Unfortunately, the tumor vasculature is reported to express reduced levels of leukocyte adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), and an aberrant overexpression of immune checkpoints including PD-L1, the death receptors FasL and TRAIL, and IDO, all of which impede the infiltration and function of activated T cells into/in the tumor microenvironment (228). This evidence concerns the gene IDO1 and neoplasm.