- Some people are less susceptible to SARS-CoV-2 infection.
- A new study suggests that T cells from prior infection by other coronaviruses, such as the common cold, may protect against SARS-CoV-2.
- These T cells target internal proteins of SARS-CoV-2.
- Vaccines that stimulate T cells are likely to give longer-lasting protection against SARS-CoV-2 and protect against new variants.
One of the mysteries of COVID-19 is why some people seem resistant to infection despite exposure to SARS-CoV-2. Scientists from Imperial College London have published a study that suggests immune cells produced in reaction to the common cold may protect against SARS-CoV-2 infection.
When you catch a cold, your immune system produces antibodies and T cells. These T cells (also called memory T cells) persist much longer than antibodies and help prevent a person from catching the same cold again.
Coronaviruses cause around 15-30% of colds. This new study suggests that pre-existing T cells from these earlier coronavirus colds can protect against SARS-CoV-2 infection.
The observational study, published in nature communications, took place in the United Kingdom, beginning in September 2020. The researchers recruited 52 people who lived with someone who had PCR-confirmed SARS-CoV-2. All participants took a PCR test on days 1, 4, and 7 of the study.
The study took place before any COVID-19 vaccines received approval.
Some resisted infection
Half of the participants subsequently tested positive for SARS-CoV-2. The remaining 26 did not contract the virus.
The researchers noted no differences between the two groups. Dr. Rhia Kundu from Imperial’s National Heart & Lung Institute and first author of the study, spoke to Medical News Today. She said: “We looked at age, biological sex, and BMI, and there were no differences between our household contacts who were PCR positive and those that remained PCR negative. […]
“Crucially, we also looked at the relationship to the index case (i.e. were they partners, child and parent, or a housemate where limited exposure would have occurred) and observed no difference between PCR+ and PCR- contacts. This suggests that exposure was similar between the two groups.”
All participants gave blood samples between days 1 and 6 of the study. The scientists analyzed these blood samples for levels of T cells from earlier coronavirus infections.
High T cell count
The scientists found that those who did not contract SARS-CoV-2 had significantly higher levels of cross-reactive T cells in their blood. These memory T cells target proteins inside the SARS-CoV-2 virus.
Speaking to MNT, Dr. Arturo Casadevall, Bloomberg Distinguished Professor and chair of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health, commented: “The study is small, but the findings are interesting and consistent with other data that prior experience with other coronavirus infections can affect a person’s susceptibility to COVID-19.”
He added: “This study reinforces the notion that an individual’s immunological history, and in particular prior infection with other coronaviruses, is a major factor in determining who gets ill.”
Direction for new vaccines
Current vaccines target the spike proteins (antigens) on SARS-CoV-2 and stimulate the production of antibodies specific to the spike proteins. The cross-reactive T cells target internal proteins in the virus.
Spike antigens on the surface of the virus frequently mutate, giving rise to new variants. The researchers suggest that second-generation vaccines should include non-spike antigens vaccines, together with spike antigens. A vaccine that stimulates T cell production will likely give longer-lasting immunity than one that stimulates only antibody production.
“By developing vaccines that target the parts of the virus that it cannot so easily change (its internal machinery that it needs to replicate), we could better future-proof an individual’s immune system against emerging variants. A T cell vaccine could represent this next step in the vaccination strategy to control SARS-CoV-2.”
–Dr. Rhia Kundu.
Dr. Casadevall supported her view: “It may be possible to make very different types of vaccines than the ones we are currently using to protect against COVID-19 by eliciting cell-mediated immunity.”
The Imperial research team is now collaborating with other research groups to develop and test second-generation vaccines.
Don’t rely on cold immunity
Dr. Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading in the U.K., told the Science Media Center: “It could be a grave mistake to think that anyone who has recently had a cold is protected against Covid-19, as coronaviruses only account for 10-15% of colds.”
Dr. Kundu reiterated this message: “Having had a cold does not necessarily mean that you have these T cells, and vaccination remains the best possible protection against SARS-CoV-2 infection and spread.”
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