Infectious delivery and long-term persistence of transgene expression in the brain by a 135-kb iBAC-FXN genomic DNA...

Novel gene-based therapies for disease will depend in many cases on long-term persistent transgene expression. To develop gene therapy strategies for Friedreich's ataxia (FRDA), we have examined the persistence of transgene expression in the brain in vivo provided by the entire 135 kb FXN genomic DNA locus delivered as an infectious bacterial artificial chromosome (iBAC) herpes simplex virus type 1 (HSV-1)-based vector injected in the adult mouse cerebellum. We constructed genomic DNA-reporter fusion vectors carrying a complete 135 kb FXN genomic locus with an insertion of the Escherichia coli lacZ gene at the ATG start codon (iBAC-FXN-lacZ). SHSY5Y human neuroblastoma cells transduced by iBAC-FXN-lacZ showed high efficiency of vector delivery and LacZ expression. Direct intracranial injection of iBAC-FXN-lacZ into the adult mouse cerebellum resulted in a large number of easily detectable transduced cells, with LacZ expression driven by the FXN genomic locus, which persisted for at least 75 days. Green fluorescent protein expression driven from the same vector but by the strong HSV-1 IE4/5 promoter was transient. Our data demonstrate for the first time sustained transgene expression in vivo by infectious delivery of a genomic DNA locus >100 kb in size. Such an approach may be suitable for gene rescue strategies in neurological disease, such as FRDA.