¹Genzyme Corporation, 31 New York Avenue, Framingham, MA 01701, USA

Correspondence: Ronald K. Scheule, Fax: +1 508 872 4091. E-mail: ronald.scheule@genzyme.com

Received 14 October 2004; Accepted 26 April 2005.

Abstract

Hepatocytes are an effective depot for protein production from gene therapy vectors. However, when gene transfer vectors or their delivery induces hepatic inflammation, adaptive immune responses against the transgene product can ensue. In BALB/c mice, hydrodynamic delivery of a CMV-driven plasmid DNA (pDNA) bearing human -galactosidase A (gal) to the liver generated antibodies against gal. This humoral immune response was more robust in a transgenic knockout for gal, the Fabry mouse. The antibody response could be attenuated in both mouse strains by using a promoter more restricted to hepatocytes. In an attempt to reduce further the humoral responses to gal, expression from the transgene was attenuated by using siRNA during the period of initial delivery-associated liver inflammation. In both mouse models and with both promoters, codelivering an gal siRNA resulted in a 2 log decrease in initial expression that then increased over the next few weeks to levels generated by the pDNA alone. This strategy led to both attenuated antibodies and an immune status approximating "tolerance" to gal. Importantly, in the Fabry mouse, an gal siRNA together with a hepatocyte-restricted promoter gave minimal anti-gal antibodies and profound tolerance, suggesting that such an approach might have clinical utility for genetic diseases.