For the first time, a vaccine has completely protected monkeys against infection with SIV, a virus related to HIV that infects the animals.
Out of 24 immunised rhesus macaques, 12 had long-term protection, with no signs of SIV a year after they were deliberately infected with the virus.
鈥淚n half the monkeys, we saw a dramatic effect on control of the virus,鈥� says , the scientific director at the International AIDS Vaccine Initiative, which collaborated in the trial. 鈥淲e see it as a significant advance.鈥�
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What made this vaccine different was the use of a live but relatively harmless virus as a host. To make it, at Oregon 午夜福利1000集合 & Science University in Beaverton and colleagues packaged SIV genes into a live virus called a rhesus cytomegalovirus (RhCMV) vector, then injected it under the skin of the monkeys.
They compared its effectiveness with that of conventional vaccines, which deliver SIV genes in harmless adenovirus vectors, similar to those that cause colds.
Lifetime guarantee
The main difference between the two types of vaccination is that RhCMV carries on replicating and producing SIV antigens throughout the monkey鈥檚 life. By contrast, the adenoviral vaccine replicates once then vanishes.
The result, Koff explains, is that RhCMV keeps the body鈥檚 immune system on constant alert for SIV, so that when an infection happens, it is instantly able to stub it out.
Monkeys injected with the RhCMV vaccine made a specific subset of white blood cells primed to destroy SIV. Called effector memory T-cells, these are ready and waiting for SIV throughout the body.
The result was that SIV was completely undetectable in 12 of the 24 monkeys. All monkeys receiving the conventional adenovirus vaccine gradually succumbed to the virus despite initially producing antibodies against it.
Humans next?
鈥淚t puts back on the agenda the possibility that HIV can be controlled by the human immune system,鈥� says Robin Shattock at Imperial College London. However, the researchers also need to explain why the response was 鈥渁ll or nothing鈥�, with half the monkeys responding brilliantly and the others apparently not responding at all, says Shattock.
None of the three vaccines tested in humans so far has shown any sign of matching the RhCMV vaccine鈥檚 ability to control SIV. Only one of the three, the RV聽144 vaccine tested in Thailand in 2009, has shown any ability to prevent infection, reducing it by about a third.
Journal reference: , DOI: 10.1038/nature10003
