I have a virology question?

Retroviruses have been used to introduce genes into animals. The rate of infection with a genetically modified retrovirus would be no different than any other retrovirus. The virus would never infect every cell because not every cell has the correct receptors required for the virus to gain entry into the cell in the first place. There is nothing you can do to speed up the process. And when using such viruses, you always have to worry about the immune system recognizing and neutralizing the virus before it has a chance to do much good. These, and other technical problems, are a large part of the reaon the we don't use them routinely. You mention HIV specifically, so you probably know that HIV only infects a re;atively small subset of cells that express CD4 along with one of two different co-receptors. Withour these recpetors, the is no virus replication.