Vectors and Other Delivery Systems for Gene Therapy
Gene delivery for gene therapy, is achieved by one of the following two methods (i) viral transduction, involving introduction of a modified virus carrying foreign gene and (ii) physical transfection involving the use of either 'chemical methods' like calcium phosphate, liposomes and molecular conjugates or 'physical methods' like electro­poration and particle acceleration (biolistics). Since transduction gives stable integration and autonomous replication. vector mediated gene transfer is preferred and a variety of vectors have been tried.

However, one of the serious problems is the nonavailability of an ideal vector, which must achieve regulated and sustained expression of foreign genes in specific cells or tissues. This requires that a foreign gene be included in a gene construct, which either replicates autonomously or gets integrated with an active region of the genome of the host. Furthermore, the whole process must be safe, efficient and selective. Among the available vectors, each vector satisfies some of these features but none fulfils all the requirements.