An experimental AIDS vaccine developed in Oregon has received an $8 million investment from the Bill & Melinda Gates Foundation.

The candidate vaccine quickly stamped out infections in an animal model of AIDS infection, and protection lasted for at least a year, in a study reported in May 2011. The vaccine uses a modified form of cytomegalovirus, or CMV, to prime the immune system to mount defenses against the AIDS virus, as

last year:

During childhood, most people become infected with a virus called cytomegalovirus, or CMV. Because this virus persists in its human hosts for life, usually without ever causing harm, scientists at Oregon Health & Science University theorized it might serve as an ideal vehicle for vaccinating people against HIV, the virus that causes AIDS.

The basic idea is straightforward: engineer the mild-mannered virus to carry a few genes from the deadly one to prime immune defenses to squelch infections. The harmless CMV virus's ability to persist indefinitely means that as a vaccine carrier, it could potentially produce lifelong immunity.

The OHSU researchers said the Gates Foundation grant will support work to boost the effectiveness of the vaccine and refine the way it is delivered. So far, it has only been tested in an animal model: the rhesus monkey.

Louis Picker and colleagues at OHSU's Vaccine and Gene Therapy Institute and Oregon National Primate Research Center in Hillsboro, vaccinated 24 monkeys with the modified CMV and exposed them to SIV, the monkey equivalent of the AIDS virus. In 13 of the monkeys, the vaccine quickly stamped out infections, and protection lasted for at least a year in 12 of them,

in the journal Nature. Levels of SIV dropped to undetectable levels in most of the protected animals.

Years of research will be needed to found out if the CMV vaccine is safe and effective for people. Misleading animal studies set the stage for a disastrous clinical trial with a vaccine candidate made by Merck. The drug company halted the trial in 2007 when it became clear the vaccine wasn't protecting volunteers – and may have made them more vulnerable. Two vaccines used together appeared to lower the risk of infection by about 30 percent compared with placebo injections in a 2009 study in Thailand. But the two-vaccine combination probably

for wider use:

A 31% level of efficacy is not high enough to warrant use of a vaccine outside a trial setting, especially for a disease as serious as HIV. Yet this was the first time an HIV vaccine efficacy trial actually showed evidence of protection against the virus, giving researchers hope that an effective HIV vaccine is possible.

The Oregon vaccine candidate failed to protect half of the experimentally exposed animals. Picker, quoted in

, said HIV in people may prove more easily stopped than SIV in monkeys:

"One promising aspect of studying SIV is that it is a more potent virus than its human counterpart. Therefore, we expect that a human form of this vaccine candidate – while still some years away – would have a higher effectiveness rate than other current candidates. However, before a human vaccine is tested, there is much more work to be done in regards to safety and other areas."

Questions remain about the safety of infecting healthy people with modified CMV. Ordinary CMV can unleash damaging attacks when it infects a developing fetus with minimal immune defenses, or an adult with a severely depleted immune system caused by drugs or an illness such as AIDS. CMV causes brain damage in about 8,000 newborns each year in the U.S. when women are first infected during pregnancy.

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