I
t is possible in the closing stages of PL 5 for scientists to develop effective forms of gene therapy. These treatments can be used on mature creatures to replace defective genes, or genes that are linked to
particular diseases, with a more benign gene. Usually this is done using modified retroviruses (viruses that can create DNA copies of their own RNA), however, several other methods exist, all of which are capable of targeting specific cells-lung or liver cells, for example-within a living organism. No gene therapy regimens are approved for use on humans in the U.S., but scientists are currently working toward that end.