CD28 and neoplasm: Specific criteria for identifying whether the non-malignant endothelial cells actually resembled tumor endothelium included: a) Enhanced FasL expression (MFI >2000); b) Upregulated TEM-1 expression (MFI >2000); and c) 200% increased apoptosis of PHA and antiCD3 anti CD28 activated splenocytes compared to non-treated.