Characterizing the Impact of MLL Fusion Variants and Fusion Partners on Leukemia Plasticity Using a Human CRISPR-Engineered MLL-Rearranged Leukemia Model [RNA-Seq Classical]

MLL fusions typically involve MLL exons 8-14, with AF4 (AFF1) and AF9 (MLLT3) being frequent partners. To investigate how fusion partners and breakpoint locations influence the disease, we developed a CRISPR/Cas9 model by introducing MLL-AF4 (t(4;11)) or MLL-AF9 (t(9;11)) fusions with MLL breakpoints in intron 9 or 11 into cord blood CD34+ cells.

The MLL-rearranged cells showed increased proliferation and stemness, as well as an altered immunophenotype involving the upregulation of AML markers. MLL(intron 9)-AF9 cells engrafted robustly in NSG mice and showed high lineage plasticity, switching from a myeloid to a B-lymphoid identity in vivo. Transcriptomic profiling confirmed the lineage switch and the transcriptomic signature revealed progressive stages of B-cell lineage commitment in individual mice.