Yes: gene therapy has been used investigationally since the 90s (http://en.wikipedia.org/wiki/Gene_therapy http://en.wikipedia.org/wiki/Gene_therapy). It has a

Yes: gene therapy has been used investigationally since the 90s (http://en.wikipedia.org/wiki/Gene_therapy http://en.wikipedia.org/wiki/Gene_therapy). It has a bad tendency to kill human patients or cause cancer, but it's very widespread in research. For example, optogenetics (http://en.wikipedia.org/wiki/Optogenetics http://en.wikipedia.org/wiki/Optogenetics) uses lentivirii to insert DNA into specific classes of neurons to get them to express a protein.