Abstract P07: Identification of the unique preleukemic bone marrow niche in acute myeloid leukemia

Abstract Preleukemic stem cells (LSCs) can remain dormant within the bone marrow (BM) for decades before disease onset, suggesting acquisition of mutations within hematopoietic stem/progenitor cells (HSPCs) alone is insufficient for acute myeloid leukemia (AML). It is likely that alterations within BM microenvironment (BMM) also occur due to dysregulated crosstalk with mutant HSCs thus favoring LSC growth over normal HSCs. Uncovering novel mechanisms by which preleukemic LSCs remodel the BMM is critical in understanding therapy resistance and to develop novel therapies targeting aberrant pathways in both the LSCs and cells within the BMM. To address this, we compared cells of the BMM of wildtype (WT) mice to our Mll-PTD;Flt3-ITD mouse model of AML, which has a distinct preleukemic phase. Using single cell RNA-sequencing we identified 17 stromal cell clusters and observed substantial changes in both cell numbers and transcriptional profiles of several key stromal cell subpopulations. Specifically, we found decreases in normal HSC regulatory populations such as LepR+ MSCs and Cdh5+ ECs (2 and 2. 7-fold decreases, respectively) and increases in pericytes and fibroblasts in preleukemic BM compared to WT (2. 7 and 3. 5-fold increase, respectively). Unlike what is observed in full-blown AML, we found an increase in CD55+ fibroblasts resulting from increased proliferation (13% vs 6% cell cycling, P=0. 0016). Importantly, co-culture assays found that CD55+ BM fibroblasts expanded LSCs at increased levels over normal HSCs (83+/-7. 5 vs 57+/-10. 1, P=0. 0006). Downregulation of several collagen genes (Col1a1, Col1a2, Col3a1, Col4a1, and Col6a1, P 0. 05) was found in these preleukemic CD55+ fibroblasts, suggesting that remodeling of the extracellular matrix might be an important mechanism by which these CD55+ fibroblast remodel the normal BMM and promote leukemogenesis. Furthermore, sequencing of full-blown leukemic BM niche cells have identified several key differences in the BM architecture, suggesting that the preleukemic BM is indeed distinct from full-blown leukemic BM and is important for disease initiation and progression, and not disease maintenance. Citation Format: Chinmayee Goda, Rohan Kulkarni, Alexander Rudich, Malith Karunasiri, Yaphet Bustos, Sadie Chidester, Ozlen Balcioglu, Elizabeth AR Garfinkle, Bethany Mundy-Bosse, Elaine R Mardis, Guido Marcucci, Ramiro Garzon, Katherine Miller, Adrienne M Dorrance. Identification of the unique preleukemic bone marrow niche in acute myeloid leukemia abstract. In: Proceedings of the Blood Cancer Discovery Symposium; 2024 Mar 4-6; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5 (2Suppl): Abstract nr P07.