A Study of AT-02 in Subjects With Systemic Amyloidosis.

Inclusion Criteria: Subject understands the study procedures and can give signed informed consent. Subject is willing and able to comply with this protocol and will be available for the entire duration of the study. Subject must have a confirmed diagnosis of SA per the diagnostic criteria specified in the parent study protocol. Subject must have participated in the study AT01-001 and wishes to receive open-label AT-02. AT02-001 Part 2: a. Subjects must have completed the last follow-up visit in AT02-001 Part 2 without significant adverse events, as determined by the Investigator. AT02-001 Part 3: a. Subjects must have completed the post-treatment imaging studies in AT02-001Part 3 (e.g., CMR, echocardiogram) without significant AEs in the parent study as determined by the Investigator. Must continue to satisfy the eligibility criteria in the parent study protocol for WOCBP, WONCBP, or male participants Exclusion Criteria: Is pregnant, breastfeeding, or is planning to become pregnant or breastfeed during this study and follow-up period. Is mentally or legally incapacitated, has significant emotional problems at the time of the study, or has a history of psychosis. Has acquired any new, clinically significant underlying illness since enrollment in the parent study. Has any clinically significant worsening of organ function associated with underlying SA or clinically significant change in concomitant medications for the treatment of SA since enrollment in the parent study. Estimated glomerular filtration (eGFR) ≤30 mL/min/1.73 m2. Currently using any prohibited concomitant medications. Any contraindication to MRI or MRI contrast. Is currently participating in an interventional clinical study or has participated in another clinical study (other than AT02-001) within the last four (4) weeks or within five (5) half-lives of the prior study treatment, whichever is longer.