Structural definition of HLA class II-presented SARS-CoV-2 epitopes reveals a mechanism to escape pre-existing CD4+ T cell immunity by Chen, Y, Mason, GH, Scourfield, DO, Greenshields-Watson, A, Haigh, TA, Sewell, AK, Long, HM, Gallimore, AM, Rizkallah, P, MacLachlan, BJ, Godkin, A