Another promising form of immunotherapy in mice: "researchers have trained mouse immune systems to eradicate skin cancer from within, using a genetic combination of human DNA from melanoma cells and a cousin of the rabies virus. The strategy, called cancer immunotherapy, uses a genetically engineered version of the vesicular stomatitis virus to deliver a broad spectrum of genes derived from melanoma cancer cells directly into tumors. In early studies, 60 percent of tumor-burdened mice were cured in fewer than three months and with minimal side effects. ... We believe that this new technique will help us to identify a whole new set of genes that encode antigens that are important in stimulating the immune system to reject cancer. In particular, we have seen that several proteins need to be expressed together to generate the most effective rejection of the tumors in mice. ... The immune system functions on a seek-and-destroy platform and has fine-tuned its capacity to identify viral invaders such as vesicular stomatitis virus. Part of the appeal of building cancer vaccines from the whole spectrum of tumor DNA is that tumors can adapt to the repeated attacks of a healthy immune system and display fewer antigens (or signposts) that the immune system can identify. Cancers can learn to hide from a normal immune system, but appear unable to escape an immune system trained by the vesicular stomatitis virus with the wide range of DNA used in the library approach. ... Nobody knows how many antigens the immune system can really see on tumor cells. By expressing all of these proteins in highly immunogenic viruses, we increased their visibility to the immune system. The immune system now thinks it is being invaded by the viruses, which are expressing cancer-related antigens that should be eliminated."