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Improved display of foreign protein moieties in combination with beneficial alteration of the viral surface properties should be of value for targeted and enhanced gene delivery. Here, we describe a vector based on Autographa californica multiple nucleopolyhedrovirus (AcMNPV) displaying synthetic IgG-binding domains (ZZ) of protein A fused to the transmembrane anchor of vesicular stomatitis virus (VSV) G protein. This display vector was equipped with a GFP/EGFP expression cassette enabling fluorescent detection in both insect and mammalian cells. The virus construct displayed the biologically active fusion protein efficiently and showed increased binding capacity to IgG. As the display is carried out using a membrane anchor of foreign origin, gp64 is left intact for virus entry, which may increase gene expression in the transduced mammalian cells. In addition, the viral vector can be targeted to any desired cell type via binding of ZZ domains when an appropriate IgG antibody is available.Key words: Baculovirus display, ZZ domains, Protein A, VSV G protein, Targeting, Gene delivery, Gene therapy. IntroductionViral vectors have become important tools in the field of gene therapy and recently baculovirus has become a target of increasing interest also in this context. During the past years, baculoviruses, especially Autographa californica multiple nucleopolyhedrovirus (AcMNPV), have widened their applications from insect pesticides (reviewed by (1)) to protein production (reviewed by (2-4)) and further, by display modifications, to foreign protein (5-7) or antigen presentation (8)(9)(10)(11) and library screening (12). In most cases, the display has been carried out by fusion of the foreign protein to a second copy of the envelope glycoprotein, gp64 (5-12), but in some studies straightly to the only copy of the same protein (13, 14).In addition, baculoviruses are currently evaluated for gene transfer to various cell types, one of the goals being gene therapy applications. A mammalian promoter element such as CMV (15)(16)(17), CAG (18, 19) or RSV LTR (17, 20), is needed for gene expression in the target cells, since baculoviral promoters appear to be silent in mammalian cells (20). The first in vitro studies indicated that baculoviruses preferentially enter hepatocytic cells (15, 20, 21). However, additional studies have shown that baculoviruses can enter multiple cell lines (16)(17)(18)(19) 22). Further, baculoviruses have been tested for gene delivery in vivo, the target organs including rabbit carotid artery (23), mouse eye (24) and rat or mouse brain (25, 26). For more specific targeting, baculoviral vectors can be modified by displaying or pseudotyping the viral surface. By this method, recombinant viruses were shown to specifically bind to certain cell lines (27) As the envelope protein gp64 is necessary for the viral infection (28), fusions to this protein may interfere with the internalization of the virus, although this does not seem to affect virus titers in insect cells. The gp64 protein has an essential...

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We have constructed a novel fusion protein "Scavidin" consisting of the macrophage scavenger receptor class A and avidin. The Scavidin fusion protein is transported to plasma membranes where the avidin portion of the fusion protein binds biotin with high affinity and forms the basis for the targeted delivery of biotinylated molecules. Subcellular fractionation analysis, immunostaining, and electron microscopy demonstrated endosomal localization of the fusion protein. According to pulse-labeling and cross-linking studies Scavidin is found as monomers (55 kDa), dimers, and multimers, of which the 220-kDa form was the most abundant. The biotin binding capacity and active endocytosis of the biotinylated ligands were demonstrated in rat malignant glioma. Local Scavidin gene transfer to target tissues could have general utility as a universal tool to deliver biotinylated molecules at systemic low concentrations for therapeutic and imaging purposes, whereby high local concentration is achieved.

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