Glioblastoma multiforme (GBM) is a lethal brain tumour in adults and children. However, DNA copy number and gene expression signatures indicate differences between adult and paediatric cases. To explore the genetic events underlying this distinction, we sequenced the exomes of 48 paediatric GBM samples. Somatic mutations in the H3.3-ATRX-DAXX chromatin remodelling pathway were identified in 44% of tumours (21/48). Recurrent mutations in H3F3A, which encodes the replication-independent histone 3 variant H3.3, were observed in 31% of tumours, and led to amino acid substitutions at two critical positions within the histone tail (K27M, G34R/G34V) involved in key regulatory post-translational modifications. Mutations in ATRX (α-thalassaemia/mental retardation syndrome X-linked) and DAXX (death-domain associated protein), encoding two subunits of a chromatin remodelling complex required for H3.3 incorporation at pericentric heterochromatin and telomeres, were identified in 31% of samples overall, and in 100% of tumours harbouring a G34R or G34V H3.3 mutation. Somatic TP53 mutations were identified in 54% of all cases, and in 86% of samples with H3F3A and/or ATRX mutations. Screening of a large cohort of gliomas of various grades and histologies (n = 784) showed H3F3A mutations to be specific to GBM and highly prevalent in children and young adults. Furthermore, the presence of H3F3A/ATRX-DAXX/TP53 mutations was strongly associated with alternative lengthening of telomeres and specific gene expression profiles. This is, to our knowledge, the first report to highlight recurrent mutations in a regulatory histone in humans, and our data suggest that defects of the chromatin architecture underlie paediatric and young adult GBM pathogenesis.

Glioblastoma (GBM) is a brain tumor that carries a dismal prognosis and displays considerable heterogeneity. We have recently identified recurrent H3F3A mutations affecting two critical amino acids (K27 and G34) of histone H3.3 in one-third of pediatric GBM. Here, we show that each H3F3A mutation defines an epigenetic subgroup of GBM with a distinct global methylation pattern, and that they are mutually exclusive with IDH1 mutations, which characterize a third mutation-defined subgroup. Three further epigenetic subgroups were enriched for hallmark genetic events of adult GBM and/or established transcriptomic signatures. We also demonstrate that the two H3F3A mutations give rise to GBMs in separate anatomic compartments, with differential regulation of transcription factors OLIG1, OLIG2, and FOXG1, possibly reflecting different cellular origins.

Summary:Infections are a major cause of morbidity and mortality in patients undergoing high-dose therapy and subsequent autologous or allogeneic haemopoietic stem cell transplantation, despite the change from topical to systemic anti-infection prophylaxis and the introduction of growth factors and new antimicrobial drugs. We report our single centre experience with data from 409 patients treated at our unit from its opening in 1990 until May 1997. Three hundred and seventy-eight patients were transplanted for the first time, 12 patients were retransplanted or boosted and 19 patients were readmitted for miscellaneous reasons. 245 patients were allografted and 157 autografted. Antimicrobial prophylaxis was mainly quinolones, fluconazole plus amphotericin-B orally, aciclovir, and TMP/SMX or pentamidine. Three hundred and nineteen (78%) developed fever of significantly longer duration in the allogeneic setting with anti-CMV seropositivity. The most frequent infection was fever of unknown origin (50.6%), followed by septicaemia (12.5%) and pneumonia (11.0%). Pathogens isolated in 24.6% of the infections were mostly grampositive bacteria (57.9%), followed by non-fermenting rods (11.2%), Aspergillus spp. and Candida spp. Systemic infection with these pathogens is associated with a poor prognosis. Antimycotic prophylaxis and the therapy must be improved.

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