CD4 and COVID-19: With PBMCs from COVID-19 convalescent donors (S1 Table), the tetramer guided epitope mapping (TGEM) approach was used to identify CD4+ T cell epitopes within Spike (S), Nucleocapsid (N) and Membrane (M) proteins of SARS-CoV-2 utilizing peptides derived from the US-WA1/2020 strain [38,39].