Mobilization-based chemotherapy-free engraftment of gene-edited human hematopoietic stem cells.

Hematopoietic stem/progenitor cell gene therapy (HSPC-GT) is proving successful to treat several genetic diseases. HSPCs are mobilized, harvested, genetically corrected ex vivo, and infused, after the administration of toxic myeloablative conditioning to deplete the bone marrow (BM) for the modified cells. We show that mobilizers create an opportunity for seamless engraftment of exogenous cells, which effectively outcompete those mobilized, to repopulate the depleted BM. The competitive advantage results from the rescue during ex vivo culture of a detrimental impact of mobilization on HSPCs and can be further enhanced by the transient overexpression of engraftment effectors exploiting optimized mRNA-based delivery. We show the therapeutic efficacy in a mouse model of hyper IgM syndrome and further developed it in human hematochimeric mice, showing its applicability and versatility when coupled with gene transfer and editing strategies. Overall, our findings provide a potentially valuable strategy paving the way to broader and safer use of HSPC-GT.

Intravenous immunoglobulins in patients with COVID-19-associated moderate-to-severe acute respiratory distress syndrome (ICAR): multicentre, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is a major complication of COVID-19 and is associated with high mortality and morbidity. We aimed to assess whether intravenous immunoglobulins (IVIG) could improve outcomes by reducing inflammation-mediated lung injury. METHODS: In this multicentre, double-blind, placebo-controlled trial, done at 43 centres in France, we randomly assigned patients (1:1) receiving invasive mechanical ventilation for up to 72 h with PCR confirmed COVID-19 and associated moderate-to-severe ARDS to receive either IVIG (2 g/kg over 4 days) or placebo. Random assignment was done with a web-based system and was stratified according to the participating centre and the duration of invasive mechanical ventilation before inclusion in the trial (<12 h, 12-24 h, and >24-72 h), and treatment was administered within the first 96 h of invasive mechanical ventilation. To minimise the risk of adverse events, the IVIG administration was divided into four perfusions of 0·5 g/kg each administered over at least 8 hours. Patients in the placebo group received an equivalent volume of sodium chloride 0·9% (10 mL/kg) over the same period. The primary outcome was the number of ventilation-free days by day 28, assessed according to the intention-to-treat principle. This trial was registered on ClinicalTrials.gov, NCT04350580. FINDINGS: Between April 3, and October 20, 2020, 146 patients (43 [29%] women) were eligible for inclusion and randomly assigned: 69 (47%) patients to the IVIG group and 77 (53%) to the placebo group. The intention-to-treat analysis showed no statistical difference in the median number of ventilation-free days at day 28 between the IVIG group (0·0 [IQR 0·0-8·0]) and the placebo group (0·0 [0·0-6·0]; difference estimate 0·0 [0·0-0·0]; p=0·21). Serious adverse events were more frequent in the IVIG group (78 events in 22 [32%] patients) than in the placebo group (47 events in 15 [20%] patients; p=0·089). INTERPRETATION: In patients with COVID-19 who received invasive mechanical ventilation for moderate-to-severe ARDS, IVIG did not improve clinical outcomes at day 28 and tended to be associated with an increased frequency of serious adverse events, although not significant. The effect of IVIGs on earlier disease stages of COVID-19 should be assessed in future trials. FUNDING: Programme Hospitalier de Recherche Clinique.

Investigating the Vascular Niche: Three-Dimensional Co-culture of Human Skeletal Muscle Stem Cells and Endothelial Cells.

Angiogenesis, the growth of new blood vessels, is crucial for efficient skeletal muscle regeneration. Myogenesis and angiogenesis take place concomitantly during muscle regeneration. Myogenic precursor cells (MPCs) are in close proximity to vessels and interact with neighboring endothelial cells (ECs) to expand and differentiate. To demonstrate functional interplay between the two cell types, we established a robust and predictive ex vivo assay to evaluate activity of MPCs on angiogenesis and vice-et-versa, of ECs on myogenesis. Here, we describe an optimized three-dimensional co-culture protocol for the assessment of biological interactions between MPCs and ECs during skeletal muscle regeneration.

Muscle Satellite Cell Cross-Talk with a Vascular Niche Maintains Quiescence via VEGF and Notch Signaling.

Skeletal muscle is a complex tissue containing tissue resident muscle stem cells (satellite cells) (MuSCs) important for postnatal muscle growth and regeneration. Quantitative analysis of the biological function of MuSCs and the molecular pathways responsible for a potential juxtavascular niche for MuSCs is currently lacking. We utilized fluorescent reporter mice and muscle tissue clearing to investigate the proximity of MuSCs to capillaries in 3 dimensions. We show that MuSCs express abundant VEGFA, which recruits endothelial cells (ECs) in vitro, whereas blocking VEGFA using both a vascular endothelial growth factor (VEGF) inhibitor and MuSC-specific VEGFA gene deletion reduces the proximity of MuSCs to capillaries. Importantly, this proximity to the blood vessels was associated with MuSC self-renewal in which the EC-derived Notch ligand Dll4 induces quiescence in MuSCs. We hypothesize that MuSCs recruit capillary ECs via VEGFA, and in return, ECs maintain MuSC quiescence though Dll4.

Myogenic Progenitor Cells Exhibit Type I Interferon-Driven Proangiogenic Properties and Molecular Signature During Juvenile Dermatomyositis.

OBJECTIVE: Juvenile dermatomyositis (JDM) is an inflammatory pediatric myopathy characterized by focal capillary loss in muscle, followed by progressive recovery upon adequate treatment with immunomodulating drugs, although some patients remain refractory to treatment. While the underlying mechanism of capillary depletion remains uncertain, recent studies have identified an up-regulation of type I interferon (IFN) expression specific to JDM. Given that myogenic precursor cells (MPCs) exert proangiogenic activity during normal skeletal muscle regeneration, we hypothesized that they may also modulate vascular remodeling/angiogenesis during JDM. The aim of this study was to investigate that hypothesis. METHODS: Human cell cocultures were used to analyze angiogenic properties in patients with JDM, patients with Duchenne's muscular dystrophy (DMD) (control patients for vascular remodeling), and healthy control subjects. Transcriptome analysis was used to examine muscle-derived MPCs. Histologic analysis of type I IFN in muscle biopsy samples was also performed. RESULTS: Using human cell cocultures, we showed highly angiogenic properties of MPCs from JDM patients in association with the expression of an angiogenic molecular signature. Transcriptome analysis of MPCs freshly isolated from muscle samples revealed type I IFN as the master regulator of the most up-regulated genes in JDM-derived MPCs. Functionally, treatment of normal MPCs with type I IFN recapitulated the molecular pattern and the proangiogenic functions of JDM-derived MPCs. In vivo histologic investigation showed that MPCs synthesized type I IFN and major proangiogenic molecules in JDM muscle. Moreover, MPCs derived from JDM muscles that were characterized by strong vasculopathy produced higher levels of type I IFN, confirming MPCs as a cellular source of type I IFN during JDM, and this correlated with the severity of the disease. CONCLUSION: These results demonstrate a new type I IFN pathway in JDM that activates the production of angiogenic effectors by MPCs, triggering their proangiogenic function to promote vessel recovery and muscle reconstruction.

Cell sorting of various cell types from mouse and human skeletal muscle.

Muscle stem cells or satellite cells are required for skeletal muscle regeneration. It has been shown that the satellite cell microenvironment, including neighboring cells such as endothelial cells, macrophages or fibroblasts are essential for complete and efficient regeneration. A deficient behavior of these cells compromises regeneration. Therefore, there is a strong interest in understanding the cellular and molecular interactions at work between these cell types during muscle regeneration. Fluorescence-activated cell sorting allows to isolate these four cell types at different time points of regeneration, for further high throughput or behavioral experiments. We present here a method for the concomitant isolation of 4 cell types present in the regenerating skeletal muscle: muscle stem cells, endothelial cells, fibro-adipogenic precursor cells and macrophages.

Coupling between Myogenesis and Angiogenesis during Skeletal Muscle Regeneration Is Stimulated by Restorative Macrophages.

In skeletal muscle, new functions for vessels have recently emerged beyond oxygen and nutrient supply, through the interactions that vascular cells establish with muscle stem cells. Here, we demonstrate in human and mouse that endothelial cells (ECs) and myogenic progenitor cells (MPCs) interacted together to couple myogenesis and angiogenesis in vitro and in vivo during skeletal muscle regeneration. Kinetics of gene expression of ECs and MPCs sorted at different time points of regeneration identified three effectors secreted by both ECs and MPCs. Apelin, Oncostatin M, and Periostin were shown to control myogenesis/angiogenesis coupling in vitro and to be required for myogenesis and vessel formation during muscle regeneration in vivo. Furthermore, restorative macrophages, which have been previously shown to support myogenesis in vivo, were shown in a 3D triculture model to stimulate myogenesis/angiogenesis coupling, notably through Oncostatin M production. Our data demonstrate that restorative macrophages orchestrate muscle regeneration by controlling myogenesis/angiogenesis coupling.

Physical Sequestration of Bacillus anthracis in the Pulmonary Capillaries in Terminal Infection.

The lung is the terminal target of Bacillus anthracis before death, whatever the route of infection (cutaneous, inhalational, or digestive). During a cutaneous infection in absence of toxins, we observed encapsulated bacteria colonizing the alveolar capillary network, bacteria and hemorrhages in alveolar and bronchiolar spaces, and hypoxic foci in the lung (endothelial cells) and brain (neurons and neuropil). Circulating encapsulated bacteria were as chains of approximately 13 µm in length. Bacteria of such size were immediately trapped within the lung capillary network, but bacteria of shorter length were not. Controlling lung-targeted pathology would be beneficial for anthrax treatment.

Skeletal Muscle Microvasculature: A Highly Dynamic Lifeline.

Skeletal muscle is highly irrigated by blood vessels. Beyond oxygen and nutrient supply, new vessel functions have been identified. This review presents vessel microanatomy and functions at tissue, cellular, and molecular levels. Mechanisms of vessel plasticity are described during skeletal muscle development and acute regeneration, and in physiological and pathological contexts.

Structural and Functional Alterations of Skeletal Muscle Microvasculature in Dystrophin-Deficient mdx Mice.

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease, caused by an absence of dystrophin, inevitably leading to death. Although muscle lesions are well characterized, blood vessel alterations that may have a major impact on muscle regeneration remain poorly understood. Our aim was to elucidate alterations of the vascular network organization, taking advantage of Flk1(GFP/+) crossed with mdx mice (model for human DMD where all blood vessels express green fluorescent protein) and functional repercussions using in vivo nuclear magnetic resonance, combining arterial spin-labeling imaging of perfusion, and (31)P-spectroscopy of phosphocreatine kinetics. For the first time, our study focused on old (12-month-old) mdx mice, displaying marked chronic muscle lesions, similar to the lesions observed in human DMD, in comparison to young-adult (3-month-old) mdx mice displaying only mild muscle lesions with no fibrosis. By using an original approach combining a specific animal model, state-of-the-art histology/morphometry techniques, and functional nuclear magnetic resonance, we demonstrated that the microvascular system is almost normal in young-adult in contrast to old mdx mice, displaying marked microvessel alterations, and the functional repercussions on muscle perfusion and bioenergetics after a hypoxic stress vary depending on stage of pathology. This original approach clarifies disease evolution and paves the way for setting up new diagnostic markers or therapeutic strategies.

Myeloid HIFs are dispensable for resolution of inflammation during skeletal muscle regeneration.

Besides their role in cellular responses to hypoxia, hypoxia-inducible factors (HIFs) are involved in innate immunity and also have anti-inflammatory (M2) functions, such as resolution of inflammation preceding healing. Whereas the first steps of the inflammatory response are associated with proinflammatory (M1) macrophages (MPs), resolution of inflammation is associated with anti-inflammatory MPs exhibiting an M2 phenotype. This M1 to M2 sequence is observed during postinjury muscle regeneration, which provides an excellent paradigm to study the resolution of sterile inflammation. In this study, using in vitro and in vivo approaches in murine models, we demonstrated that deletion of hif1a or hif2a in MPs has no impact on the acquisition of an M2 phenotype. Furthermore, using a multiscale methodological approach, we showed that muscles did not require macrophagic hif1a or hif2a to regenerate. These results indicate that macrophagic HIFs do not play a crucial role during skeletal muscle regeneration induced by sterile tissue damage.