FASLG and neoplasm: In other instances, T cells are excluded from the tumour islets due to vascular barriers such as upregulation of FasL on endothelial cells, which selectively kills T cells while leaving Tregs unaffected,22 or the downregulation of endothelial adhesion molecules intercellular adhesion molecules (ICAM) and vascular cell adhesion molecule-1 (VCAM) which are important for T cell extravasation.23