Part of the heterogeneity seen in COVID-19 disease has been suggested to be due to pre-existing cross-reactive memory T cells remaining from previous infections with common cold human corona virus (hCoV). A recent paper from the Sette lab at La Jolla Institute for Immunology confirms that notion. The authors first mapped down 142 SARS-CoV-2 CD4 T cell epitopes. Then they were able to show, in pre-COVID-19 blood samples, pre-existing CD4 memory T cells specific for hCoVs but cross-reactive to several of the SARS-CoV-2 epitopes.
The findings are important as they not only explain differences in clinical outcomes, but also may have an impact on models of herd immunity and vaccine development.