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Blood, 1 February 2004, Vol. 103, No. 3, pp. 804-810. Prepublished online as a Blood First Edition Paper on September 25, 2003; DOI 10.1182/blood-2003-05-1426.
GENE THERAPY Helper-dependent adenoviral vectors mediate therapeutic factor VIII expression for several months with minimal accompanying toxicity in a canine model of severe hemophilia AFrom the Department of Pathology and Molecular Medicine, Queen's University, Kingston, ON, Canada; and Departments of Biology and Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.
Two helper-dependent (HD) adenoviral vectors encoding a canine factor VIII B-domaindeleted transgene (cFVIII) were constructed and evaluated in 4 hemophilia A dogs. One vector was regulated by the cytomegalovirus (CMV) promoter (HD-CMV-cFVIII), while the other vector contained a tissue-restricted promoter comprised of the human FVIII proximal promoter with an upstream concatemer of 5 hepatocyte nuclear factor 1 binding sites (HD-HNF-cFVIII). We detected no toxicity at low dose (5 x 1011 vp/kg), but at higher vector doses (> 1 x 1012 vp/kg) transient hepatotoxicity and thrombocytopenia were observed. Low-level increases in FVIII activity were detected in all 3 HD-HNF-cFVIIItreated dogs, which corresponded with decreased whole blood clotting times. None of the animals receiving the HD-HNF-cFVIII vector developed FVIII inhibitors, and in 1 of the 3 animals, FVIII activity was sustained for over 6 months after treatment. One animal, which received the HD-CMV-cFVIII vector, achieved peak levels of FVIII above 19 000 mU/mL, but FVIII activity disappeared within 1 week, coincident with the development of a potent anticanine FVIII antibody response. This study supports previous demonstrations of improved safety using HD gene transfer and suggests that these vectors can provide transient FVIII expression with minimal, acute toxicity in the absence of inhibitor formation.
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