A Proof-of-Concept Study of Topical AC-203 in Patients With Bullous Pemphigoid

1. Age 20 to 90 years old, inclusive, at enrollment.

2. Diagnosis of bullous pemphigoid confirmed by histopathology and one of following assessments:

   1. Direct immunofluorescence (DIF)
   2. Indirect immunofluorescence (IIF)
   3. ELISA test (ELISA detection of immunoglobulin G (IgG) anti-BP180 autoantibodies in serum more than 9 U/mL).
3. Localized or limited BP with the occurrence of \<10 new blisters per day in the week prior to enrollment.

4. Is male, or is female and meets all the following criteria:

   1. Not breastfeeding
   2. If of childbearing potential (defined as non-post hysterectomy or non-post-menopausal [≥50 years of age and amenorrheic for at least 1 year]), must have a negative pregnancy test result (human chorionic gonadotropin, beta subunit [bhCG]) at Visit 1, and must practice and be willing to continue to practice appropriate birth control (abstinence, double barrier methods, hormonal contraceptives, intrauterine device, or tubal ligation) during the entire duration of the study
5. Is able to understand and sign the Informed Consent Form (ICF), communicate with the investigator, and understand and comply with protocol requirements.

Exclusion Criteria:

1. Diagnosis of pemphigus, dermatitis, eczema, psoriasis, or other skin condition which in the opinion of the investigator may confound diagnosis, treatment, or evaluation of bullous pemphigoid.
2. Use of oral steroids in the 2 weeks prior to enrollment at a dose greater than prednisolone equivalent dose (PED) of 10 mg/day.
3. Use of topical steroids for more than 3 consecutive days in the 2 weeks prior to enrollment.
4. Use of non-steroid immunosuppressants including but not limited to azathioprine, mycophenolate, cyclophosphamide, chlorambucil, methotrexate, tacrolimus, or cyclosporine in the 2 weeks prior to enrollment.
5. Use of systemic antibiotics in the 2 weeks prior to enrollment.
6. Use of oral dapsone in the 2 weeks prior to enrollment.
7. Treatment with intravenous immunoglobulin (IVIG) in the 8 weeks prior to enrollment.
8. Any prior use of approved or investigational biologic anti-inflammatory therapy within 6 months prior to enrollment, including but not limited to: anakinra, rilonacept, canakinumab, etanercept, adalimumab, infliximab, rituximab, certolizumab, golimumab, tocilizumab, bertilimumab, or abatacept.
9. Presence of active systemic infections.
10. Any clinically significant medical condition or laboratory value that could potentially affect study participation and/or personal well-being, as judged by the investigator.
11. History of allergy or hypersensitivity to any component of study medication or clobetasol.
12. Has participated in a clinical study within 30 days prior to enrollment.
13. Is an immediate family member (spouse, parent, child, or sibling; biological or legally adopted) of personnel directly affiliated with the study at the clinical study site, or is directly affiliated with the study at the clinical study site.
14. Is employed by the sponsor (i.e., is an employee, temporary contract worker, or designee responsible for the conduct of the study).