HERPES-SIMPLEX VIRUS VECTOR SYSTEM - ANALYSIS OF ITS IN-VIVO AND IN-VITRO CYTOPATHIC EFFECTS

With its natural propensity to infect and establish life-long latency in neurons, herpes simplex virus type 1 (HSV-1) has been successfully employed by various laboratories as vectors for gene transfer into neu rons. However, analysis of its cytopathic effects in vivo and in vitro has been limited. In this study, we examined the cytopathic effects o f 2 HSV-1 alpha 4 mutants (ts756 and d120) on adult rat hippocampus an d striatum and of d120 on hippocampal neurons in culture. We assessed damage by stringent counting of surviving neurons after infection and demonstrated that while neither ts756 nor d120 infection resulted in a ny gross anatomical or behavioral changes of the animals, ts756, but n ot d120, produced a significant amount of damage in the CA4 cell field and dentate gyrus of the hippocampus. Thus, since crude examination i s insufficient to detect subtle but significant degrees of neuron loss , the cytopathic effects of HSV or any vector system must be carefully analyzed. Furthermore, we also observed that uninfected cell lysates damaged neurons, both in vivo and in vitro. This cytotoxicity occurred within the first 24 h post-inoculation and probably arose through the activation of glutamate receptors. For the preparation of HSV vectors , purification of the virus from soluble cellular components by a simp le pelleting step can significantly decrease such acute toxicity.