IDO1 and ovarian cancer: In order to verify the hypothesis, the NAD + level in the treated endothelial cells were detected, and the results displayed that IDO1-overexpression ovarian cancer cell-derived EVs increased NAD + /NADH ratio in endothelial cells compared with that in endothelial cells incubated with IDO1-knockdown ovarian cancer cell-derived EVs or IDO1-control ovarian cancer cell-derived EVs (Fig. 8c).