After a disease-causing gene is found, correcting it is the next logical step. This can be achieved through various methods. One of the first tested methods was to obtain the faulty gene from the patient, introduce the corrected gene into cells, and finally inject the altered cells back into a blood vessel. Blood is taken from the affected individual to obtain cells with DNA carrying the faulty gene. A vector is then used to carry a healthy copy of the gene into the affected cells.
Possible vectors are retroviruses.
When the retrovirus attacks affected cells, it will commence replication, replacing the affected gene with the corrective gene. The healthy cells are then injected into the patient to continue replication in the body. An example of this procedure was first demonstrated in 1990. She had severe immune-deficiency disease caused by a faulty gene that failed to order the production of a vital enzyme. Some of the white blood she carried were extracted and introduced to genetically engineered viruses containing healthy copies of the gene.