A Study to Evaluate the Safety and Efficacy of BEAM-302 in Adult Patients With Alpha-1 Antitrypsin Deficiency (AATD)

Part A: Inclusion Criteria: * Males or females 18 - 70 years of age inclusive at the time of consent. * Diagnosis of AATD and homozygous for the PiZZ mutation (confirmed by genetic testing). * Blood total AAT level \<11 μM or equivalent protein in mg/dL. * Patients receiving augmentation therapy in regions where augmentation is not SoC must be willing to washout augmentation therapy for at least 6 weeks prior to signing the ICF and for the length of the study (unless clinically indicated) * A postbronchodilator FEV1 ≥40% of predicted and an FEV1/FVC \<70% at screening. (PFTs obtained within 1 year of signing the ICF may be used for eligibility.) * Evidence of emphysema on a historic CT scan or a DLCO ≤70% of the predicted value (corrected for hemoglobin) at screening. (PFTs obtained within 1 year of signing the ICF may be used for eligibility.) Exclusion Criteria: * Body mass index \>30 * Lung or liver transplant or on waiting list for lung or liver transplant or status post lung volume reduction surgery. * Clinical evidence of severe bronchiectasis as per the discretion of the investigator (eg, excessive sputum production or recurrent infections requiring antibiotic use \[\>4x/year\]). * Liver disease with any of the following: * FibroScan liver stiffness measurement ≥7.5 kilopascals (kPa). (For sites without access to FibroScan, APRI \>0.5 can be used as a surrogate exclusion criterion \[Yilmaz, 2011\]. * Known history of liver cirrhosis or complications of cirrhosis (eg, varices, ascites, hepatic encephalopathy). * Presence of ≥F2 liver fibrosis if a patient has previously had a liver biopsy. * Have ALT or AST \> upper limit of normal (ULN). * Total bilirubin levels \> ULN; if documented Gilbert's Syndrome, total bilirubin \>2 × ULN. * INR ≥1.2 at screening. If deemed appropriate by the investigator and/or prescribing physician, the patient may stop taking anticoagulants for an appropriate washout period or reversal with vitamin K and if indicated, a repeat INR within \<1.2 would be acceptable. * Seropositive for hepatitis B (positive surface Ag). * Active hepatitis C by hepatitis C virus (HCV) antibody. If HCV antibody positive, must be HCV RNA polymerase chain reaction (PCR) negative. Part B: Inclusion Criteria: * Males or females 18 - 70 years of age inclusive at the time of consent. * Diagnosis of AATD and homozygous for the PiZZ mutation (confirmed by genetic testing). * Evidence of METAVIR F1, F2, or F3 liver fibrosis based on a central read of a baseline liver biopsy during the screening period or a histological diagnosis made no more than 6 months before enrollment and stage confirmed by central read. * A postbronchodilator FEV1 ≥40% of predicted at screening. (PFTs obtained within 1 year of signing the ICF may be used for eligibility.) Exclusion Criteria: * Lung or liver transplant or on waiting list for lung or liver transplant or status post lung volume reduction surgery. * Clinical evidence of severe bronchiectasis as per the discretion of the investigator (eg, excessive sputum production or recurrent infections requiring antibiotic use \[\>4x/year\]) * Previous diagnosis of liver cirrhosis or complications of cirrhosis (eg, varices, ascites, hepatic encephalopathy).