The transformation of pre-leukemic cells in the context of their environment

Acute Myeloid Leukemia (AML) is a deadly bone marrow (BM) malignancy, in which stem and progenitor cells of the myeloid lineage transform into highly proliferative AML blasts. In this context, mutations in the genes DNMT3a and NPM1 are the most common mutations in AML patients. While the past years have revealed some molecular consequences of mutations in those genes, the mechanism of transformation from pre-leukemia to malignancy is still elusive. To address this question, we adopted a chimeric mouse model that aims to sequentially induce mutations in DNMT3a (R882H) and NPM1 (cA) to then track these mutant cells next to non-mutant cells over time in peripheral blood and BM. Using this model, we define a state of pre-leukemia in which mutant cells harboring both mutations do not readily transform and mice stay clinically healthy for months. Upon re-transplantation of pre-leukemic cells (preLCs), mice develop myeloid dysplastic syndrome (MDS), a hematopoietic malignancy that very often precedes AML. Strikingly, our results suggest that the transformation of preLCs is suppressed by co-transplanted naïve non-mutated BM cells, but not by non-mutated BM counterparts derived from the chimeric pre-leukemic mice (primed WT cells). Co-transplanted naive wild type cells led to the extinction of preLCs and prevented the progression to MDS. Accordingly, we performed single nuclei RNA and ATAC sequencing to decipher the crosstalk between mutated preLCs and either primed or naive WT counterparts to reveal epigenetic and transcriptomic basis of the transformation process in our model. Our findings will aid the understanding to prevent AML.