Describe the use of viral vectors in gene therapy.

gene therapy involves replacing defective genes;
desired gene is inserted into the viral genome;
viruses can be modified to infect only target cells and not self-replicate / modified for safe use;
somatic cells are removed (for receiving the new genes);
the desired gene is introduced into the target/somatic cells;
altered cells are returned to the patient for expression of the gene;
properly described verified example e.g. replacement of gene for production of ADA in SCID / introduction of gene/RPE65 (in retina) to restore vision in inherited blindness (LCA) / replacement of factor IX/blood clotting factor gene in hemophilic patients;

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