AsianScientist (Jun. 13, 2016) – Scientists from Singapore and Australia 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, published in Scientific Reports, potentially paves the way for more effective vaccines to be developed.
Malaria is caused by parasites that are spread by mosquitoes. The World Health Organization estimates that in 2015, malaria caused the deaths of 438,000 people and infected 214 million people worldwide.
Researchers have been trying to develop a successful vaccine for decades. However, even the most trialed vaccine only remained effective in a small proportion of people four years after immunization.
Most of the vaccines that have been worked on have aimed to generate antibodies against the parasites. The head of the Molecular Immunology Laboratory at the QIMR Berghofer Medical Research Institute in Australia, Dr. Michelle Wykes, and colleagues from the National University of Singapore found an alternative strategy: 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. 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,” Wykes said.
According to Wykes, about five months later, the experimental group had lower levels of antibodies than the control group, but was still resistant to malaria. However, when the researchers depleted their CD8+ T 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,” Wykes said.
The researchers believe that 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+ T cells together will provide better protection against malaria for longer.
The article can be found at: Horne-Debets et al. (2016) Mice Lacking Programmed Cell Death-1 Show a Role for CD8+ T-cells in Long-term Immunity against Blood-stage Malaria.
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Source: QIMR Berghofer Medical Research Institute; Photo: Shutterstock.
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