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Seattle Scientist Defangs Parasite In Search Of Malaria Vaccine

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Courtesy of Seattle Biomed
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Infected mosquitos bite human volunteers through a special mesh in order to test a malaria vaccine candidate.

A Seattle scientist is set to begin clinical trials of a new malaria vaccine candidate, hoping a new twist on an old approach will finally yield an effective preventive treatment for the disease.

The idea of using a weakened pathogen to stimulate the body’s immune response is not new — it is widely in use in, say, the nasal-spray version of the seasonal flu shot. In that vaccine, the idea is to hobble the virus enough that it cannot hurt the patient, but still allows the body to learn to recognize and fight the invader.

“So it’s a kind of a training program that you give the immune system,” said Stefan Kappe of Seattle Biomed. “And the training program is most robust if [the pathogens} are alive and can infect cells but then they die.”

Now Kappe trying a similar approach with malaria – the key difference being that malaria is caused not by a virus, but by a much bigger and more complicated bug.

“The parasite is an organism with 5,000 genes in its genome. It’s a very complex organism compared to a virus, which, you know, has between 10 and maybe 100 genes,” Kappe said.

Kappe’s team went into the parasite’s genome and deleted three of those genes, in hopes of preventing the parasite from reproducing inside a human’s liver.

An earlier version of this “genetically attenuated parasite,” or GAP, with just two of the genes removed did not work as well as hoped. It seemed to provide some protection, said Kappe, but failed to keep people exposed to high loads of the parasite from getting sick. He hopes deleting the additional gene will make it more effective.

To test that idea, 10 volunteers enrolled in the phase-1 trials will receive the weakened parasite through the bite of an infected mosquito. Kappe says he’ll be among the first to volunteer. The trials begin Jan. 7.

Malaria can be treated but there’s no effective vaccine yet. The World Health Organization reports that it kills more than half a million people a year.

Gabriel Spitzer is a former KNKX reporter, producer and host who covered science and health and worked on the show Sound Effect.
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