Modelling the t(7;12) leukaemia using gene editing technology

Abstract

Infant acute myeloid leukaemia (AML) carrying the chromosomal translocation t(7;12)(q36;p13) is still poorly understood. The only established molecular features are the ectopic overexpression of the MNX1 gene and the production of a fusion transcript in only 50% of patients. The lack of research models has hindered progress in understanding the biology of t(7;12), which has historically focused on MNX1 overexpression rather than the cytogenetic entity itself. In this study, in vitro modelling strategies for t(7;12) were investigated to address the need for a research model. CRISPR/Cas9 allowed the generation of the t(7;12) in vitro in the K562 cell line and human CD34+ haematopoietic progenitors. Despite successful recombination, the translocation was not sustained in long-term cultures or through serial replating of t(7;12)-carrying progenitors. In contrast, t(7;12) was propagated in K562 cells, with myeloid bias in colony morphology, expression of CD24, and baseline depletion of erythroid signatures. MNX1 overexpression in K562 captured CD24 expression, but promoted an erythroid signature, highlighting differences from t(7;12). MNX1 overexpression in mouse bone marrow caused transient self-renewal of CD24+FcgR+ cells, not seen in control cells. No erythroid bias was observed, suggesting cell-type specificity of MNX1 effects. A novel 3D haemogenic gastruloids system mimicking developmental haematopoiesis in vitro was tested to understand the effects of MNX1 overexpression in an embryonic-like environment. Preliminary data suggest that MNX1 overexpression increases proliferation and a relative expansion of early blood precursors. Finally, a pan-cancer analysis was conducted as an explorative study to identify candidate pathways and regulators linked to MNX1 overexpression, revealing tissue-specific transcriptional features. Overall, the data indicate the importance of cellular context for manifestation of t(7;12) and MNX1 effects, and captures non-overlapping features. Both t(7;12) and MNX1 overexpression can recapitulate characteristics of t(7;12) leukaemia and their comparative exploration has the potential to unravel disease biology.