Human trials of the world’s first HIV vaccine will begin this year after it proved a success in trials on monkeys.
The serum, derived from the herpes virus, cleared 60 percent of rhesus macques of SIV, the monkey version of HIV.
And 75 percent of the monkeys exposed to SIV again were resistant to the virus for up to three years.
The findings, published today, are the breakthrough Dr Louis Picker, an immunology researcher at Oregon Health & Sciences University, has been working towards for 30 years – motivated by his adopted teenage stepson, Thabo, whose parents were killed by the disease.
The shot is widely regarded as one of our best bets for combating HIV, and Dr Picker’s latest research shows it is ready to test in humans.
It has taken years of tweaking and adjusting the vaccine to strike the right note. The two papers published today in the journal Science Translational Medicine show they have found an equilibrium that is effective enough to move ahead
It uses a form of the common herpes virus cytomegalovirus (or, CMV), which is the kind that causes cold sores.
In order to prevent serious disease, it was ‘live-attenuated’ – i.e. weakened, in the same way that the MMR (measles, mumps, and rubella) and varicella (chickenpox) vaccines do not cause those diseases.
A less powerful vaccine is key.
Many people with healthy immune systems live with CMV and barely notice it unless they are run-down and have a flare-up of cold sores.
But it can be debilitating in people with weakened or strained immune systems – such as people with HIV, transplant recipients, pregnant women.
So, the diluting process was necessary, but at first it ham-strung the team’s progress. HIV is so fast-moving and elusive that barely any medication can overcome it, let alone a weakened one.
It has taken years of tweaking and adjusting to strike the right note.
The two papers published today in the journal Science Translational Medicine show they have found an equilibrium that is effective enough to move ahead.
Sixteen of the 27 immunized rhesus macaques were cleared of SIV – a 59-percent success rate, which is similar to the results they achieved with the stronger ‘non-attenuated’ form of the shot.
Over the next three years, they exposed 12 of the 27 to SIV once more to test how long the vaccine’s effects lasted, and only three of them were infected.
‘This is a level of durability that would be very important for a human HIV vaccine,’ Dr Picker said.
It paves the way for more broadly usable – but still potent – CMV-based vaccines that could be administered to individuals with weak immune systems.
It could also prevent HIV in vulnerable members of society, said Dr Picker.
The CMV vaccine has been licensed by San Francisco based Vir Biotechnology – and has been backed by the Bill & Melinda Gates Foundation.
It is already planning to lead a clinical trial with a human version of the therapy.
Vaccines with CMV have emerged as a potential treatment for diseases like HIV and have shown promise in several primate studies, said Dr Picker.
But the virus can cause severe symptoms in humans with weakened immune systems – which has limited the therapeutic potential.
So the researchers tackled this issue by engineering the vaccine to provoke responses from the intrinsic immune system – which specifically targets viruses.
By taking out a protein called pp71 it fired immune cells into action without spreading past the injection site – or to unexposed animals.
The second study found the new jab spread up to 1,000 times less than unmodified CMV in vaccinated rhesus monkeys – while still generating potent responses from the T cells that had been primed to attack HIV.
Vaccines using a similar technique are also being developed by the same team to combat tuberculosis.
Co-corresponding author Dr Klaus Fruh said: ‘This research, using rhesus CMV, provides potentially important insights into the design of a human CMV-based HIV vaccine.
‘We significantly attenuated CMV and still got the same type of immune responses as with the wild version of this vaccine.’