One approach to correct deficient protein expression is to use viral mediated gene transfer [16] . An optimal vector for gene therapy should be safe, efficient, nonimmunogenic, and available in high titers [17] . There is currently no single vector with all these advantages. SV40 based vectors are efficient gene delivery vehicles for a wide spectrum of ex vivo and in vivo targets, including hematopoetic, liver and kidney cells [18, 19] . The vector was shown to be potentially effective in a number of clinical models, including Crigler Najjar syndrome [20] , HIV, [21] SV40 evades host immune response most likely by caveolar endocytosis, followed by vesicular transport to the endoplasmic reticulum [27], thus avoiding the more common endosomal-lysosomal pathway used by most viruses [28] . SV40 vectors were found to be nonimmunogenic, allowing repeated administrations and long survival of transduced cells [29, 30] . Replication incompetent SV40 vectors in which the viral T-antigen is replaced by the gene of interest are produced in vivo in cells that supply T-anti-gen in trans-, such as COS or COT cells [31] , and high vector titers may be readily prepared [32] . Cloning capacity of these vectors is limited; nevertheless, many potentially therapeutic genes may be accommodated, as shown by the wide spectrum of applications already investigated.