Study analyzes the impact of T cells from common cold coronaviruses against SARS-CoV-2 exposure

A new study has illustrated that people having higher levels of T cells from common cold coronaviruses are not likely to get infected with SARS-CoV-2.

Image Credit: Shutterstock.

The study headed by scientists from Imperial College London, has offered the first proof of a defensive role for these T cells. While earlier studies have displayed that T cells induced by other coronaviruses has the ability to identify SARS-CoV-2, the new study analyzes for the first time how the existence of such T cells during SARS-CoV-2 exposure impacts if someone becomes infected.

The study was published in the journal Nature Communications.

Furthermore, the scientists say their findings offer a blueprint for a second-generation, universal vaccine that can prevent infection from present and future SARS-CoV-2 variants, such as Omicron.

Being exposed to the SARS-CoV-2 virus doesn’t always result in infection, and we’ve been keen to understand why. We found that high levels of pre-existing T cells, created by the body when infected with other human coronaviruses like the common cold, can protect against COVID-19 infection.”

Dr Rhia Kundu, Study First Author, National Heart & Lung Institute, Imperial College London

Kundu added, “While this is an important discovery, it is only one form of protection, and I would stress that no one should rely on this alone. Instead, the best way to protect yourself against COVID-19 is to be fully vaccinated, including getting your booster dose.”

The study started in September 2020 while most people in the United Kingdom had neither been infected nor vaccinated against SARS-CoV-2. It consisted of 52 people who lived with someone who has PCR-confirmed SARS-CoV-2 infection and who had thus been vulnerable to the virus. The participants of the study did PCR tests at the outset and after four and seven days, to identify if they developed an infection.

Blood samples from the 52 participants were obtained within one to six days of their exposure to virus. This allowed the scientists to examine the levels of pre-existing T cells induced by earlier common cold coronavirus infections that also cross-recognize SARS-CoV-2 virus proteins.

New vaccine target

The scientists discovered that there were considerably higher levels of these cross-reactive T cells in the 26 participants who did not turn infected, in comparison with the 26 participants who did get infected. Such T cells targeted internal proteins inside the SARS-CoV-2 virus, instead of the spike protein on the surface of the virus, to safeguard against infection

Present vaccines do not induce an immune response to such internal proteins. The scientists stated that—along with the present effective spike protein-targeting vaccines—these internal proteins provide a new vaccine target that can offer enduring protection since T cell responses continue longer compared to antibody responses which subside within a few months of vaccination.

Our study provides the clearest evidence to date that T cells induced by common cold coronaviruses play a protective role against SARS-CoV-2 infection. These T cells provide protection by attacking proteins within the virus, rather than the spike protein on its surface.

Ajit Lalvani, Study Senior Author, Professor and Director, NIHR Respiratory Infections Health Protection Research Unit, Imperial College London

Lalvani continued, “The spike protein is under intense immune pressure from vaccine-induced antibody which drives evolution of vaccine escape mutants. In contrast, the internal proteins targeted by the protective T cells we identified mutate much less. Consequently, they are highly conserved between the various SARS-CoV-2 variants, including omicron.”

“New vaccines that include these conserved, internal proteins would therefore induce broadly protective T cell responses that should protect against current and future SARS-CoV-2 variants,” added Lalvani.

The scientists noted few limitations to their study. Also, because it is small and 88% of participants were of white European ethnicity, it is impracticable for the scientists to model demographic factors.