It has been shown that infection with human coronaviruses (HCoVs), like OC43, HKU-1 (beta coronaviruses), NL63 and 229E (alpha coronaviruses) can induce virus-specific CD4+ and CD8+ T cell responses that display cross-reactivity with the novel emerging coronavirus SARS-CoV-2, although to a limited extent5,6. Here, CD4 is linked to infection.