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Toll-like receptor 7 (TLR7) agonists modulate broad spectrum immune activity and are evaluated in the treatment of human diseases, including cancer and chronic viral infection. RO7020531, an oral prodrug of a TLR7 agonist, is in clinical development as part of a curative regimen against chronic hepatitis B. We report the safety, tolerability, pharmacokinetics (PKs), and pharmacodynamics (PDs) of RO7020531 in healthy Chinese volunteers following single and multiple ascending doses (SAD and MAD). PK and PD samples were evaluated from four SAD cohorts and 3 MAD cohorts with 10 subjects each (8 active and 2 placebo). Safety and tolerability were monitored throughout the study. A total of 155 adverse events (AEs) were reported in 49 subjects. Fifty-one AEs in 18 subjects were assessed as treatment-related. Most of the AEs were mild; nine subjects experienced moderate AEs; there were no severe AEs. In two 150 mg MAD cohorts given every other day (q.o.d.), 7 of 20 subjects experienced pyrexia and were discontinued due to transient asymptomatic lymphopenia, which resolved 24-48 hours postdose. The PK of the active metabolite, RO7011785, increased linearly with dose from 40 mg to 170 mg. There was no PK accumulation following q.o.d. dosing. The PK profile is consistent with observations in white subjects in the global first-in-human study. SADs and MADs of RO7020531 resulted in dose-dependent increases in TLR7 response markers at 100 mg or above. Flu-like symptoms were associated with higher interferon-α levels. RO7020531 was safe and acceptably tolerated in healthy Chinese volunteers with a multiple 150 mg q.o.d. dose regimen.

Chronic infection with Hepatitis B virus (HBV) is a major risk factor for the development of advanced liver disease including fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). The relative contribution of virological factors to disease progression has not been fully defined and tools aiding the deconvolution of complex patient virus profiles is an unmet clinical need. Variable viral mutant signatures develop within individual patients due to the low-fidelity replication of the viral polymerase creating ‘quasispecies’ populations. Here we present the first comprehensive survey of the diversity of HBV quasispecies through ultra-deep sequencing of the complete HBV genome across two distinct European and Asian patient populations. Seroconversion to the HBV e antigen (HBeAg) represents a critical clinical waymark in infected individuals. Using a machine learning approach, a model was developed to determine the viral variants that accurately classify HBeAg status. Serial surveys of patient quasispecies populations and advanced analytics will facilitate clinical decision support for chronic HBV infection and direct therapeutic strategies through improved patient stratification.

Background & Aims The hallmarks of chronic HBV infection are a high viral load (HBV DNA) and even higher levels (>100-fold in excess of virions) of non-infectious membranous particles containing the tolerogenic viral S antigen (HBsAg). Currently, standard treatment effectively reduces viremia but only rarely results in a functional cure (defined as sustained HBsAg loss). There is an urgent need to identify novel therapies that reduce HBsAg levels and restore virus-specific immune responsiveness in patients. We report the discovery of a novel, potent and orally bioavailable small molecule inhibitor of HBV gene expression (RG7834). Methods RG7834 antiviral characteristics and selectivity against HBV were evaluated in HBV natural infection assays and in a urokinase-type plasminogen activator/severe combined immunodeficiency humanized mouse model of HBV infection, either alone or in combination with entecavir. Results Unlike nucleos(t)ide therapies, which reduce viremia but do not lead to an effective reduction in HBV antigen expression, RG7834 significantly reduced the levels of viral proteins (including HBsAg), as well as lowering viremia. Consistent with its proposed mechanism of action, time course RNA-seq analysis revealed a fast and selective reduction in HBV mRNAs in response to RG7834 treatment. Furthermore, oral treatment of HBV-infected humanized mice with RG7834 led to a mean HBsAg reduction of 1.09 log 10 compared to entecavir, which had no significant effect on HBsAg levels. Combination of RG7834, entecavir and pegylated interferon α-2a led to significant reductions of both HBV DNA and HBsAg levels in humanized mice. Conclusion We have identified a novel oral HBV viral gene expression inhibitor that blocks viral antigen and virion production, that is highly selective for HBV, and has a unique antiviral profile that is clearly differentiated from nucleos(t)ide analogues. Lay summary We discovered a novel small molecule viral expression inhibitor that is highly selective for HBV and unlike current therapy inhibits the expression of viral proteins by specifically reducing HBV mRNAs. RG7834 can therefore potentially provide anti-HBV benefits and increase HBV cure rates, by direct reduction of viral agents needed to complete the viral life cycle, as well as a reduction of viral agents involved in evasion of the host immune responses.

The role of bone morphogenic protein 9 (BMP9) signaling in angiogenesis has been controversial, with a number of studies showing that it acts either as a pro-angiogenic or, conversely, as an anti-angiogenic factor in a context-dependent manner. Notably, BMP9 was also reported to function in both pro- or anti-tumorigenic roles during tumor progression. It has therefore remained unclear, whether selective BMP9 inhibition is a useful target for antibody therapy of cancer. To shed light on these questions, we characterized BMP9 expression in plasma of patients with different cancer indications and found elevated levels of pro-domains and precursor BMP9 with a strong response in renal cell carcinoma (RCC). These studies prompted us to evaluate the potential of selective anti-BMP9 cancer therapy in RCC. We generated a novel monoclonal therapeutic antibody candidate, mAb BMP9-0093, that selectively targets all different BMP9 variants but does not bind to the closest homolog BMP10. In vitro , mAb BMP9-0093 treatment inhibited signaling, endothelin-1 (ET-1) production and spreading of endothelial cells and restored BMP9-induced decrease in pericyte migration and attachment. Furthermore, BMP9-mediated epithelial–mesenchymal transition of renal cell carcinoma cells was reversed by mAb BMP9-0093 treatment in vitro . In vivo , mAb BMP9-0093 showed significant anti-tumor activity that was associated with an increase in apoptosis as well as a decrease in tumor cell proliferation and ET-1 release. Furthermore, mAb BMP9-0093 induced mural cell coverage of endothelial cells, which was corroborated by a reduction in vascular permeability, demonstrated by a diminished penetration of omalizumab-Alexa 647 into tumor tissue. Our findings provide new evidence for a better understanding of BMP9 contribution in tumor progression and angiogenesis that may result in the development of effective targeted therapeutic interventions.

Summary Purpose To investigate the safety and clinical activity of comprehensive human epidermal growth factor receptor (HER) family receptor inhibition using lumretuzumab (anti-HER3) and pertuzumab (anti-HER2) in combination with paclitaxel in patients with metastatic breast cancer (MBC). Methods This phase Ib study enrolled 35 MBC patients (first line or higher) with HER3-positive and HER2-low (immunohistochemistry 1+ to 2+ and in-situ hybridization negative) tumors. Patients received lumretuzumab (1000 mg in Cohort 1; 500 mg in Cohorts 2 and 3) plus pertuzumab (840 mg loading dose [LD] followed by 420 mg in Cohorts 1 and 2; 420 mg without LD in Cohort 3) every 3 weeks, plus paclitaxel (80 mg/m2 weekly in all cohorts). Patients in Cohort 3 received prophylactic loperamide treatment. Results Diarrhea grade 3 was a dose-limiting toxicity of Cohort 1 defining the maximum tolerated dose of lumretuzumab when given in combination with pertuzumab and paclitaxel at 500 mg every three weeks. Grade 3 diarrhea decreased from 50% (Cohort 2) to 30.8% (Cohort 3) with prophylactic loperamide administration and omission of the pertuzumab LD, nonetheless, all patients still experienced diarrhea. In first-line MBC patients, the objective response rate in Cohorts 2 and 3 was 55% and 38.5%, respectively. No relationship between HER2 and HER3 expression or somatic mutations and clinical response was observed. Conclusions Combination treatment with lumretuzumab, pertuzumab and paclitaxel was associated with a high incidence of diarrhea. Despite the efforts to alter dosing, the therapeutic window remained too narrow to warrant further clinical development. Trial registration: on ClinicalTrials.gov with the identifier NCT01918254 first registered on 3rd July 2013.

Differentiation of hematopoietic stem cells follows a hierarchical program of transcription factor regulated events1-3. Early myeloid cell differentiation is dependent on PU.1 and CEBPA (CCAAT/enhancer binding protein alpha), late myeloid differentiation is orchestrated by CEBPE (CCAAT/enhancer binding protein epsilon)4. The influence of SWI/SNF (SWItch/Sucrose Non-Fermentable) chromatin remodelling factors as novel master regulators of hematopoietic differentiation is only beginning to be explored3,5,6. Here, we identify SMARCD2 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily d, member 2) as a critical regulator of myeloid differentiation in humans, mice, and zebrafish. Studying patients from three unrelated pedigrees characterized by neutropenia, specific granule deficiency, myelodysplasia with excess of blast cells and various developmental aberrations, we identified three loss-of-function mutations in SMARCD2. Using mice and zebrafish as model systems, we showed that SMARCD2 controls early steps in the differentiation of myeloid-erythroid progenitor cells. In vitro, SMARCD2 interacts with the transcription factor CEBPE and controls expression of neutrophil proteins stored in specific granules. Defective expression of SMARCD2 leads to transcriptional and chromatin changes in acute myeloid leukemia (AML) human promyelocytic cells. In summary, SMARCD2 is a key factor controlling myelopoiesis and a potential tumor suppressor in leukemia.

Severe congenital neutropenia (SCN) is characterized by low numbers of peripheral neutrophil granulocytes and a predisposition to life-threatening bacterial infections. We describe a novel genetic SCN type in 2 unrelated families associated with recessively inherited loss-of-function mutations in CSF3R, encoding the granulocyte colony-stimulating factor (G-CSF) receptor. Family A, with 3 affected children, carried a homozygous missense mutation (NM_000760.3:c.922C>T, NP_000751.1:p.Arg308Cys), which resulted in perturbed N-glycosylation and aberrant localization to the cell surface. Family B, with 1 affected infant, carried compound heterozygous deletions provoking frame shifts and premature stop codons(NM_000760.3:c.948_963del, NP_000751.1: p. Gly316fsTer322 and NM_000760.3:c.1245del, NP_000751.1:p.Gly415fsTer432). Despite peripheral SCN, all patients had morphologic evidence of full myeloid cell maturation in bone marrow. None of the patients responded to treatment with recombinant human G-CSF. Our study highlights the genetic and morphologic SCN variability and provides evidence both for functional importance and redundancy of G-CSF receptor-mediated signaling in human granulopoiesis.

BACKGROUND: Neutrophils are the predominant phagocytes that provide protection against bacterial and fungal infections. Genetically determined neutrophil disorders confer a predisposition to severe infections and reveal novel mechanisms that control vesicular trafficking, hematopoiesis, and innate immunity. METHODS: We clinically evaluated seven children from five families who had neutropenia, neutrophil dysfunction, bone marrow fibrosis, and nephromegaly. To identify the causative gene, we performed homozygosity mapping using single-nucleotide polymorphism arrays, whole-exome sequencing, immunoblotting, immunofluorescence, electron microscopy, a real-time quantitative polymerase-chain-reaction assay, immunohistochemistry, flow cytometry, fibroblast motility assays, measurements of apoptosis, and zebrafish models. Correction experiments were performed by transfecting mutant fibroblasts with the nonmutated gene. RESULTS: All seven affected children had homozygous mutations (Thr224Asn or Glu238Lys, depending on the child's ethnic origin) in VPS45, which encodes a protein that regulates membrane trafficking through the endosomal system. The level of VPS45 protein was reduced, as were the VPS45 binding partners rabenosyn-5 and syntaxin-16. The level of ?1 integrin was reduced on the surface of VPS45-deficient neutrophils and fibroblasts. VPS45-deficient fibroblasts were characterized by impaired motility and increased apoptosis. A zebrafish model of vps45 deficiency showed a marked paucity of myeloperoxidase-positive cells (i.e., neutrophils). Transfection of patient cells with nonmutated VPS45 corrected the migration defect and decreased apoptosis. CONCLUSIONS: Defective endosomal intracellular protein trafficking due to biallelic mutations in VPS45 underlies a new immunodeficiency syndrome involving impaired neutrophil function. (Funded by the National Human Genome Research Institute and others.).

Background Myb-like, SWIRM, and MPN domains 1 (MYSM1) is a transcriptional regulator mediating histone deubiquitination. Its role in human immunity and hematopoiesis is poorly understood. Objectives We sought to investigate the clinical, cellular, and molecular features in 2 siblings presenting with progressive bone marrow failure (BMF), immunodeficiency, and developmental aberrations. Methods We performed genome-wide homozygosity mapping, whole-exome and Sanger sequencing, immunophenotyping studies, and analysis of genotoxic stress responses. p38 activation, reactive oxygen species levels, rate of apoptosis and clonogenic survival, and growth in immune and nonimmune cells were assessed. The outcome of allogeneic hematopoietic stem cell transplantation (HSCT) was monitored. Results We report 2 patients with progressive BMF associated with myelodysplastic features, immunodeficiency affecting B cells and neutrophil granulocytes, and complex developmental aberrations, including mild skeletal anomalies, neurocognitive developmental delay, and cataracts. Whole-exome sequencing revealed a homozygous premature stop codon mutation in the gene encoding MYSM1. MYSM1-deficient cells are characterized by increased sensitivity to genotoxic stress associated with sustained induction of phosphorylated p38 protein, increased reactive oxygen species production, and decreased survival following UV light–induced DNA damage. Both patients were successfully treated with allogeneic HSCT with sustained reconstitution of hematopoietic defects. Conclusions Here we show that MYSM1 deficiency is associated with developmental aberrations, progressive BMF with myelodysplastic features, and increased susceptibility to genotoxic stress. HSCT represents a curative therapy for patients with MYSM1 deficiency.

Summary The Polycomb Group (PcG) of chromatin modifiers regulates pluripotency and differentiation. Mammalian genomes encode multiple homologs of the Polycomb repressive complex 1 (PRC1) components, including five orthologs of the Drosophila Polycomb protein (Cbx2, Cbx4, Cbx6, Cbx7, and Cbx8). We have identified Cbx7 as the primary Polycomb ortholog of PRC1 complexes in embryonic stem cells (ESCs). The expression of Cbx7 is downregulated during ESC differentiation, preceding the upregulation of Cbx2, Cbx4, and Cbx8, which are directly repressed by Cbx7. Ectopic expression of Cbx7 inhibits differentiation and X chromosome inactivation and enhances ESC self-renewal. Conversely, Cbx7 knockdown induces differentiation and derepresses lineage-specific markers. In a functional screen, we identified the miR-125 and miR-181 families as regulators of Cbx7 that are induced during ESC differentiation. Ectopic expression of these miRNAs accelerates ESC differentiation via regulation of Cbx7. These observations establish a critical role for Cbx7 and its regulatory miRNAs in determining pluripotency., Graphical Abstract Highlights ► Cbx7 is the primary Pc ortholog of the PRC1 complex in pluripotent cells ► Cbx7 repress its homologs to regulate PRC1 composition during ESC differentiation ► Cbx7 promotes a stem-cell-like state by repressing differentiation ► miR-181 and miR-125 regulate Cbx7 expression during ESC differentiation

The diphthamide on human eukaryotic translation elongation factor 2 (eEF2) is the target of ADP ribosylating diphtheria toxin (DT) and Pseudomonas exotoxin A (PE). This modification is synthesized by seven dipthamide biosynthesis proteins (DPH1-DPH7) and is conserved among eukaryotes and archaea. We generated MCF7 breast cancer cell line-derived DPH gene knockout (ko) cells to assess the impact of complete or partial inactivation on diphthamide synthesis and toxin sensitivity, and to address the biological consequence of diphthamide deficiency. Cells with heterozygous gene inactivation still contained predominantly diphthamide-modified eEF2 and were as sensitive to PE and DT as parent cells. Thus, DPH gene copy number reduction does not affect overall diphthamide synthesis and toxin sensitivity. Complete inactivation of DPH1, DPH2, DPH4, and DPH5 generated viable cells without diphthamide. DPH1ko, DPH2ko, and DPH4ko harbored unmodified eEF2 and DPH5ko ACP- (diphthine-precursor) modified eEF2. Loss of diphthamide prevented ADP ribosylation of eEF2, rendered cells resistant to PE and DT, but does not affect sensitivity toward other protein synthesis inhibitors, such as saporin or cycloheximide. Surprisingly, cells without diphthamide (independent of which the DPH gene compromised) were presensitized toward nuclear factor of kappa light polypeptide gene enhancer in B cells (NF-κB) and death-receptor pathways without crossing lethal thresholds. In consequence, loss of diphthamide rendered cells hypersensitive toward TNF-mediated apoptosis. This finding suggests a role of diphthamide in modulating NF-κB, death receptor, or apoptosis pathways.

The microbiome and the phage meta-genome within the human gut are influenced by antibiotic treatments. Identifying a novel mechanism, here we demonstrate that bacteria use the universal communication molecule AI-2 to induce virulence genes and transfer them via phage release. High concentrations (i.e. 100 μM) of AI-2 promote dispersal of bacteria from already established biofilms, and is associated with release of phages capable of infecting other bacteria. Enterococcus faecalis V583ΔABC harbours 7 prophages in its genome, and a mutant deficient in one of these prophages (i.e. prophage 5) showed a greatly reduced dispersal of biofilm. Infection of a probiotic E. faecalis strain without lytic prophages with prophage 5 resulted in increased biofilm formation and also in biofilm dispersal upon induction with AI-2. Infection of the probiotic E. faecalis strain with phage-containing supernatants released through AI-2 from E. faecalis V583ΔABC resulted in a strong increase in pathogenicity of this strain. The polylysogenic probiotic strain was also more virulent in a mouse sepsis model and a rat endocarditis model. Both AI-2 and ciprofloxacin lead to phage release, indicating that conditions in the gastrointestinal tract of hospitalized patients treated with antibiotics might lead to distribution of virulence genes to apathogenic enterococci and possibly also to other commensals or even to beneficial probiotic strains., Author Summary All higher organisms live in intimate contact with bacteria and viruses in their direct environment. Some of these bacteria in our gut can switch between being harmless commensals and causing severe and sometimes lethal infections. This involves a tight regulation of the mechanisms needed to initially colonize and later to harm the host. Here we describe a novel mechanism by which phages (i.e. viruses that infect bacteria) contribute to virulence in commensal gut bacteria. Our results show that bacteria "sense" the number of bacteria present at any given moment through a process called quorum sensing and this provides them with the information needed to assess the specific step during the infectious process. At late stages of infection bacteria are usually present in high numbers, and at this point release viruses that can infect nearby bacteria and transfer genes that are needed to cause infection, thereby enabling previously harmless bacteria to become dangerous pathogens.

Infectious pseudovirions based on HIV show the morphology of the parent virus and a genome that is partially expressed in infected cells. The constructs are capable of a single round of infection. In this study, we generated vesicular stomatitis virus (VSV) glycoprotein (G) pseudotyped HIV-1-derived pseudovirions that contain a codonoptimized p17/p24 HIV-1 gag or the green fluorescent protein (GFP) gene as transgene. BALB/c mice were immunized in a DNA prime pseudovirion boost fashion. Immunization induced a Gag-specific antibody response, high titers of neutralizing antibodies directed against the VSV-G protein and a Gag-specific IFN-gamma-secreting cytotoxic T lymphocyte (CTL) response. CTL responses were induced by both structural proteins contained in the pseudovirion preparation and through expression of the transgene. Infection properties similar to those of live attenuated HIV and the immunogenicity observed make infectious pseudovirions valuable tools to further study the mechanism of immune stimulation in models of HIV infection.

The analysis of individuals with severe congenital neutropenia (SCN) may shed light on the delicate balance of factors controlling the differentiation, maintenance and decay of neutrophils. We identify 9 distinct homozygous mutations in the JAGN1 gene encoding Jagunal homolog 1 in 14 individuals with SCN. JAGN1-mutant granulocytes are characterized by ultrastructural defects, a paucity of granules, aberrant N-glycosylation of multiple proteins and increased incidence of apoptosis. JAGN1 participates in the secretory pathway and is required for granulocyte colony-stimulating factor receptor-mediated signaling. JAGN1 emerges as a factor that is necessary in the differentiation and survival of neutrophils.

Severe congenital neutropenia (SCN) is a heterogeneous group of disorders characterized by defective production and viability of neutrophil granulocytes and predisposition to life-threatening bacterial infections. Currently, OMIM lists five defined monogenic SCN: SCN1 ELANE, SCN2 GFI1, SCN3 HAX1, SCN4 G6PC3. Here, we describe a novel SCN subtype (SCN6) caused by recessively-inherited loss-of-function mutations in the gene encoding the granulocyte colony-stimulating receptor (CSF3R). We have identified four affected children in two distinct families. Family A had a homozygous missense mutation in close proximity of the highly conserved WSXWS motif (c.922T, p.Arg308Cys) and family B had two compound heterozygous small deletions provoking frameshift mutations (p.Gly316fs and p.Gly415fs). Mutated G-CSFR p.Arg308Cys protein was characterized by perturbed N-glycosylation and aberrant localization to cell surface. G-CSF induced phosphorylation of STAT3 and STAT5 was greatly diminished. In contrast to other SCN subtypes, all patients had morphological evidence of full myeloid cell maturation in bone marrow. However, none of the patients responded to granulocyte colony-stimulating growth factor (GCSF) treatment in vivo, confirming aberrant GCSF-receptor dependent signaling. Our studies highlight the genetic and morphological variability of SCN and provide evidence both for functional importance and redundancy of G-CSFR-mediated signaling in human granulopoiesis. Disclosures: No relevant conflicts of interest to declare.

Here we describe a novel, spontaneous, 4035 basepairs long deletion in the DNA cross-link repair 1C (Dclre1c)-locus in C57BL/6-mice, which leads to loss of exons 10 and 11 of the gene encoding for Artemis, a protein involved into V(D) J-recombination of antigen receptors of T and B cells. While several spontaneous mutations of Artemis have been described to cause SCID in humans, in mice, only targeted deletions by knockout technology are known to cause the same phenotype so far. The deletion we observed causes a loss of Artemis function in the C57BL/6 strain and, consequently, the absence of T and B cells, in presence of normal numbers of NK cells and cells of the myeloid lineage. Thus, for the first time we present T(-)B(-)NK(+) severe combined immunodeficiency (SCID) phenotype after spontaneously occurring modification of Artemis gene in mice. Our mouse model may serve as a valuable tool to study mechanisms as well as potential therapies of SCID in humans.

Differentiation of hematopoietic stem cells follows a hierarchical program of transcriptional-regulated events. We here identify SMARCD2 (Swi/Snf-related matrix associated actin dependent regulator of chromatin, subfamily D, member 2) as critical regulator of myelopoiesis in humans, mice, and zebrafish. We studied four patients from three unrelated pedigrees presenting with a novel syndromatic phenotype comprising congenital neutropenia, specific granule deficiency, susceptibility to myelodysplasia with excess of blasts, and various skeletal anomalies. All patients had homozygous loss-of-function mutations in SMARCD2. In contrast to wildtype alleles, the variant alleles did not give rise to proteins with capacity to interact with the SWI/SNF subunits BRG1, BAF170, BAF155, and BAF47, as shown by co-immunoprecipitation experiments. In vitro, knockdown of SMARCD2 in promyelocytic NB4 cells, differentiated in the presence of ATRA, led to decreased expression of genes encoding the primary granule proteins cathelicidin (CAMP) and alpha-1-antitrypsin (AAT) as well as specific granule proteins matrix metalloproteinase-8 (MMP8), transcobalamin (TCN1) and lactoferrin (LTF). This phenotype is reminiscent of patients with specific granule deficiency, characterized by mutations in CEBPE, a known transcription factor controlling terminal neutrophil development. We therefore hypothesized that SMARCD2 may act via CEBPe and performed immunoprecipitation studies in transfected cells. Upon pull-down of SMARCD2, CEPBE could be detected, and vice versa, suggesting that both proteins physically interact to control transcriptional networks. To interrogate effects of SMARCD2 deficiency on global chromatin accessibility we made use of ATAC sequencing of undifferentiated and ATRA-differentiated NB4 cells and compared this data with comprehensive RNA-sequencing results. A specific subset of genes was found deregulated in both assays, affecting vesicular trafficking, migration and signalling pathways. To validate a role for SMARCD2 in hematopoiesis in vivo, we generated murine and zebrafish model systems. We generated Smarcd2-/- mice by injection of Smarcd2+/- murine ES cells into blastocysts, transfer into pseudo-pregnant mice and interbreeding of heterozygous Smarcd2+/- offsprings. The mutant allele was inherited in a Mendelian fashion but no viable mice were born. 14.5dpc embryos were characterized by anemia and reduced size compared to their littermates. Analysis of fetal liver hematopoiesis revealed a complete absence of CD11b+Gr1+ and CD11b+Ly6c+ cells, whereas the number of LSK stem cells was not affected. Futhermore, Smarcd2-/- embryos showed aberrations in erythroid cells such as extensive anisocytosis, multinucleated cells, and perturbed mitosis. In cytokine-driven colony forming unit assays, GM-CSF, M-CSF, and G-CSF induced myeloid cell differentiation was decreased. Transcriptional profiling of LSK stem cells revealed a striking dysbalance affecting genes involved in signaling pathways and host defence, including CEBPE-dependent genes. Among a total of 12362 detected genes, we found 4290 to be differentially expressed (DESeq2, FDR 1.4, FDR Disclosures Abboud: Novartis: Honoraria; MAST Therapeutics: Research Funding; Eli Lilly and Company: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees.

Inherited bone marrow failure syndromes comprise a heterogeneous group of genetic disorders characterized by dysfunction of hematopoietic stem or progenitor cells. We present a consanguineous pedigree with two siblings with early-onset, progressive bone marrow failure (neutropenia, anemia, thrombocytopenia) associated with trigonocephaply, hyperplastic gingiva, cataract, accessory mammilla, dental changes and mild neurocognitive developmental delay. Pancytopenia at birth as well as non-compaction cardiomyopathy was observed in one of the patients. Bone marrow histology showed marked hypocellularity with decrease of all hematopoietic cell lines but without cellular atypia, monocytosis, blast excess or fibrosis. Fanconi anemia was excluded by mitomycin C induced chromosomal breakage studies. Immunophenotyping of peripheral blood cells showed a reduction of mature B cells, reduced switched memory B cells, whereas the level of activated B-cells and plasma blasts were increased. T cell proliferation upon PHA and specific antigens was normal. Using whole exome sequencing in patients and both parents we could identify a single potentially disease causing homozygous stop codon mutation (NM_001085487: c.1168G>T: p.E390*) in MYSM1 (Myb-Like, SWIRM And MPN Domain-Containing Protein 1). A family with two affected patients carrying the same mutation has been reported previously (Alsultan A et al, Blood 122:3844, 2013). MYSM1 is a Histone H2A deubiquitinase that has previously been implicated in controlling hematopoietic stem cells, progenitor B cells, and NK cells in mice (Nijnik A et al, Blood 119:1370, 2012). MYSM1 protein was absent in patients' EBV-transformed B cell lines (EBV-LCLs). MYSM1-deficient EBV-LCLs had elevated γ-H2AX levels, indicative of increased genomic instability. Upon exposure to UV light, we observed a sustained expression of p53 and phospho-p53 as well as p38 MAPK and phospho-p38 MAPK in patients' fibroblasts in comparison to fibroblasts from healthy individuals. In view of the progressive pancytopenia, both siblings underwent allogeneic hematopoietic stem cell transplantation from 10/10 HLA-matched family donors after reduced intensity conditioning with alemtuzumab, fludarabine and treosulfan at 2 and 4 years of age, respectively. The procedure was well tolerated, and both siblings exhibit full donor hematopoietic reconstitution at 21 and 26 months after transplant. In summary, we here identify a novel human bone marrow failure syndrome caused by MYSM1-deficiency that can be cured by allogeneic hematopoietic stem cell transplantation. Disclosures No relevant conflicts of interest to declare.

CD95 (Fas/Apo-1) triggers apoptotic cell death via a caspase-dependent pathway. Inhibition of caspase activation blocks proapoptotic signaling and thus, prevents execution of apoptosis. Besides induction of apoptotic cell death, CD95 has been reported to trigger necrotic cell death in susceptible cells. In this study, we investigated the interplay between apoptotic and necrotic cell death signaling in T cells. Using the agonistic CD95 antibody, 7C11, we found that caspase inhibition mediated by the pancaspase inhibitor, zVAD-fmk, prevented CD95-triggered cell death in Jurkat T cells but not in A3.01 T cells, although typical hallmarks of apoptosis, such as DNA fragmentation or caspase activation were blocked. Moreover, the caspase-independent cell death in A3.01 cells exhibited typical signs of necrosis as detected by a rapid loss of cell membrane integrity and could be prevented by treatment with the radical scavenger butylated hydroxyanisole (BHA). Similar to CD95-induced cell death, apoptosis triggered by the DNA topoisomerase inhibitors, camptothecin or etoposide was shifted to necrosis when capsase activation was inhibited. In contrast to this, ZVAD was fully protective when apoptosis was triggered by the serpase inhibitor, Nalpha-tosyl-phenyl-chloromethyl ketone (TPCK). TPCK was not protective when administered to anti-CD95/ZVAD-treated A3.01 cells, indicating that TPCK does not possess anti-necrotic activity but fails to activate the necrotic death pathway. Our findings show (a) that caspase inhibition does not always protect apoptotic T cells from dying but merely activates a caspase-independent mode of cell death that results in necrosis and (b) that the caspase-inhibitor-induced shift from apoptotic to necrotic cell death is dependent on the cell type and the proapoptotic stimulus.

Stimulation of tumor necrosis factor receptor 1 (TNF-R1) triggers both caspase-dependent and caspase-independent signaling activities. The caspase-dependent signaling pathway induces apoptotic cell death in susceptible cells, whereas the caspase-independent signaling cascade leads to activation of nuclear factor kappa B and induces antiapoptotic signaling activities. Stimulation of nuclear factor kappa B via TNF-R1 is known to activate human immunodeficiency virus (HIV) replication in infected cells. Here we show that the broad range caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (ZVAD) activates HIV replication in the chronically infected T-cell line ACH-2. Virus activation was caused by a sensitization of TNF-R1 toward endogenously produced tumor necrosis factor alpha (TNF-alpha). Neutralizing anti-TNF-alpha antibodies completely abolished the virus-inducing activity of ZVAD. Treatment of cells with TNF-alpha in the presence of ZVAD caused increased expression of TNF-alpha and induced enhanced virus replication. Activation of CD95, another member of the TNF receptor family, similarly triggered HIV replication, which was further enhanced in the presence of ZVAD. Our data show that caspase inhibitors sensitize both CD95 and TNF-R1 to mediate activation of HIV in latently infected cells. Activation of HIV replication in latent virus reservoirs is currently discussed as a therapeutic strategy to achieve eradication of HIV in patients treated with antiretroviral therapy. Our results point to a novel role for caspase inhibitors as activators of virus replication in vivo.

Background: Polycomb group proteins form multicomponent complexes that are important for establishing lineage-specific patterns of gene expression. Mammalian cells encode multiple permutations of the prototypic Polycomb repressive complex 1 (PRC1) with little evidence for functional specialization. An aim of this study is to determine whether the multiple orthologs that are co-expressed in human fibroblasts act on different target genes and whether their genomic location changes during cellular senescence. Results: Deep sequencing of chromatin immunoprecipitated with antibodies against CBX6, CBX7, CBX8, RING1 and RING2 reveals that the orthologs co-localize at multiple sites. PCR-based validation at representative loci suggests that a further six PRC1 proteins have similar binding patterns. Importantly, sequential chromatin immunoprecipitation with antibodies against different orthologs implies that multiple variants of PRC1 associate with the same DNA. At many loci, the binding profiles have a distinctive architecture that is preserved in two different types of fibroblast. Conversely, there are several hundred loci at which PRC1 binding is cell type-specific and, contrary to expectations, the presence of PRC1 does not necessarily equate with transcriptional silencing. Interestingly, the PRC1 binding profiles are preserved in senescent cells despite changes in gene expression. Conclusions: The multiple permutations of PRC1 in human fibroblasts congregate at common rather than specific sites in the genome and with overlapping but distinctive binding profiles in different fibroblasts. The data imply that the effects of PRC1 complexes on gene expression are more subtle than simply repressing the loci at which they bind.

Congenital neutropenia (CN) is a heterogeneous disorder. More than 30 distinct genetic defects have been discovered in patients with genetic diseases associated with decreased numbers of peripheral neutrophil granulocytes. Currently, most molecular diagnostic laboratories use Sanger-based sequencing techniques to define disease-causing mutations in patients with CN. In approximately 50% of patients no known genetic disorder can be found. To identify novel genes that can be causative for unexplained CN cases we embarked on next-generation whole-exome sequencing using SOLiD 5500™ and Ion Proton™ sequencers. Up to date we sequenced whole exomes of 49 families, in which children were diagnosed with CN. The fragment libraries were constructed using the SureSelect™ V4+UTRs System (Agilent) allowing us to target whole coding sequence and the majority of UTRs of human genome (approx. 71 Mb). The vast majority of the families were analysed in the “Trio” approach and suitable homozygous or compound heterozygous rare variations (frequency below 1%) in protein coding regions or in splice sites were chosen for further validations. In seven cases mutations previously described as causative for neutropenia were identified including G6PC3, HAX1, and ELANE. Four other rare variants are currently being analysed for their potential to cause CN. In 35 patients, no plausible candidate could be identified so far. When we assessed variants within the genes related to CN, our data revealed unequal coverage pattern over these genes. Around 10% of the exons were insufficiently covered (coverage of less than 10) to allow for reliable variant and genotype call. These facts limit the power of whole exome sequencing as a diagnostic tool, as mutations at the non-covered positions cannot be ruled out, and demonstrate the need of an alternative comprehensive approach. We are currently assessing sensitivity and specificity of a robust, rapid, and cost-effective approach that comprehensively analyses the sequence of 34 CN-relevant genes. Our approach is based on enrichment of specific exon regions by amplification using custom made AmpliSeq™ (Life Technologies) panel. For 25 genes we are able to sequence coding region as well as both UTR sequences, for 9 genes sequencing is limited to coding regions. This approach will provide a reliable, quick, and inexpensive diagnostic strategy for CN patients which will be offered free-of-charge to patients worldwide, independent of ethnic, national, or financial considerations. Disclosures: No relevant conflicts of interest to declare.

Analysis of patients with severe congenital neutropenia (SCN) may shed light on the delicate balance of factors controlling differentiation, maintenance, and decay of neutrophil granulocytes. Mutations in ELANE, GFI1, HAX1, G6PC3, WAS, and VPS45 are known to cause SCN. We here describe a new monogenetic SCN variant with biallelic mutations in the gene encoding Jagunal homolog 1 (JAGN1). We studied an index family from Northern Africa with a total of 5 children suffering from SCN. An Affymetrix SNP array-based genetic linkage analysis was performed and identified a single interval of perfect segregation with highly significant multi-marker LOD scores of at least 4.5spanning approximately 1.5Mbp from 9.52Mb to 11.04Mb on chromosome 3 of NCBI’s human genome build 36.3. This interval contained a total of 30 genes, including JAGN1 which encodes an ER-resident protein. Sanger sequencing revealed a homozygous mutation c.3G>A in exon 1 of the JAGN1 gene; this mutation leads to disruption of the defined start of translation. Systematic analysis of a cohort of 90 SCN patients identified 9 distinct homozygous mutations in the gene encoding Jagunal homolog 1 (JAGN1) in 14 SCN patients, thus accounting for approximately 10% of SCN patients. The clinical phenotype was variable and included failure to thrive, developmental delay and bone skeletal abnormalities. The only consistent finding in all JAGN1-deficient patients was SCN and partial or complete refractoriness to therapy with rh-GCSF. JAGN1 is the human ortholog of a gene originally identified in Drosophila melanogaster. Jagunal-deficient oocytes are characterized by defective ER reorganization and aberrant membrane trafficking during vitellogenesis. We found that JAGN1-mutant human granulocytes showed aberrantly enlarged ER structures and paucity of secretory vesicles. We hypothesized that that ER aberrations may be associated with defective N-glycosylation of multiple proteins in neutrophil granulocytes and found that JAGN1-mutant neutrophil granulocytes exhibited anomalous N-glycomic profiles characterized by a marked reduction in fucosylation of all their multi-antennary glycans. JAGN1-deficient neutrophil granulocytes showed increased apoptosis in response to TNFa and staurosporine, likely accounting for the lack of mature neutrophils in these patients. Additional studies in JAGN1-knockdown cells indicate that JAGN1 participates in the secretory pathway and is required for granulocyte-colony stimulating factor receptor-mediated signaling. Global proteomic analysis of the JAGN1-interactome identified a limited number of interaction partners including members of the Coat Protein I (COPI) complex (COPA, COPB2, and COPG2) which suggest a role for JAGN1 in vesicular trafficking from Golgi to ER. Taken together, JAGN1 emerges as a hitherto unrecognized factor necessary in differentiation and survival of neutrophil granulocytes and a novel gene implicated in SCN. Disclosures: No relevant conflicts of interest to declare.

Misexpression of Polycomb repressive complex 1 (PRC1) components in human cells profoundly influences the onset of cellular senescence by modulating transcription of the INK4a tumor suppressor gene. Using tandem affinity purification, we find that CBX7 and CBX8, two Polycomb (Pc) homologs that repress INK4a, both participate in PRC1-like complexes with at least two Posterior sex combs (Psc) proteins, MEL18 and BMI1. Each complex contains a single representative of the Pc and Psc families. In primary human fibroblasts, CBX7, CBX8, MEL18 and BMI1 are present at the INK4a locus and shRNA-mediated knockdown of any one of these components results in de-repression of INK4a and proliferative arrest. Sequential chromatin immunoprecipitation (ChIP) reveals that CBX7 and CBX8 bind simultaneously to the same region of chromatin and knockdown of one of the Pc or Psc proteins results in release of the other, suggesting that the binding of PRC1 complexes is interdependent. Our findings provide the first evidence that a single gene can be regulated by several distinct PRC1 complexes and raise important questions about their configuration and relative functions.