Sonia Cellot

An RNAi Screen Identifies Msi2 and Prox1 as Having Opposite Roles in the Regulation of Hematopoietic Stem Cell Activity

In this study, we describe an in vivo RNA interference functional genetics approach to evaluate the role of 20 different conserved polarity factors and fate determinants in mouse hematopoietic stem cell (HSC) activity. In total, this screen revealed three enhancers and one suppressor of HSC-derived reconstitution. Pard6a, Prkcz, and Msi2 shRNA-mediated depletion significantly impaired HSC repopulation. An in vitro promotion of differentiation was observed after the silencing of these genes, consistent with their function in regulating HSC self-renewal. Conversely, Prox1 knockdown led to in vivo accumulation of primitive and differentiated cells. HSC activity was also enhanced in vitro when Prox1 levels were experimentally reduced, identifying it as a potential antagonist of self-renewal. HSC engineered to overexpress Msi2 or Prox1 showed the reverse phenotype to those transduced with corresponding shRNA vectors. Gene expression profiling studies identified a number of known HSC and cell cycle regulators as potential downstream targets to Msi2 and Prox1.

Asymmetric segregation and self-renewal of hematopoietic stem and progenitor cells with endocytic Ap2a2

The stem cell-intrinsic model of self-renewal via asymmetric cell division (ACD) posits that fate determinants be partitioned unequally between daughter cells to either activate or suppress the stemness state. ACD is a purported mechanism by which hematopoietic stem cells (HSCs) self-renew, but definitive evidence for this cellular process remains open to conjecture. To address this issue, we chose 73 candidate genes that function within the cell polarity network to identify potential determinants that may concomitantly alter HSC fate while also exhibiting asymmetric segregation at cell division. Initial gene-expression profiles of polarity candidates showed high and differential expression in both HSCs and leukemia stem cells. Altered HSC fate was assessed by our established in vitro to in vivo screen on a subcohort of candidate polarity genes, which revealed 6 novel positive regulators of HSC function: Ap2a2, Gpsm2, Tmod1, Kif3a, Racgap1, and Ccnb1. Interestingly, live-cell videomicroscopy of the endocytic protein AP2A2 shows instances of asymmetric segregation during HSC/progenitor cell cytokinesis. These results contribute further evidence that ACD is functional in HSC self-renewal, suggest a role for Ap2a2 in HSC activity, and provide a unique opportunity to prospectively analyze progeny from HSC asymmetric divisions.

Association Between Corticosteroids and Infection, Sepsis, and Infectious Death in Pediatric Acute Myeloid Leukemia (AML): Results From the Canadian Infections in AML Research Group

BACKGROUND Infection continues to be a major problem for children with acute myeloid leukemia (AML). Objectives were to identify factors associated with infection, sepsis, and infectious deaths in children with newly diagnosed AML. METHODS We conducted a retrospective, population-based cohort study that included children ≤ 18 years of age with de novo, non-M3 AML diagnosed between January 1995 and December 2004, treated at 15 Canadian centers. Patients were monitored for infection from initiation of AML treatment until recovery from the last cycle of chemotherapy, conditioning for hematopoietic stem cell transplantation, relapse, persistent disease, or death (whichever occurred first). Consistent trained research associates abstracted all information from each site. RESULTS 341 patients were included. Median age was 7.1 years (interquartile range [IQR], 2.0-13.5) and 29 (8.5%) had Down syndrome. In sum, 26 (7.6%) experienced death as a first event. There were 1277 courses of chemotherapy administered in which sterile site microbiologically documented infection occurred in 313 courses (24.5%). Sepsis and infectious death occurred in 97 (7.6%) and 16 (1.3%) courses, respectively. The median days of corticosteroid administration was 2 per course (IQR, 0-6). In multiple regression analysis, duration of corticosteroid exposure was significantly associated with more microbiologically documented sterile site infection, bacteremia, fungal infection, and sepsis. The only factor significantly associated with infectious death was days of corticosteroid exposure (odds ratio, 1.05; 95% confidence interval, 1.02-1.08; P = .001). CONCLUSIONS In pediatric AML, infection, sepsis, and infectious death were associated with duration of corticosteroid exposure. Corticosteroids should be avoided when possible for this population.

RNAi screen identifies Jarid1b as a major regulator of mouse HSC activity

Histone methylation is a dynamic and reversible process proposed to directly impact on stem cell fate. The Jumonji (JmjC) domain-containing family of demethylases comprises 27 members that target mono-, di-, and trimethylated lysine residues of histone (or nonhistone) proteins. To evaluate their role in regulation of hematopoietic stem cell (HSC) behavior, we performed an in vivo RNAi-based functional screen and demonstrated that Jarid1b and Jhdm1f play opposing roles in regulation of HSC activity. Decrease in Jarid1b levels correlated with an in vitro expansion of HSCs with preserved long-term in vivo lymphomyeloid differentiation potential. Through RNA sequencing analysis, Jarid1b knockdown was associated with increased expression levels of several HSC regulators (Hoxa7, Hoxa9, Hoxa10, Hes1, Gata2) and reduced levels of differentiation-associated genes. shRNA against Jhdmlf, in contrast, impaired hematopoietic reconstitution of bone marrow cells. Together, our studies identified Jarid1b as a negative regulator of HSC activity and Jhdmlf as a positive regulator of HSC activity.

A role for GPx3 in activity of normal and leukemia stem cells

High levels of glutathione peroxidase 3 (GPx3) expression correlate with adverse prognosis in acute myeloid leukemia, and enhance activity of long-term repopulating hematopoietic stem cells in mice.

Zfx: At the Crossroads of Survival and Self-Renewal

As the molecular mechanisms that govern stem cell fate are beginning to be unraveled, Galan-Caridad et al. (2007) report in this issue of Cell a common role for the transcription factor Zfx in the self-renewal/maintenance of both embryonic stem cells and hematopoietic stem cells. Their work suggests that a regulator of self-renewal can be shared between two different cell types.

Predictors and outcomes of viridans group streptococcal infections in pediatric acute myeloid leukemia: from the Canadian infections in AML research group.

Background: Viridans group streptococci (VGS) cause significant morbidity in children treated for acute myeloid leukemia (AML). Our goals were to determine the occurrence and impact of these infections in children treated for AML and to understand the factors that increase the risk of VGS infections and viridans streptococcal shock syndrome (VSSS) in this population. Methods: We conducted a retrospective, population-based cohort study that included children ⩽18 years of age with de novo AML treated at 15 Canadian centers. We evaluated factors related to VGS infection and VSSS. Results: Among 341 children with AML, VGS occurred in 78 (22.9%) children over the entire course of therapy and 16 had recurrent episodes. VGS infection occurred in 97 of 1277 courses of chemotherapy (7.6%). VSSS occurred in 19.6% of these episodes and included 11 patients who required intensive care services with 2 VGS infections resulting in death. In multiple regression analysis, factors independently related to VGS included treatment on a Medical Research Council-based protocol (odds ratio (OR) 2.87, 95% confidence interval (CI) 1.53–5.39; P = 0.001), cytarabine dose per gram/m2 (OR 1.04, 95% CI 1.01–1.07; P = 0.002) and prolonged neutropenia (OR 1.58, 95% CI: 0.97–2.56; P = 0.06). None of the evaluated factors were predictive of VSSS. Conclusions: VGS infections occur in 7.6% of chemotherapy courses and remain an important cause of morbidity and even mortality in children being treated for AML. Interventions to reduce VGS need to be identified.

Entinostat Prevents Leukemia Maintenance in a Collaborating Oncogene‐Dependent Model of Cytogenetically Normal Acute Myeloid Leukemia

The incidence of refractory acute myeloid leukemia (AML) is on the increase due in part to an aging population that fails to respond to traditional therapies. High throughput genomic analysis promises better diagnosis, prognosis, and therapeutic intervention based on improved patient stratification. Relevant preclinical models are urgently required to advance drug development in this area. The collaborating oncogenes, HOXA9 and MEIS1, are frequently co‐overexpressed in cytogenetically normal AML (CN‐AML), and a conditional transplantation mouse model was developed that demonstrated oncogene dependency and expression levels comparable to CN‐AML patients. Integration of gene signatures obtained from the mouse model and a cohort of CN‐AML patients using statistically significant connectivity map analysis identified Entinostat as a drug with the potential to alter the leukemic condition toward the normal state. Ex vivo treatment of leukemic cells, but not age‐matched normal bone marrow controls, with Entinostat validated the gene signature and resulted in reduced viability in liquid culture, impaired colony formation, and loss of the leukemia initiating cell. Furthermore, in vivo treatment with Entinostat resulted in prolonged survival of leukemic mice. This study demonstrates that the HDAC inhibitor Entinostat inhibits disease maintenance and prolongs survival in a clinically relevant murine model of cytogenetically normal AML. STEM Cells2013;31:1434–1445

Invasive fungal infections in paediatric acute myeloid leukaemia

Invasive fungal infections (IFIs) are a major cause of morbidity and mortality in paediatric acute myeloid leukaemia (AML). This study describes risk factors for IFI and IFI‐related sepsis in this population. We conducted a population‐based, retrospective cohort study of children with AML in Canada. IFIs during chemotherapy and prior to haematopoietic stem cell transplantation, relapse, persistent disease or death were identified. Risk factors for proven or probable IFI were examined. Among courses complicated by IFI, risk factors for sepsis were also evaluated. There were 341 children with AML included of which 41 (12.0%) experienced 46 different episodes of IFI. Candida species accounted for 23 (50.0%) of IFIs and Aspergillus spp. accounted for 14 (30.4%). Days of broad‐spectrum antibiotics, days of corticosteroids and neutropenia at start of the course were independently associated with IFI. Only days of fever were independently associated with IFI‐related sepsis. Invasive fungal infections occurred in 12.0% of paediatric AML patients. Risk factors for IFI and IFI‐related sepsis were identified. This knowledge may help to consider targeted strategies.

Clostridium difficile infection in pediatric acute myeloid leukemia: from the Canadian Infections in Acute Myeloid Leukemia Research Group.

Background: The prevalence and severity of Clostridium difficile infection (CDI) has increased over time in adult patients, but little is known about CDI in pediatric cancer. The primary objectives were to describe the incidence and characteristics of CDI in children with de novo acute myeloid leukemia (AML). The secondary objective was to describe factors associated with CDI. Method: We performed a multicenter, retrospective cohort study of children with de novo AML and evaluated CDI. Recurrence, sepsis and infection-related death were examined. Factors associated with CDI were also evaluated. Results: Forty-three CDI occurred in 37 of 341 (10.9%) patients during 42 of 1277 (3.3%) courses of chemotherapy. There were 6 children with multiple episodes of CDI. Three infections were associated with sepsis, and no children died of CDI. Only 2 children had an associated enterocolitis. Both days of broad-spectrum antibiotics (odds ratio 1.03, 95% confidence interval: 1.01 to 1.06; P = 0.003) and at least 1 microbiologically documented sterile site infection (odds ratio 10.81, 95% confidence interval: 5.88 to 19.89; P < 0.0001) were independently associated with CDI. Conclusions: CDI occurred in 11% of children receiving intensive chemotherapy for AML, and outcomes were not severe. CDI is not a prominent issue in pediatric AML in terms of prevalence, incidence or associated outcomes.