Retargeting of adenoviral vectors to neurons using the H-c fragment of tetanus toxin

The H-C fragment of tetanus toxin (H-C) retains the specific nerve cell bin ding and transport properties of the holotoxin, but lacks any toxicity. We are investigating the potential for utilising its neurotropism for targeted gene delivery to the central nervous system. Previously we reported the us e of H-C-polylysine conjugates for selective gene transfer into neuronal ce lls in vitro. However, as attempts to apply these constructs in vivo were n ot successful, we have extended these studies to modification of the tropis m of adenoviral vectors. Either H-C-polylysine conjugates or the Fab fragme nt of a neutralising anti-knob antibody covalently bound to H-C were attach ed to the virus. Infection of neuronal and nonneuronal cell lines with reta rgeted virus showed highly increased neuronal cell selectivity, but no sign ificant enhancement of gene delivery into these cells. High concentrations of free H-C blocked the infectivity of the retargeted vector efficiently. I ntramuscular injection of retargeted virus into mouse tongues resulted in s elective gene transfer to the neurons of the hypoglossal nucleus, where no pathological changes were observed As differentiated neurons do not undergo cell division, appropriate vectors carrying a thymidine kinase gene, which allows selective elimination of dividing cells, may be exploitable for the treatment of tumours of the central nervous system. The demonstrated suita bility of the H-C fragment of tetanus toxin as targeting moiety for viral v ectors also indicates a potential for gene therapy of inherited neurodegene rative diseases such as spinal muscular atrophy.