We evaluated the outcome of 482 children with acute myeloid leukemia (AML) enrolled in the Associazione Italiana di Ematologia e Oncologia Pediatrica AML 2002/01 trial. Treatment was stratified according to risk group; hematopoietic stem cell transplantation (HSCT) was used in high-risk (HR) children. Patients with core binding factor leukemia achieving complete remission (CR) after the first induction course were considered standard risk (SR; 99 patients), whereas the others (n = 383) were assigned to the HR group. Allogeneic (ALLO) or autologous (AUTO) HSCT was employed, respectively, in 141 and 102 HR patients after consolidation therapy. CR, early death, and induction failure rates were 87%, 3%, and 10%, respectively. Relapse occurred in 24% of patients achieving CR. The 8-year overall survival (OS), event-free survival (EFS), and disease-free survival (DFS) were 68%, 55%, and 63%, respectively. OS, EFS, and DFS for SR and HR patients were 83%, 63%, and 66% and 64%, 53%, and 62%. DFS was 63% and 73% for HR patients given AUTO-HSCT and ALLO-HSCT, respectively. In multivariate analysis, risk group, white blood cell >100 × 10⁹/L at diagnosis, and monosomal karyotype predicted poorer EFS. Risk-oriented treatment and broad use of HSCT result in a long-term EFS comparing favorably with previously published studies on childhood AML. Key Points Risk-adapted therapy and broad use of HSCT resulted in a significant improvement in outcome. AUTO- or ALLO-HSCT in high-risk patients resulted in a cumulative incidence of leukemia relapse superimposable to that of SR.

Posttranscriptional control of gene expression is important for defining both normal and pathological cellular phenotypes. In vitro, RNA-binding proteins (RBPs) have recently been shown to play important roles in posttranscriptional regulation; however, the contribution of RBPs to cell specification is not well understood. Here, we determined that the RBP insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) is specifically overexpressed in mixed lineage leukemia–rearranged (MLL-rearranged) B-acute lymphoblastic leukemia (B-ALL), which constitutes a subtype of this malignancy associated with poor prognosis and high risk of relapse. IGF2BP3 was required for the survival of B-ALL cell lines, as knockdown led to decreased proliferation and increased apoptosis. Enforced expression of IGF2BP3 provided murine BM cells with a strong survival advantage, led to proliferation of hematopoietic stem and progenitor cells, and skewed hematopoietic development to the B cell/myeloid lineage. Cross-link immunoprecipitation and high throughput sequencing uncovered the IGF2BP3-regulated transcriptome, which includes oncogenes MYC and CDK6 as direct targets. IGF2BP3 regulated transcripts via targeting elements within 3′ untranslated regions (3′UTR), and enforced IGF2BP3 expression in mice resulted in enhanced expression of Myc and Cdk6 in BM. Together, our data suggest that IGF2BP3-mediated targeting of oncogenic transcripts may represent a critical pathogenetic mechanism in MLL-rearranged B-ALL and support IGF2BP3 and its cognate RNA-binding partners as potential therapeutic targets in this disease.

Pediatric cytogenetically normal acute myeloid leukemia (CN-AML) is a heterogeneous subgroup of myeloid clonal disorders that do not harbor known mutations. To investigate the mutation spectrum of pediatric CN-AML, we performed whole-transcriptome massively parallel sequencing on blasts from 7 CN-AML pediatric patients. In 3 patients we identified a recurrent cryptic inversion of chromosome 16, encoding a CBFA2T3-GLIS2 fusion transcript. In a validation cohort of 230 pediatric CN-AML samples we identified 17 new cases. Among a total of 20 patients with CBFA2T3-GLIS2 fusion transcript out of 237 investigated (8.4%), 10 patients (50%) did not belong to the French–American–British (FAB) M7 subgroup. The 5-year event-free survival for these 20 children was worse than that for the other CN-AML patients (27.4% vs 59.6%; P = .01). These data suggest that the presence of CBFA2T3-GLIS2 fusion transcript is a novel common feature of pediatric CN-AML, not restricted to the FAB M7 subtype, predicting poorer outcome. Key Points The CBFA2T3-GLIS2 fusion transcript is common in pediatric cytogenetically normal AML and not restricted to FAB M7 subtype. The CBFA2T3-GLIS2 fusion transcript is associated with poor prognosis in pediatric patients with AML.

The cyclic AMP–responsive element binding protein (CREB) is documented to be overexpressed in leukemia, but the underlying mechanism remains unknown. Here, microRNAs (miRNA), which act as negative regulators of gene expression principally through translational repression, are investigated for the mediation of high CREB protein levels. A series of miRNAs that target CREB were identified. Real-time quantitative PCR revealed that miR-34b was expressed significantly less in myeloid cell lines, previously known for high CREB protein levels. Exogenous miR-34b expression was induced, and results revealed a direct interaction with the CREB 3′-untranslated region, with the consequent reduction of the CREB protein levels in vitro. miR-34b restored expression caused cell cycle abnormalities, reduced anchorage-independent growth, and altered CREB target gene expression, suggesting its suppressor potential. Using reverse-phase protein array, CREB target proteins (BCL-2, cyclin A1, cyclin B1, cyclin D, nuclear factor-κB, Janus-activated kinase 1, and signal transducer and activator of transcription 3), as well as many downstream protein kinases and cell survival signaling pathways (AKT/mammalian target of rapamycin and extracellular signal-regulated kinase) usually elicited by CREB, were observed to have decreased. The miR-34b/miR-34c promoter was shown to be methylated in the leukemia cell lines used. This epigenetic regulation should control the observed miR-34b expression levels to maintain the CREB protein overexpressed. In addition, the inverse correlation between miR-34b and CREB expression was found in a cohort of 78 pediatric patients at diagnosis of acute myeloid leukemia, supporting this relationship in vivo. Our results identify a direct miR-34b target gene, provide a possible mechanism for CREB overexpression, and provide new information about myeloid transformation and therapeutic strategies. [Cancer Res 2009;69(6):2471–8

Mitochondria are key players in the regulation of T cell biology by dynamically responding to cell needs, but how these dynamics integrate in T cells is still poorly understood. We show here that the mitochondrial pro-fission protein Drp1 fosters migration and expansion of developing thymocytes both in vitro and in vivo. In addition, we find that Drp1 sustains in vitro clonal expansion and cMyc-dependent metabolic reprogramming upon activation, also regulating effector T cell numbers in vivo. Migration and extravasation defects are also exhibited in Drp1-deficient mature T cells, unveiling its crucial role in controlling both T cell recirculation in secondary lymphoid organs and accumulation at tumor sites. Moreover, the observed Drp1-dependent imbalance toward a memory-like phenotype favors T cell exhaustion in the tumor microenvironment. All of these findings support a crucial role for Drp1 in several processes during T cell development and in anti-tumor immune-surveillance.