How vaccine manufacturers can be less reliant on a single tree species

The global vaccine industry currently has a lot riding on the Chilean soapbark tree – but new research might make it less reliant.

The Chilean soapbark tree (Quillaja saponaria) is a rich source of saponins, which work as powerful adjuvants: substances that provoke the immune system into reacting more strongly to a vaccine.

Saponins from the soapbark tree appear in several vaccines, including shingles, malaria, and the Novavax COVID vaccine.

These vaccines are dependent on the soapbark tree for their materials: until now, no-one has been able to make or grow the saponins anywhere else.

But a team of UK researchers has announced that they’ve managed to grow one of the most common saponin molecules, QS-21, in tobacco.

They’ve published their findings in Nature Chemical Biology.

“Our study opens unprecedented opportunities for bioengineering vaccine adjuvants,” says Professor Anne Osbourn, a group leader at the John Innes Centre, UK.

“We can now investigate and improve these compounds to promote the human immune response to vaccines and produce QS-21 in a way which does not depend on extraction from the soapbark tree.”

The researchers searched the genomic sequence of the soapbark tree to find which genes might lead to enzymes which produced the right saponins.

They eventually narrowed their search down to 70 candidate genes, which they transferred into tobacco plants using genetic modification.

Then, after examining the plants that were produced, the researchers figured out the 20 key genes needed to make QS-21.

“This is the first time QS-21 has been produced in a heterologous expression system. This means we can better understand how this molecule works and how we might address issues of scale and toxicity,” says first author Dr Laetitia Martin, also at the John Innes Centre.

The researchers have partnered with a local biotechnology company, Plant Bioscience Limited, to commercialise their process.

“What is so rewarding is that this molecule is used in vaccines, and by being able to make it more sustainably my project has an impact on people’s lives,” says Martin.

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