## Current state of gene therapies

According to the European Medicines Agency (EMA), gene therapy is the name given to medical products consisting of or containing recombinant nucleic acids. These are used or administered with the aim of regulating, repairing, replacing, adding or removing a specific DNA sequence. The therapeutic, prophylactic, or diagnostic effect of the gene therapy is directly related to the sequence of recombinant nucleic acids that the gene therapy contains, or to the expression product of that sequence. According to the mode of administration, gene therapy can be divided into in vivo and ex vivo. In vivo therapy is administered directly to the patient, while in ex vivo therapy, cells are first isolated from the patient and then genetically modified. The cells are then selected, allowed to proliferate, and administered to the patient. The major advantage of the ex vivostrategy is that the modified cells can be selected and only those with the desired characteristics (corrected gene) are kept. However, this approach is limited to the dividing cells of the bloodstream, particularly the hematopoietic cells ensuring the formation of red and white blood cells and platelets. For the other tissues, a different approach must be taken (Figure 10.4).