This study is designed as a long-term extension to Study APL2-C3G-310, and is being conducted to establish the long-term safety and efficacy of pegcetacoplan in patients with C3 glomerulopathy (C3G) or immune-complex membranoproliferative glomerulonephritis (IC-MPGN).

Inclusion Criteria:

• Completed participation in Study APL2-C3G-310 through the week 52 visit requirements
• Experienced clinical benefit from pegcetacoplan while participating in the previous trial, in the opinion of the investigator
• Must remain on a stable regimen for C3G or IC-MPGN treatment according to the requirements of Study APL2-C3G-310
• Received vaccinations against S pneumoniae, N meningitidis (types A, C, W, Y, and B), and H influenzae (type B) according to the requirements of Study APL2-C3G-310 and agree to receive any additional vaccinations recommended according to ACIP recommendations for adults or children with complement deficiencies and/or immunocompromising conditions or other similar local applicable guidelines
• Female participants of childbearing potential, defined as any woman who has experienced menarche and who is not permanently sterile or postmenopausal, must have a negative urine pregnancy test at visit 1 and must agree to use protocol-defined methods of contraception for the duration of the study through at least 90 days after receiving the last dose of pegcetacoplan
• Male participants must agree to use protocol-defined methods of contraception and agree to refrain from donating semen for the duration of the study through at least 90 days after receiving the last dose of pegcetacoplan
• Participants above the legal age of consent, in accordance with local regulations, must be willing and able to provide informed consent. The legally authorized representative of participants under the legal age of consent must be willing and able to provide informed consent; where appropriate, participants under the legal age of consent must also give their assent to participation in the study
• Willing and able to self-administer pegcetacoplan or have an identified caregiver who can perform the administration

Exclusion Criteria:

• Female participants who are or are planning to become pregnant or who are currently breastfeeding and are unwilling to discontinue for the duration of the study and for at least 90 days after the final dose of study drug
• Inability or unwillingness to cooperate with the requirements of the protocol
• Any condition that, in the opinion of the investigator, creates an undue risk for the participant by participating in the study or is likely to confound interpretation of the study results
• Evidence of ongoing drug or alcohol abuse or dependence, in the opinion of the investigator