Another major advantage with SV40 vectors is that they may be constructed in vitro by packaging DNA of choice in recombinant capsids [45] . These vectors, which combine efficient gene delivery of viral vectors with safety and flexibility of non-viral vectors, were shown to have similar tropism as standard SV40 vectors such as the SV/luc described here [30] . Furthermore, these vectors accommodate plasmids as large as 17 kb, significantly larger than SV40 DNA, and may be therefore used to deliver a variety of genes with complex regulatory signals [46] . Furthermore, these vectors do not require any SV40 sequences, providing additional safety margin [47] [48] [49] .