Figure 2. Theoretical possibilities for explaining in vitro activation of T cells from healthy donors (HD) by a hypothetical immunogenic SARS-CoV-2 peptide (“peptide-A”) that has no perfect sequence match in the CCCoVs.

Even if the CCCoVs do possess a very similar sequence, the in vitro activation does not need to be indicative for peptide-A being an epitope for in vivo cross-virus T cell memory. In the model, peptide-A is either used directly or as part of pMHC complexes, and the T cells are stimulated after their isolation or as part of PBMC.