IDO1 and glioblastoma: Functionally, the triple combination therapy resulted in a median survival of 31.5 days in the older subjects, which was significantly decreased as compared to the younger 8-week-old mice with a survival of 40.5 days (p < 0.001), suggesting that the increased brain IDO expression during advanced age has a directly negative effect on immunotherapeutic efficacy in subjects with GBM.