IDO1 and neoplasm: <i>In vitro</i> assays confirmed that endothelial cells were educated by SLC1A3<sup>hi</sup> tumor cells that undergo malignant transition, drastically upregulating immune-suppressive factors, including <i>CD274</i>, <i>TGFB1</i>, <i>IL10</i>, and <i>IDO1</i>.