Increased IDO expression and regulatory T cells in acute myeloid leukemia: implications for immune escape and therapeutic targeting

This study aimed to determine the frequency of regulatory T cells (Tregs) (CD4⁺/FOXP3⁺) and indoleamine 2,3-dioxygenase (IDO) expression in patients with acute myeloid leukemia (AML).

This cross-sectional case–control study was conducted between Jan 2022 and Dec 2023. Bone marrow samples were collected from 20 healthy individuals and 15 patients with AML. Flow cytometry, real-time polymerase chain reaction (PCR), and western blotting were used to evaluate the frequency of Treg and IDO expression levels.

The Treg percentage among total lymphocytes was lower in the AML group than that in the normal group. However, Treg percentage among T-helper (Th) lymphocytes was significantly higher in the AML group than that in the normal group (p < 0.05). The mean IDO expression in the AML group was significantly higher than that in the normal group (p = 0.004). A significant relationship was observed between IDO expression and Treg percentage among Th lymphocytes in the AML group (correlation = 0.637; p = 0.003). Moreover, western blot analysis showed a significant increase in IDO protein intensity in the AML group compared with that in the control group (p < 0.001). A significant difference was observed between the IDO concentrations in the AML group and that in the control group (p < 0.001). In addition, a significant difference between TGF-β levels in the AML group and those in the control group (p < 0.01) was observed.

IDO inhibition using novel IDO inhibitors along with chemotherapy is a promising approach to overcome the immune escape mechanisms in patients with AML, who exhibit increased levels of IDO expression and Tregs.