Memory cytotoxic SARS-CoV-2 spike protein-specific CD4+ T cells associate with viral control

Abstract Little is known of the role of cytotoxic CD4 + T-cells in the control of viral replication. Here, we investigate CD4 + T-cell responses to three dominant SARS-CoV-2 epitopes and evaluate antiviral activity, including cytotoxicity and antiviral cytokine production. Diverse T cell receptor (TCR) usage including public TCRs were identified; surprisingly, cytotoxic CD4 + T-cells were found to have signalling and cytotoxic pathways distinct from classical CD8 + T-cells, with increased expression of chemokines and tissue homing receptors promoting migration. We show the presence of cytolytic CD4 + T-cells during primary infection associates with COVID-19 disease severity. Robust immune memory 6-9 months post-infection or vaccination provides CD4 + T-cells with potent antiviral activity. Our data support a model where CD4 + killer cells drive immunopathogenesis during primary infection and CD4 + memory responses are protective during secondary infection. Our study highlights the unique features of cytotoxic CD4 + T-cells that use distinct functional pathways, providing preventative and therapeutic opportunities.