Vaccine Partially Blocks Transmission of HIV-Like Virus in Monkeys

For the "first time," a vaccine for simian immunodeficiency virus, which produces AIDS-like symptoms and usually kills infected primates within two years, has successfully prevented viral SIV transmission in some monkeys after a year-long clinical trial, researchers from the University of California-San Francisco report in the Aug. 2 issue of the Journal of Virology. The San Francisco Examiner reports that researchers at UCSF, led by Raul Andino, associate professor of microbiology and immunology, "piggy-back[ed]" the DNA of HIV and SIV onto the 40-year-old Sabin oral polio vaccine with the aim of initiating an immune response in the mucosal surfaces of the vagina and rectum, two points of entry for the virus. The Sabin vaccine was developed to "buil[d] up" an immune response in the mucous membranes to prevent transmission of polio from infected feces through the mouth. The team then administered the vaccine to nine cynomolgus macaques at the University of California-Davis' primate center and exposed them, along with 12 non-vaccinated monkeys, to SIV (Mezin, San Francisco Examiner, 7/23). A year later, all of the non-vaccinated monkeys tested SIV-positive and six had developed AIDS-like symptoms. In comparison, all nine of the vaccinated monkeys remained healthy, including two that were completely protected from the virus (Norton, Reuters Health, 7/23).

Guarded Optimism
Andino cautioned against hopes for similar success with a human vaccine, saying, "[M]onkeys are monkeys and humans are humans" and it is "possible that [the vaccine] could not work in humans." Andino and colleagues worked from an existing human vaccine rather than developing a new primate vaccine to facilitate adapting the vaccine for human trials. The researchers also used a "very high concentration" of SIV to ensure that the monkeys would be infected. Although scientists do not know the amount of HIV that must be transmitted sexually for infection to occur, it is "likely to be 100 to 10,000 times less" than the amount of virus used in the experiment (San Francisco Examiner, 7/23). If further primate testing is successful, human clinical trials could follow, although the polio vaccine used as a base was discontinued in the United States because it was found to transmit polio in some cases. Andino said that the HIV vaccine would be "safe," adding that if it were to prove effective, it would be a "cheap and easy" way to administer a vaccine in developing countries (Reuters Health, 7/23).