SANTA MONICA, California — A recently-developed vaccine for an HIV-like virus, Simian Immunodeficiency Virus, has been shown to cure monkeys of the infection, suggesting a similar vaccine may be able to save humans.
In a study by Oregon Health and Science University, rhesus macaque monkeys were inoculated with the new vaccine and exposed to SIV, which is up to 100 times more deadly than HIV. Infected monkeys generally die within two years, but the treatment eradicated the virus in nine of the 16 monkeys. Researchers found that, in the cured monkeys, SIV initially persisted but gradually disappeared. Monkeys that showed vaccine protection showed consistently undetectable levels of SIV for more than three years after being infected, suggesting that the vaccine has long-term results.
“It’s remarkable because HIV is a virus that everyone thought of as permanent,” said Professor Louis Picker, from the Vaccine and Gene Therapy Institute at Oregon Health and Science University. “This is really the first demonstration that a pathogenic virus can be eliminated by the patient’s own immune system.” Although there are antiretroviral medications to suppress HIV in humans, they are expensive, must be taken every day to be effective and do not have the ability to eliminate the virus.
The vaccine contains another virus called cytomegalovirus (CMV)—belonging to the herpes family—which has been genetically engineered to produce certain proteins identical to those of the SIV virus. “It maintains an armed force that patrols all the tissues of the body, all the time, indefinitely,” said Picker. Therefore, when a monkey is inoculated, its immune system will recognize and attack the SIV virus if infected.
The team’s research involved a closer examination of how this successful vaccination prevented the spread of SIV, and also whether any of the SIV virus’ genetic material remained over time. They found that the protected monkeys had immune responses that were able to restrain the virus only after its initial spread. Picker said his team was also trying to figure out why vaccine tests usually only work in about half of the monkey subjects. “It could be the fact that SIV is so pathogenic that this is the best you are ever going to get,” he said.
When researchers injected blood from vaccine-protected monkeys into uninfected monkeys, SIV was not transmitted. On the other hand, blood samples from SIV-infected unvaccinated monkeys did transmit the infection. The researchers are now working on a way to use the vaccine to cure monkeys post-infection, and eventually to use the vaccine in humans.
“We have now engineered a CMV virus which generates the same immune response but has been attenuated to the point where we think it is unequivocally safe,” said Picker. This would have to be further tested and passed by regulatory authorities, but there is a promising chance that clinical trials in humans can start as early as 2015.
Picker admits that extra precautions should be taken when developing the herpes-based CMV virus for humans—he doesn’t want to exchange one virus for another. But the researchers maintain that they have found “compelling evidence for progressive clearance of [SIV] infection,” as well as a “promising candidate” for the prevention and cure of HIV/AIDS and other chronic infections in humans. If development continues, the vaccine may be able to have a profound positive impact on the global epidemic.
– Mari LeGagnoux