In general, an altered gene can be inserted into a patient using a viral or a non-viral vector. Essentially all cells of the body contain genes, making them suitable for gene therapy. Broadly cells can be divided into somatic (most cells of the body) or germline (eggs or sperm). It is possible to manipulate either somatic cells or germ cells in terms of genetic composition and it also serves as the basis of gene therapy. Gene therapy using germ cells result in permanent changes that are subsequently passed on to next generation. Gene therapy using somatic cells are not passed on to the next generation. Somatic cell gene therapy is safer than the germ line gene therapy because it targets only the affected cells in the patient's body. Somatic cell gene therapy can be done exterior (where cells are modulated in vitro and then transplanted back) or interior (where genes are changed in vivo ).

Gene Doping:   The non-therapeutic use of cells, genes, genetic elements, or of the modulation of gene expression, having the capacity to improve athletic performance is defined as Gene Doping by the World Anti-Doping Agency (WADA).

1.1 Qualities of a suitable vector

1)  An optimal vector should be one that can be made available in a highly intense form using an ideal and reproducible production plan.

2)  The vector must be competent of directing the cell type most relevant for the disease, either it be multiplying or non-multiplying cells.

3)  Those vectors that can accomplish site-specific integration are more preferred and desirable in case of insertional mutagenesis.

4)  A perfect vector should be harmless and should not cause any noxious effect on human health.