Researchers Find New Avenue to HIV Hope--Via Monkeys

Researchers have found promising new leads in the fight against AIDS, both involving monkeys.

British scientists have hit on a new angle in the quest for a vaccine against HIV by modifying a simian virus and creating a new inoculation that boosts monkeys' ability to fend off SIV, the simian version of the virus that causes AIDS, reported the BBC News on May 12.

HIV is thought to be an adaptation of SIV that jumped from monkeys to humans. Such viral jumps from one species to another are not uncommon. The new inoculation creates antigens that target SIV and destroy the virus, even months--possibly years--later.

The new vaccine provided protection against SIV to half of the trial's two dozen monkeys, the article said. Study author Louis J Picker, who is with the Vaccine and Gene Therapy Institute in Oregon, told the media that the 13 monkeys that benefited from the treatment seemed to have the virus eliminated from their systems.

Though modern drug regimens can reduce the viral load in human patients to undetectable levels, the virus is still present and would rapidly replicate in the absence of daily doses of anti-retrovirals. In only one case has a human patient seemingly been "cured" of HIV, a bone marrow transplant patient who received marrow from a donor with a mutation that naturally gave him resistance to the virus.

Health experts are cautious, however, about declaring the patient cured, because HIV can shelter in the body's tissues for years and reemerge later on.

Still, in the case of the monkey vaccine trials, scientists were optimistic, the BBC article reported.

"I'm excited by the science because it really does demonstrate that it may be possible to eradicate the HIV virus by a strong immune response," Oxford University's Sir Andrew McMichael said. "But at the same time I'm scratching my head how to take this approach into humans."

The problem lies with the vaccine's synthesis from a simian disease, rhesus cytomegalovirus, which could pose a health threat of its own to human subjects.

"The breakthrough here is in using a viral-delivered vaccine that persists--essentially using an engineered virus to thwart a pathogenic virus," explained Imperial College's Robin Shattock. "The tricky part will be showing it is safe and effective in humans."

However, the risks may be small to begin with.

"On one level 99% of people in sub-Saharan Africa are CMV-positive and half the people in the developed world are, so we know at lot about it and it's mostly non-pathogenic, except in vulnerable populations like pregnant women," said Picker. "We're fully aware to make it available to humans, then the next step is to make a virus which retains or has an enhanced ability to make effector memory cells, but no longer has the capacity to infect vulnerable parts of the population."

Researchers also noted that monkeys benefitting from the vaccine seemed to have a genetic basis for their response, AFP reported on May 5.

"It tells us--probably much to our surprise--that there will likely be in humans certain genes expressed by some people but not in others that may well be contributing to protection," said Harvard Medical School's Norman Letvin. "So that we not only have to look at vaccine-induced antibody responses but we also have to look at the genetic makeup of the individuals who are being vaccinated because these data in monkeys suggest that both of these can be contributing."

The new study relates to a 2009 study in which a vaccine was tested on monkeys and showed promising results--but then the protective effect faded in a few years.

"We have demonstrated in the [earlier] vaccine trial that with existing technologies we see modest protection against HIV infections," noted Letvin. "If we couple that optimistic data in humans with the kind of data we generated in this study with monkeys, as well as other studies in monkeys, it suggests that if we can induce an even better antibody response through vaccination.

"Maybe with our next generation vaccine we can get that up to 50 percent or 60 percent or even higher levels of protection, and that protection can be even more durable," Letvin added.