 Because of these advances, it is now considered safe to use such integrating vectors for gene therapy.An advantage is that the lentiviral vectors integrate the DNA permanently, whereas other, non-integrating, viruses' effect is transient.For those viruses such as gammaretroviruses that tend to integrate their DNA in genetically unfavorable locations, the severity of any ensuing mutation depends entirely on the location within the host's genome wherein the viral DNA is inserted.