Gene expression profiling of 44 JMML patients and 7 healthy donors (discovery cohort)

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. Gene expression was measured on Agilent in 44 JMML patients and 7 healthy donors in the discovery cohort. A validation cohort of 38 patients and 9 healthy donors was measured on Affymetrix. All patient data can be found in Supplementary Table S1.

幼年型粒单核细胞白血病（Juvenile myelomonocytic leukemia, JMML）是一种极为罕见且具有侵袭性的干细胞疾病，主要发生于幼儿群体。RAS激活是其致癌信号通路的核心组成部分。此外，四分之一JMML患者的白血病原始细胞存在7号染色体单体（-7），而超过半数患者的年龄校正胎儿血红蛋白（HbF）水平升高。目前，造血干细胞移植是JMML的标准治疗方案，但其无事件生存期仅为50%~60%，这表明亟需开发新型分子靶向治疗手段。

本研究通过对82例患者样本的大型队列进行基因表达谱分析，旨在解析JMML的分子生物学机制，并鉴定出一种此前未被识别的分子亚型，该亚型以高LIN28B表达为特征。值得注意的是，LIN28B过表达与更高的HbF水平显著相关，而携带-7的患者极少表现出LIN28B高表达。结合LIN28B作为胎儿造血介质的已知功能，这解释了为何携带-7的患者极少被诊断为年龄校正HbF水平升高这一现象。

此外，这一新型胎儿样JMML亚型的let-7微小RNA家族多数成员的表达水平降低，且呈现胎儿造血相关基因与干细胞自我更新相关基因的特征性过表达。最后，在本研究的JMML患者队列中，高LIN28B表达与不良临床结局相关，但该关联并不独立于年龄、年龄校正HbF水平等其他预后因素。

综上，本研究鉴定出LIN28B是JMML中一种新型胎儿样亚型的核心关键分子。发现队列中，44例JMML患者与7名健康供者的基因表达通过安捷伦（Agilent）平台进行检测；验证队列包含38例患者与9名健康供者，其基因表达通过Affymetrix平台检测。所有患者数据均可参见补充表S1。