Engineered HSV vector achieves safe long-term transgene expression in the central nervous system.

Area of Science:

• Neuroscience
• Gene Therapy
• Virology

Background:

• Herpes simplex virus type 1 (HSV-1) vectors are being developed for gene therapy.
• Previous HSV-1 vectors had high viral gene expression, limiting their use.
• New vectors are designed to be functionally devoid of viral immediate early (IE) genes.

Purpose of the Study:

• To evaluate the gene expression capabilities of novel, highly defective HSV-1 vectors in neuronal and non-neuronal cells.
• To assess the long-term expression, cell specificity, and safety of these vectors in the rat brain.

Main Methods:

• Stereotactic injection of HSV-1 vectors into various rat brain regions.
• Insertion of reporter gene cassettes into specific loci (ICP4, intergenic region) within the vector.
• Analysis of reporter gene activity, cell-type specificity, and potential toxicity over time.

Main Results:

• ICP4 locus cassette enabled robust, neuron-restricted reporter gene expression in diverse brain regions.
• Sustained transgene expression was observed for up to 6 months in the hippocampus.
• Expression cassettes in other locations (latency locus, intergenic region) showed differential activity, highlighting promoter and insertion site importance.
• No significant neuronal toxicity or inflammatory response was detected.

Conclusions:

• Highly defective HSV-1 vectors with ICP4 locus insertion facilitate sustained, neuron-specific gene expression.
• These vectors show promise for therapeutic applications in central nervous system disorders.
• The findings underscore the critical role of vector design, including promoter and insertion site, for targeted gene delivery.