Amendment 1 provided a number of clarifications to the original protocol: • Re-designation of other efficacy variables to secondary efficacy variables. • Proteinuria eligibility range was changed to a single value. • Clarification on handling study drug added, recording concomitant medications, to collect only relevant medication history. • Corrections made to subject numbering and administrative updates. • Updates added to clarify urine pregnancy test will be performed at the investigative sites. • Provided procedures for pregnancy reporting and follow-up.

Amendment 2 provided a number of clarifications to the original protocol: • Edited text to keep text consistent with European Medicines Agency guideline wording. • Increased criterion window to allow for varying institutional standards. • Revised visit day when recording of diary data begins. • Clarification of blood draw occurring at the Baseline visit does not apply to the pSC#2 trough as results are reported after first investigational product dose. • Added explanation of intent of criterion “The subject has known Selective Immunoglobulin A (IgA) Deficiency (with or without antibodies to IgA).” • Revised to exclude other IgG products as it is unnecessary to wait 3 months prior to screening a subject if they have received another investigational IgG product. • Revision to define a minimum time frame and human immunodeficiency virus screening results based on updated information from the Central Lab results timing. • Clarification of delegated medical monitor role. • “SC” added as it was intended only to be applicable to the investigational product Treatment Phase. • Expansion of visit window added for subject scheduling accommodation. • Expanded adverse event reporting criterion to include potential systemic infusion reactions. • Removed X-ray requirement during Screening for pediatric subjects to limit radiation exposure and comply with local requirements for adult subjects. • Moved initial use of the SC infusion diary from Screening to Baseline visit. • Removed requirement to repeat Screening safety labs as Screening/Previous Regimen Phase window is limited to 8 weeks and such lab parameters are not anticipated to significantly change in this timeframe for the targeted study population. • Revised for clarification on timing of withdrawal due to pregnancy. • Revisions made for internal consistency. • Removed IgG row to avoid an additional blood draw for certain subjects.

Amendment 3 provided a number of clarifications to the original protocol: • Added requirement of assent as both consent and assent are required for inclusion. • Removed weight measurement at every clinic visit as it was not accurate. • The restriction to local infusion site reaction (ISRs) was removed to allow for the collection of all ISRs. • Added additional vial size of 20 mL that contains 4 grams of immune globulin. • Infusion rates were revised to reflect recently published data supporting the safety of higher infusion rates. • Clarification that the delegated medical monitor role may be consulted for such cases. • Deleted beginning time period of 4 weeks for clarity due to variable dosing intervals. • Added timing for consistency within the protocol. • Heading was revised as Visit #2 only applies to pIV dosing. • Expanded IgG trough sample collection window to accommodate subject visit logistics across sites • Added criterion for removal of subjects who develop an SBI prior to first dose of IGSC 20%.