Analysis of a multi-mutant herpes simplex virus type 1 for gene transfer into sympathetic preganglionic neurons and a comparison to adenovirus vectors

Abstract

A non-replicating triple-mutant herpes simplex virus (14H Δ3vhsZ) expressing the bacterial marker enzyme β-galactosidase, was assessed for neurotropism and cytopathic effects as a vector for gene transfer into differentiated phaeochromocytoma 12 cells in vitro and into spinal sympathetic neurons in vivo. In the in vivo study, the 14H Δ3vhsZ was injected into the adrenal gland of hamsters. For comparison, an evaluation of two adenovirus vectors, AdCA17lacZ and AdCA36lacZ, was performed. Infection of the differentiated phaeochromocytoma 12 cells by 14H Δ3vhsZ resulted in intense β-galactosidase staining in 80–90% of the cells without changes in cell morphology, detected by light microscopy, after a period of four days. No cytoskeletal disruption was detected by immunocytochemistry for the neurofilament protein and no apoptosis was demonstrated by the Hoescht stain for nuclear chromatin in virus-infected cells in comparison to mock-infected control cells. Two to three days after adrenal inoculation with 14H Δ3vhsZ, β-galactosidase was detected in 240 preganglionic neurons per hamster ( n=8), a number equal to about 25% of the population of targeted neurons. The β-galactosidase reaction product extended throughout the normal kite-shaped neuronal somata and extensive dendritic arbour. The number decreased to 120 by five days ( n=3) and to two by eight days ( n=4). This decrease was presumably due to loss of expression of the marker gene and not to cell death because, at eight days, the number of sympathetic preganglionic neurons in the nucleus intermediolateralis, pars principalis, that were immunoreactive for the neurotransmitter enzyme choline acetyltransferase, and demonstrated nicotinamide adenine dinucleotide phosphate-diaphorase activity, were the same on the infected left side of the cord as on the uninfected right side. Inflammatory cells surrounded some of the infected neurons at five days but by eight days the infiltrate was reduced. Infection of differentiated phaeochromocytoma 12 cells by AdCA17lacZ and AdCA36lacZ also resulted in marker gene expression in a large proportion of the cells (80–90%) in the absence of cytopathic effects. In contrast, four days after adrenal injection of AdCA17lacZ or AdCA36lacZ ( n=5 for each) only an average of three preganglionic neurons per hamster expressed β-galactosidase activity, despite clear adrenal infection. AdCA17lacZ and AdCA36lacZ both produced light patches of staining confined to the neuronal soma. These neurons had normal morphology but sometimes were surrounded by an inflammatory infiltrate. In conclusion, the non-replicating herpes simplex virus, 14H Δ3vhsZ, had minimal cytotoxic effects in neurons, in vitro or in vivo, and was efficiently transported from the adrenal gland to infect many sympathoadrenal preganglionic neurons. In contrast, very few neurons demonstrated β-galactosidase activity after injection into the adrenal gland of AdCA17lacZ and AdCA36lacZ. Therefore, 14H Δ3vhsZ is a more suitable vector than either of the adenovirus vectors tested for eliciting short-term changes in preganglionic neuron gene expression.