cancer. Howard Fine and colleagues at Harvard Medical School's Dana Farber Cancer Institute said they had engineered an adenovirus -- a member of a common family of viruses -- so it would target tumor cells specifically. Writing in the journal Nature Medicine, they said rats who had brain tumors induced, and then were injected with the adapted virus, lived longer than rats who did not get the virus. They were working on the basis of studies that showed giving patients an injection of adenovirus, and then giving them the antiviral drug ganciclovir, helped stop tumor cells from growing. Fine's group engineered the virus so it would act on E2F promoter genes, which are common in tumor cells. Normal cells have E2F too but have another protein that inactivates it. Thus a virus that targets E2F should damage tumor cells but not normal ones, they said. They said their technique might eventually prove useful in other attempts at gene therapy to treat other kinds of cancer.