Semin Thromb Hemost 2004; 30(2): 161-171
DOI: 10.1055/s-2004-825630
Copyright © 2004 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA.

Preclinical Gene Therapy Studies for Hemophilia Using Adeno-Associated Virus (AAV) Vectors

Linda B. Couto1 , 2
  • 1Senior Director, Pre-clinical Research, Avigen, Inc., Alameda, California
  • 2Current affiliation: Couto Consulting, Pleasanton, California
Further Information

Publication History

Publication Date:
07 May 2004 (online)

Preview

Gene therapy offers a potential cure for hemophilia and several gene transfer vectors have been evaluated for their ability to treat this disease. This article reviews the studies that have been performed to evaluate the ability of recombinant adeno-associated virus (AAV) vectors to achieve safely the sustained expression of clotting factors following intramuscular, intravenous, and intrahepatic delivery to several animal models. These routes of administration are all effective in providing sustained and therapeutic levels of factor IX (FIX), although the levels vary. Intrahepatic delivery is more efficacious than intravenous administration, which is superior to intramuscular delivery. The recent development of efficient factor VIII (FVIII) expression cassettes has made AAV-based gene therapy for hemophilia A also within reach. Although no acute toxicity has been observed with any route of administration, an increased risk of antibody formation against FIX has been noted following intramuscular delivery. Biodistribution studies concluded that the vector disseminates to most tissues in a dose-dependent and time-dependent manner, but the majority of the vector resides in the targeted tissue. In addition, the risk of germline transmission has been shown to be low or absent. The relatively recent isolation of new AAV serotypes has resulted in the identification of vectors that have enhanced tropism for certain tissues. This combined with the potential of these new vectors to evade the immune response to AAV2, makes them attractive candidates for gene therapy. Although much progress has been made using AAV to treat hemophilia, there are several outstanding issues that need to be addressed. Delivery of AAV to large animals has not been reproducible, which could be due to nonoptimized delivery and/or immune responses to the vector or transgene product. In addition, a complete understanding of the biology of these vectors is required to assess their long-term safety. Solving these issues will lead to the development of a successful gene therapy product.

REFERENCES

Linda B CoutoPh.D. 

Couto Consulting

7814 Oak Creek Dr., Pleasanton

CA 94588

Email: coutoconsulting@yahoo.com