Treating Transthyretin Amyloidosis via Adeno-Associated Virus Vector Delivery of Meganucleases

Transthyretin amyloidosis (ATTR) is a progressive and fatal disease caused by transthyretin (TTR) amyloid fibril accumulation in tissues, which disrupts organ function. As the TTR protein is primarily synthesized by the liver, liver transplantation can cure familial ATTR but is not an option for the predominant age-related wild-type ATTR. Approved treatment approaches include TTR stabilizers and an RNA-interference therapeutic, but these require regular re-administration. Gene editing could represent an effective one-time treatment. We evaluated adeno-associated virus (AAV) vector-delivered, gene-editing meganucleases to reduce TTR levels. We used engineered meganucleases targeting two different sites within the TTR gene. AAV vectors expressing TTR meganuclease transgenes were first tested in immunodeficient mice expressing the human TTR sequence delivered using an AAV vector and then against the endogenous TTR gene in rhesus macaques. Following a dose of 3 × 10¹³ genome copies per kilogram, we detected on-target editing efficiency of up to 45% insertions and deletions (indels) in the TTR genomic DNA locus and >80% indels in TTR RNA, with a concomitant decrease in serum TTR levels of >95% in macaques. The significant reduction in serum TTR levels following TTR gene editing indicates that this approach could be an effective treatment for ATTR.