Cross-reactivity of public Tfh clonotypes. (A) Cells expressing TCR-017 or -018 were cocultured with HEK293T cells expressing the indicated HLAs and S proteins derived from the indicated CoVs. (B) Cells expressing TCR-017 or -018 were stimulated with 1 μg/ml of peptide pool derived from HCoV-OC43 S protein. (C) Sequences of peptides from HCoVs corresponding to S_867–881 of SARS-CoV-2. Amino acids that are the same as those in SARS-CoV-2 in the core epitope are shown in black. (D) Cells expressing TCR-017 or -018 were stimulated with 1 μg/ml of the peptides shown in C. Data are representative of two independent experiments (A, B, and D). pep, peptide; Unstim, unstimulated.