New HIV vaccine hope?

“Vaccine 'clears HIV-like virus' in monkeys,” reports BBC News. It says that the US researchers involved “say they now want to use a similar approach to test a vaccine for HIV in humans”.

The study in question tested the vaccine in rhesus macaque monkeys, which were then exposed to the SIV virus – which is similar to HIV. The vaccine had shown promise in a previous study, and was again found to protect up to over half of the monkeys depending on how they were exposed to the virus. The researchers also found that in monkeys that showed vaccine protection, the virus initially lingered in the body, but eventually appeared to be cleared completely.

The authors cautiously note that they cannot rule out the possibility that the virus is still present at very low levels that are not detectable with current technology or in tissues that they did not test. However, they say their data do strongly suggest that the virus has been cleared from the monkeys’ bodies.

As the authors say, these findings are promising, and are likely to galvanise further research into the potential for this type of vaccine to be used in humans against HIV.

Where did the story come from?

The study was carried out by researchers from Oregon Health & Science University and other research centres in the US. It was funded by the National Institute of Allergy and Infectious Diseases (NIAID), the Bill & Melinda Gates Foundation, the International AIDS Vaccine Initiative (IAVI) and its donors, including the US Agency for International Development (USAID), the National Center for Research Resources, and the National Cancer Institute. The study was published in the peer-reviewed journal Nature.

The BBC provides good coverage of the story, with a headline that clearly indicates what the findings of the study are without overextrapolating to humans.

What kind of research was this?

This was an animal study that assessed the effects of a vaccine against the monkey equivalent of the HIV virus (called the SIV virus). The researchers hope that if they can develop an SIV vaccine that is effective in monkeys, this will help them to develop effective HIV vaccines for humans.

Infection with the HIV and SIV viruses is thought to be permanent, with even the best currently available treatments only controlling the virus. It is thought that the virus might be most vulnerable in the first few hours or days of infection, and so researchers have been trying to develop a vaccination that would allow the immune system to recognise and attack the virus as soon as an infection occurred.

Researchers have developed a vaccine that targets the SIV virus in monkeys, and found that it protected about half of the rhesus macaques vaccinated against infection with SIV. The vaccine involves using another virus called cytomegalovirus (CMV), which has been genetically engineered to produce some of the same proteins as the SIV virus, so that the immune system will recognise and attack the SIV virus when it sees it.

Monkeys vaccinated with the CMV vaccine showed the SIV virus in their bloodstream for a short period before it reduced to undetectable levels. The monkeys occasionally had detectable SIV in their bloodstream over time, but these gradually became less common, and by one year they only had trace levels of the virus’ genetic material detectable in their tissues. One of the 13 monkeys that had initially shown vaccine protection against the virus showed recurrence of SIV in their blood at day 77 after infection that increased over time.

What did the research involve?

The current study wanted to look more closely at exactly how the vaccine prevented the spread of SIV through the bodies of the monkeys in which the vaccine was successful, and whether any residual SIV was eventually cleared from their bodies.

The researchers carried out a wide range of experiments. Essentially, they vaccinated rhesus macaque monkeys against the SIV virus and then exposed them to the virus through the rectum, vagina, or by injection into a vein. They then measured the levels in SIV in the monkeys’ blood and tissues over time, and tested whether the monkeys’ blood was capable of infecting other monkeys.

What were the basic results?

The researchers found that five vaccinated monkeys infected rectally showed protection against the virus, although it wasn’t clear whether this was all of the monkeys they infected rectally. They also tested the effect of different routes of infection, and found that the vaccine offered protection against infection in nine of 16 monkeys infected vaginally (56%), and two of the six monkeys infected by injection into a vein (33%).

The researchers found that regardless of how they exposed the monkeys to SIV, the monkeys that showed vaccine protection had immune responses that controlled the virus after its initial spread. SIV virus that was still capable of multiplying did remain present at several sites in the monkeys’ bodies for weeks to months.

However, over time these monkeys lost signs of SIV infection. Ten monkeys that showed vaccine protection were followed for over three years and they showed consistently undetectable levels of the virus in their blood and other tissues up to 172 weeks (more than three years) after they had been exposed to the virus.

Injecting uninfected monkeys with blood samples from these vaccine-protected monkeys did not transmit the infection, while blood samples from SIV-infected unvaccinated monkeys did transmit the infection.

How did the researchers interpret the results?

The researchers concluded that their data provide “compelling evidence for progressive clearance of [SIV] infection”. They say that the type of vaccine they used in their study (a CMV-based vaccine) is a “promising candidate” for strategies that aim to prevent and cure HIV/AIDS and other chronic infections.

Conclusion

This fascinating research has looked into the effects of a vaccine against the monkey equivalent of the HIV virus (called SIV). The vaccine previously showed the ability to protect about half of the monkeys vaccinated against infection, and the current study wanted to investigate this effect further. The results suggest that the vaccine can protect the monkeys against SIV infection from various routes. They also suggest that in monkeys that show vaccine protection after an initial period where the virus lingers, they eventually seem able to clear the infection from their body.