TDO2 and colorectal carcinoma: In at least 3 out of 4 CRC clusters we also revealed striking upregulation of genes involved in immune system activation, including TNFSF9 (CD137L), TMEM173 (STING) and ICOS. A significant fraction (40%) of genes involved in suppression in tumor microenvironment including CXCL1, CXCL2, CXCR2, MIF (macrophage migration inhibitory factor), IDO1 (Indoleamine 2,3-dioxygenase 1), TDO2 (TRP-2,3-dioxygenase 2), ARG2 (arginase 2), and VEGFA (vascular endothelial growth factor A) displayed upregulation in at least 3 out of 4 CRC clusters (Figure 3B).