APL2-C3G-310

This is a Phase 3 study to assess the efficacy and safety of twice-weekly subcutaneous (SC) doses of pegcetacoplan compared to placebo in patients with C3 glomerulopathy (C3G) or immune-complex membranoproliferative glomerulonephritis (IC-MPGN) on the basis of a reduction in proteinuria.

Inclusion Criteria:

1. Aged at least 18 years; where approved, adolescents (aged 12-17 years) weighing at least 30 kg may also be enrolled.

2. A diagnosis of primary C3G or IC-MPGN (with or without previous renal transplant).

3. Evidence of active renal disease, based on one or more of the following:

   1. In adults or adolescents with a baseline renal biopsy (either one collected during screening or a historic biopsy collected within 28 weeks prior to randomization), at least 2+ C3c staining on the baseline renal biopsy.

   2. In adolescents not providing a baseline renal biopsy, at least one of the

Following:

• Plasma sC5b-9 level above the upper limit of normal during screening

• Serum C3 below the LLN during screening

• Presence of an active urine sediment during screening, as evidenced by hematuria with at least 5 red blood cells (RBCs) per high-power field (HPF) and/or red blood cell casts on local or central microscopic analysis of urine.

• Presence of C3 nephritic factor within 6 months of screening, based on central laboratory results or medical history.

1. No more than 50% global glomerulosclerosis or interstitial fibrosis on the baseline biopsy for adult participants or adolescent participants providing a baseline biopsy.

2. At least 1 g/day of proteinuria on a screening 24-hour urine collection and a uPCR of at least 1000 mg/g in at least 2 first-morning spot urine samples collected during screening.

3. eGFR ≥30 mL/min/1. 73 m2 calculated by the Chronic Kidney Disease-Epidemiology Collaboration creatinine equation for adults or the Bedside Schwartz equation for adolescents.

4. Stable regimen for C3G/IC-MPGN treatment, as described below:

   1. Angiotensin-converting enzyme inhibitor/, angiotensin receptor blocker, and/or sodium-glucose cotransporter-2 inhibitor therapy that is stable and optimized, in the opinion of the investigator, for at least 12 weeks prior to randomization

   2. Stable doses of other medications that can affect proteinuria (eg, steroids, mycophenolate mofetil, and/or other allowed immunosuppressants that the participant is receiving for treatment of C3G or IC-MPGN) for at least 812 weeks prior to the baseline renal biopsy and randomization.

   3. If a participant is on prednisone (or other systemic corticosteroid) for C3G or IC-MPGN treatment, the dosage is stable and no higher than 20 mg/day (or equivalent dosage of a corticosteroid other than prednisone) for at least 12 weeks prior to randomization.

5. Have received vaccinations against S pneumoniae, N meningitidis (types A, C, W, Y, and B), and H influenzae (type B) within 5 years prior to randomization or agree to receive vaccinations during screening.

Exclusion Criteria:

1. Previous exposure to pegcetacoplan.

2. C3G/IC-MPGN secondary to another condition (eg, infection, malignancy, monoclonal gammopathy, a systemic autoimmune disease such as systemic lupus erythematosus, chronic antibody-mediated rejection, or a medication), in the opinion of the investigator.

3. Current or prior diagnosis of human immunodeficiency virus (HIV), hepatitis B (HBV), or hepatitis C (HCV) infection or positive serology during screening that is indicative of infection with any of these viruses.

4. Body weight greater than 100 kg at screening.

5. Hypersensitivity to pegcetacoplan or to any of the excipients.

6. History of meningococcal disease.

7. Malignancy, except for the following:

   1. Cured basal or squamous cell skin cancer

   2. Curatively treated in situ disease

   3. Malignancy-free and off treatment for ≥5 years

8. Severe infection (eg, requiring IV antibiotic therapy) within 14 days prior to the first dose of pegcetacoplan.

9. An absolute neutrophil count