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)

This study is designed to compare two different weekly doses of a medicine called Alpha1-Proteinase Inhibitor given by injection under the skin with the standard doses of the same medicine given through a vein. Adults with Alpha-1 Antitrypsin Deficiency will take part. Participants will be randomly assigned to one of the treatment groups, and both the study doctors and participants will know which treatment is being given. The main goals of the study are to understand how the body processes the medicine (pharmacokinetics) and to assess how safe and well tolerated the different weekly doses are.

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 \