The Quest for QS-21

Researchers, led by Professor Anne Osbourn (OBE, FRS) at the John Innes Centre are working to decipher how one immune-boosting compound, QS-21, is produced by the Chilean Soapbark tree

Humans have used plants for thousands of years to help treat disease and improve health, and the global pandemic highlights the value of these treatments.

The Chilean Soapbark tree (Quillaja saponaria) is one such plant. Historically bark from the tree has been used as detergent, and later as a food additive and in beauty products. The useful, soapy compounds in the bark of the quillay tree belong to a group of complex specialised chemicals called saponins. Many plants produce saponins and it is believed their role inside plants is to defend against diseases.

Saponins have a role not just in plant health, but in human health too. Claimed benefits include cholesterol reduction, antioxidant activity and cancer risk reduction.

In 1925 it was first shown that the addition of saponin in early treatments to prime the immune system, enhanced antibody responses to diseases such as diphtheria and tetanus. It was later found that one saponin from the Chilean Soapbark tree was most effective in producing a suitable immune boosting effect – named QS-21.

QS-21 is an adjuvant, a word which describes molecules that boost the immune response of a vaccine. The addition of an adjuvant to a vaccine stimulates the human body to produce more antibodies, reducing the amount of vaccine needed and potentially increasing the efficacy of the vaccine.

Despite advances in the field of adjuvants, only a few have been licensed for human use. QS-21 is one. The first vaccine containing QS-21 was approved in 2017. This means that demand is high and is expected to increase as vaccines are developed in response to the coronavirus pandemic.

Researchers at the John Innes Centre are studying how QS-21 is made in plants, with the hope that this could lead to an alternative way to make this medicinal molecule.

Extracts from "The quest for QS-21". Advances, a John Innes Centre magazine; Issue #34 Winter 2020-2021.  Read the article in full here.

Contact: Dr Georgina Pope

Anne Osbourn
John Innes Centre (Norwich, UK)