Scientists have developed a new technique that protects mice and monkeys from AIDS and may one day lead to a method for vaccinating humans against the deadly virus that causes AIDS. The method bypasses the natural immune response and relies instead on synthetic immune system molecules called immunoadhesins. Researchers engineered a segment of DNA that produces the artificial antibodies and inserted it into a virus that was then injected into the muscles of monkey subjects. When they were later exposed to SIV, a simian virus that is closely related to HIV, most of the animals did not contract(病気にかかる)the disease.