Abstract: Improved methods for making non-cytotoxic helper virus-free preparations of herpes virus amplicon vectors or particles, the vectors themselves, recombinant helper virus and cells and methods of using same to treat patients and as tools in therapy and prevention, immunology, molecular biology, biotechnology and genetic engineering. In one embodiment, an amplicon plasmid vector contains at least one transgene that encodes a transgene product which is an interfering RNA molecule that can be converted into a siRNA by the cell machinery.