Inclusion Criteria:

• Patients must have characteristic clinical features of BP (e.g., urticarial or eczematous or erythematous plaques, bullae, pruritus) at the screening and baseline visits.
• Study participants are required to have histological and serological confirmation of BP by a confirmed diagnosis of BP based on histopathology, immunopathology, and serology at the baseline visit which includes. Required for inclusion:
  • Skin Compatible histopathologic findings on a skin biopsy showing an specimen supporting a diagnosis of BP (e.g., a subepidermal blister with eosinophils within the cleft, a mixed cellular inflammatory infiltrate mainly consisting of that includes eosinophils and); AND
  • Positive Characteristic direct immunofluorescence (findings on a skin biopsy specimen demonstrating linear IgG and/or C3 at the basement membrane zone) or indirect immunofluorescence (IgG on the roof of salt-split skin); AND
  • At least 1 of the following serologic assessments (utilizing a peripheral blood specimen):
  • Positive indirect immunofluorescence demonstrating IgG antibodies localizing to the roof (epidermal side) of split-skin substrate;
  • Increased IgG serum antibody levels by immunoassay to BP antigens, BPAG1 (230-kd, also known as BP230) and/or BPAG2 (180-kd, also known as BP180)
  • NOTE: Histopathology, immunopathology, and serologic testing performed at a local laboratory with results available within 6 months of the screening visit that confirm the diagnosis of BP are acceptable to fulfill the above criteria for diagnostic confirmation of BP.
• BPDAI activity score ≥ 24 at baseline and screening visits.
• Baseline peak pruritus NRS score for maximum itch intensity ≥ 4.
  • NOTE: Baseline peak pruritus NRS score for maximum itch intensity will be determined based on the average of daily NRS scores for maximum itch intensity (the daily score ranges from 0 to 10) during the 7 days immediately preceding randomization. A minimum of 3 daily scores out of the 7 days is required to calculate the baseline average score.
• Male or female, age 18 to 90 at the screening visit (age 20 to 90 for sites in Japan).
• Karnofsky performance status score ≥ 50% at the screening visit.
• Willing and able to comply with clinic visits and study-related procedures.
• Willing and able to understand and complete study-related questionnaires.
• Willing and able to provide voluntary signed informed consent.

Exclusion Criteria:

• Forms of pemphigoid other than classic BP (e.g., Brunsting-Perry cicatrial cicatricial pemphigoid, anti-p200 pemphigoid, epidermolysis bullosa acquisita, or BP with concomitant pemphigus vulgaris).
• Patients who are receiving treatments known to cause or exacerbate BP (e.g., angiotensin converting enzyme inhibitors, penicillamine, furosemide, phenacetin, dipeptidyl peptidase 4 inhibitor) who have not been on a stable dose of these medications for at least 4 weeks prior to the screening visit.
• Have ever received treatment with an IL-4 or IL-13 antagonist such as dupilumab, tralokinumab, or lebrikizumab.
• Treatment with systemic corticosteroids within 2 weeks 7 days before the baseline visit.
• Treatment with topical corticosteroids of medium potency or higher, topical calcineurin inhibitor, or topical crisaborole within 1 week 7 days before the baseline visit.
• Treatment with oral or topical antihistamines within 1 week before the baseline visit.
• Initiation, discontinuation, or change in the dosage regimen of systemic antihistamines within 7 days before the baseline visit. Patients on a stable dose of systemic antihistamines for at least 7 days prior to the baseline visit may be included in the study; however, the dose of these medications should remain unchanged for the duration of the study.
• Treatment with an antibiotic (such as doxycycline or dapsone) directed at the treatment of BP within 2 weeks 7 days before the baseline visit.
• Treatment with nicotinamide directed at the treatment of BP within 2 weeks 7 days prior to the baseline visit (note: use of multivitamins containing nicotinamide is allowed).
• Treatment with non-steroidal immunosuppressive/immunomodulating drug(s) (e.g., mycophenolate mofetil, azathioprine, or methotrexate) within 4 weeks before the baseline visit.
• Treatment with BP-directed biologics as follows:
  • Any cell-depleting agents including but not limited to rituximab: within 12 months before the baseline visit, or until lymphocyte and CD 19+ lymphocyte count returns to normal, whichever is longer;
  • Other biologics (such as IL-5 inhibitors benralizumab or mepolizumab): within 5 halflives (if known) or 16 weeks prior to the baseline visit, whichever is longer;
  • Intravenous immunoglobulin within 16 weeks prior to the baseline visit.
• Treatment with a live (attenuated) vaccine within 4 weeks before the baseline visit.
• Planned or anticipated use of any prohibited medications or procedures during study treatment.
• Any active infection requiring systemic treatment; patients with such infection must have their infection resolved at least 1 week before baseline to be eligible to enroll in the study.
• Diagnosed active endoparasitic infections; suspected or high risk of endoparasitic infection, unless clinical and (if necessary) laboratory assessment have ruled out active infection before randomization.
• Known or suspected history of immunosuppression, including history of invasive opportunistic infections (e.g., tuberculosis [TB], histoplasmosis, listeriosis, coccidioidomycosis, pneumocystosis, aspergillosis) despite infection resolution: or unusually frequent, recurrent, or prolonged infections, per investigator’s judgment.
• History of human immunodeficiency virus (HIV) infection or positive HIV serology at screening.
• With a current diagnosis of hepatitis B viral infection at the time of screening as evidenced by:
  • Positive hepatitis B surface antigen (HBsAg); or
  • Positive total hepatitis B core antibody (HBcAb) confirmed by positive hepatitis B virus (HBV) DNA.
  • NOTE: Patients who have gained immunity for hepatitis B virus infection after vaccination (patients who are HBsAg negative, hepatitis B surface antibody [HBsAb] positive, and HBcAb negative) or after natural infection (patients who are HBsAg negative, hepatitis B surface antibody [HBsAb] positive, and HBcAb positive) are eligible for the study. These patients will be allowed to enroll into the study, but will be followed using routine clinical and liver function tests.
• In case of results showing HBsAg negative, HBsAb negative, and HBcAb positive, an HBV DNA testing will be performed prior to randomization to rule out a false positivity and to confirm current infection.
• With a current diagnosis of hepatitis C viral infection at the time of screening as evidence by:
  • Positive hepatitis C virus (HCV) Ab; AND
  • Positive HCV RNA.
• On current treatment for hepatic disease including, but not limited to, acute or chronic hepatitis, cirrhosis, or hepatic failure, or has evidence of liver disease as indicated by persistent (confirmed by repeated tests ≥ 2 weeks apart) elevated transaminases (alanine aminotransferase [ALT] and/or aspartate aminotransferase [AST]) more than 3 times the upper limit of normal (ULN) during the screening period.
• Presence of any 1 or more of the following abnormalities in laboratory test results at screening: a. Platelet count ≤ 100×10^3 /μL b. Neutrophil count ≤ 1.5×10^3 /μL.
• Presence of skin comorbidities that may interfere with study assessments.
• History of malignancy within 5 years before the baseline visit, except completely treated in situ carcinoma of the cervix, or completely treated and resolved non-metastatic squamous or basal cell carcinoma of the skin.
• Known systemic hypersensitivity to dupilumab or the excipients of the drug product.
• Patients having a contraindication to systemic corticosteroids (e.g., severe osteoporosis, adrenal insufficiency, Cushing’s disease) that, in the investigator’s judgment, would adversely affect the patient’s participation in the study.
• Severe concomitant illness(es) that, in the investigator’s judgment, would adversely affect the patient’s participation in the study. Examples include, but are not limited to, patients with short life expectancy, patients with uncontrolled diabetes (HbA1c ≥ 9%), patients with cardiovascular conditions (e.g., stage III or IV cardiac failure according to the New York Heart Association classification), severe renal conditions (e.g., patients on dialysis), debilitating neurological conditions (e.g., demyelinating diseases), active major autoimmune diseases (e.g., lupus, inflammatory bowel disease, rheumatoid arthritis, etc.), other severe endocrinological, gastrointestinal, hepatobiliary, metabolic, pulmonary, or lymphatic diseases. The specific justification for patients excluded under this criterion will be noted in study documents.
• Any other medical or psychological condition (including relevant laboratory abnormalities at screening) that, in the opinion of the investigator, may suggest a new and/or insufficiently understood disease, may present an unreasonable risk to the study patient as a result of his/her participation in this clinical trial, may make patient’s participation unreliable, or may interfere with study assessments. The specific justification for patients excluded under this criterion will be noted in study documents.
• History of alcohol or drug abuse within 2 years before the screening visit.
• Patients who are committed to an institution by virtue of an order issued either by the judicial or the administrative authorities.
• Pregnant or breastfeeding women or planning to become pregnant or breastfeed during the patient’s participation in this study.
• Women of childbearing potential (WOCBP)* who are unwilling to practice highly effective contraception prior to the initial dose/start of the first treatment, during the study, and for at least 12 weeks after the last dose. Highly effective contraceptive measures include:
  • stable use of combined (estrogen- and progestogen-containing) hormonal contraception (oral, intravaginal, transdermal) or progestogen-only hormonal contraception (oral, injectable, implantable) associated with inhibition of ovulation initiated 2 or more menstrual cycles prior to screening;
  • intrauterine device; intrauterine hormone-releasing system;
  • bilateral tubal ligation;
  • vasectomized partner (provided that the male vasectomized partner is the sole sexual partner of the WOCBP study participant and that the vasectomized partner has obtained medical assessment of surgical success for the procedure);
  • and/or sexual abstinence †, ‡. *Women of childbearing potential are defined as women who are fertile following menarche until becoming postmenopausal, unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy, and bilateral oophorectomy. A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high follicle-stimulating hormone (FSH) level in the postmenopausal range may be used to confirm a postmenopausal state in women not using hormonal contraception or hormonal replacement therapy. However, in the absence of 12 months of amenorrhea, a single FSH measurement is insufficient to determine the occurrence of a postmenopausal state. The above definitions are according to Clinical Trial Facilitation Group guidance. Pregnancy testing and contraception are not required for women with documented hysterectomy or tubal ligation. †Sexual abstinence is considered a highly effective method only if defined as refraining from heterosexual intercourse during the entire period of risk associated with the study drugs. The reliability of sexual abstinence needs to be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. ‡Periodic abstinence (calendar, symptothermal, post-ovulation methods), withdrawal (coitus interruptus), spermicides only, and lactational amenorrhea method are not acceptable methods of contraception. Female condom and male condom should not be used together.
• Patient is a member of the investigational team or his/her immediate family.