Scientists in Japan have developed a vaccination approach that could lead to protection against a wide range of coronaviruses – not just the one that causes Covid-19.
Developing a more widely applicable vaccine has been a major goal of researchers, as some existing vaccines have proved to be less effective against emerging variants of Sars-CoV-2.
The strategy of the researchers in Japan could potentially be used to provide protection even against new pandemics caused by different coronaviruses. Their strategy, described in a newly published paper in the Journal of Experimental Medicine, involved genetically engineering proteins from Sars-CoV-2.
Central to the research was the spike protein of the virus, which includes the receptor-binding domain that latches on to a receptor on human cells called ACE2. After the spike protein attaches to ACE2, the virus enters cells and multiplies.
A part of the receptor-binding domain, known as the head region, is highly specialised, but another section, the core region, is by contrast similar in multiple coronaviruses.
Immunity induced by vaccination typically involves the production of antibodies against the specialised head region, making the protection very specific to a particular coronavirus.
To get around this, researchers at Osaka University in Japan genetically engineered the receptor-binding domain of the spike protein to have sugar molecules attached to the head region.
Mice exposed to these engineered proteins produced a greater proportion of antibodies against the core region instead of, as would normally be the case, the head region.
The antibodies they made were a type of what scientists call broadly neutralising antibodies, and in tests, these were found to neutralise not just Sars-CoV-2, but also Sars-CoV-1, which caused the Sars outbreak of 2002.
They were effective too against three similar coronaviruses in pangolins and bats, an important finding as coronaviruses currently found in some animals could, in the future, go on to infect people.
“Given that prior coronavirus epidemics such as Sars-CoV-1 and Mers-CoV [Middle East Respiratory Syndrome] have occurred due to zoonotic coronaviruses crossing the species barrier, the potential for the emergence of similar viruses in the future poses a significant threat to global public health, even in the face of effective vaccines for current viruses,” one researcher involved in the study, Prof Tomohiro Kurosaki, from the WPI Immunology Frontier Research Centre at Osaka University in Japan, said.
The way that some current Covid-19 vaccines are less effective against emerging variants of Sars-CoV-2, particularly the Delta variant, demonstrates that the immunity they confer is highly specific.
Updated vaccines that cope with a wider variety of variants are being developed, but producing them takes time and then people have to be re-vaccinated, so a universal coronavirus vaccine would be preferable.
While the researchers in Japan focused on antigens (foreign substances that stimulate an immune response) that are common to different coronaviruses, researchers in the US, also working on mice, took a different approach.
In a study published in February, they described how mice could be given immunity against a range of coronaviruses with a “mosaic vaccine” made of multiple antigens.
Because of challenges such as ensuring that immunity is durable and broad enough to cope with emerging diseases, scientists have predicted that it may take several years to develop a universal coronavirus vaccine.
Dr Andrew Freedman, an infectious diseases specialist at Cardiff University in the UK, said while he has not analysed the latest study in mice, it was “probably realistic” to hope that a universal coronavirus vaccine could be developed.
“There’s almost certainly cross-immunity,” he said.
“We know you can get repeated coronavirus infections, so immunity is not perfect, but part of the immune response to one coronavirus will almost certainly give you cross-immunity to other coronaviruses. There are shared parts of coronaviruses.”
He cautioned, however, that with the latest study having been carried out on mice, “there would be a long way to go” before such broad-based protection in humans could be created.
Updated: October 10th 2021, 6:46 AM