There's a gene found in all human cells called *dCK that can be used to activate anticancer drugs. Then there's HIV which inserts its genetic material into the human genome to multiply abnormally.
So researchers in Strasbourg introduced dCK into an HIV genome to make a more effective cancer fighter. Source: Scienceblog.com, and excerpt:
Through HIV multiplication, the CNRS team has selected a “library” of nearly 80 mutant proteins and tested them on tumor cells in the presence of an anticancer drug. The results have enabled them to identify a dCK variant that is more effective than the wild-type (non-mutated) protein, inducing the death of tumor cells in culture. In combination with this protein, the anticancer drugs showed identical effectiveness at 1/300 the dose. The possibility of reducing the doses of anticancer drugs would palliate the problems posed by their components’ toxicity, reduce their side effects and, most importantly, improve their effectiveness.
Alas, human testing is years away.