A Non-inferiority Pharmacokinetic and Safety/Tolerability Study of Two Different Doses of Weekly SC Alpha1-PI 15% Compared With Corresponding Standard IV Alpha1-PI in Participants With Alpha1-Antitrypsin Deficiency (AATD)

Inclusion Criteria: * Have a diagnosis of congenital AATD with an allelic combination of ZZ, SZ, Z(null), (null)(null), S(null), or "at-risk" alleles (patients with "at-risk" alleles must be individually evaluated for eligibility by the Medical Monitor). If the genotype has yet to be documented, a blood draw for genotyping (i.e., allelic discrimination) and phenotyping will be obtained at the Screening Visit. * Participants may be naïve to alpha1-PI augmentation therapy or may be currently receiving alpha1-PI augmentation therapy or received alpha1-PI augmentation therapy in the past. If the total alpha1-PI serum (alpha-1 antitrypsin \[AAT\]) level has yet to be documented as in a treatment-naïve patient, a blood draw for total alpha1-PI serum level will be obtained at the Screening Visit. For participants currently receiving alpha1-PI augmentation, a pre-alpha1-PI augmentation AAT level must be documented in the participant's medical history/records. * All participants must have a documented total alpha1-PI serum level \<11 μM (80mg/dL if measured by radial immunodiffusion or 50 mg/dL if measured by nephelometry) which is documented pre-alpha1-PI augmentation for participants receiving AAT augmentation. * At the Screening Visit, have post-bronchodilator Forced Expiratory Volume in 1 second (FEV₁) ≥25% and \<80% predicted of predicted FEV₁/Forced Vital Capacity (FVC) \<70% (Global Initiative for Chronic Obstructive Lung Disease \[GOLD\] stage II-III, and some individuals are…