Modified viruses bring malaria vaccine hope
07 August 2008
An effective malaria vaccine is a step closer thanks to work by an international collaboration of researchers, led by Dr Simon Draper from Oxford University. The team used modified cold and pox viruses to deliver a malaria vaccine that offers complete protection from the disease in animals and also strongly limits the growth of human malaria in vitro.
In the study, which was part-funded by the Wellcome Trust, the researchers genetically modified an adenovirus that causes the common cold and a pox virus so that they expressed on their surfaces a protein found in the malaria parasite's coat.
This kind of virus technology has been used before to evoke a strong T-cell response - the immune reaction needed to destroy the malaria parasite in the early part of infection, the liver stage. As expected, when the pox virus was given to mice 8 weeks after the cold virus in this study, the animals showed a strong T-cell response.
However, in this study the vaccine also triggered another kind of immune response - the production of antibodies. This is the first time that a vaccine based on modified viruses has triggered such a strong antibody response, which is vital in fighting the blood stage of malaria, during which those who are infected become sick.
This unexpected effect is a result of much optimisation, both in terms of the make-up of the vaccine and in the timing of the prime vaccination and the booster jab.
"This work is the end of a slow iterative process," says lead author Dr Draper. "In the end however, the results were startling, and we could use these viruses to induce very high levels of antibodies for the first time."
The team is now preparing to launch a Phase I trial of a human form of the vaccine to test its immune effects and safety. The trial, which will be carried out in healthy adults in Oxford, is expected to begin in early 2009.
Image: CDC/Dr Mae Melvin
References
Draper SJ et al. Effective induction of high-titer antibodies by viral vector vaccines. Nat Med 2008 [Epub ahead of print].