Key Inclusion Criteria:

   1. Male or female adults, ≥ 18 years of age at time of informed consent.

   2. Clinical diagnosis of IgG4-RD.

   3. Fulfillment of the 2019 ACR/EULAR classification criteria.

   4. Experiencing (or recently experienced) an IgG4-RD flare that requires initiation or
   continuation of glucocorticoid (GC) treatment at the time of informed consent.

   5. IgG4-RD affecting at least 2 organs/sites at any time in the course of IgG4-RD

   6. Non-sterilized male subjects who are sexually active with a female partner of
   childbearing potential must use a condom with spermicide from Day 1 through to the end
   of the study and must agree to continue using such precautions for at least 6 months
   after the final dose of IP. Females of childbearing potential who are sexually active
   with a non-sterilized male partner must use a highly effective method of contraception

Key Exclusion Criteria:

   1. History of solid organ or cell-based transplantation or known immunodeficiency
   disorder .

   2. Active malignancy or history of malignancy that was active within the last 10 years
   (some specific situations for cervical, skin or prostate cancer are acceptable).

   3. Receipt of any biologic B cell-depleting therapy or non-depleting B-cell-directed
   therapy in prior 6 months

   4. Receipt of non-biologic DMARD or immunosuppressive agent other than GCs within prior 4
   weeks

   5. Active tuberculosis or high risk for tuberculosis; hepatitis C infection in absence of
   curative treatment; evidence of hepatitis B infection

   6. Live vaccine or therapeutic agent in prior 2 weeks

   7. Glomerular filtration rate < 30 mL/min/1.73 m2