The purpose of this study is to evaluate the efficacy, safety, pharmacokinetics (PK), and pharmacodynamics (PD) of KP104 in participants with IgAN and C3G. The study will start with enrolling the IgAN cohort. Approximately 42 participants with IgAN will be enrolled in 2 stages: Stage 1 will be used to collect safety, immunogenicity, PK, and PD data to select the optimal biologic dose (OBD) of KP104 for IgAN, as well as to preliminarily explore the effect of KP104 on C3G. Stage 2 will be used to collect safety, immunogenicity, PK, PD, and efficacy data at the OBD dose of KP104 for IgAN and C3G. As soon as the OBD for IgAN is determined, eligible participants with C3G will be enrolled and dosed at the OBD for IgAN for a minimum of 48 weeks for weekly maintenance dosing and a minimum of 47 weeks for biweekly maintenance dosing. Approximately 10 participants with C3G will be enrolled.
Weight of >35 kilograms (kg) at Screening
Body mass index (BMI) of <35 kilograms per square meter (kg/m²)
UPCR >1.0 grams per gram (g/g) by 24-hour urine collection at Screening
Diagnosis of IgAN verified by biopsy taken within the past 3 years prior to enrolment.
Any clinically significant, poorly controlled underlying illness other than IgAN or C3G, as determined by the investigator
Treatment of any infection with IV (within 30 days of Screening) or oral (within 14 days of Screening) antibiotics, antivirals, or antifungals
History of infections with encapsulated organisms
History of untreated tuberculosis
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Treatment groupsSee each treatment group below.