A common virus that is harmless to people can destroy cancerous cells in the body and might be developed into a new cancer therapy, US researchers said. The virus, called adeno-associated virus type 2, or AAV-2, infects an estimated 80 percent of the population. Our results suggest that adeno-associated virus type 2, which infects the majority of the population but has no known ill effects, kills multiple types of cancer cells yet has no effect on healthy cells," said Craig Meyers, a professor of microbiology and immunology at the Penn State College of Medicine in Pennsylvania. "We believe that AAV-2 recognizes that the cancer cells are abnormal and destroys them. This suggests that AAV-2 has great potential to be developed as an anti-cancer agent," Meyers said in a statement. AAV-2 is a small virus that cannot replicate itself without the help of another virus. But with the help of a second virus it kills cells. For their study, Meyers and colleagues first infected a batch of human cells with HPV, some strains of which cause cervical cancer. They then infected these cells and normal cells with AAV-2. After six days, all the HPV-infected cells died. The same thing happened with cervical, breast, prostate and squamous cell tumor cells. "One of the most compelling findings is that AAV-2 appears to have no pathologic effects on healthy cells," Meyers said. "So many cancer therapies are as poisonous to healthy cells as they are to cancer cells. A therapy that is able to distinguish between healthy and cancer cells could be less difficult to endure for those with cancer."