Defects in NK cell development and function correlate to clinical outcomes in acute myeloid leukemia (AML). To understand mechanism(s) contributing to these defects, we evaluated epigenetic, transcriptional and functional changes in NK cell precursors and mature NK cells using ex vivo, in vivo and in vitro methods coupled with scRNAseq, DNA Illumina Methylation analysis, and high dimensional flow cytometry. 

We discovered NK cells in AML patients have significant alterations in development and function and a correlating increase in AP-1 activity. These changes are driven by hypomethylation of AP-1 transcription factor (TF) motifs (****p<0.0001), creating an epigenetic signature consistent with functional exhaustion and hyper-maturation, including enhanced JunB pathway activity. Findings from a murine model of AML revealed the presence of unique NK cell clusters in leukemic mice that were defined by enhanced MEK/AP-1 activity, consistent with NK cells in AML patients. These unique clusters were TCF-1+ (***p<0.001) with heterogeneous expression of LAG-3 and TIM-3. To determine which branch(es) of the AP-1 signaling pathway were driving these changes in AML, we inhibited each major branch of the AP-1 pathway (JNK, p38 and MEK/ERK) in NK-AML co-culture development assays and found that only MEK inhibition prevented functional exhaustion (***p<0.001) and hyper-maturation (****p<0.0001) in committed NK cells and promoted the development of NK cells generated from CD34+ HSCs (*p <0.05) or innate lymphoid cell-restricted precursors(*p<0.05). Interestingly, MEK/ERK/JunB inhibition promoted the development of anti-leukemic NK cells at the expense of pro-leukemic ILC3s (**p<0.01).

Collectively, our data suggest that dysregulation of the MEK/ERK/AP-1 signaling axis contributes to defects in NK cell development and function in AML by reprogramming NK cell precursors and mature NK cells, and that MEK inhibition can reverse these defects thus offering a potential therapeutic strategy to reinvigorate NK cell surveillance in AML.