A Study to Evaluate the Efficacy and Safety of Birtamimab in Mayo Stage IV Patients With AL Amyloidosis

Key Inclusion Criteria for Double-blind Phase: * Aged ≥18 years and legal age of consent according to local regulations * Newly diagnosed and AL amyloidosis treatment-naïve with cardiac involvement * Confirmed diagnosis of AL amyloidosis * Confirmed Mayo Stage IV AL Amyloidosis as defined by NT-proBNP ≥1800 pg/mL and Troponin-T ≥0.025 ng/mL or high sensitivity cardiac troponin T≥40ng/L and dFLC ≥18 mg/dL * Planned first-line chemotherapy contains bortezomib administered subcutaneously weekly Inclusion Criteria for Open-label (OLE) Phase: * Must not have discontinued treatment in Double-blind Phase * WOCBP must have a negative pregnancy test and must agree to use highly effective contraception through 90 days following last study drug administration * Male subjects must be surgically sterile or agree to use highly effective contraception through 90 days following last study drug administration * Ability to understand and willingness to sign an ICF prior to initiating the OLE Phase Key Exclusion Criteria for Double-blind Phase: * Non-AL amyloidosis * NT-proBNP \>8500 pg/mL * Meets the International Myeloma Working Group (IMWG) definition of multiple myeloma except for malignancy biomarker of involved/uninvolved serum free light chain ratio ≥100 * Subject is eligible for and plans to undergo ASCT or organ transplant during the study * Myocardial infarction, uncontrolled angina, severe uncontrolled ventricular arrhythmias, or ECG evidence of acute ischemia, within 6 months p…