CD4 and neoplasm: Several studies have found that the Gly-Ala repeat sequence (GAr) within EBNA1 inhibits the ability to present MHC class I-restricted antigens, a very important mechanism in the immune system that helps CD8 + T cells to recognise and clear abnormal (e.g. tumour) or infected cells47–49.HLA-DR+ mDC are myeloid-derived dendritic cells that express MHC II molecules and are primarily responsible for presenting exogenous antigens to CD4+ T cells to initiate an adaptive immune response.