Repetitive intrathecal injections of poliovirus replicons result in gene expression in neurons of the central nervous system without pathogenesis

Poliovirus-based vectors (replicons) can be used for gene delivery to motor neurons of the CNS. In the current study, a replicon encoding green fluorescent protein (GFP) was encapsidated into authentic poliovirions, using established procedures. Intrathecal delivery of encapsidated replicons encoding GFP to the CNS of mice transgenic for the human poliovirus receptor did not result in any functional deficits as judged by behavioral testing. Histological analysis of the CNS of mice given a single intrathecal injection of poliovirus replicons encoding GFP revealed no obvious pathogenesis in neurons (or other cell types) within the CNS. The expression of GFP was confined to motor neurons throughout the neuroaxis; a time course of expression of GFP revealed that expression was detectable 24 hr postinoculation and returned to background levels by 120 hr postinoculation. A procedure was devised to allow repetitive inoculation of replicons within the same animal. Behavioral testing of animals that had received 6 to 13 independent inoculations of replicons revealed no functional deficits. Histological analysis of the CNS from animals that had received 6 to 13 sequential inoculations of replicons revealed no obvious abnormalities in neurons or other cell types in the CNS; expression of GFP was demonstrated in neurons 24 to 72 hr after the final inoculation of the replicon. Furthermore, there was no obvious inflammatory response in the CNS after the multiple inoculations. These studies establish the safety and efficacy of replicons for gene delivery to the CNS and are discussed with respect to use of replicons as new therapeutic strategies for spinal cord injuries and/or neurological diseases.