183. Developing Strategies To Improve the Current Clinical Vector AAV1-CB-AAT for Alpha-One Antitrypsin Deficiency

Abstract

Alpha-one antitrypsin deficiency (AATD) is a genetic disorder that causes defective production of alpha-one antitrypsin (AAT), leading to decreased AAT activity in the blood and lungs, and deposition of excessive mutant Z-AAT protein in liver cells. There are several forms and degrees of deficiency, principally depending on whether the patient has one or two copies of the affected gene. Approximately 4% of the North American and Northern European populations possess at least one copy of a mutant allele.The current standard of care is protein replacement by frequent infusions, but gene replacement therapy could provide long-term correction of the serum levels after a one-time treatment only, which would offer a significant improvement in the quality of life of the patients. Towards this goal, a recent clinical trial tested injecting recombinant adeno-associated virus serotype 1 expressing M-AAT intramuscularly. However the therapeutic AAT serum threshold of 11μμM was not reached. Future efforts to achieve therapeutic levels will revolve around dose escalation and more efficient physical delivery.While the next trial may achieve therapeutic levels with the current AAV1-CB-AAT vector, it is worth further optimizing as it may result in a more efficient vector requiring a lower dose to achieve therapeutic levels. Achieving therapy with a lower dose has substantial benefits in the long run in terms of cost of production and more importantly potential immune responses to capsid. The current AAV1-CB-AAT gene therapy vector will be optimized through four independent strategies hypothetically leading to an increase of alpha-one antitrypsin serum levels in mice: 1) replacement of the secretion signal by secretion signals from other human secreted proteins, 2) modification of the AAV capsid either by triple tyrosine mutation or DNA shuffling, 3) optimization of the transgene to create self-complementary vectors with a codon-optimized AAT sequence, 4) addition of a hepatocyte-specific cis-regulatory module allowing recruitment of liver-specific transcription factors.In vivo data will be presented for each strategy. Future work will combine the validated candidates into a single vector for further evaluation; the use of this optimized vector may translate into a therapeutic effect for the AATD patients.