Milder disease in COVID-19 patients linked to T cells from previous coronavirus infections

Editor's Note

In this study, researchers from Stanford University School of Medicine found that some COVID-19 patients experience milder symptoms than others because they have more CD8+ T cells (killer T cells) that remember previous encounters with seasonal coronaviruses.

The researchers first confirmed that some portions of the SARS-CoV-2’s sequence were identical to portions of one or more of the four widespread common-cold-causing coronavirus strains. They then assembled 24 different peptide sequences that were either unique to proteins made by SARS-CoV-2 or were also found on proteins made by the seasonal cold coronavirus strains.

Using blood samples from COVID-19 patients, the researchers found that COVID-19 patients with milder symptoms had killer-T cells directed at the peptides that SARS-CoV-2 shared with other coronavirus strains. In other words, they were in memory mode, and memory cells are the most active in infectious-disease defense.

Sicker patients’ had killer-T cells targeting only peptides unique to the SARS-CoV-2, which meant they had started from scratch in their response to the virus.

The researchers noted that the reason children rarely develop severe COVID-19 may be because cold-causing seasonal coronavirus strains are rampant among children.