By: Kimani Chege and David Dickson


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Development work on a pair of possible AIDS vaccines that had, until now, been widely seen as one of the most promising ways of combating the disease may be abandoned following disappointing results in clinical trials.

Two candidate vaccines, designed to be administered jointly, have been developed by scientists in the Kenya Aids Vaccine Initiative (KAVI), in collaboration with researchers at the University of Nairobi and at the University of Oxford in the United Kingdom.

The vaccines were designed after sex workers in a Nairobi slum were found to possess immune systems that were able to destroy the HIV virus. They are intended to stimulate the same cell-mediated immune response in other individuals.

The vaccines — known as DNA.HIVA and MVA.HIVA — have been developed as what is known as a 'prime-boost' pair. They are intended to be given in combination, the DNA.HIVA being administered first, and the MVA.HIVA — the 'boost' — second. The hypothesis has been that a combination of the two may be better at eliciting an immune response than one candidate alone.

When the vaccine trials were launched in 2001, the head of the International AIDS Vaccine Initiative, one of the trials' main sponsors, described the approach they embodied as "our best hope for ending the cycle of new HIV infections".

But preliminary results of trials on 205 volunteers in Kenya, Uganda and the United Kingdom, presented to a conference in Lausanne, Switzerland, earlier this week, showed that the immunity to HIV/AIDS was only boosted in about one quarter.

This is far lower than the 60 per cent that IAVI requires to judge a vaccine undergoing clinical trials to be considered successful.

The results have triggered a mixed response from those responsible for the trials. Andrew McMichael, director of the Human Immunology Unit of Britain's Medical Research Council — the other main sponsor — admitted that the results were disappointing.

But he said that he and his team were still keen to continue exploring the approach used in the vaccine design. "With a project of this type you realistically have to expect to modify the vaccine as you go, and that it might be a second or third generation vaccine which actually ends up being successful."

In contrast, the reaction from IAVI about future prospects for the vaccine has been more negative. Indeed the organisation has said that, if the final results of the clinical results are no more promising, it will shift its support to alternative vaccine designs.

In a statement, IAVI accepted that the trials had shown that the vaccine was "generally safe and well tolerated". But it added that the data "falls short of expectations" and that the promise manifested in preclinical studies "has not held up in humans."

"Unless there are new immune response data that are dramatically different, IAVI will not develop the candidates further, and will focus on its other research and development projects," says Chrispin Kambili, head of IAVI's Kenyan office.

The news about the poor results in the clinical trials has been received with disappointment in Kenya by AIDS patients who had hoped that the vaccine would prove to be an effective way of combating the disease.

Others, however, argue that it is wrong to describe the trials as a 'flop', as they have already produced a significant amount of useful information. "At least we now know that DNA-based vaccines are safe for human beings," Pamela Mandala, one of the first volunteers in the trials, said in an interview with the East African Standard.

 Despite the lack of success in the vaccine trials, Kenya remains one of the few countries in sub Saharan Africa with the capacity to undertake a HIV vaccine research due to state-of-the-art facilities at KAVI.

So far, the vaccine trials have cost more than US$80 million.  As a result of the disappointing results, IAVI has decided to cancel further clinical trials that were due to take place in both Rwanda and the Netherlands, arguing that remaining questions about the candidate vaccines "can be answered by the trials that will be completed in Kenya and the United Kingdom".

Meanwhile McMichael says that, if IAVI funding for future development of the two vaccines is withdrawn, his research team at Oxford may seek other sources of financial support.

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