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Could cells that fight the common cold help people beat Covid-19?

HONG KONG — Long before the coronavirus that causes Covid-19 was detected, four other coronaviruses had been circulating among people, causing about one in five common colds.

HONG KONG — Long before the coronavirus that causes Covid-19 was detected, four other coronaviruses had been circulating among people, causing about one in five common colds.

While much is unknown about the novel coronavirus, evidence is emerging that these cold-causing viruses might leave behind “memories” in our immune system that could affect how the body fights Covid-19.

New research published by separate teams in the US and Germany suggests certain immune cells involved in the defence against the common cold also react when exposed to SARS-CoV-2, as the novel coronavirus is known.

While neither study showed whether this pre-existing immune cell memory affects Covid-19 clinical outcomes, both teams said evidence of a “cross-reactive” immune response could explain why some people have much more severe responses to Covid-19 than others, but more research was needed.

The research comes as scientists around the world try to understand how the human immune system fights Covid-19 to help them design vaccines and drugs to fight it.

One study, led by researchers from Germany and published in preview form in the journal Nature last week, found that one in three of their subjects who had had no prior exposure to SARS-CoV-2 had a certain kind of immune cell — known as helper T-cells — that was capable of recognising the virus.

“This finding might have significant epidemiological implications regarding herd immunity thresholds and projections for the Covid-19 pandemic,” said the study, which was led by Charite university hospital in Berlin and the Max Planck Institute for Molecular Genetics, also in the German capital.

The findings were based on an examination of how helper T-cells responded to synthetic fragments of SARS-CoV-2 in the blood of 68 healthy individuals, alongside a study of the same kind of immune response in 18 infected patients.

When it comes to immune response, neutralising antibodies that stop the virus from entering human cells has been a focus of Covid-19 vaccine and other research. T-cells are another arm of the body’s immune response that experts say are important to understand and could have implications for vaccine development.

Helper T-cells in general are thought to boost immune response from other cells and antibodies, but their role fighting SARS-CoV-2 infection remains unknown.

One of the authors of the German study, Dr Leif Erik Sander from Charite, said it was possible these cells could have a protective effect.

“In this case, a recent bout of the common cold would probably result in less severe Covid-19 symptoms,” he said.

“However, it is also possible that cross-reactive immunity could lead to a misdirected immune response and potentially negative effects on the clinical course of Covid-19.”

Researchers who conducted a second study, which was published in the journal Science on Tuesday, examined a similar question, and identified how structural similarities between the novel coronavirus and cold-causing coronaviruses caused T-cells to respond.

“This study provides very strong direct molecular evidence that memory T-cells can ‘see’ sequences that are very similar between common cold coronaviruses and SARS-CoV-2,” said study co-leader Alessandro Sette from the La Jolla Institute for Immunology in the US.

Despite the findings, Dr Ashley St. John, an immunologist and associate professor at Duke-NUS Medical School who was not involved in the studies, said larger-scale studies were needed to understand their implications.

In general, cross-reactivity of immune cells could have a variety of outcomes, ranging from inconsequential to helping the immune response, or in rare cases, causing more harm, she said.

Dr Joanna Kirman, an associate professor in the department of microbiology and immunology at University of Otago in New Zealand, said it was interesting to see the long-lived T-cell immune response in the results.

“But we don’t know whether (they) are going to be impactful in terms of controlling infection,” she said.

However, additional research into cross-reactivity could have far-reaching benefits for future vaccines.

“In the very long term, we should study the influence of cross-reactive immunity with the hope of developing vaccines that are able to use T-cells in a helpful way, specifically to cross-protect from new strains of SARS-CoV-2 or other coronaviruses that may emerge many years in the future,” Dr St. John said.

Dr Kirman agreed, saying: “Having the potential to vaccinate in a broad sense against coronaviruses would be a massive benefit to the world’s population.” SOUTH CHINA MORNING POST

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Covid-19 coronavirus study

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