Successful Combination of Sequential Gene Therapy and Rescue Allo-HSCT in Two Children with X-CGD - Importance of Timing.

We report on a series of sequential events leading to long-term survival and cure of pediatric X-linked chronic granulomatous disease (X-CGD) patients after gamma-retroviral gene therapy (GT) and rescue HSCT. Due to therapyrefractory life-threatening infections requiring hematopoietic stem cell transplantation (HSCT) but absence of HLAidentical donors, we treated 2 boys with X-CGD by GT. Following GT both children completely resolved invasive Aspergillus nidulans infections. However, one child developed dual insertional activation of ecotropic viral integration site 1 (EVI1) and signal transducer and activator of transcription 3 (STAT3) genes, leading to myelodysplastic syndrome (MDS) with monosomy 7. Despite resistance to mismatched allo-HSCT with standard myeloablative conditioning, secondary intensified rescue allo-HSCT resulted in 100 % donor chimerism and disappearance of MDS. The other child did not develop MDS despite expansion of a clone with a single insertion in the myelodysplasia syndrome 1 (MDS1) gene and was cured by early standard allo-HSCT. The slowly developing dominance of clones harboring integrations in MDS1-EVI1 may guide clinical intervention strategies, i.e. early rescue allo-HSCT, prior to malignant transformation. GT was essential for both children to survive and to clear therapy-refractory infections, and future GT with safer lentiviral self-inactivated (SIN) vectors may offer a therapeutic alternative for X-CGD patients suffering from life-threatening infections and lacking HLA-identical HSC donors.

Selective inhibition of tumor growth by clonal NK cells expressing an ErbB2/HER2-specific chimeric antigen receptor.

Natural killer (NK) cells are an important effector cell type for adoptive cancer immunotherapy. Similar to T cells, NK cells can be modified to express chimeric antigen receptors (CARs) to enhance antitumor activity, but experience with CAR-engineered NK cells and their clinical development is still limited. Here, we redirected continuously expanding and clinically usable established human NK-92 cells to the tumor-associated ErbB2 (HER2) antigen. Following GMP-compliant procedures, we generated a stable clonal cell line expressing a humanized CAR based on ErbB2-specific antibody FRP5 harboring CD28 and CD3ζ signaling domains (CAR 5.28.z). These NK-92/5.28.z cells efficiently lysed ErbB2-expressing tumor cells in vitro and exhibited serial target cell killing. Specific recognition of tumor cells and antitumor activity were retained in vivo, resulting in selective enrichment of NK-92/5.28.z cells in orthotopic breast carcinoma xenografts, and reduction of pulmonary metastasis in a renal cell carcinoma model, respectively. γ-irradiation as a potential safety measure for clinical application prevented NK cell replication, while antitumor activity was preserved. Our data demonstrate that it is feasible to engineer CAR-expressing NK cells as a clonal, molecularly and functionally well-defined and continuously expandable cell therapeutic agent, and suggest NK-92/5.28.z cells as a promising candidate for use in adoptive cancer immunotherapy.

Telomere disruption results in non-random formation of de novo dicentric chromosomes involving acrocentric human chromosomes.

Genome rearrangement often produces chromosomes with two centromeres (dicentrics) that are inherently unstable because of bridge formation and breakage during cell division. However, mammalian dicentrics, and particularly those in humans, can be quite stable, usually because one centromere is functionally silenced. Molecular mechanisms of centromere inactivation are poorly understood since there are few systems to experimentally create dicentric human chromosomes. Here, we describe a human cell culture model that enriches for de novo dicentrics. We demonstrate that transient disruption of human telomere structure non-randomly produces dicentric fusions involving acrocentric chromosomes. The induced dicentrics vary in structure near fusion breakpoints and like naturally-occurring dicentrics, exhibit various inter-centromeric distances. Many functional dicentrics persist for months after formation. Even those with distantly spaced centromeres remain functionally dicentric for 20 cell generations. Other dicentrics within the population reflect centromere inactivation. In some cases, centromere inactivation occurs by an apparently epigenetic mechanism. In other dicentrics, the size of the alpha-satellite DNA array associated with CENP-A is reduced compared to the same array before dicentric formation. Extra-chromosomal fragments that contained CENP-A often appear in the same cells as dicentrics. Some of these fragments are derived from the same alpha-satellite DNA array as inactivated centromeres. Our results indicate that dicentric human chromosomes undergo alternative fates after formation. Many retain two active centromeres and are stable through multiple cell divisions. Others undergo centromere inactivation. This event occurs within a broad temporal window and can involve deletion of chromatin that marks the locus as a site for CENP-A maintenance/replenishment.

Topoisomerase I suppresses genomic instability by preventing interference between replication and transcription.

Topoisomerase I (Top1) is a key enzyme in functioning at the interface between DNA replication, transcription and mRNA maturation. Here, we show that Top1 suppresses genomic instability in mammalian cells by preventing a conflict between transcription and DNA replication. Using DNA combing and ChIP (chromatin immunoprecipitation)-on-chip, we found that Top1-deficient cells accumulate stalled replication forks and chromosome breaks in S phase, and that breaks occur preferentially at gene-rich regions of the genome. Notably, these phenotypes were suppressed by preventing the formation of RNA-DNA hybrids (R-loops) during transcription. Moreover, these defects could be mimicked by depletion of the splicing factor ASF/SF2 (alternative splicing factor/splicing factor 2), which interacts functionally with Top1. Taken together, these data indicate that Top1 prevents replication fork collapse by suppressing the formation of R-loops in an ASF/SF2-dependent manner. We propose that interference between replication and transcription represents a major source of spontaneous replication stress, which could drive genomic instability during the early stages of tumorigenesis.

Telomere dysfunction as a cause of genomic instability in Werner syndrome.

Werner syndrome (WS) is a rare human premature aging disease caused by mutations in the gene encoding the RecQ helicase WRN. In addition to the aging features, this disorder is marked by genomic instability, associated with an elevated incidence of cancer. Several lines of evidence suggest that telomere dysfunction is associated with the aging phenotype of the syndrome; however, the origin of the genomic instability observed in WS cells and the reason for the high incidence of cancer in WS have not been established. We previously proposed that WRN helicase activity was necessary to prevent dramatic telomere loss during DNA replication. Here we demonstrate that replication-associated telomere loss is responsible for the chromosome fusions found in WS fibroblasts. Moreover, using metaphase analysis we show that telomere elongation by telomerase can significantly reduce the appearance of new chromosomal aberrations in cells lacking WRN, similar to complementation of WS cells with WRN. Our results suggest that the genome instability in WS cells depends directly on telomere dysfunction, linking chromosome end maintenance to chromosomal aberrations in this disease.

Hodgkin's lymphoma cell lines are characterized by frequent aberrations on chromosomes 2p and 9p including REL and JAK2.

Four Hodgkin's lymphoma cell lines (KM-H2, HDLM-2, L428, L1236) were analyzed for cytogenetic aberrations, applying multiplex fluorescence in situ hybridization, chromosome banding and comparative genomic hybridization. Each line was characterized by a highly heterogeneous pattern of karyotypic changes with a large spectrum of different translocated chromosomes (range 22-57). A recurrent finding in all cell lines was the presence of chromosomal rearrangements of the short arm of chromosome 2 involving the REL oncogene locus. Furthermore, multiple translocated copies of telomeric chromosomal segments were frequently detected. This resulted in a copy number increase of putative oncogenes, e.g., JAK2 (9p24) in 3 cell lines, FGFR3 (4p16) and CCND2 (12p13) in 2 cell lines as well as MYC (8q24) in 1 cell line. Our data confirm previous cytogenetic results from primary Hodgkin's tumors suggesting an important pathogenic role of REL and JAK2 in this disease. In addition, they provide evidence for a novel cytogenetic pathomechanism leading to increased copy numbers of putative oncogenes from terminal chromosomal regions, most probably in the course of chromosomal stabilization by telomeric capture.

DNA ligase IV-dependent NHEJ of deprotected mammalian telomeres in G1 and G2.

BACKGROUND: Telomeres are required to prevent end-to-end chromosome fusions. End-to-end fusions of metaphase chromosomes are observed in mammalian cells with dysfunctional telomeres due to diminished function of telomere-associated proteins and in cells experiencing extensive attrition of telomeric DNA. However, the molecular nature of these fusions and the mechanism by which they occur have not been elucidated. RESULTS: We document that telomere fusions resulting from inhibition of the telomere-protective factor TRF2 are generated by DNA ligase IV-dependent nonhomologous end joining (NHEJ). NHEJ gives rise to covalent ligation of the C strand of one telomere to the G strand of another. Breakage of the resulting dicentric chromosomes results in nonreciprocal translocations, a hallmark of human cancer. Telomere NHEJ took place before and after DNA replication, and both sister telomeres participated in the reaction. Telomere fusions were accompanied by active degradation of the 3' telomeric overhangs. CONCLUSIONS: The main threat to dysfunctional mammalian telomeres is degradation of the 3' overhang and subsequent telomere end-joining by DNA ligase IV. The involvement of NHEJ in telomere fusions is paradoxical since the NHEJ factors Ku70/80 and DNA-PKcs are present at telomeres and protect chromosome ends from fusion.

Study of 30 patients with unexplained developmental delay and dysmorphic features or congenital abnormalities using conventional cytogenetics and multiplex FISH telomere (M-TEL) integrity assay.

Cryptic subtelomeric chromosome rearrangements are a major cause of mild to severe mental retardation pointing out the necessity of sensitive screening techniques to detect such aberrations among affected patients. In this prospective study a group of 30 patients with unexplained developmental retardation and dysmorphic features or congenital abnormalities were analysed using the recently published multiplex FISH telomere (M-TEL) integrity assay in combination with conventional G-banding analysis. The patients were selected by one or more of the following criteria defined by de Vries et al.: (a) family history with two or more affected individuals, (b) prenatal onset growth retardation, (c) postnatal growth abnormalities, (d) facial dysmorphic features, (e) non-facial dysmorphism and congenital abnormalities. In addition, we included two patients who met these criteria and revealed questionable chromosome regions requiring further clarification. In four patients (13.3%) cryptic chromosome aberrations were successfully determined by the M-TEL integrity assay and in two patients with abnormal chromosome regions intrachromosomal aberrations were characterized by targetted FISH experiments. Our results accentuate the requirement of strict selection criteria prior to patient testing with the M-TEL integrity assay. Another essential precondition is high-quality banding analysis to identify structural abnormal chromosomes. The detection of familial balanced translocation carriers in 50% of the cases emphasizes the significance of such an integrated approach for genetic counselling and prenatal diagnosis.