A Study to Evaluate the Effectiveness and Safety of Sibeprenlimab in Participants With Primary Membranous Nephropathy, Immune-mediated Focal Segmental Glomerulosclerosis, and Minimal Change Disease

• Sibeprenlimab (Drug), also known as VIS649: SC injection

Primary outcomes

• pMN: Percentage of Participants With More Than (>) 80 Percent (%) Reduction From Baseline in Anti-Phospholipase A2 Receptor (PLA2R) [Week 25]
• IM-FSGS and MCD: Percentage of Participants Remaining in Remission (Complete or Partial Remission) at Week 25 [Week 25]: Complete or partial remission will be determined from the urinary protein/creatinine ratio \[uPCR\] and serum albumin measurements. The criteria for complete remission include uPCR less than \[<\] 0.3 gram per gram \[g/g\] and normal serum albumin > 3.5 grams per liter \[g/L\]). Criteria for partial remission include uPCR < 1.0 g/g and normal serum albumin > 3.5 g/L.

Secondary outcomes

• pMN: Change From Baseline in Anti-PLA2R [Baseline, Week 25]
• pMN, IM-FSGS, and MCD: Number of Participants With Treatment Emergent Adverse Events (TEAEs) and Serious TEAEs [Up to Week 37]
• pMN, IM-FSGS, and MCD: Number of Participants With Clinically Significant Change in Laboratory Assessments From Baseline [Baseline, Week 37]
• pMN, IM-FSGS, and MCD: Number of Participants With Clinically Significant Change in Vital Sign Measurements From Baseline [Baseline, Week 37]
• pMN, IM-FSGS, and MCD: Number of Participants With Clinically Significant Change in Physical Examination Findings From Baseline [Baseline, Week 37]
• pMN, IM-FSGS, and MCD: Change From Baseline in Serum Drug Concentration [Baseline, Week 37]
• pMN, IM-FSGS, and MCD: Change From Baseline in A Proliferation Inducing Ligand (APRIL) Concentrations [Baseline, Week 37]
• pMN, IM-FSGS, and MCD: Number of Participants With Serum Anti-Drug Antibodies (ADA) [Up to Week 37]

Sex: All, ages: 18 Years to 75 Years

Inclusion Criteria:

For people with pMN:

1. Be experiencing their first episode of pMN, or have pMN that has returned after getting better (relapsed), with ongoing signs of significant kidney disease based on urine and blood tests.
2. Have a blood test showing high levels of antibodies against PLA2R, a protein linked to pMN, and these antibody levels must not have improved significantly over the previous 8 to 24 weeks.
3. Be taking a stable, maximum tolerated dose of a kidney-protective medication (such as an angiotensin converting enzyme (ACE) inhibitor or angiotensin II receptor blockers \[ARB\]) for at least 3 months before screening. Other medications that help reduce protein in the urine may also be allowed if the dose has remained unchanged for at least 3 months.

For people with IM-FSGS or MCD:

1. Have previously been diagnosed with IM-FSGS or MCD, confirmed by a kidney biopsy.
2. Currently have their disease well controlled, either in complete remission or partial remission, based on urine and blood test results.
3. Have a disease that depends on immunosuppressive treatment (medications that reduce immune system activity), meaning:

   * They need ongoing treatment with medications such as steroids or calcineurin inhibitors (CNIs) to keep the disease under control; and
   * Within the last 18 months, they experienced a return of nephrotic syndrome (severe kidney disease symptoms) shortly after reducing or stopping immunosuppressive treatment.
4. Be taking a stable dose of steroids or CNIs for at least 4 weeks before screening.

Exclusion Criteria:

1. Have a kidney condition other than pMN, IM-FSGS or MCD, or have previously received a kidney transplant.
2. Have another serious autoimmune disease that could affect their health or study results.
3. Have a serious active infection, such as human immunodeficiency virus (HIV), hepatitis B, hepatitis C, tuberculosis (TB), or other significant chronic infections.
4. Have uncontrolled high or low blood pressure.
5. Have a serious medical condition, including certain cancers, that could make study participation unsafe.
6. Have Type 1 diabetes or poorly controlled Type 2 diabetes.
7. Have recently received certain immune-suppressing treatments or other medications that could interfere with the study.
8. Are currently participating in another clinical trial or have recently received an investigational medicine.
9. Have a history of a severe allergic reaction to ingredients in the study drug.
10. Have recent alcohol or substance abuse that could interfere with participation.
11. Are unable to follow study procedures or attend required study visits.

Note: Other protocol-specified Inclusion/Exclusion criteria may apply.