• Documentation of IgAN diagnosis established on kidney biopsy obtained any time prior to or during the Screening Period for participants with eGFR ≥ 30 mL/min/1.73 m\^2.

• For participants in the AdKD cohorts, eGFR 20 to 29 mL/min/1.73 m2 a kidney biopsy is required within 6 months prior to Screening or during the Screening Period.

• UPCR ≥ 0.75 g/g or UP ≥1 g/day calculated from the mean of two 24-hour urine during the Screening Period.

• Estimated GFR ≥ 30 mL/min/1.73 m2 at Screening.

• Stable and maximum allowed or tolerated RASI (ACEI and/or ARB) dose for ≥ 3 months prior to Screening with no planned change during Screening through Week 106.

• Participants who are receiving SGLT2I, DEARA, MRA or ERA must be on a stable and maximum allowed or tolerated dose for ≥ 3 months prior to Screening with no planned change in dose through Week 106.