Common Cold Viruses :(REUTERS) – The modified common cold viruses behind high-profile COVID-19 vaccine candidates from China’s CanSino Biologics and Russia’s Gamaleya Institute have been studied for decades, but are still not widely utilized.
The altered adenovirus type 5 (Ad5) viruses used in these vaccines were first created by Canadian researcher Dr. Frank Graham at a Dutch laboratory in the 1970s.
Graham planned to use them to examine mechanisms underlying cancer and distributed the human kidney cell line which makes them called HEK293, to researchers throughout the world.
“The cells became tremendously widespread and popular” among investigators, said Graham, now retired in Italy.
Vectors are materials used as mechanisms to carry genetic information into individual cells. Modified viruses that can’t replicate by themselves and so will not cause infection can be used as vectors to carry genes from the goal virus into human cells to induce an immune response against that virus.
Ad5 vectors were tested in ancient gene therapy, which aims to install a missing gene or replace a mutated or damaged one. They were largely abandoned after an 18-year-old died in 1999 from an immune system overreaction after receiving a large dose during a gene therapy trial.
Some researchers believe the powerful immune response that caused problems with gene therapy makes these vectors ideal for vaccines, where much lower doses are used and protective immune response is an objective.
At McMaster University in Canada, Graham and collaborators developed a wide variety of Ad5 vectors, such as for a rabies vaccine used on wild raccoons in the province of Ontario.
He and other researchers began developing an Ad5-based vaccine against Severe Acute Respiratory Syndrome (SARS) in 2003 and published preclinical data. It was set aside when that pandemic ended.
In 2011, CanSino licensed an experimental tuberculosis vaccine according to Ad5 from McMaster researchers.
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The Chinese company’s focus later shifted to an Ad5-based Ebola vaccine at the request of the Chinese military, according to Dr. Thomas Evans, now a chief scientific officer at Vaccitech, who was involved with the tuberculosis project. The Ebola vaccine was approved for military use in 2017.
Russia’s Gamaleya Research Institute, which developed Russia’s coronavirus vaccine, also used the Ad5 platform to develop an Ebola vaccine, which they said was administered to about 2,100 people.
Along with the Ad5-based COVID-19 vaccines, an inhaled version of the experimental tuberculosis vaccine is still under development at McMaster, according to Dr. Zhou Xing. His group is also in the early stages of developing an inhaled COVID-19 vaccine, testing Ad5, and another vector based on a chimpanzee adenovirus.