166. Recombinant Baculovirus Vectors Containing Inverted Terminal Repeats from Adeno-Associated Virus Improve Gene Expression in Neurons and Astrocytes

Abstract

Baculovirus vectors are recently emerging as a promising gene delivery vector for mammalian cells. These vectors can transduce neurons and astrocytes in the central nervous system (CNS), but provide only transient gene expression, which limits effective application of the vectors for gene therapy of CNS diseases and disorders that usually requires sustained expression of therapeutic genes. In this study, we investigated whether using inverted terminal repeats (ITRs) from adeno-associated virus (AAV) to flank a reporter gene cassette harboring a cellular promoter could improve baculovirus-mediated transgene expression in a cell-type specific manner in the brain. When compared with control baculovirus vectors containing a strong cytomegalovirus (CMV) immediately early gene enhancer/promoter, baculovirus vectors with either a neuron-specific or an astrocyte-specific promoter clearly prolonged expression of a luciferase reporter gene in cultured cells and in the rat brain, although initial expression levels were usually lower. With ITR flanking, the viral vectors with a cellular promoter further increased gene expression up to 10-folds over those provided by the vectors without ITRs in the brain, reaching the levels comparable to those obtained by the control vectors with the CMV promoter in earlier stages and being significantly higher at later time points. Detectable transgene expression in the brain after single injection of the baculovirus vectors with ITRs lasted for at least 90 days. ITRs did not affect the specificity of the cellular promoters placed into baculovirus vectors, as demonstrated by immunohistological analysis and an axonal retrograde transport assay. Our study provides a successful example of using AAV ITRs to enhance and prolong gene expression driven by a cellular promoter in the context of baculovirus vectors.