Vaccine that completely blocks HIV in monkeys found

A new oral vaccine has been found to completely stop rhesus macaque monkeys from being infected with SIV, the monkey equivalent of HIV. The vaccine also reduced the number of SIV particles that were present in monkeys who were already infected with SIV.

The new vaccine works in the opposite way to most vaccines - by suppressing, rather than triggering, an immune response. This is because HIV and SIV actually require immune cells known as CD4 T-cells in order to proliferate and establish an infection in the body.

The new vaccine works by stimulating the production of a previously unknown group of immune cells known as CD8 T-cells, which then stop the monkeys’ CD4 cells from recognising SIV. This prevents any immune response and stops SIV from hijacking the CD4 cells and spreading around the body.
The vaccine works because it's made up of inactivated SIV, but, importantly, it’s given alongside doses of bacteria that are familiar to the body and are recognised as ‘friendly’ - in this case, strains used in probiotics.
The researchers tested variations of the vaccine, involving different bacteria strains, in 29 rhesus macaques - they were either given it as a vaginal gel, a rectal douche, an oral vaccine or an oral probiotic-type drink.
So far all 15 monkeys given the vaccine orally have been completely protected against SIV infection, with the vaccinated monkeys still able to suppress viral reproduction four years after vaccination.
The results are extremely positive, but the researchers admit they’re still mystified as to why something as simple as giving inactivated SIV alongside what is essentially a probiotic preparation produces such a strong immune-suppressing result. When inactive SIV is given alone, it stimulates the immune system as normal vaccines would.
Either way, the researchers are now looking into whether the same approach would work in humans. Of course, SIV isn’t identical to HIV, and previously vaccines that have looked extremely promising in animals studies have failed to work in humans, so it’s important to keep these results in perspective.
Two initial safety trials are now planned in humans both in HIV-negative and HIV-positive volunteers.