CRISPR/Cas9-mediated t(4;11) translocation in human hematopoietic stem/precursor cells demonstrates plasticity to differentiate into either the myeloid or lymphoid lineage.

The chromosomal translocation t(4;11)(q21;q23) is frequently diagnosed in KMT2A-r Acute Leukemia patients. Although we understand much about the function of both wildtype KMT2A and AFF1 multiprotein complexes, little is known about the molecular actions the two fusion proteins KMT2A::AFF1 and AFF1::KMT2A during the very early steps of disease onset and progression. Most published data have been generated in t(4;11) cell lines or transplanted mouse models, where exactly this process remains a black box. Here, we present the results of our efforts to establish a t(4;11) chromosomal translocation in human hematopoietic stem/precursor cells by CRISPR/Cas9. These genetically modified cells can be expanded over 5-6 months in vitro and their potential to differentiate was examined with IL-7 supplementation. The benefit of this model system is that (1) both reciprocal fusion proteins are concomitantly present, and (2) a molecular surveillance is possible at any timepoint through analysis of RNA, DNA or protein. Thus, the CRISPR/Cas9 technique allowed us to create a bona fide model system to study the very early steps of leukemia onset at the molecular level. In conclusion, this approach is the fastest way to investigate and characterize KMT2A-r fusions in primary human cells.