This is an open-label, proof-of-concept, single group study in adult participants with newly diagnosed, moderate to extensive BP.

Inclusion Criteria:

1. Males or females, ≥ 60 years of age.

2. Karnofsky performance status > 60%

3. Newly diagnosed, Bullous Pemphigoid per standard diagnostic criteria:

   • Clinical presentation [2]
   • Skin biopsy from a fresh blister showing subepidermal clefting and an inflammatory infiltrate consisting mainly of eosinophils
   • Immunofluorescence (IF) studies performed on uninvolved skin collected approximately 1 cm away from a fresh blister showing linear deposition of IgG and/or C3 along the basement membrane zone.

4. Moderate to extensive Bullous Pemphigoid defined by the mean number of new bullae and urticarial plaques that have appeared over the course of 3 days as determined by the investigator or referring physician (moderate disease defined by > 1 and ≤ 10 new bullae daily and ≥ 5 urticarial plaques and extensive disease by >10 new bullae daily) [3].

5. Adequate cardiac, renal and hepatic function as determined by the Investigator and demonstrated by screening laboratory evaluations, vital sign measurement, ECG recording and physical examination results.

6. Females of childbearing potential must agree to use effective contraception consistently throughout the study (such as hormonal contraception or two forms of barrier contraception) and have a negative serum pregnancy test at screening and a negative urine pregnancy test per the schedule of visits. Women are considered post-menopausal and not of childbearing potential if they have had 12 months of amenorrhea or have had surgical bilateral oophorectomy (with or without hysterectomy) or tubal ligation at least six weeks previously.

7. Males must have had a vasectomy or have expressed that they have no interest in fertility in the future.

8. Fertile males must agree to use effective contraception consistently throughout the study and for a period of four months following the end of study drug administration.

9. Willing and able to adhere to the study visit schedule and other protocol requirements.

10. Willing and able to provide voluntary written informed consent or written informed consent from a legally authorized representative with assent from the patient.

Exclusion criteria:

1. Patients with severe medical or surgical conditions at screening or baseline including, but not limited to, severe dementia or mental impairment, severe stroke, severe cardiac insufficiency, severe arterial hypertension, severe or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, cardiac, neurologic, cerebral, psychiatric, or any other severe acute or chronic medical condition that may increase the risk associated with study participation/treatment or may interfere with the interpretation of study results and, in the Investigator's opinion, would make the patient inappropriate for study entry.

2. Presence of any malignancy that has been under active treatment (e.g., radiotherapy or chemotherapy) within the 2 years prior to baseline or is anticipated to require treatment during the study period (including follow up) with the exception of patients with removal of uncomplicated basal cell carcinoma or cutaneous squamous cell carcinoma, who may take part in the study.

3. Congenital or acquired immunodeficiency (e.g., common variable immunodeficiency, organ transplantation).

4. Clinically significant vital sign measurements or ECG findings as determined by the Investigator.

5. Clinically significant abnormal laboratory test results, unless regarded by the Investigator as related to BP, including but not limited to:

   • Hemoglobin level <10.0 g/dL
   • White blood cell count < 3 x 103/μL
   • Lymphocyte count < 0.5 x 103/μL
   • Platelet count <100 x 103/μL or >1200 x 103/μL
   • Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) >3 the upper limit of normal (ULN)
   • Alkaline phosphatase >3 ULN
   • Serum creatinine >2 ULN

6. Patients with mild, relapsed or refractory Bullous Pemphigoid. Mild disease defined by the mean number of new lesions that have appeared over the course of 3 days as determined by the investigator or referring physician, as follows: ≤ 1 bulla or < 5 urticarial plaques.

7. Concomitant skin conditions preventing physical evaluation of Bullous Pemphigoid.

8. Active or recent history of clinically significant infection within 1 month of baseline.

9. Pregnant or breast-feeding, or planning to become pregnant during the study.

10. Participation in a clinical trial of an investigational (unapproved) product within 4 weeks of baseline.

11. Known hypersensitivity to bertilimumab or any of the drug excipients.

12. Use of prednisone or other systemic steroids (excluding inhaled or ocular use of steroids) within 4 weeks prior to baseline. (Concomitant oral corticosteroids administered as part of the study protocol, from Day 0 onward, are allowed). Use of class 1 and 2 topical steroids (such as clobetasol propionate cream, reference Appendix D for further guidance) within 4 weeks prior to baseline. (Use of other topical steroids is allowed throughout the study at the discretion of the investigator).

13. Treatment with immunosuppressants (e.g., azathioprine, methotrexate) within 4 weeks prior to baseline.

14. Treatment with biologics (e.g., etanercept, adalimumab, ustekinumab, infliximab, intravenous Ig) within 4 months of baseline. Patients who have received rituximab within 1 year of baseline will be excluded from study participation.

15. Treatment with macrolides or tetracyclines within 4 weeks prior to baseline.

16. Received a vaccine or other immunostimulator within 4 weeks prior to baseline. Subject has current clinical, radiographic or laboratory evidence of active mycobacterium tuberculosis (TB) infection or prior evidence of active TB that, in the opinion of the investigator, has not been adequately treated or controlled and that represents a reactivation risk. If in the investigator's opinion the patient is at risk for latent TB, the patient should be evaluated for active/latent TB as applicable (e.g. PPD, QFT, and/or chest x-ray).

18. Evidence of an active disease of hepatitis B (HBsAg positive or HBcAb positive) or hepatitis C (HCV ab positive), CMV (IgM positive) or human immunodeficiency virus (HIV) infection (HIV1/2 Ab positive 19. Active abuse of alcohol or drugs. 20. Any other condition, which in the opinion of the Investigator would place the patient at an unacceptable risk if participating in the study protocol.