IDO1 and cervical cancer: To explore the potential function of IDO1 in CSC behavior, we firstly examined its expression between two cultivation methods of conventional two-dimensional (2D) and tumorsphere, a cell culture based method to enrich CSCs [17,18], and found that IDO1 protein expression was upregulated in cervical tumorspheres from HeLa and SiHa cervical cancer cells (Figure 1B).