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Cerebral cavernous malformation (CCM) is a neurovascular disease distinguished by clusters of leaky, mulberry-like blood vessels. KRIT1 bi-allelic loss-of-function mutations in endothelial cells are known to trigger brain cavernomas; however, human preclinical models are needed to unveil the importance of germline KRIT1 heterozygous mutations in CCM pathogenesis. We generated three induced pluripotent stem cells (iPSCs) from patients with CCM with hereditary KRIT1 heterozygous mutations. Patient-derived vascularized organoids exhibited intricate and abnormal vascular structures with cavernoma-like morphology, and iPSC-derived endothelial cells displayed phenotypic abnormalities at the junctional and transcriptional levels. Upon injection into brain explants, CCM endothelial cells integrated into the normal vasculature and created vascular anomalies. Lastly, transcriptional analysis showed that the endothelial progenitor marker paternally expressed gene 3 (PEG3) was highly expressed in iPSC-derived CCM endothelial cells, and this was further confirmed in familial and sporadic cavernoma biopsies. Overall, our study sheds light on the molecular consequence of KRIT1 heterozygous mutations in endothelial cells and the potential implications in cavernoma pathogenesis.

Background

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults, characterized by aggressive growth and a dismal prognosis. Interleukin-33 (IL-33) and its receptor ST2 have emerged as regulators of glioma growth, but their exact function in tumorigenesis has not been deciphered. Indeed, previous studies on IL-33 in cancer have yielded somewhat opposing results as to whether it is pro- or anti-tumorigenic.

Methods

IL-33 expression was assessed in a GBM tissue microarray and public databases. As in vivo models we used orthotopic xenografts of patient-derived GBM cells, and syngenic models with grafted mouse glioma cells.

Results

We analyzed the role of IL-33 and its receptor ST2 in nonmalignant cells of the glioma microenvironment and found that IL-33 levels are increased in cells surrounding the tumor. Protein complexes of IL-33 and ST2 are mainly found outside of the tumor core. The IL-33-producing cells consist primarily of oligodendrocytes. To determine the function of IL-33 in the tumor microenvironment, we used mice lacking the ST2 receptor. When glioma cells were grafted to ST2-deficient mouse brains, the resulting tumors exhibited a more invasive growth pattern, and are associated with poorer survival, compared to wild-type mice. Tumors in ST2-deficient hosts are more invasive, with increased expression of extracellular matrix remodeling enzymes and enhanced tumor angiogenesis. Furthermore, the absence of ST2 leads to a more immunosuppressive environment.

Conclusions

Our findings reveal that glia-derived IL-33 and its receptor ST2 participate in modulating tumor invasiveness, tumor vasculature, and immunosuppression in glioma.

T cells can exchange parts of their plasma membrane along with membraneassociated proteins through trogocytosis. During trogocytosis only certain subsets of membrane-associated proteins seem to be exchanged suggesting a finetuned mechanism regulating the selection of what can be transferred. In this review, we describe potential models of trogocytosis and discuss mechanisms that could regulate this process in T cells. Additionally, we delve into how exchanged proteins polarize on the surface of recipient cells, discuss how trogocytosis allows T cells to acquire new functions, and summarize ways to modulate this process in T cells. Understanding trogocytosis can help us better understand the immune response and develop more effective immunotherapies.

Trogocytosis is an exchange of membrane-associated molecules between cells that can either halt or boost immune responses. However, the mechanism that regulates trogocytosis in T cells and its consequences are not yet clear. Here, we demonstrate that T cells can exchange chimeric antigen receptors (CARs) by trogocytosis, thereby arming recipient T cells with the capacity to respond to tumor antigens by up-regulating proteins associated with a cytotoxic response and killing of target cells. We demonstrate that although trogocytosis is dependent on cell-cell contact, the exchange of a specific cell membrane protein does not require a cognate binding partner on the surface of recipient cells. Instead, the probability that a protein is exchanged by trogocytosis is determined by its transmembrane domain. This finding opens new avenues for modulating this process in CAR-T cells.

Compromised vascular integrity facilitates extravasation of cancer cells and promotes metastatic dissemination. CD93 has emerged as a target for antiangiogenic therapy, but its importance for vascular integrity in metastatic cancers has not been evaluated. Here, we demonstrate that CD93 participates in maintaining the endothelial barrier and reducing metastatic dissemination. Primary melanoma growth was hampered in CD93^–/– mice, but metastatic dissemination was increased and associated with disruption of adherens and tight junctions in tumor endothelial cells and elevated expression of matrix metalloprotease 9 at the metastatic site. CD93 directly interacted with vascular endothelial growth factor receptor 2 (VEGFR2) and its absence led to VEGF-induced hyperphosphorylation of VEGFR2 in endothelial cells. Antagonistic anti-VEGFR2 antibody therapy rescued endothelial barrier function and reduced the metastatic burden in CD93^–/– mice to wild-type levels. These findings reveal a key role of CD93 in maintaining vascular integrity, which has implications for pathological angiogenesis and endothelial barrier function in metastatic cancer.

The blood-brain barrier (BBB) serves as a crucial vascular specialization, shielding and nourishing brain neurons and glia while impeding drug delivery. Here, we conducted single-cell mRNA sequencing of human cerebrovascular cells from 13 surgically resected glioma samples and adjacent normal brain tissue. The transcriptomes of 103,230 cells were mapped, including 57,324 endothelial cells (ECs) and 27,703 mural cells (MCs). Both EC and MC transcriptomes originating from lower-grade glioma were indistinguishable from those of normal brain tissue, whereas transcriptomes from glioblastoma (GBM) displayed a range of abnormalities. Among these, we identified LOXL2-dependent collagen modification as a common GBM-dependent trait and demonstrated that inhibiting LOXL2 enhanced chemotherapy efficacy in both murine and human patient-derived xenograft (PDX) GBM models. Our comprehensive single-cell RNA sequencing-based molecular atlas of the human BBB, coupled with insights into its perturbations in GBM, holds promise for guiding future investigations into brain health, pathology, and therapeutic strategies.

Brain metastases are clinically challenging due to the unique brain microenvironment. In this issue of Cancer Cell, Bejarano et al. use transcriptional profiling and data integration to shed light on the molecular and cellular composition of the vasculature in brain metastases, identifying CD276 as an immunomodulatory target for therapy.

Semliki Forest virus (SFV) is a neuropathogenic alphavirus which is of interest both as a model neurotropic alphavirus and as an oncolytic virus with proven potency in preclinical cancer models. In laboratory mice, peripherally administered SFV infiltrates the central nervous system (CNS) and causes encephalitis of varying severity. The route of SFV CNS entrance is poorly understood but has been considered to occur through the blood-brain barrier. Here we show that neuroinvasion of intravenously administered SFV is strictly dependent on very-low-density-lipoprotein receptor (VLDLR) which acts as an entry receptor for SFV. Moreover, SFV primarily enters the CNS through the blood-cerebrospinal fluid (B-CSF) barrier via infecting choroid plexus epithelial cells which show distinctly high expression of VLDLR. This is the first indication of neurotropic alphavirus utilizing choroid plexus for CNS entry, and VLDLR playing a specific and crucial role for mediating SFV entry through this pathway.

Regulation of vascular permeability to plasma is essential for tissue and organ homeostasis and is mediated by endothelial cell-to-cell junctions that tightly regulate the trafficking of molecules between blood and tissue. The single-pass transmembrane glycoprotein CD93 is upregulated in endothelial cells during angiogenesis and controls cytoskeletal dynamics. However, its role in maintaining homeostasis by regulating endothelial barrier function has not been elucidated yet. Here, we demonstrate that CD93 interacts with vascular endothelial (VE)-cadherin and limits its phosphorylation and turnover. CD93 deficiency in vitro and in vivo induces phosphorylation of VE-cadherin under basal conditions, displacing it from endothelial cell–cell contacts. Consistent with this, endothelial junctions are defective in CD93^−/− mice, and the blood–brain barrier permeability is enhanced. Mechanistically, CD93 regulates VE-cadherin phosphorylation and turnover at endothelial junctions through the Rho/Rho kinase-dependent pathway. In conclusion, our results identify CD93 as a key regulator of VE-cadherin stability at endothelial junctions, opening up possibilities for therapeutic strategies directed to control vascular permeability.

Chimeric antigen receptor (CAR)-T cell therapy is rapidly advancing as cancer treatment, however, designing an optimal CAR remains challenging. A single-chain variable fragment (scFv) is generally used as CAR targeting moiety, wherein the complementarity-determining regions (CDRs) define its specificity. We report here that the CDR loops can cause CAR clustering, leading to antigen-independent tonic signalling and subsequent CAR-T cell dysfunction. We show via CARs incorporating scFvs with identical framework and varying CDR sequences that CARs may cluster on the T cell surface, which leads to antigen-independent CAR-T cell activation, characterized by increased cell size and interferon (IFN)-& gamma; secretion. This results in CAR-T cell exhaustion, activation-induced cell death and reduced responsiveness to target-antigen-expressing tumour cells. CDR mutagenesis confirms that the CAR-clustering is mediated by CDR-loops. In summary, antigen-independent tonic signalling can be induced by CDR-mediated CAR clustering, which could not be predicted from the scFv sequences, but could be tested for by evaluating the activity of unstimulated CAR-T cells.