The immune system's T cells target a "broad range of sites" on the novel coronavirus, not just the spike protein which enables it to infect hosts, suggests a new study which says this may help the body counter variants of the virus.

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The research, published in the journal Cell Reports Medicine, assessed T cells from 100 people who had recovered from the SARS-CoV-2 infection and took a close look at the genetic sequence of the virus. According to the scientists, including those from the La Jolla Institute for Immunology (LJI) in the US, the study is the most detailed analysis so far of which proteins on the coronavirus stimulate the strongest responses from the immune system's "helper" CD4+ T cells, and "killer" CD8+ T cells.

The findings revealed that not all parts of the virus induce the same strong immune response in everyone. Based on the analysis, the scientists said T cells can recognise dozens of targets on the SARS-CoV-2 virus which change from person to person. They said, on average, each study participant had the ability to recognise about 17 CD8+ T cell and 19 CD4+ T cell targets. While earlier studies revealed that the immune system mounts a strong response against a particular site on the viral "spike" protein, the scientists said this region is "not as good at inducing a strong response from CD4+ helper T cells." However, without a strong CD4+ T cell response, the researchers believe people may be slow to mount the kind of neutralising immune response that quickly wipes out the virus. "We are now armed with the knowledge of which parts of the virus are recognized by the immune system," said study co-author Alessandro Sette from LJI.

The scientists are currently studying how T cells could combat different variants of SARS-CoV-2 which have shown mutations in the spike protein. By targeting many vulnerable sites on the spike protein, they said the immune system would still be able to fight infection even if some sites on the virus change due to mutations. "The immune response is broad enough to compensate for that," said Alba Grifoni, another co-author of the study from LJI.