Impact of constitutive FLT3 signaling on dendritic cell development and function in a genetically-engineered mouse model of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a hematological cancer with a very poor prognosis. FLT3-ITD mutations that cause constitutive FLT3 signaling are commonly seen in patients. Our lab and others have shown that AML patient samples exhibit hallmarks of immune exhaustion such as T cell dysfunction, increased MDSCs, and increased Tregs that associate with worse survival. In solid tumor models DCs have been shown to be important for anti-tumor T cell activity and we aim to further describe the role of DCs in the immune response to leukemia. FLT3 signaling is critical for DC development but the effects of FLT3-ITD on DCs and how it contributes to leukemogenesis remains unclear. In a novel FLT3-ITD driven AML mouse model we found that DCs from these mice have elevated pFLT3, indicating constitutive FLT3 signaling. Moreover, significantly expanded DC progenitors and DCs in the bone marrow and spleen are observed. Analysis of serum cytokines identified increased levels of IL-27, IL-10, and IL-17a in leukemia mice compared to healthy controls, suggesting that the expansion of DCs in these leukemia mice may be driving pathogenic expansion of T helper subsets. Furthermore, we measured higher levels of circulating Th2, Th17, and Treg phenotypes in the blood compared to healthy controls. Thus, we hypothesize that FLT3-ITD DCs are a significant contributor to T cell skewing in AML resulting in poor anti-tumor responses. We are using scRNA-seq methods to identify transcriptional changes in FLT3-ITD DCs that lead to the phenotypes we identified. Understanding how FLT3-ITD DCs contribute to AML immune suppression is critical to interpreting leukemia etiology and the development of targeted therapies such as immune checkpoint blockade or small molecule inhibitors.