The immune system’s ‘memory’ T cells keep track of the viruses they have seen before. This immune cell memory gives the cells a headstart in recognizing and fighting off repeat invaders.
In a new study, researchers found that memory helper T cells that recognize common cold coronaviruses also recognize matching sites on SARS-CoV-2, the virus that causes COVID-19.
The findings may explain why some people have milder COVID-19 cases than others—though the researchers emphasize that this is speculation and much more data is needed.
The research was conducted by scientists at La Jolla Institute for Immunology (LJI) and elsewhere.
The new work builds on a recent study which showed that 40% to 60% of people never exposed to COVID-19 had T cells that reacted to the virus.
Their immune systems recognized fragments of the virus it had never seen before.
This finding turned out to be a global phenomenon and was reported in people from the Netherlands, Germany, the United Kingdom, and Singapore.
Scientists wondered if these T cells came from people who had previously been exposed to common cold coronaviruses—what Sette calls SARS-CoV-2’s “less dangerous cousins.”
If so, was exposure to these cold viruses leading to immune memory against SARS-CoV-2?
In the new study, the researchers relied on a set of samples collected from study participants who had never been exposed to SARS-CoV-2.
They defined the exact sites of the virus that are responsible for the cross-reactive T cell response.
Their analysis showed that unexposed individuals can produce a range of memory T cells that are equally reactive against SARS-CoV-2 and four types of common cold coronaviruses.
This discovery suggests that fighting off a common cold coronavirus can indeed teach the T cell compartment to recognize some parts of SARS-CoV-2 and provides evidence for the hypothesis that common cold viruses can, in fact, induce cross-reactive T cell memory against SARS-CoV-2.
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.
Looking closer, the researchers found that while some cross-reactive T cells targeted the SARS-CoV-2’s spike protein, the region of the virus that recognizes and binds to human cells, pre-existing immune memory was also directed to other SARS-CoV-2 proteins.
This finding is relevant since most vaccine candidates target mostly the spike protein.
These findings suggest the hypothesis that the inclusion of additional SARS-CoV-2 targets might enhance the potential to take advantage of this cross-reactivity and could further enhance vaccine potency.
One author of the study is LJI Research Assistant Professor Daniela Weiskopf, Ph.D.
The study is published in Science.
Copyright © 2020 Knowridge Science Report. All rights reserved.
