Gene therapy

the process of inserting a gene into an organism (in selected cells) for therapeutic purposes; to replace or repair gene function to treat a disease or genetic defect

Definition
Commonly, gene therapy is understood as the introduction of DNA fragments, be it into the genome or as episomatic entities, into the cells to be treated. This can occur using viral vectors or non-viral DNA and using a range of methods for transfer (transduction). A principal categorisation of gene therapy is that of ex vivo treatment, which involves removing stem or progenitor cells from the patient, manipulation of these cells in vitro and their reimplantation into the patient (applied, e.g., to hematopoietic stem cells) and of in situ, which attempts treatment in the patient, e.g., because the target cells cannot easily be removed for manipulation (as is the case for gene therapy of the central nervous system). The legal definition of gene therapy varies from country to country, so that the introduction of non-coding RNAs or their chemical analogs might also be categorised as gene therapy.