A Study to Evaluate the Safety and Efficacy of FB102 in Patients With Severe to Very Severe Alopecia Areata.

This is a randomized, double-blind, placebo-controlled study evaluating the safety and efficacy of FB102 in patients with severe to very severe alopecia areata (AA).

Up to approximately 32 participants who meet all the Screening eligibility criteria will be randomized in a 3:1 ratio to receive FB102, or placebo dosing to match.

Inclusion Criteria: * Males aged 18-60 years and females aged 18-75 years at Screening. * Clinical diagnosis of severe to very severe AA with ≥50% scalp hair loss (including AT or AU) confirmed by SALT score and central photo review; no other cause of hair loss. * AT = complete scalp hair loss; AU = complete scalp, facial, and body hair loss. Note: There are additional inclusion criteria. The study center will determine if participant meets all of the criteria Exclusion Criteria: * Other types of alopecia (e.g., diffuse AA, traction, scarring alopecia, telogen effluvium, trichotillomania, chemotherapy-induced hair loss, androgenetic alopecia). * Other scalp diseases impacting AA assessment (e.g., psoriasis, dermatitis, tinea capitis). * Active systemic diseases causing hair loss (e.g., lupus, thyroiditis, systemic sclerosis, lichen planus, syphilis). Note: There are additional exclusion criteria. The study center will determine if participant meets all of the criteria