SAN ANTONIO, April 11 (UPI) -- A candidate HIV vaccine prevented female monkeys in a study from acquiring the AIDS virus despite being repeatedly exposed to it, according to researchers in Texas.
Researchers at the Texas Biomedical Research Institute report a vaccine they are testing with Mymetics Corporation protected the monkeys, repeating the results of smaller tests done with both monkeys and humans in China.
The researchers were asked to repeat studies in China which protected the same type of monkeys from repeated exposure to the virus, and showed the vaccine was safe and could be tolerated by humans.
While the new study showed significant protection for the monkeys, as the level of virus they were exposed to increased, the vaccine provided less protection.
"We are encouraged by the initial strong protection provided by the vaccine candidate, which is in line with the results from an earlier primate study performed in China that we were asked to repeat," Dr. Ruth Ruprecht, director of the Texas Biomed AIDS Research Program, said in a press release. "The fact that the vaccine-induced immune defenses were eventually overcome requires a careful analysis to understand the mechanisms of the initial vaccine action and to learn what other immune defenses can be enlisted to yield even more potent antiviral action."
For the study, which has not yet been published in a peer-reviewed journal, researchers exposed 36 origin rhesus macaque monkeys to one of two vaccination regimens or a placebo, before the monkeys were exposed to HIV.
With each exposure, the researchers increased the viral challenge dose by 50 percent, eventually reaching levels more 100,000 times the average amount of virus normally passed from an infected man to a partner. Overall, the vaccine was 87 percent effective at delaying the time to persistent infection after exposure when compared to the placebo group.
"We are pleased that Mymetics HIV virosome-based vaccine could strongly prevent virus transmission under conditions that mimic male-to female sexual transmission," said Sylvain Fleury, chief science officer at Mymetics. "Especially as these protection results are coming from two studies conducted in two different countries, with two different sub-species of macaques, with different vaccine lots and without an adjuvant. The observed protection in genetically different animals raised in different housing and environmental conditions gives more weight to these observations."