A group of researchers led by Philip R. Johnson of The Children’s Hospital of Philadelphia has induced immunity to the simian immunodeficiency virus, which causes an AIDS-like condition in Rhesus monkeys. The team synthesized antibody-like proteins, called immunoadhesins, which bind to the SIV and prevent SIV from infecting cells. They then created DNA that coded for the immunoadhesin proteins and inserted the DNA into a carrier virus. When the carrier virus was injected into the monkeys’ muscle tissue, it transferred DNA into cells, which then began to produce the protective immunoadhesin proteins. These proteins were released from the cells and found their way into the bloodstream, where they protected the monkeys against SIV infection. Most of the vaccinated monkeys were completely immune to infection by SIV and the rest did not develop any AIDS-like condition as a result of infection. A control group of monkeys was entirely infected by the virus and suffered a 66-percent mortality rate due to an AIDS-like condition. Levels of the specific immunoadhesins in the inoculated monkeys were stable for a year. The novel SIV vaccine is not like most vaccines, which work by stimulating an immune response in the body to virus substances called antigens. When exposed to an antigen, immune cells take some time to recognize it and produce the proper defense compounds, called antibodies. Antibodies chemically tag the virus so that other cells can prevent infection, destroy the virus or clear the virus from the body. The cells needed to produce these antibodies have to multiply so that enough antibodies can be produced. During the time that it takes for these responses to occur, the virus can infect cells and rapidly multiply. Once enough antibodies are produced, however, an infection usually ends. HIV and SIV are different from most viral infections in that they evade the immune response by remaining latent within cells. HIV and SIV also challenge the immune system by infecting the very cells responsible for initiating an immune response. Normally, vaccination involves exposure either to a weakened form of a virus or to just viral antigens. These kinds of vaccinations do not seem to work with HIV or SIV. Johnson and his team have created a method of vaccination that bypasses the immune response altogether. This research has implications far beyond the hope of an HIV vaccine. It essentially creates the possibility of a second immune system in animals. The research means that animals can be genetically engineered or altered to resist specific infections without an immune-mediated response. People, for instance, could be genetically engineered for immunity to all sorts of pathogens in such a way that they would pass this protection on to their offspring genetically. However, this sort of immunity would only last for more stable viruses. Our immune systems adapt to viral mutation, but this kind of genetically engineered immune system would not have that level of adaptability. Because HIV is a rapidly mutating virus, immunoadhesin immunity to HIV may not last.