Indoleamine 2,3-dioxygenase 1 alters the proportions of B cell subpopulations in the microenvironment of acute myeloid leukemia

Acute myeloid leukemia (AML), the most common leukemia in adults, exhibits immune escape characteristics like solid tumors. The expression of indoleamine 2,3-dioxygenase 1 (IDO1), a well-recognized immune checkpoint, has been detected in AML blast cells and is associated with poor clinical outcome. Although an imbalance of B cell subpopulations exists in AML patients' bone marrow microenvironment, the role of B cells and their interaction with IDO1 in AML have yet to be elucidated. Herein, with bioinformatic analysis, we found the close correlations between IDO1 expression and survival and B cell subpopulation proportions in AML patients. Further, our investigation into IDO1 expression and activity, B cell subpopulation proportions and immunosuppressive interleukin-10 (IL-10) level in AML cells and clinical samples revealed significant findings. Using a co-culture system of healthy human PBMCs and AML cell lines, we demonstrated that high IDO1 expression in AML cells could alter the proportions of total B, regulatory B and memory B cells, and increased the level of IL-10. Finally, with the IDO1 inhibitor RY103 designed by our laboratory, we found that IDO1 inhibition had good anti-leukemic effect and restored the abnormal proportions of B cell subpopulations in AML mice. Our study is the first to reveal the modulation of IDO1 on B cell subpopulations in AML, making a significant breakthrough in understanding the immune escape mechanisms of AML. Application of IDO1 inhibitor, such as RY103, targeting the imbalance of B cell subpopulations can lead to innovative treatments for AML.