Phase 2b Open-Label Repeat Kidney Biopsy Study

Prior treatment

• Participants who are breast-feeding and/or who have a positive pregnancy test result prior to receiving sibeprenlimab.
• Participant is currently receiving or has received within 24 weeks prior to the firstdose of sibeprenlimab, systemic corticosteroids or immunosuppression (note:
  • topical, ophthalmic, rectal, intra-articular, inhaled corticosteroids are allowed).
• Participants who would be likely to require prohibited concomitant therapy during the trial.

Other illness

• Participant has coexisting chronic kidney disease, other than IgAN.
• Participant has uncontrolled hypertension (defined as systolic blood pressure \> 140 mmHg or diastolic blood pressure \> 90 mmHg).

Lab values

• Participant has a serum IgG value \<600 mg/dL at screening.

• Participants must be at least 18 years of age or older at the time of signing the informed consent/assent.
• Source-verified kidney biopsy confirmed diagnosis of IgAN.
• Participant has eGFR \> 45 mL/min/1.73 m2 using serum creatinine based on CKD-EPI 2021 equation. Serum creatinine assessments for the determination of eGFR should be taken when the participant is considered to be in a steady state without recent changes in volume status, medications that could impact the result (eg, nonsteroidal anti-inflammatory drugs \[NSAIDs\], aminoglycosides, trimethoprim, cimetidine, pyrimethamine, fenofibrate, or creatine supplements), or changes in dietary protein intake.