A Study to Evaluate IGSC 20% Biweekly Dosing in Treatment-Experienced Participants and Loading/Maintenance Dosing in Treatment-Naïve Participants With Primary Immunodeficiency

Inclusion Criteria: Inclusion Criteria only for Treatment-Experienced Participants

• Participants 18 years to 75 years (inclusive) at screening
• Participants with documented and confirmed pre-existing diagnosis of PrimaryImmunodeficiency (PI) with features of hypogammaglobulinemia requiring ImmunoglobulinG (IgG) replacement therapy including but not limited to the following humoral-basedimmunodeficiency syndromes (example, X-linked agammaglobulinemia, common variableimmunodeficiency), and combined immunodeficiency syndromes without lymphocytopenia (example, hyper immunoglobulin M immunodeficiency syndrome).
• Participants have not had an Serious bacterial infection (SBI) or been hospitalizedfor infection of any etiology (example, viral, fungal, parasitic) within the last 3months prior to screening or during screening.
• Participants currently receiving IgG replacement therapy for ≥3 months via Intravenous (IV) or SC infusion. Participants receiving IVIG prior to study must receive a dosageof at least 200 mg/kg per infusion.
• Participants whose screening IgG trough levels must be ≥500 milligram per deciliter (mg/dL).
• Participants have signed an informed consent form. Inclusion Criteria only for Treatment-Naïve Participants
• Participants 6 years to 75 years (inclusive) at screening.
• Participants with documented and confirmed diagnosis of PI with features ofhypogammaglobulinemia requiring IgG replacement therapy including but not limited tothe following humoral-based immunodeficiency syndromes (example, X-linkedagammaglobulinemia, common variable immunodeficiency), and combined immunodeficiencysyndromes without lymphocytopenia (example, hyper immunoglobulin M immunodeficiencysyndrome).
• Participants have never received IgG replacement treatment (ie, no prior immuneglobulin replacement therapy).
• Participants whose screening IgG level must be ≤400 mg/dL.
• Participants do not have an SBI nor requires hospitalization for infection of anyetiology (example, viral, fungal, parasitic) during screening or at baseline.
• Participants have signed an informed consent.

Exclusion Criteria:

• Participants with clinical evidence of any significant acute or chronic disease that,in the opinion of the investigator, may interfere with successful completion of thetrial or place the participant at undue medical risk.
• Participants have had a known serious adverse reaction (AR) to immunoglobulin or anyanaphylactic reaction to blood or any blood-derived product.
• Participants who have a history of blistering skin disease, clinically significantthrombocytopenia, bleeding disorder, diffuse rash, recurrent skin infections, or otherdisorders where SC therapy would be contraindicated during the study.
• Participants have known isolated IgG subclass deficiency; isolated specific antibodydeficiency (SAD) or selective IgG deficiency; or transient hypogammaglobulinemia ofinfancy.
• Participants have known Selective Immunoglobulin A (IgA) Deficiency (with or withoutantibodies to IgA).
• Participants have significant proteinuria (≥3+ or known urinary protein loss >1 gramg/24 hours or nephrotic syndrome), has acute renal failure, is on dialysis, and/or hassevere renal impairment on Screening laboratory testing (blood urea nitrogen [BUN] orcreatinine more than 2.5 times the upper limit of normal [ULN]).
• Participants have screening values of aspartate aminotransferase (AST) or alanineaminotransferase (ALT) levels exceeding more than 2.5 times the ULN for the expectednormal range for the testing laboratory.
• Participants have hemoglobin <9 gram per deciliter (g/dL) at screening.
• Participants have a history (either 1 episode within the year prior to the ScreeningVisit or 2 previous episodes over a lifetime) of or current diagnosis ofthromboembolism (example, myocardial infarction, cerebrovascular accident or transientischemic attack) or deep venous thrombosis.
• Participants are currently receiving anti-coagulation therapy which would make SCadministration inadvisable (vitamin K antagonists, nonvitamin K antagonist oralanticoagulants [example, dabigatran etexilate targeting Factor IIa, rivaroxaban,edoxaban, and apixaban targeting Factor Xa], and parenteral anticoagulants [example,fondaparinux]).
• Participants currently have a known hyperviscosity syndrome.
• Participants have an acquired medical condition that is known to cause secondaryimmune deficiency, such as chronic lymphocytic leukemia, lymphoma, multiple myeloma,chronic or recurrent neutropenia (absolute neutrophil count less than 1000/microliter (μL) [1.0 x10^9/L]), or human immunodeficiency virus infection/acquired immunedeficiency syndrome.
• Participants have a known previous infection with or clinical signs and symptomsconsistent with current hepatitis B virus or hepatitis C virus infection.
• Participants are receiving any of the following medications: (a) immunosuppressantsincluding chemotherapeutic agents; (b) immunomodulators; (c) long-term systemiccorticosteroids defined as daily dose >1 mg of prednisone equivalent/kg/day for >30days. Note: Intermittent courses of corticosteroids of not more than 10 days would notexclude a participant. Inhaled or topical corticosteroids are allowed.
• Participants (if <18 years of age) have non-controlled arterial hypertension at alevel of greater than or equal to the 90th percentile blood pressure (either systolicor diastolic) for their age and height or the adult participant has non-controlledarterial hypertension (systolic blood pressure [SBP] >160 millimeter per mercury (mmHg) and/or diastolic blood pressure [DBP] >100 mmHg).