Targeting the microenvironment in the treatment of arteriovenous malformations.

Extracranial arteriovenous malformations (AVMs) are regarded as rare diseases and are prone to complications such as pain, bleeding, relentless growth, and high volume of shunted blood. Due to the high vascular pressure endothelial cells of AVMs are exposed to mechanical stress. To control symptoms and lesion growth pharmacological treatment strategies are urgently needed in addition to surgery and interventional radiology. AVM cells were isolated from three patients and exposed to cyclic mechanical stretching for 24 h. Thalidomide and bevacizumab, both VEGF inhibitors, were tested for their ability to prevent the formation of circular networks and proliferation of CD31+ endothelial AVM cells. Furthermore, the effect of thalidomide and bevacizumab on stretched endothelial AVM cells was evaluated. In response to mechanical stress, VEGF gene and protein expression increased in patient AVM endothelial cells. Thalidomide and bevacizumab reduced endothelial AVM cell proliferation. Bevacizumab inhibited circular network formation of endothelial AVM cells and lowered VEGF gene and protein expression, even though the cells were exposed to mechanical stress. With promising in vitro results, bevacizumab was used to treat three patients with unresectable AVMs or to prevent regrowth after incomplete resection. Bevacizumab controlled bleeding, pulsation, and pain over the follow up of eight months with no patient-reported side effects. Overall, mechanical stress increases VEGF expression in the microenvironment of AVM cells. The monoclonal VEGF antibody bevacizumab alleviates this effect, prevents circular network formation and proliferation of AVM endothelial cells in vitro. The clinical application of bevacizumab in AVM treatment demonstrates effective symptom control with no side effects.

Somatic RIT1 delins in arteriovenous malformations hyperactivate RAS-MAPK signaling amenable to MEK inhibition.

Arteriovenous malformations (AVM) are benign vascular anomalies prone to pain, bleeding, and progressive growth. AVM are mainly caused by mosaic pathogenic variants of the RAS-MAPK pathway. However, a causative variant is not identified in all patients. Using ultra-deep sequencing, we identified novel somatic RIT1 delins variants in lesional tissue of three AVM patients. RIT1 encodes a RAS-like protein that can modulate RAS-MAPK signaling. We expressed RIT1 variants in HEK293T cells, which led to a strong increase in ERK1/2 phosphorylation. Endothelial-specific mosaic overexpression of RIT1 delins in zebrafish embryos induced AVM formation, highlighting their functional importance in vascular development. Both ERK1/2 hyperactivation in vitro and AVM formation in vivo could be suppressed by pharmacological MEK inhibition. Treatment with the MEK inhibitor trametinib led to a significant decrease in bleeding episodes and AVM size in one patient. Our findings implicate RIT1 in AVM formation and provide a rationale for clinical trials with targeted treatments.

Protection from UV light is an evolutionarily conserved feature of the haematopoietic niche.

Haematopoietic stem and progenitor cells (HSPCs) require a specific microenvironment, the haematopoietic niche, which regulates HSPC behaviour1,2. The location of this niche varies across species, but the evolutionary pressures that drive HSPCs to different microenvironments remain unknown. The niche is located in the bone marrow in adult mammals, whereas it is found in other locations in non-mammalian vertebrates, for example, in the kidney marrow in teleost fish. Here we show that a melanocyte umbrella above the kidney marrow protects HSPCs against ultraviolet light in zebrafish. Because mutants that lack melanocytes have normal steady-state haematopoiesis under standard laboratory conditions, we hypothesized that melanocytes above the stem cell niche protect HSPCs against ultraviolet-light-induced DNA damage. Indeed, after ultraviolet-light irradiation, unpigmented larvae show higher levels of DNA damage in HSPCs, as indicated by staining of cyclobutane pyrimidine dimers and have reduced numbers of HSPCs, as shown by cmyb (also known as myb) expression. The umbrella of melanocytes associated with the haematopoietic niche is highly evolutionarily conserved in aquatic animals, including the sea lamprey, a basal vertebrate. During the transition from an aquatic to a terrestrial environment, HSPCs relocated into the bone marrow, which is protected from ultraviolet light by the cortical bone around the marrow. Our studies reveal that melanocytes above the haematopoietic niche protect HSPCs from ultraviolet-light-induced DNA damage in aquatic vertebrates and suggest that during the transition to terrestrial life, ultraviolet light was an evolutionary pressure affecting the location of the haematopoietic niche.

Functional assessment of two variants of unknown significance in TEK by endothelium-specific expression in zebrafish embryos.

Vascular malformations are most often caused by somatic mutations of the PI3K/mTOR and the RAS signaling pathways, which can be identified in the affected tissue. Venous malformations (VMs) commonly harbor PIK3CA and TEK mutations, whereas arteriovenous malformations (AVMs) are usually caused by BRAF, RAS or MAP2K1 mutations. Correct identification of the underlying mutation is of increasing importance, since targeted treatments are becoming more and more relevant, especially in patients with extensive vascular malformations. However, variants of unknown significance (VUSs) are often identified and their pathogenicity and response to targeted therapy cannot be precisely predicted. Here, we show that zebrafish embryos can be used to rapidly assess the pathogenicity of novel VUSs in TEK, encoding for the receptor TIE2, present on endothelial cells of VMs. Endothelium-specific overexpression of TEK mutations leads to robust induction of VMs, whereas MAP2K1 mutations cause AVMs in our zebrafish model. TEK mutations are often found as double mutations in cis; using our model, we show that double mutations have an additive effect in inducing VMs compared with the respective single variants. The clinically established mTOR-inhibitor sirolimus (rapamycin) efficiently abrogates the development of VMs in this zebrafish model. In summary, endothelium-specific overexpression of patient-derived TEK variants in the zebrafish model allows assessment of their pathogenic significance as well as testing of candidate drugs in a personalized and mutation-specific approach.

C-terminal variants in CDC42 drive type I interferon-dependent autoinflammation in NOCARH syndrome reversible by ruxolitinib.

C-terminal variants in CDC42 encoding cell division control protein 42 homolog underlie neonatal-onset cytopenia, autoinflammation, rash, and hemophagocytic lymphohistiocytosis (NOCARH). Pyrin inflammasome hyperactivation has been shown to contribute to disease pathophysiology. However, mortality of NOCARH patients remains high despite inflammasome-focused treatments. Here, we demonstrate in four NOCARH patients from three families that cell-intrinsic activation of type I interferon (IFN) is a previously unrecognized driver of autoinflammation in NOCARH. Our data show that aberrant innate immune activation is caused by sensing of cytosolic nucleic acids released from mitochondria, which exhibit disturbances in integrity and dynamics due to CDC42 dysfunction. In one of our patients, treatment with the Janus kinase inhibitor ruxolitinib led to complete remission, indicating that inhibition of type I IFN signaling may have an important role in the management of autoinflammation in patients with NOCARH.

Rhabdomyosarcoma xenotransplants in zebrafish embryos.

Rhabdomyosarcomas (RMS) are the most common pediatric soft tissue sarcomas. High-risk and metastatic disease continues to be associated with very poor prognosis. RMS model systems that faithfully recapitulate the human disease and provide rapid, cost-efficient estimates of antitumor efficacy of candidate drugs are needed to facilitate drug development and personalized medicine approaches. Here, we present a new zebrafish-based xenotransplant model allowing for rapid and easily accessible drug screening using low numbers of viable tumor cells and relatively small amounts of water-soluble chemicals. Under optimized temperature conditions, embryonal RMS xenografts were established in zebrafish embryos at 3 h postfertilization (hpf). In proof-of-principle experiments, chemotherapy drugs with established clinical anti-RMS efficacy (vincristine, dactinomycin) and the mitogen-activated protein kinase kinase inhibitor trametinib were shown to significantly reduce the cross-sectional area of the tumors by 120 hpf. RMS xenograft models in zebrafish embryos henceforth could serve as a valuable addition to cell culture and mammalian models of RMS and represent a rapid and cost-effective solution for preclinical candidate drug testing.

Additive value of transarterial embolization to systemic sirolimus treatment in kaposiform hemangioendothelioma.

Kaposiform hemangioendothelioma (KHE) is a rare vascular tumor in children, which can be accompanied by life-threatening thrombocytopenia, referred to as Kasabach-Merritt phenomenon (KMP). The mTOR inhibitor sirolimus is emerging as targeted therapy in KHE. As the sirolimus effect on KHE occurs only after several weeks, we aimed to evaluate whether additional transarterial embolization is of benefit for children with KHE and KMP. Seventeen patients with KHE and KMP acquired from 11 hospitals in Germany were retrospectively divided into two cohorts. Children being treated with adjunct transarterial embolization and systemic sirolimus, and those being treated with sirolimus without additional embolization. Bleeding grade as defined by WHO was determined for all patients. Response of the primary tumor at 6 and 12 months assessed by magnetic resonance imaging (MRI), time to response of KMP defined as thrombocyte increase >150 × 103 /µL, as well as rebound rates of both after cessation of sirolimus were compared. N = 8 patients had undergone additive embolization to systemic sirolimus therapy, sirolimus in this group was started after a mean of 6.5 ± 3 days following embolization. N = 9 patients were identified who had received sirolimus without additional embolization. Adjunct embolization induced a more rapid resolution of KMP within a median of 7 days vs 3 months; however, tumor response as well as rebound rates were similar between both groups. Additive embolization may be of value for a more rapid rescue of consumptive coagulopathy in children with KHE and KMP compared to systemic sirolimus only.

Severe adverse events during sirolimus "off-label" therapy for vascular anomalies.

OBJECTIVES: Clinical studies have shown low toxicity and a favorable safety profile for sirolimus in vascular anomalies. Here, we describe severe adverse events (SAEs) observed during "off-label use" for vascular anomalies. METHODS: We performed a retrospective, multicenter chart review for SAEs during "off-label" sirolimus therapy for vascular anomalies and analyzed these cases by a predesigned workflow. RESULTS: We identified 17 SAEs in 14 patients diagnosed with generalized lymphatic anomaly (n = 4), Gorham-Stout disease (n = 2), central conducting lymphatic anomaly (n = 1), lymphatic malformation (n = 4), tufted angioma (n = 1), kaposiform hemangioendothelioma (n = 1), and venous malformation in a patient with CLOVES syndrome (n = 1). Three patients presented two SAEs each. The age at initiation of sirolimus therapy was under 2 years (n = 5), 2-6 years (n = 5), and older than 12 years (n = 4). SAEs occurred during the first 3 months of sirolimus therapy (n = 7), between 3 and 12 months (n = 7) and after 1 year of therapy (n = 3). The most frequent SAE was viral pneumonia (n = 8) resulting in one death due to a metapneumovirus infection in a 3 months old and a generalized adenovirus infection in a 28-month-old child. Sirolimus blood level at the time of SAEs ranged between 2.7 and 21 ng/L. Five patients were on antibiotic prophylaxis. CONCLUSIONS: Most SAEs are observed in the first year of sirolimus therapy; however, SAEs can also occur after a longer treatment period. SAEs are potentially life threatening, especially in early infancy. Presence of other risk factors, that is, underlying vascular anomaly or immune status, may contribute to the risk of SAEs. Sirolimus is an important therapeutic option for vascular anomalies, but patients and physicians need to be aware that adequate monitoring is necessary, especially in patients with complex lymphatic anomalies that are overrepresented in our cohort of SAEs.

Assessment of a novel NRAS in-frame tandem duplication causing a myelodysplastic/myeloproliferative neoplasm.

Myelodysplastic/myeloproliferative diseases of childhood cause a relevant disease burden, and many of these diseases may have a fatal course. The use of next-generation sequencing (NGS) has led to the identification of novel genetic variants in patients with these diseases, advancing our understanding of the underlying pathophysiology. However, novel mutations can often only be interpreted as variants of unknown significance (VUS), hindering adequate diagnosis and the use of a targeted therapy. To improve variant interpretation and test targeted therapies in a preclinical setting, we are using a rapid zebrafish embryo model that allows functional evaluation of the novel variant and possible therapeutic approaches within days. Thereby, we accelerate the translation from genetic findings to treatment options. Here, we establish this workflow on a novel in-frame tandem duplication in NRAS (c.192_227dup; p.G75_E76insDS65_G75) identified by Sanger sequencing in a 2.5-year-old patient with an unclassifiable myelodysplastic/myeloproliferative neoplasm (MDS/MPN-U). We show that this variant results in a myeloproliferative phenotype in zebrafish embryos with expansion of immature myeloid cells in the caudal hematopoietic tissue, which can be reversed by MEK inhibition. Thus, we could reclassify the variant from likely pathogenic to pathogenic using the American College of Medical Genetics (ACMG) criteria.

Extracranial Vascular Anomalies Driven by RAS/MAPK Variants: Spectrum and Genotype-Phenotype Correlations.

BACKGROUND: We aimed to correlate alterations in the rat sarcoma virus (RAS)/mitogen-activated protein kinase pathway in vascular anomalies to the clinical phenotype for improved patient and treatment stratification. METHODS AND RESULTS: This retrospective multicenter cohort study included 29 patients with extracranial vascular anomalies containing mosaic pathogenic variants (PVs) in genes of the RAS/mitogen-activated protein kinase pathway. Tissue samples were collected during invasive treatment or clinically indicated biopsies. PVs were detected by the targeted sequencing of panels of genes known to be associated with vascular anomalies, performed using DNA from affected tissue. Subgroup analyses were performed according to the affected genes with regard to phenotypic characteristics in a descriptive manner. Twenty-five vascular malformations, 3 vascular tumors, and 1 patient with both a vascular malformation and vascular tumor presented the following distribution of PVs in genes: Kirsten rat sarcoma viral oncogene (n=10), neuroblastoma ras viral oncogene homolog (n=1), Harvey rat sarcoma viral oncogene homolog (n=5), V-Raf murine sarcoma viral oncogene homolog B (n=8), and mitogen-activated protein kinase kinase 1 (n=5). Patients with RAS PVs had advanced disease stages according to the Schobinger classification (stage 3-4: RAS, 9/13 versus non-RAS, 3/11) and more frequent progression after treatment (RAS, 10/13 versus non-RAS, 2/11). Lesions with Kirsten rat sarcoma viral oncogene PVs infiltrated more tissue layers compared with the other PVs including other RAS PVs (multiple tissue layers: Kirsten rat sarcoma viral oncogene, 8/10 versus other PVs, 6/19). CONCLUSIONS: This comparison of patients with various PVs in genes of the RAS/MAPK pathway provides potential associations with certain morphological and clinical phenotypes. RAS variants were associated with more aggressive phenotypes, generating preliminary data and hypothesis for future larger studies.

Complex Lymphatic Anomalies: Report on a Patient Registry Using the Latest Diagnostic Guidelines.

Background: Generalized lymphatic anomaly (GLA), Gorham-Stout disease (GSD), kaposiform lymphangiomatosis (KLA), and central conducting lymphatic anomaly (CCLA) are rare, multisystem lymphatic disorders, referred to as complex lymphatic anomalies (CLAs). Their etiology remains poorly understood; however, somatic activating mutations have recently been discovered, and the results of targeted treatments are promising. This study aimed to elaborate on the phenotypic description of CLA. Methods: Thirty-six consecutive patients were recruited for the "GLA/GSD Registry" of the University Hospital of Freiburg, Germany (2015-2021). Clinical data were prospectively collected provided that a signed informed consent form was obtained. The latest proposed diagnostic guidelines were retrospectively applied. Results: Thirty-two patients (38% males) were included in the study; 15 GLA, 10 GSD, 3 KLA, and 4 CCLA patients were identified. Eighty-four percent already had symptoms by the age of 15 years. Osteolysis and periosseous soft-tissue infiltration were associated with GSD (p < 0.001 and p = 0.011, respectively), ascites and protein-losing enteropathy with CCLA (p = 0.007 and p = 0.004, respectively), and consumption coagulopathy with KLA (p = 0.006). No statistically significant differences were found in organ involvement, distribution of osteolytic lesions, number of affected bones and fractures. Twenty-five patients had complications; one patient with GLA died despite multimodal treatment. Spontaneous regression was seen in one patient with untreated KLA. Conclusions: CLA are rare, and their overlapping clinical presentations make differential diagnosis difficult. The characterization of our case series contributes to the phenotypic description and differentiation of these four clinical entities. A further understanding of their pathogenesis is crucial for evaluating targeted therapies and optimizing medical care.

The VASCERN-VASCA Working Group Diagnostic and Management Pathways for Venous Malformations.

To elaborate expert consensus patient pathways to guide patients and physicians toward efficient diagnostics and management of patients with venous malformations. Methods: VASCERN-VASCA (https://vascern.eu/) is a European network of multidisciplinary centers for Vascular Anomalies. The Nominal Group Technique was used to establish the pathways. Two facilitators were identified: one to propose initial discussion points and draw the pathways, and another to chair the discussion. A dermatologist (AD) was chosen as first facilitator due to her specific clinical and research experience. The draft was subsequently discussed within VASCERN-VASCA monthly virtual meetings and annual face-to-face meetings. Results: The Pathway starts from the clinical suspicion of a venous type malformation (VM) and lists the clinical characteristics to look for to support this suspicion. Strategies for subsequent imaging and histopathology are suggested. These aim to inform on the diagnosis and to separate the patients into 4 subtypes: (1) sporadic single VMs or (2) multifocal, (3) familial, multifocal, and (4) combined and/or syndromic VMs. The management of each type is detailed in subsequent pages of the pathway, which are color coded to identify sections on (1) clinical evaluations, (2) investigations, (3) treatments, and (4) associated genes. Actions relevant to all types are marked in separate boxes, including when imaging is recommended. When definite diagnoses have been reached, the pathway also points toward disease-specific additional investigations and recommendations for follow up. Options for management are discussed for each subtype, including conservative and invasive treatments, as well as novel molecular therapies. Conclusion: The collaborative efforts of VASCERN-VASCA, a network of the 9 Expert Centers, has led to a consensus Diagnostic and Management Pathways for VMs to assist clinicians and patients. It also emphasizes the role of multidisciplinary expert centers in the management of VM patients. This pathway will become available on the VASCERN website (http://vascern.eu/).

5-alpha-reductase type I (SRD5A1) is up-regulated in non-small cell lung cancer but does not impact proliferation, cell cycle distribution or apoptosis.

BACKGROUND: Non-small cell lung cancer (NSCLC) is one of the most frequent malignancies and has a high mortality rate due to late detection and lack of efficient treatments. Identifying novel drug targets for this indication may open the way for new treatment strategies. Comparison of gene expression profiles of NSCLC and normal adjacent tissue (NAT) allowed to determine that 5-alpha-reductase type I (SRD5A1) was up-regulated in NSCLC compared to NAT. This raised the question whether SRD5A1 was involved in sustained proliferation and survival of NSCLC. METHODS: siRNA-mediated silencing of SRD5A1 was performed in A549 and NCI-H460 lung cancer cell lines in order to determine the impact on proliferation, on distribution during the different phases of the cell cycle, and on apoptosis/necrosis. In addition, lung cancer cell lines were treated with 4-azasteroids, which specifically inhibit SRD5A1 activity, and the effects on proliferation were measured. Statistical analyses using ANOVA and post-hoc Tamhane-T2-test were performed. In the case of non-parametric data, the Kruskal-Wallis test and the post-hoc Mann-Whitney-U-test were used. RESULTS: The knock-down of SRDA51 expression was very efficient with the SRD5A1 transcripts being reduced to 10% of control levels. Knock-down efficiency was furthermore confirmed at the protein level. However, no effect of SRD5A1 silencing was observed in the proliferation assay, the cell cycle analysis, and the apoptosis/necrosis assay. Treatment of lung cancer cell lines with 4-azasteroids did not significantly inhibit proliferation. CONCLUSIONS: In summary, the results suggest that SRD5A1 is not a crucial enzyme for the sustained proliferation of NSCLC cell lines.

Comprehensive Analyses of Coagulation Parameters in Patients with Vascular Anomalies.

BACKGROUND: Vascular anomalies comprise a diverse group of rare diseases with altered blood flow and are often associated with coagulation disorders. The most common example is a localized intravascular coagulopathy in venous malformations leading to elevated D-dimers. In severe cases, this may progress to a disseminated intravascular coagulopathy with subsequent consumption of fibrinogen and thrombocytes predisposing to serious bleeding. A separate coagulopathy is the Kasabach-Merritt phenomenon in kaposiform hemangioendothelioma characterized by platelet trapping leading to thrombocytopenia and eventually consumptive coagulopathy. Our previous work showed impaired von Willebrand factor and platelet aggregometry due to abnormal blood flow, i.e., in ventricular assist devices or extracorporeal membrane oxygenation. With altered blood flow also present in vascular anomalies, we hypothesized that, in particular, the von Willebrand factor parameters and the platelet function may be similarly impacted. METHODS: We prospectively recruited 73 patients with different vascular anomaly entities and analyzed their coagulation parameters. RESULTS: Acquired von Willebrand syndrome was observed in both of our patients with Kasabach-Merritt phenomenon. In six out of nine patients with complex lymphatic anomalies, both the vWF antigen and activity were upregulated. Platelet aggregometry was impaired in both patients with Kasabach-Merritt phenomenon and in seven out of eight patients with an arteriovenous malformation. CONCLUSIONS: The analysis of coagulation parameters in our patients with vascular anomalies advanced our understanding of the underlying pathophysiologies of the observed coagulopathies. This may lead to new treatment options for the, in part, life-threatening bleeding risks in these patients in the future.

The VASCERN-VASCA working group diagnostic and management pathways for lymphatic malformations.

Lymphatic malformations (LMs) are developmental defects of lymphatic vessels. LMs are histologically benign lesions, however, due to localization, size, and unexpected swelling, they may cause serious complications that threaten vital functions such as compression of the airways. A large swelling of the face or neck may also be disfiguring and thus constitute a psychological strain for patients and their families. LMs are also highly immunologically reactive, and are prone to recurrent infections and inflammation causing pain as well as chronic oozing wounds. The European Reference Network on Rare Multisystemic Vascular Diseases (VASCERN) is dedicated to gathering the best expertise in Europe. There are only few available guidelines on management and follow up of LMs, which commonly focus on very specific situations, such as head and neck LM (Zhou et al., 2011). It is still unclear, what constitutes an indication for treatment of LMs and how to follow up the patients. The Vascular Anomalies Working Group (VASCA-WG) of VASCERN decided to develop a diagnostic and management pathway for the management of LMs with a Nominal Group Technique (NGT), a well-established, structured, multistep, facilitated group meeting technique used to generate consensus statements. The pathway was drawn following 2 face-to-face meetings and multiple web meetings to facilitate discussion, and by mail to avoid the influence of most authoritative members. The VASCA-WG has produced this opinion statement reflecting strategies developed by experts and patient representatives on how to approach patients with lymphatic malformations in a practical manner; we present an algorithmic view of the results of our work.

The VASCERN-VASCA working group diagnostic and management pathways for severe and/or rare infantile hemangiomas.

The European Reference Network on Rare Multisystemic Vascular Diseases (VASCERN), is dedicated to gathering the best expertise in Europe and provide accessible cross-border healthcare to patients with rare vascular diseases. Infantile Hemangiomas (IH) are benign vascular tumors of infancy that rapidly growth in the first weeks of life, followed by stabilization and spontaneous regression. In rare cases the extent, the localization or the number of lesions may cause severe complications that need specific and careful management. Severe IH may be life-threatening due to airway obstruction, liver or cardiac failure or may harbor a risk of functional impairment, severe pain, and/or significant and permanent disfigurement. Rare IHs include syndromic variants associated with extracutaneous abnormalities (PHACE and LUMBAR syndromes), and large segmental hemangiomas. There are publications that focus on evidence-based medicine on propranolol treatment for IH and consensus statements on the management of rare infantile hemangiomas mostly focused on PHACES syndrome. The Vascular Anomalies Working Group (VASCA-WG) decided to develop a diagnostic and management pathway for severe and rare IHs with a Nominal Group Technique (NGT), a well-established, structured, multistep, facilitated group meeting technique used to generate consensus statements. The pathway was drawn following two face-to-face meetings and in multiple web meetings to facilitate discussion, and by mail to avoid the influence of most authoritative members. The VASCA-WG has produced this opinion statement reflecting strategies developed by experts and patient representatives on how to approach patients with severe and rare IH in a practical manner; we present an algorithmic view of the results of our work.

Efficacy of Sirolimus in Patients Requiring Tracheostomy for Life-Threatening Lymphatic Malformation of the Head and Neck: A Report From the European Reference Network.

Extensive lymphatic malformations (LMs) of the head and neck region may require tracheostomy to secure the airway. Treatment of these life-threatening LMs is usually multimodal and includes sclerotherapy and surgery, among others. Recently, systemic therapy with sirolimus has been introduced as an effective treatment for venous and lymphatic malformations; its efficacy and safety profile in patients with extensive LM requiring tracheostomy are, however, as yet not fully known. We performed a retrospective, multicenter review and identified 13 patients with an extensive LM of the head and neck region, who previously underwent placement of tracheostomy and subsequently received sirolimus treatment with the aim to improve the local respiratory situation and remove the tracheostomy. Under sirolimus therapy, tracheostomy could be reversed in 8/13 (62%) patients, a further 2/13 (15%) patients improved markedly, and removal of the tracheostomy was planned at the time of writing, while 3/13 (23%) patients showed insufficient or absent response to sirolimus, rendering tracheostomy reversal not feasible. The median duration of sirolimus treatment until removal of tracheostomy was 18 months (range, 8 months to 5.6 years). Adverse events of sirolimus therapy were common [10/13 (77%) patients], yet the majority of these were mild [9/10 (90%) patients] and only one severe adverse event was recorded, with ulceration and necrosis at a catheter insertion site. In conclusion, sirolimus can be considered an effective and safe salvage treatment in patients with extensive LM even after placement of a tracheostomy, as closure of the latter was possible in the majority of patients (62%) of our retrospective cohort. A better understanding of when to start sirolimus therapy, of the duration of treatment, and of factors allowing the prediction of treatment response will require further investigation.

A distinct CD38+CD45RA+ population of CD4+, CD8+, and double-negative T cells is controlled by FAS.

The identification and characterization of rare immune cell populations in humans can be facilitated by their growth advantage in the context of specific genetic diseases. Here, we use autoimmune lymphoproliferative syndrome to identify a population of FAS-controlled TCRαß+ T cells. They include CD4+, CD8+, and double-negative T cells and can be defined by a CD38+CD45RA+T-BET- expression pattern. These unconventional T cells are present in healthy individuals, are generated before birth, are enriched in lymphoid tissue, and do not expand during acute viral infection. They are characterized by a unique molecular signature that is unambiguously different from other known T cell differentiation subsets and independent of CD4 or CD8 expression. Functionally, FAS-controlled T cells represent highly proliferative, noncytotoxic T cells with an IL-10 cytokine bias. Mechanistically, regulation of this physiological population is mediated by FAS and CTLA4 signaling, and its survival is enhanced by mTOR and STAT3 signals. Genetic alterations in these pathways result in expansion of FAS-controlled T cells, which can cause significant lymphoproliferative disease.

A metabolic interplay coordinated by HLX regulates myeloid differentiation and AML through partly overlapping pathways.

The H2.0-like homeobox transcription factor (HLX) regulates hematopoietic differentiation and is overexpressed in Acute Myeloid Leukemia (AML), but the mechanisms underlying these functions remain unclear. We demonstrate here that HLX overexpression leads to a myeloid differentiation block both in zebrafish and human hematopoietic stem and progenitor cells (HSPCs). We show that HLX overexpression leads to downregulation of genes encoding electron transport chain (ETC) components and upregulation of PPARδ gene expression in zebrafish and human HSPCs. HLX overexpression also results in AMPK activation. Pharmacological modulation of PPARδ signaling relieves the HLX-induced myeloid differentiation block and rescues HSPC loss upon HLX knockdown but it has no effect on AML cell lines. In contrast, AMPK inhibition results in reduced viability of AML cell lines, but minimally affects myeloid progenitors. This newly described role of HLX in regulating the metabolic state of hematopoietic cells may have important therapeutic implications.

Generation of vascular endothelial and smooth muscle cells from human pluripotent stem cells.

The use of human pluripotent stem cells for in vitro disease modelling and clinical applications requires protocols that convert these cells into relevant adult cell types. Here, we report the rapid and efficient differentiation of human pluripotent stem cells into vascular endothelial and smooth muscle cells. We found that GSK3 inhibition and BMP4 treatment rapidly committed pluripotent cells to a mesodermal fate and subsequent exposure to VEGF-A or PDGF-BB resulted in the differentiation of either endothelial or vascular smooth muscle cells, respectively. Both protocols produced mature cells with efficiencies exceeding 80% within six days. On purification to 99% via surface markers, endothelial cells maintained their identity, as assessed by marker gene expression, and showed relevant in vitro and in vivo functionality. Global transcriptional and metabolomic analyses confirmed that the cells closely resembled their in vivo counterparts. Our results suggest that these cells could be used to faithfully model human disease.