Insertion of microRNA-125b-1, a human homologue of lin-4, into a rearranged immunoglobulin heavy chain gene locus in a patient with precursor B-cell acute lymphoblastic leukemia Leukemia

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive subtype of acute leukemia, the cell of origin of which is considered to be precursors of plasmacytoid dendritic cells (pDCs). Since translocation (6;8)(p21;q24) is a recurrent anomaly for BPDCN, we demonstrate that a pDC-specific super-enhancer of RUNX2 is associated with the MYC promoter due to t(6;8). RUNX2 ensures the expression of pDC-signature genes in leukemic cells, but also confers survival and proliferative properties in BPDCN cells. Furthermore, the pDC-specific RUNX2 super-enhancer is hijacked to activate MYC in addition to RUNX2 expression, thereby promoting the proliferation of BPDCN. We also demonstrate that the transduction of MYC and RUNX2 is sufficient to initiate the transformation of BPDCN in mice lacking Tet2 and Tp53 , providing a model that accurately recapitulates the aggressive human disease and gives an insight into the molecular mechanisms underlying the pathogenesis of BPDCN.

We examined the incidence and prognostic effect of IDH1 and IDH2 mutations in 233 Japanese adults with acute myeloid leukemia (AML). IDH1 R132 mutations were detected in 20 (8.6%) patients with AML. IDH2 mutations were found in 19 (8.2%, 17 R140 and two R172) patients. IDH1 and IDH2 mutations were mutually exclusive and were associated with normal karyotype AML, cytogenetic intermediate-risk group, and NPM1 mutations. Five-year overall survival (OS) rates were significantly lower (15.6%) in patients harboring the IDH mutations than in patients lacking the IDH mutation (32.0%) in the entire cohort of AML (P = 0.005). Among patients aged 59 yr or younger with IDH mutations, 5-yr OS in patients who underwent allogeneic stem cell transplantation (SCT) was significantly higher than that in those not receiving allogeneic SCT (50% vs. 10.6%, P = 0.020). Of 51 patients with NPM1 mutations, there was no significant difference in 5-yr OS rates between patients with and those without the IDH mutations. In contrast, among 175 patients lacking the NPM1 mutations, 5-yr OS rate in patients with IDH mutations was significantly lower than that in those without IDH mutations (0% vs. 34.7%, P = <0.001). These data suggest that IDH mutations have an unfavorable effect in AML, especially AML with the NPM1 wild type and younger AML patients with IDH mutations may benefit from allogeneic SCT.

C/EBPalpha plays an essential role as a transcription factor in myeloid cell differentiation. Here, we describe a Japanese family in which two individuals with acute myeloid leukemia (AML) and one healthy individual had an identical 4-base pair insertion in the N-terminal region of CEBPA (350_351insCTAC), resulting in the termination at codon 107 (I68fsX107). The father and a son at diagnosis of AML had different in-frame insertion mutations in the C-terminal region of C/EBPalpha. These C-terminal mutations disappeared upon remission in both patients. Interestingly, the father showed different in-frame insertion mutations in the C-terminal CEBPA at the time of diagnosis and relapse. These data strongly suggest that the N-terminal C/EBPalpha mutation predisposes to the occurrence of a C-terminal C/EBPalpha mutation as a secondary genetic hit, causing AML.

Alterations in the IKZF1 gene are associated with poor prognosis in pediatric B-cell acute lymphoblastic leukemia (B-ALL). We examined the relationship between IKZF1 alterations and clinical findings in 78 adult patients with B-ALL. Aberrant isoforms of IKZF1 were detected using RT-PCR. The copy numbers of IKZF1 exons and fusion genes caused by exon deletions were determined using RQ-PCR and genomic PCR, respectively. We detected aberrant IKZF1 isoforms in 20 of the 78 patients (13 Ik6 and seven Ik10) and deletions of the entire or parts of the IKZF1 gene in 40 of 70 patients. No IKZF1 point mutations were detected by direct sequencing. Nineteen Ik6 and Ik10 isoforms had been generated through genomic exon deletions, but one through aberrant splicing. In total, 41 of the 78 (52.6%) patients harbored IKZF1 alterations, which were identified in 20 of 24 (83.3%) patients with Philadelphia chromosome (Ph)-positive B-ALL compared with 21 of 54 (38.9%) Ph-negative B-ALL (P = 0.0004). IKZF1 alterations are highly involved even in adults with B-ALL. To fully detect IKZF1 alterations, several methods with alternative approaches are required. To elucidate the clinical significance of IKZF1 alterations in adult B-ALL, our study warrants prospective clinical studies with a full analysis of IKZF1 alterations.