Only hematopoietic stem and progenitor cells from cord blood are susceptible to malignant transformation by MLL-AF4 translocations

MLL rearrangements (MLLr) play a crucial role in leukemogenesis. Dependent on age, major differences exist regarding disease frequency, main fusion partners and prognosis. In infants, up to 80% of acute lymphoid leukemia (ALL) bear t(4;11) resulting in a poor prognosis. In contrast, in adults only 10% of acute myeloid leukemia (AML) bear t(9;11) with an intermediate prognosis. The reasons for these differences are only poorly understood. Recently, we established an efficient human patient-specific CRISPR/Cas9-based MLLr model in hematopoietic stem and progenitor cells (HSPCs) derived from human cord blood (huCB) faithfully mimicking the underlying biology of the disease. Here, we transfer this model into an adult system using HSPCs from adult bone marrow (huBM) allowing us to investigate the impact of the cell of origin and fusion partner on disease development. RNA-Seq uncovered an absent downregulation of FFAR2 in t(4;11) huBM, an epigenetic tumor suppressor, potentially responsible for the inability of MLL-AF4 to immortalize adult cells under myeloid conditions. Overall design: huCB and huBM CD34+ cells were engineered to bear endogenous MLL-AF4 or MLL-AF9 translocations. Generated cells were cultured to a purity of 100 translocated cells. Control cells were maintained in culture for an equal period of time. RNA sequencing was performed using NextSeq mRNA Stranded Sequencing (Illumina) of two biological replicates comparing tranlocated and control cells in regard to translocation partners and cell of origin.