A novel human fetal liver-derived model reveals that MLL-AF4 drives a distinct fetal gene expression program in infant ALL
Rice S., Jackson T., Crump N., Fordham N., Elliott N., O’Byrne S., Inglott S., Ladon D., Wright G., Bartram J., Ancliff P., Mead A., Halsey C., Roberts I., Milne T., Roy A.
ABSTRACT Although 90% of children with acute lymphoblastic leukemia (ALL) are now cured 1 , the prognosis of infant-ALL (diagnosis within the first year of life) remains dismal 2 . Infant-ALL is usually caused by a single genetic hit that arises in utero rearrangement of the MLL/KMT2A gene ( MLL-r ). This is sufficient to give rise to a uniquely aggressive and treatment-refractory leukemia compared to older children with the same MLL-r 3–5 . The reasons for disparate outcomes in patients of different ages with identical driver mutations are unknown. This paper addresses the hypothesis that fetal-specific gene expression programs co-operate with MLL-AF4 to initiate and maintain infant-ALL. Using direct comparison of fetal and adult HSC and progenitor transcriptomes we identify fetal-specific gene expression programs in primary human cells. We show that MLL-AF4 -driven infant-ALL, but not MLL-AF4 childhood-ALL, displays expression of fetal-specific genes. In a direct test of this observation, we find that CRISPR-Cas9 gene editing of primary human fetal liver cells to produce a t(4;11)/ MLL-AF4 translocation replicates the clinical features of infant-ALL and drives infant-ALL-specific and fetal-specific gene expression programs. These data strongly support the hypothesis that fetal-specific gene expression programs co-operate with MLL-AF4 to initiate and maintain the distinct biology of infant-ALL.