A ground-breaking discovery by South African scientists, opening up a new approach that could prove key to producing an Aids vaccine, was announced by the Centre for the Aids Programme of Research in South Africa (Caprisa) on Monday.
The discovery involves a unique feature of HIV that enables some infected people to make antibodies that are able to kill a wide range of the HIV strains.
A study published in the journal Nature Medicine describes how a unique change in the outer covering of the virus found in two HIV-infected South African women enabled them to make potent antibodies which are able to kill up to 88% of HIV types from around the world.
Over the past five years, Caprisa has been studying how certain HIV-infected people develop very powerful antibody responses.
'Broadly neutralising antibodies'
These antibodies are referred to as broadly neutralising antibodies because they kill a wide range of HIV types from different parts of the world.
The Caprisa team initially discovered that two KwaZulu-Natal women could make these rare antibodies.
Through long-term follow-up laboratory studies of the two women, it was discovered that a sugar - known as a glycan - on the surface protein coat of the virus at a specific position (referred to as position 332) forms a site of vulnerability in the virus and enables the body to mount a broadly neutralising antibody response.
"Understanding this elaborate game of 'cat and mouse' between HIV and the immune response of the infected person has provided insights into how broadly neutralising antibodies arise," said Dr Penny Moore of South Africa's National Institute for Communicable Diseases (NICD).
These were the kind of antibodies that would be needed for a vaccine, Moore added.
'New approach to making a vaccine'
"Up to now, we've known that up to about a fifth of people make those antibodies, but we've never known how. We just haven't understood what the process is," she said.
"What we are showing today is one of the pathways - there are others, but this is one pathway for developing broadly neutralising antibodies.
"The reason it is significant is that it gives us a new way of thinking about how to make a vaccine, which is the next step ... It gives us a new strategy that we can exploit, where we try to mimic what happens in infected people, but in the absence of the virus and just doing that by vaccination," Moore said.
Head of Aids Research at the NICD, Professor Lynn Morris, explained that it was a surprise to find that the virus strain which caused infection in many cases did not have this antibody target on its outer covering.
"But over time, the virus was pressured by the body's immune reaction to cover itself with the sugar that formed a point of vulnerability, and so allowed the development of antibodies that hit that weak spot," she said.
'Our researchers have done us proud'
Commenting on the significance of the finding, Professor Salim Abdool Karim, director of Caprisa and President of South Africa's Medical Research Council, said that broadly neutralising antibodies were considered to be the key to making an Aids vaccine.
"This discovery provides new clues on how vaccines could be designed to elicit broadly neutralising antibodies," Karim said.
Health Minister Aaron Motsoaledi on Monday paid tribute to the scientists involved in the study, while highlighting the importance of their finding.
"Our researchers have done us proud. Today's announcement bears testimony to the kind of scientists in our country," Motsoaledi said.
The government's funding for the study was proof of its commitment to fund not only treatment but also research to find solutions to the epidemic, Motsoaledi said.
Science and Technology Minister Derek Hanekom, who also applauded the scientists involved in the study, said that a number of groups, including his department, had co-sponsored the study.
The scientists, among them young and female scientists, were making major breakthroughs in the fight against HIV/Aids and had made the country proud, Hanekom said.