IL-6/JAK2/STAT3 axis mediates non-classical monocyte-induced Th17-like conversion of activated Tregs in acute myeloid leukemia patients

Regulatory T cells (Tregs) promote tumor escape. Here we show CD45RA^-FoxP3^highCD4⁺ activated Tregs (aTreg, Fr. II) acquired a Th17-like phenotype in acute myeloid leukemia (AML). The primary objective of this study was to explore the specific roles of non-classical monocytes in regulating the increased Fr. II plasticity to Th17-like phenotype to form the immunosuppressive microenvironment.

We stratified phenotypically heterogeneous FoxP3⁺CD4⁺ T cells from AML patients into three subsets based on FoxP3 and CD45RA, aiming to dissect their functional diversity by flow cytometry. Flow cytometric sorting, co-culture assays, in vitro neutralization experiments, and JAK2 blockade assays were employed to demonstrate that non-classical monocytes induce Th17-like Fr. II cells through the IL-6/JAK2/STAT3 pathway.

CD45RA^-FoxP3^high Fr. II, which performed a major inhibitory role in three FoxP3⁺CD4⁺ T subsets, were reduced in numbers but enhanced their immunosuppressive capacity in AML. Besides, Fr. II had a Th17-like phenotypic shift (marked by augmented IL-17 A and RORγt expression). Co-culture assays and in vitro neutralization experiments demonstrated that IL-6 secreted by non-classical monocytes regulates the conversion of Fr. II toward a Th17-like phenotype. Furthermore, JAK2 inhibitor reduced the phosphorylation of STAT3 and impaired Th17-like differentiation potency of Fr. II in AML patients. Notably, IL-17 A⁺ Fr. II were reduced after treatment.

Taken together, we found that non-classical monocytes drive the differentiation of Th17-like Fr. II via the IL-6/JAK2/STAT3 signaling pathway in AML. IL-17 A⁺ Fr. II may correlate with disease activity. Our finding reveals a new immune-evasion mechanism in AML, and offers a potential therapeutic target in the immunotherapy of AML.