L’implication de la peptide-déformylase (PDF) dans la leucémie aiguë lymphoblastique de l’enfant

La leucémie aiguë lymphoblastique (LAL) est le cancer pédiatrique le plus fréquent, comptant pour 25% de toutes les tumeurs pédiatriques. Les thérapies actuelles permettent d'obtenir des taux de survie d’environ 90%. Cependant, les patients qui ne répondent pas aux traitements actuels représentent la cause principale de mortalité liée au cancer chez l’enfant. Afin d’approfondir nos connaissances sur les causes de cette maladie et de comprendre l’architecture génétique sous-jacente de la LAL de l’enfant, nous proposons d’identifier les mutations conductrices de la leucémogénèse, dites mutations « drivers ». L’utilisation du séquençage de nouvelle génération sur la cohorte QcALL du CHU Sainte-Justine, 389 enfants atteints de la LAL de type pré-B, nous a permis d’identifier des mutations somatiques. Certaines de ces mutations possèdent un haut potentiel d’avoir un impact fonctionnel et sont ainsi considérées comme des candidats « drivers » de la leucémie. Nous avons ainsi mis en évidence une mutation somatique faux-sens c.t697a dans le gène PDF (peptide-deformylase mitochondrial) partagée par trois patients. Notre hypothèse de recherche est que cette mutation est conductrice de la leucémogénèse. Dans le but de déterminer le potentiel conducteur (driver) de la nouvelle mutation récurrente c.t697a dans PDF, nous avons évalué son effet dans des cellules leucémiques grâce à des tests de mesure de l’activité métabolique, de l’apoptose et de la prolifération cellulaire. Il s’est avéré que cette mutation, lorsqu’elle était surexprimée dans les cellules leucémiques, menait notamment à une baisse de la production d’ATP et à une augmentation de l’apoptose. Ainsi, la mutation c.t697a dans le gène PDF n’est pas une mutation conductrice de la leucémogénèse. L’identification de nouvelles mutations conductrices permet de mieux comprendre l’étiologie de la LAL et éventuellement d’élaborer des approches personnalisées pour la gestion et le soin des enfants atteints de cette maladie.Acute lymphoblastic leukemia (ALL) is the most common childhood cancer, representing 25% of all pediatric tumors. With the current therapies the survival rate is about 90%. However, the remaining patients who do not respond to current treatments still represent the principal cause of mortality related to children’s cancer. To deepen our knowledge on the causes of this disease and to understand the underlying genetic architecture of ALL, we performed a depth study of childhood ALL by characterizing mutations that can drive to leukemogenesis, called driver mutations. The use of high throughput sequencing on a cohort of 389 ALL pre-B pediatric patients led us to identify somatic mutations. Several of these mutations had strong predicted functional impact and were thus considered as putative driver mutations of leukemia. One of these mutations, the non-sense somatic mutation c.t697a on the PDF (peptide deformylase, mitochondrial) gene was shared by three patients. Our research hypothesis is that this mutation is a driver of leukemogenesis. In order to determine the driver potential of the new recurrent mutation c.t697a in PDF, we evaluated its effect in leukemic cells by measuring metabolic activity, apoptosis, and cellular proliferation. It was found that this mutation, when overexpressed in leukemic cells, led to a decrease in ATP production and an increase in apoptosis. Thus, the c.t697a mutation in the PDF gene is not a driver mutation of leukemia. Identification of novel driver mutations will further increase our understanding of the ALL etiology and eventually allow personalized approaches for the management of children attained by this disease

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

COVID-19 and Sickle Cell Disease in the Province of Quebec, Canada: Outcomes after Two Years of the Pandemic

Background: Patients with sickle cell disease (SCD) are considered at higher risk of severe COVID-19 infection. However, morbidity and mortality rates are variable among countries. To date, there are no published reports that document outcomes of SCD patients with COVID-19 in Canada. Methods: A web-based registry was implemented in June 2020 capturing outcomes of SCD patients with COVID-19 from March 2020 to April 2022 and comparing them to the general population of Quebec, Canada. Results: After 24 months of the pandemic, 185 SCD patients with confirmed SARS-CoV-2 infection were included in the registry. Overall, the population was young (median age 12 years old) and had few comorbidities. No deaths were reported. Risk of hospitalization and admission to intensive care unit (ICU) because of COVID-19 was higher in patients with SCD than in the general population (relative risks (RR) 5.15 (95% confidence interval (95% CI) 3.84–6.91), p ˂ 0.001 and 4.56 (95% CI 2.09–9.93) p ˂ 0.001). A history of arterial hypertension or acute chest syndrome in the past 12 months was associated with a higher risk of severe disease (RR = 3.06 (95% CI 1.85–5.06) p = 0.008 and 2.27 (95% CI 1.35–3.83) p = 0.01). Hospitalized patients had lower hemoglobin F than non-hospitalized patients (12% vs. 17%, p = 0.02). For those who had access to vaccination at the time of infection, 25 out of 26 patients were adequately vaccinated and had mild disease. Conclusions: The SCD population is at higher risk of severe disease than the general population. However, we report favorable outcomes as no deaths occurred. Registries will continue to be critical to document the impact of novel COVID-19 specific therapy and vaccines for the SCD population