Scientist discover five new malaria vaccine targets

Scientists have discovered five new malaria vaccine targets that lead to reduction in the parasite's ability to enter the red blood cells.

The finding, published in the journal Proceedings of the National Academy of Sciences, shows that future malaria vaccines may be most effective if they target multiple parasite factors.

Researchers at the Wellcome Trust Sanger Institute in the UK and colleagues studied the malaria parasite at its most vulnerable stage - when invading human red blood cells.

They identified five targets that lead to a reduction in the parasite's ability to enter red blood cells.

Nearly half of the world's population is at the risk of malaria and more than 200 million people are infected each year. The disease caused the deaths of almost half a million people globally in 2015, researchers said.

Despite the large number of deaths, there is no highly effective vaccine currently available for malaria, they said.

In the new study, scientists discovered five targets for future malaria vaccine development, which they suggest should be targeted in combination.

The team screened 29 potential targets that were all thought to play a role in the parasite's ability to invade human red blood cells.

Red blood cell invasion is an essential step in the parasite's lifecycle, and is a stage when the parasite is at its most vulnerable and exposed to the immune system.

Researchers raised rabbit antibodies against all 29 targets, then tested the antibodies against two different strains of the deadly Plasmodium falciparum malaria, one from Africa and one from Asia.

Of the 29 antibodies, the team discovered five that reduced the parasite's ability to invade red blood cells in both malaria strains.

"Producing a successful vaccine against parasites is challenging because they are very complex organisms with many components, making it difficult to know which ones to target," said Gavin Wright from the Wellcome Trust Sanger Institute.

"By studying the parasite's genome and working backwards, in a process known as reverse vaccinology, we have discovered five vaccine targets which, if combined, show promise for further development," said Wright.

People naturally exposed to malaria can develop immunity over time. The team worked with collaborators in the US and Mali to see whether the five antibodies they identified were associated with natural protection against malaria in people.

Scientists found that alone, no single antibody gave protection against malaria in people, however combinations of the antibodies did protect against the parasite.

To investigate what was happening at the cellular level, researchers used video microscopy to watch the parasite attempt to invade red blood cells with and without the presence of antibodies.

The team discovered that the different antibodies were attacking the parasite at different steps as it invaded the red blood cell.

Scientists found that pairing antibodies that each acted at different steps led to a more effective combination.