miRNA expression profiling of 21 JMML patients and 4 healthy donors

Juvenile myelomonocytic leukemia (JMML) is a very rare and aggressive stem cell disease that mainly occurs in young children. RAS activation constitutes the core component of oncogenic signaling. In addition, the leukemic blasts of a quarter of JMML patients present with monosomy 7 (-7), whereas more than half of the patients show enhanced age-adjusted fetal hemoglobin (HbF) levels. Hematopoietic stem cell transplantation is the current standard of care. This results in an event-free survival of 50 - 60%, indicating that novel molecular driven therapeutic options are urgently needed. Using gene expression profiling in an extensive series of 82 patient samples, we aimed at understanding the molecular biology behind JMML and identified a previously unrecognized molecular subgroup characterized by high LIN28B expression. Interestingly, LIN28B overexpression was significantly correlated with higher HbF levels whereas patients with -7 seldom showed enhanced LIN28B expression. In line with LIN28B’s role as mediator of fetal hematopoiesis, this explains the biology behind the observation that patients with -7 are rarely diagnosed with high age-adjusted HbF levels. In addition, this new fetal-like JMML subgroup presented with reduced levels of most members of the let-7 microRNA family and showed characteristic overexpression of genes involved in fetal hematopoiesis and stem cell self-renewal. Finally, high LIN28B expression was associated with poor clinical outcome in our JMML patient series, but not independent from other prognostic factors such as age and age-adjusted HbF levels. In conclusion, we identified LIN28B as a crucial molecular player at the heart of a novel fetal-like subgroup in JMML. miRNA expression was measured on a qPCR-based platform in 21 JMML patients and 4 healthy donors in the discovery cohort. Corresponding mRNA and lncRNA expression data were measured on Agilent. All patient data can be found in Supplementary Table S1.