Unless all the cells that carry the virus are removed, the host may still be attacked when the virus becomes re-activated. One limitation of the new triple therapy treatments for HIV is that these drugs do not remove the virus that has integrated into some cells. With either type of virus vector, not all of the cells in the animal host, are transformed. The progeny of the infected animal will likely not be transformed. Because the cells that give rise to gametes, eggs or sperm, have not been transformed.
Heritable transformation requires that the germ line cells are transformed.
There are a number of methods used to produce transgenic animals, and I will describe two of these methods. Unlike plants, it is extremely difficult to regenerate a fully differentiated animal from a single transformed cell growing in culture. I used to say it was impossible, but the arrival of Dolly, the cloned sheep, now makes it just extremely difficult but not impossible. The first method is injection of DNA directly into the nucleus of fertilized eggs . Overhead of process of injection, and pictures.