The magic bullet to protect against Aids is no closer today than it was when the virus that causes the deadly disease was first identified about 25 years ago.Though both public and private-sector researchers have done their best to find a single potent injection, HIV's unparalleled ability to evade the body's immune system seems to have trounced medical science.
Earlier this year, the second Aids vaccine to complete efficacy testing failed in SA. The Phambili trial was halted after results from sister trials around the world found the Merck vaccine candidate, which showed promise, was ineffective and could possibly raise the infection risk. The vaccine did not show protection against HIV infection, nor did it reduce the viral load of volunteers who later became infected.
There is consensus that approaches based on stimulating antibody production - the traditional way in which vaccines work - is ineffective against HIV because of its extraordinary ability to "cloak" itself by changing its protein shell.
Now researchers worldwide see no realistic prospects of producing a miracle vaccine in the immediate future. Nobel laureate Prof David Baltimore, who is one of the leading authorities on Aids, summed up the state of despair recently as: "It's such a sad topic. The [research] community is depressed because we see no hopeful route to success."
The lack of progress suggests that, in the near future, a vaccine will not be able to contain the global scourge of HIV/Aids. "It can be a year or 100 years before the world gets the magic vaccine. You can't put a time tag on the discovery," says Dr Glenda Gray, executive director of the Chris Hani Baragwanath perinatal HIV research unit.
But that doesn't mean they are ready to give up. SA researchers have, for the first time, developed their own vaccines - two - that will go on trial in the country and the US early next year. SA has been involved in many HIV/Aids clinical trials, but the vaccines have been produced in the US. "This is a paradigm shift. It's very exciting," says Gray. Phase 1 of the trials will be tested on 48 volunteers in Cape Town and Johannesburg, and 12 at the Fenway Community Health Center in Boston in the US. The 18-month trials will involve HIV negative adults who are at low risk of contracting the virus.
The vaccines, costing about US$10m to produce, were developed by South African sisters Annalise and Karolyn Williamson, with the help of a team of local scientists. They already have approval from the Food & Drug Administration (FDA) in the US, and the researchers are awaiting the green light from the local regulator, the Medicines Control Council.
"We're hoping to start trials at the beginning of next year. We're potentially sitting on a breakthrough," says Gray who is in charge of the clinical development of the trials in humans. "If it's positive, then we will take the vaccine to hundreds of people to try and get new responses. If that phase is a success, then we will take it to thousands of people."
The new vaccines are an improved model of what was used in the trials on 800 volunteers earlier this year. Gray says that taught researchers a lot more about the immune system. So, why have they been so stumped at producing a vaccine that is successful at penetrating the virus? Gray cites three major problems:
- No-one has ever recovered from an HIV infection, so researchers can't test what cured them.
- The virus is so diverse that it is difficult to try to find a portion of it that is stable and not changing so that doctors can use it to get an immune response that is predictable and sustainable.
- There is no animal model that can be used as a base to modify testing for human trials.
But that hasn't stopped scientists in their search for the wonder vaccine. Baltimore, who has a major grant from the Bill & Melinda Gates Foundation, is researching a new approach to HIV therapy and treatment. He won a Nobel prize in 1975 for the discovery of reverse transcriptase, an enzyme later found to be used by HIV to reproduce in human cells.
In his latest research, he is using gene therapy to modify stem cells so they can produce altered immune system cells, which can make specialised proteins not found in nature, that can attack HIV. If this works, it will first be used in new HIV therapies before his team tries to adapt it into a vaccine.
