Scientists at QIMR Berghofer Medical Research Institute believe they’ve found the reason why none of the vaccines developed for malaria to date has protected against the disease for long. The discovery potentially paves the way for more effective vaccines down the track.
Malaria is caused by parasites that are spread by mosquitoes. Researchers have been trying to develop a successful vaccine for decades. However, even the most trialled vaccine only remained effective in a small proportion of people four years after immunisation.
Most of the vaccines that have been worked on have aimed to generate antibodies against the parasites.
The head of the Molecular Immunology Laboratory, Dr Michelle Wykes, along with Joshua Horne-Debets and Deshapriya Karunarathne, found that activating immune cells known as CD8+ T cells was crucial in protecting mice against malaria in the longer term.
“We compared two groups of mice,” Dr Wykes said.
“The first was a control group. In the other group we activated the CD8+ T cells by removing a molecule that otherwise puts the brakes on this immune cell.
“We found that compared to the control group, the experimental group was much more resistant to the malaria.
“About five months later, the experimental group had lower levels of antibodies than the control group, but was still resistant to malaria. However, when we depleted their CD8+ immune cells, those same mice lost resistance to malaria.
“This is the first time there has been evidence to show that these immune cells are crucial for protecting against blood stage malaria – which is when symptoms start to show – in the long term. In other words, we’ve found that antibodies on their own aren’t enough to maintain protection against malaria.
“We think this is the missing link that explains why none of the vaccines developed to date offers long-term protection from malaria.
“These findings suggest that in future, vaccines that generate antibodies and activate CD8+ immune cells together will have a much better success rate at protecting against malaria for longer”.
The World Health Organisation estimates that in 2015 malaria caused the deaths of 438,000 people and infected 214 million people worldwide.
The study has been published in the journal Scientific Reports. It involved collaborators from the National University of Singapore.