Two new studies found that patients with COVID-19, as well as some people who have not been infected with SARS-CoV-2, possess T-cells that target the virus. In the case of those who haven’t had COVID-19, this is likely because they were previously infected with other coronaviruses, such as the common cold. Both studies were able to identify strong T-cell responses to the virus, although they did not explore whether recovered patients have increased immunity to the virus in the future.
Researchers at the La Jolla Institute for Immunology identified that CD4+ and CD8+ T cells provoked the most powerful responses against the coronavirus infection. The study, which was published in Cell, found CD8+ and CD4+ T cells in around 70% and 100% of recovered COVID-19 patients, respectively. SARS-CoV-2−reactive CD4+ T cells were also found in around 40-60% of blood samples from uninfected individuals, including among stored samples that were collected between 2015 and 2018, well before the onset of the current pandemic. Researchers think the T cells in uninfected patients were triggered by past infection with one of the human coronaviruses that cause colds, which are structurally similar to those of SARS-CoV-2.
These findings are in line with another study by immunologist Andreas Thiel, MD, of the Charité University Hospital in Berlin, that was published on medRxiv. Dr. Thiel’s team was able to identify CD4+ T cells targeting the virus in 15 out of 18 patients hospitalized with COVID-19. In addition, the team analyzed blood samples from 68 uninfected patients and found that 34% also hosted T cells that recognized the virus, albeit at lower frequencies.
The results suggest that some small residual immunity from exposure to common cold viruses could be one reason that some of the population may be less susceptible to the virus. Further study will be needed to establish whether people who exhibit this cross reactivity are less likely to suffer severe complications from COVID-19.