Its only proven ligand is HVEM (Herpes Virus Enter Mediator), a member of the TNF receptor family, expressed on CD4+ and CD8+ T-cells (strongly on resting T cells, downregulated upon activation), naïve and memory but not activated B-cells, monocytes, DC, solid organs, tumor-associated endothelial cells or on various cancer cells including BC [209,210,211,212]. This evidence concerns the gene CD4 and breast cancer.