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

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