MEMORY T cells that recognise common cold coronaviruses may teach the immune system to recognise matching sites on SARS-CoV-2, potentially explaining why some people have milder COVID-19 symptoms.
Although the researchers at La Jolla Institute for Immunology, San Diego, California, USA, emphasise that this is speculation and their research requires more data, their results have preliminarily shown that memory helper T cells that recognise common cold coronaviruses also recognise SARS-CoV-2, the virus that causes COVID-19. “Immune reactivity may translate to different degrees of protection, having a strong T-cell response, or a better T-cell response may give you the opportunity to mount a much quicker and stronger response,” stated Prof Alessandro Sette.
The new study builds on findings from previous results from Prof Sette’s laboratory which showed that 40–60% of individuals who were never exposed to SARS-CoV-2 had T cells that reacted to the virus. Therefore, the team considered whether exposure to T cells from patients previously exposed to common cold coronaviruses, which the team regarded as the ‘less dangerous cousins’ of SARS-CoV-2, would lead to immune memory against SARS-CoV-2. Analysis of the T-cell response, from participants who had never been exposed to the virus, showed that they can produce a range of memory T cells that are cross-reactive with comparable affinity to SARS-CoV-2 and the common cold coronaviruses HCoV-OC43, HCoV-229E, HCoV-NL63, or HCoV-HKU1.
These findings suggest that previous exposure to a common cold coronavirus can teach the immune system to recognise certain parts of SARS-CoV-2. In response to the study, Prof Sette added: “We knew there was pre-existing reactivity, and 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.” The study also found that while some T cells targeted the SARS-CoV-2’s spike protein, the region of the virus that recognises and binds to human cells, pre-existing immune memory was also directed to other SARS-CoV-2 proteins. This is highly relevant because current vaccine candidates target the spike protein specifically, and this new information may prove beneficial in finding new therapeutic approaches to treat COVID-19.