A potential reason why celecoxib enhanced inflammatory and immune responses to CDA is that celecoxib blocked local increase in CDA-induced IDO activity, a potent suppressor of innate and adaptive immunity.15 This finding is consistent with previous reports that COX2-specific inhibitors blocked IDO induction in acute myeloid leukemia cells and in mice with LLC tumors.14 32 However, contrasting outcomes following co-treatments with CDA and celecoxib or lindrostat imply that IDO blockade only partially explains the superior antitumor effects of celecoxib. This evidence concerns the gene IDO1 and acute myeloid leukemia.