The Shaggy Dog Movie Poster

Dave Douglas (Tim Allen) is a deputy district attorney who prosecutes activists who have broken into the pharmaceutical corporation Grant and Strictland, which the activists accuse of animal experimentation while searching for a "Fountain of Youth." This distances Douglas from his activist daughter Carly (Zena Grey).
The greedy geneticists working for Mr. Lance Strictland (Philip Baker Hall), led by Dr. Kozak (Robert Downey, Jr.), have stolen from a Tibetan Buddhist monastery a sacred dog Khyi Yang Po (a Bearded Collie), whose DNA carries a mutation granting an extraordinary lifespan. Seeking to obtain his immortality for themselves, the geneticists carry out several experiments which fail spectacularly. Unable to isolate the specific gene that provided for the dog's lifespan, they injected the dog's gene sequence into the test subjects, resulting in unwanted side effects. The scientists determine that Khyi Yang Po's genetic sequence, when isolated and put into a vaccination, invades and alters the cells and DNA of a victim. Unlike normal sicknesses, Khyi Yang Po's code can not be defeated by natural immune systems and so it will remain and invade the entire host.
Khyi Yang Po manages to escape the facility, with some of the vaccine remaining on his mouth and face.