A novel and relatively simple vaccine that can be administered orally has managed to completely block rectal infection with SIV, the monkey equivalent of HIV, in rhesus macaques and produced rapid re-suppression of viral load in monkeys who were previously infected with SIV.
The vaccine, whose success at blocking infection was described by its own designers as ‘surprising’ and ‘unexpected’, appears to work by stimulating the production of a previously unknown group of CD8 T-cells that stopped the monkeys’ CD4 cells from recognising SIV as a foreign invader, thereby preventing an immune response to SIV. This suppressant effect – which works in the opposite way to a traditional vaccine – means that the SIV is deprived of the SIV-specific immune-activated CD4 cells it needs in order to proliferate and establish an infection in the body.
The vaccine consisted of inactivated SIV administered alongside doses of familiar bacteria – in the first case the TB-suppressant bacterium BCG, and subsequently with gut bacteria of the Lactobacillus genus, including one type commonly used in probiotic supplements. This suggests that if human studies replicate the success seen in monkeys (by no means assured in vaccine studies) the vaccine could be administered in a drink.
Two initial safety trials are now planned in humans. In one, HIV-negative volunteers at low risk of HIV will be given the vaccine to see if it stimulates the same immune- and virus-suppressant responses. In the other, HIV-positive volunteers on fully-suppressive antiviral therapy will be given the vaccine and then taken off ART six months later if test tube results suggest the vaccine has produced such responses.
First published – Aug 26 2014 – AIDS Map