1. ¹Board of Governors Gene Therapeutics Research Institute, Cedars-Sinai Medical Center, Los Angeles, California, USA
2. ²Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
3. ³Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
4. ⁴Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA

Correspondence: Maria G. Castro, Board of Governors Gene Therapeutics Research Institute, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Davis Building, Research Pavilion, Room 5090, Los Angeles, California 90048, USA. E-mail: castromg@cshs.org

Received 5 June 2007; Accepted 7 November 2007; Published online 8 January 2008.

Abstract

Immune responses against vectors or encoded transgenes can impose limitations on gene therapy. We demonstrated that tetracycline-regulated high-capacity adenoviral vectors (HC-Ads) sustain regulated transgene expression in the brain even in the presence of systemic pre-existing immune responses against adenoviruses. In this study we assessed whether systemic pre-existing immune responses against the transgene products, i.e., -Gal or the tetracycline-dependent (TetON) regulatory transcription factors (rtTA2^SM2 and the tTS^Kid), affect transgene expression levels and the safety profile of HC-Ads in the brain. We pre-immunized mice with plasmids encoding the TetON switch expressing rtTA2^SM2 and the tTS^Kid or -Gal. HC-Ads expressing -Gal under the control of the TetON switch were then injected into the striatum. We assessed levels and distribution of -Gal expression, and evaluated local inflammation and neuropathological changes. We found that systemic immunity against -Gal, but not against the TetON switch, led to inflammation and reduction of transgene expression in the striatum. Therefore, the regulatory TetON switch appears to be safe to use, and capable of sustaining transgene expression in the brain even in the presence of an immune response against its components. Systemic immunity against the transgene had the effect of curtailing its expression, thereby affecting the efficacy and safety of gene delivery to the brain. This factor should be considered when developing gene therapies for neurological use.