A Study of PRN1008 in Patients With Pemphigus

Inclusion Criteria: * Male or female participants, aged 18 to 80 years old with moderate to severe, newly diagnosed or relapsing PV or PF, with a clinical presentation and histopathology consistent with PV or PF. * Positive circulating anti-desmoglein 1 (anti-dsg1) or 3 autoantibody titer. * At screening, pemphigus disease area index score of at least 9 points for relapsing participants or at least 15 points for newly diagnosed participants. * Adequate hematologic, hepatic, and renal function. * Effective means of contraception. Exclusion Criteria: * Suspected paraneoplastic pemphigus and other forms of pemphigus that were not PV or PF. * Previous use of a Bruton tyrosine kinase inhibitor. * Pregnant or lactating women. * Electrocardiogram clinically significant abnormalities. * A history of malignancy of any type within 5 years before Day 1, other than surgically excised non-melanoma skin cancers or in situ cervical cancer. * Use of immunologic response modifiers as concomitant medication and with the washout period. * Use of proton pump inhibitor drugs such as omeprazole and esomeprazole within 3 days of Day 1. * Concomitant use of known strong-to-moderate inducers or inhibitors of cytochrome P450 3A (CYP3A) within 3 days or 5 half-lives (whichever is longer) of Day 1 * Use of CYP3A-sensitive substrate drugs. * Had received any investigational drug within the 30 days before Day 1. * History of drug abuse within the previous 12 months. * Alcoholism or excessive alcohol us…