Human genes can be directly modified, with the help of a virus to deliver new DNA, in a process called gene therapy.
Human gene therapy uses recombinant DNA technology to modify a person's genes to combat an illness. This technology takes advantage of the fact that viruses insert their DNA into the cells of the organisms they infect. A normal human gene can be isolated and cloned, then inserted into a harmless virus. When that virus is injected into a patient, the virus inserts its DNA, along with the isolated human gene, into the patient's cells. As the patient's cells replicate, the new DNA is incorporated and copied alongside the patient's own DNA. The gene can then be transcribed and translated to produce a protein that the patient is missing or one to specifically target an illness. Gene therapy has great potential for curing many illnesses and has shown great promise toward curing certain genetic conditions. However, some instances of gene therapy have led to unexpected negative results, including death. Gaining FDA approval for these types of treatments has thus been a slow process. The first gene therapy treatment was approved in 2017 to treat a form of leukemia. The potential for future treatments is even greater with the development of CRISPR (clustered regularly interspaced short palindromic repeats), a group of bacterial DNA sequences that are used to defend against viruses. It can be used to target and modify specific gene sequences. This gene-modification technique finds and snips specific sequences of DNA, which can permanently alter the genes of an organism. It can be used to add or remove almost any DNA sequence within a genome. Possible applications reach beyond medicine, including agricultural improvements and even designer organisms. The technique was successfully used to modify pigs, which was one step toward using pigs as organ donors for humans. In the future CRISPR may make it possible to correct human mutations at their specific locations within the genome and thus treat genetic causes of diseases. As with any DNA technology, however, ethical concerns involving direct human genetic modification are always present.