Although it has been shown that mast cell-deficient mice have diminished innate immune responses against bacteria, the most important immunoprotective factors secreted from activated mast cells have not been identified. Mouse mast cell protease 6 is a tetramer-forming tryptase. This serine protease is abundant in the secretory granules and is exocytosed upon bacterial challenge. Here we have described the generation of a mast cell protease-6-null mouse. Our discovery that mice lacking this neutral protease cannot efficiently clear Klebsiella pneumoniae from their peritoneal cavities reveals an essential role for this serine protease, and presumably its human ortholog, in innate immunity.Approximately 50% of the weight of a mature tissue mast cell (MC) 2 consists of protease-serglycin proteoglycan complexes stored in the secretory granules. In humans, ␤ tryptases are the most abundant MC-restricted neutral proteases (1-3). The corresponding tryptases in mice are mouse MC protease (mMCP)-6 (4, 5) and mMCP-7 (6), with mMCP-6 being the most similar in amino acid sequence and substrate specificity to human tryptase (hTryptase) ␤1 (7-9). MCs are the only cells that express mMCP-6, and this serine protease is particularly abundant in those MCs that reside in the peritoneal cavity, skin, and lung (4,5,10).Numerous biochemical studies have been carried out to understand the biosynthesis and substrate preference of mMCP-6. This tryptase is initially translated as a zymogen with a 245-mer mature domain. When the signal and propeptides are proteolytically removed, the mature protease spontaneously forms tetramers with the active site of each monomer facing the central core of the tetramer unit, as first described for its human ortholog (11). A positively charged face forms on the surface of each monomer, thereby allowing mature mMCP-6 to interact with negatively charged serglycin proteoglycans in the Golgi complex. The resulting tryptase-serglycin macromolecular complexes are then targeted and packaged in the cell secretory granules. When exocytosed, these complexes are retained in connective tissues for hours because of their large sizes (12). Protease inhibitors are abundant in blood. Nevertheless, no circulating protease inhibitor has been identified that rapidly inactivates mMCP-6 or hTryptase ␤1. Substrate specificity studies carried out using varied peptide combinatorial libraries revealed that recombinant mMCP-6 (7) and hTryptase ␤1 (8, 9) prefer to cleave peptides having a Pro at residues P2 to P5 and a Lys or Arg at residue P1. However, due to the unique structural constraints of the tetramer unit, the abilities of mMCP-6 and hTryptase ␤1 to cleave large-sized proteins are very limited. Thus, the importance of these evolutionally conserved enzymes in MC-dependent reactions remains to be determined.MC development in vivo is highly dependent on the cytokine kit ligand/stem cell factor on the surface of mesenchymal cells and its tyrosine kinase receptor c-Kit/CD117 on the surface of MC-committed progenitors. Signaling...

Epithelial tumor cells transit to a mesenchymal state in response to extracellular cues, in a process known as epithelial-to-mesenchymal transition (EMT). The precise nature of these cues has not been fully defined, an important issue given that EMT is an early event in tumor metastasis. Here, we have found that a population of metastasis-prone mouse lung adenocarcinoma cells expresses Notch and Notch ligands and that the Notch ligand Jagged2 promotes metastasis. Mechanistically, Jagged2 was found to promote metastasis by increasing the expression of GATA-binding ( IntroductionLung cancer is the foremost cause of cancer-related death in Western countries, and metastasis is the leading cause of death in patients with lung cancer. Improving clinical outcomes will require a better understanding of the biological processes that initiate metastasis. Toward that goal, mouse models have been generated that develop lung adenocarcinomas with high or low propensities for invasion and metastasis. Mice that express K-ras G12D alleles inducibly, conditionally, or somatically develop lung adenocarcinomas with low invasive and metastatic potential (1-5), whereas mice that express K-ras G12D and p53 R172H alleles develop lung adenocarcinomas that metastasize widely (6-9). Thus, K-ras-driven mouse models of lung cancer acquire metastatic potential with the addition of a second mutation commonly found in lung cancer.Investigators have used mouse models of cancer to study the biological basis of metastasis. In one working hypothesis, epithelial tumor cells acquire the ability to invade and disseminate by undergoing epithelial-to-mesenchymal transition (EMT), which is characterized by a loss of cell-cell attachments and apical-basal polarization and gain of mesenchymal and invasive properties (10-19). The process of EMT is regulated by several transcriptional suppressor families, including the zinc-finger proteins Snail1 and Snail2, the 2-handed zinc-finger δEF1 family factors

Background Although mortality due to COVID-19 has been reportedly low among children with cancer, changes in health-care services due to the pandemic have affected cancer care delivery. This study aimed to assess the effect of the COVID-19 pandemic on childhood cancer care worldwide. Methods A cross-sectional survey was distributed to paediatric oncology providers worldwide from June 22 to Aug 21, 2020, through the St Jude Global Alliance and International Society for Paediatric Oncology listservs and regional networks. The survey included 60 questions to assess institution characteristics, the number of patients diagnosed with COVID-19, disruptions to cancer care (eg, service closures and treatment abandonment), adaptations to care, and resources (including availability of clinical staff and personal protective equipment). Surveys were included for analysis if respondents answered at least two thirds of the items, and the responses were analysed at the institutional level. Findings Responses from 311 health-care professionals at 213 institutions in 79 countries from all WHO regions were included in the analysis. 187 (88%) of 213 centres had the capacity to test for SARS-CoV-2 and a median of two (range 0–350) infections per institutution were reported in children with cancer. 15 (7%) centres reported complete closure of paediatric haematology-oncology services (median 10 days, range 1–75 days). Overall, 2% (5 of 213) of centres were no longer evaluating new cases of suspected cancer, while 43% (90 of 208) of the remaining centers described a decrease in newly diagnosed paediatric cancer cases. 73 (34%) centres reported increased treatment abandonment (ie, failure to initiate cancer therapy or a delay in care of 4 weeks or longer). Changes to cancer care delivery included: reduced surgical care (153 [72%]), blood product shortages (127 [60%]), chemotherapy modifications (121 [57%]), and interruptions to radiotherapy (43 [28%] of 155 institutions that provided radiotherapy before the pandemic). The decreased number of new cancer diagnoses did not vary based on country income status (p=0·14). However, unavailability of chemotherapy agents (p=0·022), treatment abandonment (p<0·0001), and interruptions in radiotherapy (p<0·0001) were more frequent in low-income and middle-income countries than in high-income countries. These findings did not vary based on institutional or national numbers of COVID-19 cases. Hospitals reported using new or adapted checklists (146 [69%] of 213), processes for communication with patients and families (134 [63%]), and guidelines for essential services (119 [56%]) as a result of the pandemic. Interpretation The COVID-19 pandemic has considerably affected paediatric oncology services worldwide, posing substantial disruptions to cancer diagnosis and management, particularly in low-income and middle-income countries. This study emphasises the urgency of an equitably distributed robust glo...

Background Previous studies have shown that children and adolescents with COVID-19 generally have mild disease. Children and adolescents with cancer, however, can have severe disease when infected with respiratory viruses. In this study, we aimed to understand the clinical course and outcomes of SARS-CoV-2 infection in children and adolescents with cancer. Methods We did a cohort study with data from 131 institutions in 45 countries. We created the Global Registry of COVID-19 in Childhood Cancer to capture de-identified data pertaining to laboratory-confirmed SARS-CoV-2 infections in children and adolescents (<19 years) with cancer or having received a haematopoietic stem-cell transplantation. There were no centre-specific exclusion criteria. The registry was disseminated through professional networks through email and conferences and health-care providers were invited to submit all qualifying cases. Data for demographics, oncological diagnosis, clinical course, and cancer therapy details were collected. Primary outcomes were disease severity and modification to cancer-directed therapy. The registry remains open to data collection. Findings Of 1520 submitted episodes, 1500 patients were included in the study between April 15, 2020, and Feb 1, 2021. 1319 patients had complete 30-day follow-up. 259 (19•9%) of 1301 patients had a severe or critical infection, and 50 (3•8%) of 1319 died with the cause attributed to COVID-19 infection. Modifications to cancer-directed therapy occurred in 609 (55•8%) of 1092 patients receiving active oncological treatment. Multivariable analysis revealed several factors associated with severe or critical illness, including World Bank low-income or lower-middle-income (odds ratio [OR] 5•8 [95% CI 3•8-8•8]; p<0•0001) and upper-middle-income (1•6 [1•2-2•2]; p=0•0024) country status; age 15-18 years (1•6 [1•1-2•2]; p=0•013); absolute lymphocyte count of 300 or less cells per mm³ (2•5 [1•8-3•4]; p<0•0001), absolute neutrophil count of 500 or less cells per mm³ (1•8 [1•3-2•4]; p=0•0001), and intensive treatment (1•8 [1•3-2•3]; p=0•0005). Factors associated with treatment modification included upper-middle-income country status (OR 0•5 [95% CI 0•3-0•7]; p=0•0004), primary diagnosis of other haematological malignancies (0•5 [0•3-0•8]; p=0•0088), the presence of one of more COVID-19 symptoms at the time of presentation (1•8 [1•3-2•4]; p=0•0002), and the presence of one or more comorbidities (1•6 [1•1-2•3]; p=0•020).Interpretation In this global cohort of children and adolescents with cancer and COVID-19, severe and critical illness occurred in one fifth of patients and deaths occurred in a higher proportion than is reported in the literature in the general paediatric population. Additionally, we found that variables associated with treatment modification were not the same as those associated with greater disease severity. These data could inform clinical practice guidelines and raise awareness globally that children and adolescents with cancer are at high-risk of developing severe COVID-19 illn...

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Mast cell degranulation is a highly regulated, calciumdependent process, which is important for the acute release of inflammatory mediators during the course of many pathological conditions. We previously found that Synaptotagmin-2, a calcium sensor in neuronal exocytosis, was expressed in a mast cell line. We postulated that this protein may be involved in the control of mast cell-regulated exocytosis, and we generated Synaptotagmin-2 knock-out mice to test our hypothesis. Mast cells from this mutant animal conferred an abnormally decreased passive cutaneous anaphylaxis reaction on mast cell-deficient mice that correlated with a specific defect in mast cell-regulated exocytosis, leaving constitutive exocytosis and nonexocytic mast cell effector responses intact. This defect was not secondary to abnormalities in the development, maturation, migration, morphology, synthesis, and storage of inflammatory mediators, or intracellular calcium transients of the mast cells. Unlike neurons, the lack of Synaptotagmin-2 in mast cells was not associated with increased spontaneous exocytosis. Mast cells (MCs)2 participate in adaptive and innate immune responses. Their secreted products play important roles in immunoglobulin E (IgE)-dependent inflammatory reactions such as allergic asthma and anaphylaxis (1) and are also involved in other forms of inflammation such as immune arthritis (2, 3) and innate immune responses to bacterial infections (4, 5). Upon activation, MCs exhibit three main secretory responses: release of granule contents (i.e. degranulation), secretion of prostaglandins and leukotrienes, and secretion of cytokines and growth factors (6). The exocytic release of preformed mediators (e.g. histamine and proteases) stored in secretory granules is immediate and regulated at the step of fusion between the membrane of the granule and the plasma membrane. Thus, it is an example of regulated exocytosis, like neuronal synaptic neurotransmitter release and insulin secretion (7). Another early event is the release of metabolites of arachidonic acid (e.g. prostaglandin D 2 (PGD 2 ) and leukotriene C 4 (LTC 4 )). These eicosanoids cross the plasma membrane using transmembrane transporters (8), and their production is regulated by the activation of their synthetic enzymes (9). A late response after MC activation is the secretion of cytokines and growth factors (e.g. tumor necrosis factor-␣ (TNF-␣) and interleukin-4 (IL-4)). The gap in time of minutes to hours between stimulation and the secretion of these mediators is explained by the fact that regulation is at the transcriptional and post-transcriptional levels, with secretion occurring via constitutive exocytosis (10).A common intracellular mediator linking the stimulation event to these three MC responses is calcium (Ca 2ϩ ) that is released into the cytoplasm from intracellular stores and introduced from the extracellular environment via specialized channels. Increase in the cytoplasmic concentration of Ca 2ϩ ([Ca 2ϩ ] i ) is required for the activation of phospholi...

As a central regulator of cell polarity, the activity of CDC42 GTPase is tightly controlled in maintaining normal hematopoietic stem and progenitor cell (HSC/P) functions. We found that transformation of HSC/P to acute myeloid leukemia (AML) is associated with increased CDC42 expression and activity in leukemia cells. In a mouse model of AML, the loss of Cdc42 abrogates -induced AML development. Furthermore, genetic ablation of CDC42 in both murine and human MLL-AF9 (MA9) cells decreased survival and induced differentiation of the clonogenic leukemia-initiating cells. We show that MLL-AF9 leukemia cells maintain cell polarity in the context of elevated Cdc42-guanosine triphosphate activity, similar to nonmalignant, young HSC/Ps. The loss of Cdc42 resulted in a shift to depolarized AML cells that is associated with a decrease in the frequency of symmetric and asymmetric cell divisions producing daughter cells capable of self-renewal. Importantly, we demonstrate that inducible CDC42 suppression in primary human AML cells blocks leukemia progression in a xenograft model. Thus, CDC42 loss suppresses AML cell polarity and division asymmetry, and CDC42 constitutes a useful target to alter leukemia-initiating cell fate for differentiation therapy.

The COVID-19 pandemic has considerably changed health services for children with cancer worldwide by creating barriers throughout the care continuum. Reports available at this time suggest that asymptomatic and mild upper and lower respiratory tract syndromes are the most common presentation of COVID-19 in children with cancer. Nonetheless, severe cases of COVID-19 and deaths secondary to the infection have been reported. In addition to the direct effects of the severe acute respiratory syndrome coronavirus 2, children with cancer have suffered from the collateral consequences of the pandemic, including decreased access to diagnosis and cancer-directed therapy. The COVID-19 pandemic has presented unprecedented challenges to safe and effective care of children with cancer, including their enrollment in therapeutic clinical trials. Data from the Children’s Oncology Group and Cancer Research U.K. Clinical Trials Unit show variability in the enrollment of children with cancer in clinical trials during the COVID-19 pandemic. However, the overall effects on outcomes for children with cancer undergoing care during the pandemic remain largely unknown. In this article, we review the current knowledge about the direct and collateral effects of the COVID-19 pandemic, including on clinical trial enrollment and operations.