants with severe AA who experienced hair regrowth as participants in Part A of the study. Participants enrolled in the Open Label Extension Cohort will receive bempikibart (ADX-914) for a duration of 6 months followed by a 16-week follow-up period.

Part B Open Label Extension Cohort is a multicenter, open-label extension to assess the long-term efficacy, safety, and tolerability of bempikibart (ADX-914) in participants with severe AA who experienced hair regrowth as participants in Part B of the study. Participants enrolled in the Open Label Extension Cohort will receive bempikibart (ADX-914) for a treatment period of 36 weeks, and follow-up period of 16 weeks, for a total study duration of up to 52 weeks.

Key Inclusion Criteria:

1. Adult men and women, aged 18 to 75 years, inclusive, at the time of informed consent.
2. Clinical diagnosis of severe to very severe alopecia areata, defined as the presence of ≥50% total scalp hair loss at screening and baseline as measured by the SALT score.

Key Exclusion Criteria:

1. History of or diagnosis at screening of any another form of alopecia based on assessment by investigator.
2. History (lifetime) or presence of hair transplants.
3. History (lifetime) or presence of micropigmentation of the scalp (Note: Microblading of the eyebrows is permitted).
4. Use of systemic, topical, or device-based therapy for AA.
5. History of, recent, or current clinically serious viral, bacterial, fungal, or parasitic infection or mycobacterial infection or at risk of serious infection.

Part A was double blind-randomized. Part B and OLE are open label.