All-trans retinoic acid induces durable tumor immunity in IDH-mutant gliomas by rescuing transcriptional repression of the CRBP1-retinoic acid axis

Diffuse gliomas are epigenetically dysregulated, immunologically cold, and fatal tumors characterized by mutations in isocitrate dehydrogenase (IDH). Although IDH mutations yield a uniquely immunosuppressive tumor microenvironment, the regulatory mechanisms that drive the immune landscape of IDH mutant (IDHm) gliomas remain unknown. Here, we reveal that transcriptional repression of retinoic acid (RA) pathway signaling impairs both innate and adaptive immune surveillance in IDHm glioma through epigenetic silencing of retinol binding protein 1 (RBP1) and induces a profound anti-inflammatory landscape marked by loss of inflammatory cell states and infiltration of suppressive myeloid phenotypes. Restorative retinoic acid therapy in murine glioma models promotes clonal CD4 + T cell expansion and induces tumor regression in IDHm, but not IDH wildtype (IDHwt), gliomas. Our findings provide a mechanistic rationale for RA immunotherapy in IDHm glioma and is the basis for an ongoing investigator-initiated, single-center clinical trial investigating all-trans retinoic acid (ATRA) in recurrent IDHm human subjects.

A longitudinal single-cell and spatial multiomic atlas of pediatric high-grade glioma

Pediatric high-grade glioma (pHGG) is an incurable central nervous system malignancy that is a leading cause of pediatric cancer death. While pHGG shares many similarities to adult glioma, it is increasingly recognized as a molecularly distinct, yet highly heterogeneous disease. In this study, we longitudinally profiled a molecularly diverse cohort of 16 pHGG patients before and after standard therapy through single-nucleus RNA and ATAC sequencing, whole-genome sequencing, and CODEX spatial proteomics to capture the evolution of the tumor microenvironment during progression following treatment. We found that the canonical neoplastic cell phenotypes of adult glioblastoma are insufficient to capture the range of tumor cell states in a pediatric cohort and observed differential tumor-myeloid interactions between malignant cell states. We identified key transcriptional regulators of pHGG cell states and did not observe the marked proneural to mesenchymal shift characteristic of adult glioblastoma. We showed that essential neuromodulators and the interferon response are upregulated post-therapy along with an increase in non-neoplastic oligodendrocytes. Through in vitro pharmacological perturbation, we demonstrated novel malignant cell-intrinsic targets. This multiomic atlas of longitudinal pHGG captures the key features of therapy response that support distinction from its adult counterpart and suggests therapeutic strategies which are targeted to pediatric gliomas.

Outcomes and Treatment Algorithm in Glioblastoma Patients 80 Years and Older

OBJECTIVE

The current standard of care for patients with glioblastoma (GBM) is maximal safe resection followed by adjuvant radiation therapy with concurrent temozolomide chemotherapy. Previous studies that identified this treatment regimen focused on younger patients with GBM. The proportion of patients with GBM over the age of 80 years is increasing. We investigate whether elderly patients benefit from the current standard of care with additional maximal safe resection.

METHODS

Clinical, operative, radiographic, demographic, genetic, and outcomes data were retrospectively collected for patients treated for histologically confirmed World Health Organization grade 4 GBM at University of Pittsburgh Medical Center from 2009 to 2020. Only patients 80 years and older were included (n = 123). Statistically significant values were set at P < 0.05.

RESULTS

A univariate Cox proportional hazards analysis of GBM patients aged >80 years identified the use of temozolomide, radiation, Karnofsky Performance Status (KPS) > 70, and methylguanine DNA methyltransferase methylation with increased overall survival (OS). Further multivariate Cox proportional hazards model analysis showed that the variables identified in the univariate analysis passed multicollinearity testing, and that use of temozolomide, KPS >70, and gross total resection were shown to significantly impact survival. Survival analysis showed that patients with biopsy alone had a shorter median OS compared with patients who received resection, temozolomide, and radiation (P < 0.0001, median OS 1.6 vs. 7.5 months). Additionally, patients who underwent biopsy and then received temozolomide and radiation had a shorter median OS when compared with patients who received resection, temozolomide, and radiation (P = 0.0047, median OS 3.6 vs. 7.5 months).

CONCLUSIONS

For elderly patients with KPS >70, GTR followed by radiation and temozolomide is associated with maximum OS.

Genetically modified IL2 bone-marrow-derived myeloid cells reprogram the glioma immunosuppressive tumor microenvironment

Gliomas are one of the leading causes of cancer-related death in the adolescent and young adult (AYA) population. Two-thirds of AYA glioma patients are affected by low-grade gliomas (LGGs), but there are no specific treatments. Malignant progression is supported by the immunosuppressive stromal component of the tumor microenvironment (TME) exacerbated by M2 macrophages and a paucity of cytotoxic T cells. A single intravenous dose of engineered bone-marrow-derived myeloid cells that release interleukin-2 (GEMys-IL2) was used to treat mice with LGGs. Our results demonstrate that GEMys-IL2 crossed the blood-brain barrier, infiltrated the TME, and reprogrammed the immune cell composition and transcriptome. Moreover, GEMys-IL2 extended survival in an LGG immunocompetent mouse model. Here, we report the efficacy of an in vivo approach that demonstrates the potential for a cell-mediated innate immunotherapy designed to enhance the recruitment of activated effector T and natural killer cells within the glioma TME.

Distinguishing Progression from Pseudoprogression in Glioblastoma Using 18F-Fluciclovine PET

Rationale: Accurate differentiation between tumor progression (TP) and pseudoprogression remains a critical unmet need in neuro-oncology. ¹⁸F-fluciclovine is a widely available synthetic amino acid PET radiotracer. In this study, we aimed to assess the value of ¹⁸F-fluciclovine PET for differentiating pseudoprogression from TP in a prospective cohort of patients with suspected radiographic recurrence of glioblastoma. Methods: We enrolled 30 glioblastoma patients with radiographic progression after first-line chemoradiotherapy who were planned for surgical resection. Patients underwent pre-operative ¹⁸F-fluciclovine PET and MRI. Relative percentages of viable tumor and therapy-related changes observed in histopathology were quantified and categorized as TP (≥50% viable tumor), mixed TP (<50% and >10% viable tumor), or pseudoprogression (≤10% viable tumor). Results: Eighteen patients had TP, 4 mixed TP, and 8 pseudoprogression. Patients with TP/mixed TP had significantly higher 40-50 minutes SUV_max (6.64+ 1.88 vs 4.11± 1.52, P = 0.009) compared to patients with pseudoprogression. A 40-50 minutes SUV_max cut-off of 4.66 provided 90% sensitivity and 83% specificity for differentiation of TP/mixed TP from pseudoprogression (Area under the curve (AUC)=0.86). Relative cerebral blood volume (rCBVmax) cut-off 3.672 provided 90% sensitivity and 71% specificity for differentiation of TP/mixed TP from Pseudoprogression (AUC=0.779). Combining a 40-50 minutes SUV_max cut-off of 4.66 and a rCBVmax cut-off of 3.67 on MRI provided 100% sensitivity and 80% specificity for differentiating TP/mixed TP from Pseudoprogression (AUC=0.95). Conclusion: ¹⁸F-fluciclovine PET uptake can accurately differentiate pseudoprogression from TP in glioblastoma, with even greater accuracy when combined with multi-parametric MRI. Given the wide availability of ¹⁸F-fluciclovine, larger, multicenter studies are warranted to determine whether amino acid PET with ¹⁸F-fluciclovine should be used in the routine assessment of post-treatment glioblastoma.

Risk of intracranial hemorrhage with direct oral anticoagulants vs low molecular weight heparin in glioblastoma: A retrospective cohort study

BACKGROUND

Glioblastoma (GBM) is associated with a high incidence of venous thromboembolism (VTE), but there are little data to guide anticoagulation in patients with GBM, in whom the risks of VTE must be balanced against the risk of intracranial hemorrhage (ICH).

METHODS

We performed a single-institution retrospective cohort study of patients with GBM diagnosed with VTE from 2014 to 2021 who were treated with low molecular weight heparin (LMWH) or a direct oral anticoagulant (DOAC). The incidence of ICH was compared between the LMWH and DOAC groups. The primary outcome was clinically relevant ICH within the first 30 days of anticoagulation, defined as any ICH that was fatal, symptomatic, required surgical intervention, and/or led to cessation of anticoagulation. Secondary outcomes included clinically relevant ICH within 6 months, fatal ICH within 30 days and 6 months, and any bleeding within 30 days and 6 months.

RESULTS

One hundred twenty-one patients were identified in the cohort for 30-day outcome analyses (DOAC, n = 33; LMWH, n = 88). For 6-month outcome analyses, the cohort included only patients who were maintained on their initial anticoagulant (DOAC, n = 32; LMWH, n = 75). The incidence of clinically relevant ICH at 30 days was 0% in the DOAC group and 9% in the LMWH group (P = .11). The cumulative incidence of clinically relevant ICH at 6 months was 0% in the DOAC group and 24% in the LMWH group (P = .001), with 4 fatal ICHs in the LMWH group.

CONCLUSIONS

DOACs are associated with a lower incidence of clinically relevant ICH in patients with GBM-associated VTE compared to LMWH.

Loss of MAT2A compromises methionine metabolism and represents a vulnerability in H3K27M mutant glioma by modulating the epigenome

Diffuse midline gliomas (DMGs) bearing driver mutations of histone 3 lysine 27 (H3K27M) are incurable brain tumors with unique epigenomes. Here, we generated a syngeneic H3K27M mouse model to study the amino acid metabolic dependencies of these tumors. H3K27M mutant cells were highly dependent on methionine. Interrogating the methionine cycle dependency through a short-interfering RNA screen identified the enzyme methionine adenosyltransferase 2A (MAT2A) as a critical vulnerability in these tumors. This vulnerability was not mediated through the canonical mechanism of MTAP deletion; instead, DMG cells have lower levels of MAT2A protein, which is mediated by negative feedback induced by the metabolite decarboxylated S-adenosyl methionine. Depletion of residual MAT2A induces global depletion of H3K36me3, a chromatin mark of transcriptional elongation perturbing oncogenic and developmental transcriptional programs. Moreover, methionine-restricted diets extended survival in multiple models of DMG in vivo. Collectively, our results suggest that MAT2A presents an exploitable therapeutic vulnerability in H3K27M gliomas.

Matched analysis of patient gender and meningioma resection outcomes

PURPOSE

Gender is a known social determinant of health (SDOH) that has been linked to neurosurgical outcome disparities. To improve quality of care, there exists a need to investigate the impact of gender on procedure-specific outcomes. The objective of this study was to assess the role of gender on short- and long-term outcomes following resection of meningiomas - the most common benign brain neoplasm of adulthood - between exact matched patient cohorts.

MATERIAL AND METHODS

All consecutive patients undergoing supratentorial meningioma resection (n = 349) at a single, university-wide health system over a 6-year period were analyzed retrospectively. Coarsened exact matching was employed to match patients on numerous key characteristics related to outcomes. Primary outcomes included readmission, ED visit, reoperation, and mortality within 30 and 90 days of surgery. Mortality and reoperation were also assessed during the entire follow-up period. Outcomes were compared between matched female and male cohorts.

RESULTS

Between matched cohorts, no significant difference was observed in morbidity or mortality at 30 days (p = 0.42-0.75), 90-days (p = 0.23-0.69), or throughout the follow-up period (p = 0.22-0.45). Differences in short-term mortality could not be assessed due to the low number of mortality events.

CONCLUSIONS

After matching on characteristics known to impact outcomes and when isolated from other SDOHs, gender does not independently affect morbidity and mortality following meningioma resection. Further research on the role of other SDOHs in this population is merited to better understand underlying drivers of disparity.

A Novel 5-Aminolevulinic Acid-Enabled Surgical Loupe System-A Consecutive Brain Tumor Series of 11 Cases

BACKGROUND

The concept of maximally safe resection (MSR) has been shown to improve clinical outcomes in the treatment of high-grade gliomas (HGGs). To achieve MSR, surgical adjuncts such as functional imaging, neuronavigation, intraoperative mapping, ultrasound, and fluorescence-guided surgery are routinely used. 5-Aminolevulinic acid (5-ALA) is an oral agent that has been increasingly adopted in fluorescence-guided resection of HGG. In randomized clinical trials of 5-ALA, it has been shown to increase the extent of resection and progression-free survival in HGG. Current commercially available 5-ALA detection systems are all microscope-based and can sometimes be cumbersome to use.

OBJECTIVE

To present our experience using a novel 5-ALA-enabled surgical loupe system.

METHODS

5-ALA-enabled loupes were used in 11 consecutive patients with either suspected HGG on magnetic resonance imaging or recurrence of known lesions. Lesion appearance was examined under white light, 5-ALA loupes, and a 5-ALA microscope. Tumor specimens were checked for fluorescence and sent for pathologic examination.

RESULTS

In our experience, a 5-ALA-enabled surgical loupe system offers excellent visualization of 5-ALA in patients with HGG. In 10 of 11 patients, fluorescent tissue was confirmed to be high-grade glioma by pathology. In 1 patient, tissue was not fluorescent, and final pathology was World Health Organization grade I meningioma.

CONCLUSION

A 5-ALA-enabled surgical loupe system offers excellent intraoperative visualization of 5-ALA fluorescence in HGG and can be a viable surgical adjunct for achieving MSR of HGG.

A liquid fraction of extracellular matrix inhibits glioma cell viability in vitro and in vivo

Suppressive effects of extracellular matrix (ECM) upon various cancers have been reported. Glioblastoma multiforme has poor prognosis and new therapies are desired. This work investigated the effects of a saline-soluble fraction of urinary bladder ECM (ECM-SF) upon glioma cells. Viability at 24 hours in 1, 5, or 10 mg/mL ECM-SF-spiked media was evaluated in primary glioma cells (0319, 1015, 1119), glioma cell lines (A172, T98G, U87MG, C6), and brain cell lines (HCN-2, HMC3). Viability universally decreased at 5 and 10 mg/mL with U87MG, HCN-2, and HCM3 being least sensitive. Apoptosis in 0319 and 1119 cells was confirmed via NucView 488. Bi-weekly intravenous injection of ECM-SF (120 mg/kg) for 10 weeks in Sprague-Dawley rats did not affect weight, temperature, complete blood count, or multi-organ histology (N = 5). Intratumoral injection of ECM-SF (10 uL of 30 mg/mL) at weeks 2–4 post C6 inoculation in Wistar rats increased median survival from 24.5 to 51 days (hazard ratio for death 0.22) and decreased average tumor volume at time of death from 349 mm³ to 90 mm³ over 10 weeks (N = 6). Mass spectrometry identified 2,562 protein species in ECM-SF, parent ECM, and originating tissue. These results demonstrate the suppressive effects of ECM on glioma and warrant further study.

Percutaneous fixation for the treatment of metastatic spinal disease provides effective symptom palliation with low rates of hardware failure

Background:

The incidence of survival from metastatic spinal disease (MSD) continues to rise. However, open surgery for MSD is associated with significant perioperative morbidity, while minimally invasive percutaneous pedicle screw fixation (MIPPSF) offers reduced tissue trauma, less blood loss, and a reduction in complications. Lytic bone disease plus perioperative radiation further increase risk for instrument failure, especially in long construct MIPPSF. Here, we compared 6 short construct and 14 long construct outcomes for MIPPSF performed in MSD patients, including multiple myeloma (MM).

Methods:

For 20 patients undergoing MIPPSF for MSD, we evaluated disease type, location, the extent of surgery, outcomes, and survival rates. Statistical comparisons were performed between long-segment construct and short-segment construct patients utilizing Kaplan–Meier survival curves, Mann–Whitney U, and Chi-squared tests.

Results:

No instrument failure and comparable symptomatic relief were observed for both short and long MIPPSF constructs. However, long construct patients experienced; a higher incidence of postoperative complications, including screw loosening, but exhibited longer overall survivals (likely related to underlying type of MSD, with MM patients making up the largest portion of long construct patients).

Conclusion:

Long construct MIPPSF in MSD did not have increased risk of construct failure and offered effective symptomatic relief, including for MM patients, without introducing a greater risk construct instability.

In vivo efficacy of decitabine as a natural killer cell-mediated immunotherapy against isocitrate dehydrogenase mutant gliomas

OBJECTIVE

Isocitrate dehydrogenase (IDH) mutations are found in more than 80% of low-grade gliomas and in the majority of secondary glioblastomas. IDH mutation (IDHmut) leads to aberrant production of an oncogenic metabolite that promotes epigenetic dysregulation by inducing hypermethylation to suppress transcription of various tumor suppressor genes. Hypermethylation in IDHmut gliomas leads to transcriptional repression of NKG2D ligands, especially UL16-binding protein (ULBP)-1 and ULBP-3, and subsequent evasion of natural killer (NK) cell-mediated lysis. The demethylating agent 5-aza-2'deoxycytodine (decitabine [DAC]) is a DNA methyltransferase 1 inhibitor that prevents hypermethylation and is capable of restoring NKG2D ligand expression in IDHmut gliomas to resensitize them to NK cells. Given its capacity for sustained epigenetic reprogramming, the authors hypothesized that DCA would be an effective immunotherapeutic agent in treating IDHmut gliomas in an NK cell-dependent manner by upregulating epigenetically repressed activating NKG2D ligands in IDHmut tumors. In this study, the authors sought to use a glioma stem cell, preclinical animal model to determine the efficacy of DAC in IDHmut and IDH wild-type (IDHwt) tumors, and to characterize whether the activity of DAC in gliomas is dependent on NK cell function.

METHODS

Xenograft models of IDHwt and IDHmut gliomas were established in athymic-nude mice. When tumors were grossly visible and palpable, mice were treated with either DCA or dimethylsulfoxide intraperitoneally every 7 days. Tumor sizes were measured every 2 to 3 days. After the animals were euthanized, xenografts were harvested and analyzed for the following: tumor expression of NKG2D ligands, tumor susceptibility to human and murine NK cells, immunohistochemistry for NK infiltration, and tumor-infiltrating lymphocyte characterization.

RESULTS

DAC significantly inhibited the growth of IDHmut xenografts in the athymic nude mice. This effect was abrogated with NK cell depletion. Ex vivo analysis of tumor cells from harvested xenografts confirmed that DAC increased NKG2D ligand ULBP-1 and ULBP-3 expressions, and enhanced susceptibility to lysis of both human and murine IDHmut glial cells with corresponding NK cells. Immunohistochemical analysis of the xenografts indicated that DCA-treated IDHmut gliomas had a greater level of NK infiltration into the tumor compared with the negative control. Finally, DCA radically altered the tumor-infiltrating lymphocyte landscape of IDHmut glioma xenografts by increasing NK cells, dendritic cells, and M1 macrophages, while decreasing suppressive monocyte infiltration.

CONCLUSIONS

DCA displayed novel immunotherapeutic functions in IDHmut gliomas. This effect was critically dependent on NK cells. Additionally, DCA significantly altered the tumor immune landscape in IDHmut gliomas from suppressive to proinflammatory.

History of atopy confers improved outcomes in IDH mutant and wildtype lower grade gliomas

PURPOSE

A history of atopy or allergy has been shown to be protective against the development of glioma, however the effect of atopy on patient outcomes, especially in conjunction with the survival benefit associated with IDH mutation, has not yet been investigated, and is the focus of the study we present here.

METHODS

Low grade glioma (LGG) data from the TCGA was downloaded, along with IDH, TERT, 1p/19q and ATRX mutational status and genetic alterations. History of asthma, eczema, hay fever, animal, or food allergies, as documented in TCGA, was used to determine patient atopy status. Patients with missing variables were excluded from the study.

RESULTS

374 LGG studies were included. Patients with a history of atopy demonstrated longer overall survival (OS) compared to those without (145.3 vs. 81.5 months, p = 00.0195). IDH mutant patients with atopy had longer OS compared those without atopy (158.8 vs. 85 months, p = 0.035). Multivariate cox regression analysis demonstrated that the effects of atopy on survival were independent of IDH and histological grade, (p = 0.002, HR 0.257, 95% 0.109-0.604), (p =  < 0.001, HR 0.217, 95% 0.107-0.444), and (p = 0.004, HR 2.72, 95% 1.373-5.397), respectively. In terms of treatment outcomes, patients with atopy did not differ in treatment response compared to their counterpart. Pathway analysis demonstrated an upstream activation of the BDNF pathway (p = 0.00027).

CONCLUSION

A history of atopy confers a survival benefit in patients with diffuse low-grade glioma. Activation of the BDNF pathway may drive the observed differences.

Headlight and loupe-based fluorescein detection system in brain tumor surgery; a firstin-human experience

BACKGROUND

Fluorescein is an agent that accumulates in areas of blood-brain barrier breakdown and is commonly used in neurosurgical oncology to assist with lesion localization and visualizing the extent of resection. It is considered to be cost-effective and has a favorable safety profile. Studies on the utilization of fluorescein demonstrate an improved extent of tumor resection and increased overall survival. Currently, fluorescein detection systems are all microscope based, leading to limitations such as decreased maneuverability, limited visualization of the entire operative field, and significant cost associated with obtaining and maintaining a neurosurgical operating microscope.

METHODS

Three consecutive craniotomy patients for tumor resection were included, and surgery was carried out under loupe fluorescence guidance using the ReVeal 450 System, and also a surgical microscope for comparison.

RESULTS

Loupe-mounted fluorescence system enabled excellent visualization of fluorescence in all three cases.

CONCLUSIONS

In this manuscript, we describe our experience with a loupe-mounted fluorescein detection system in 3 patients with malignant gliomas. We found that the loupe-mounted system offered excellent ability to visualize fluorescein fluorescence. Although loupe-mounted systems are not an alternative to surgical microscopes, they could be a useful surgical adjunct for superficial lesions and in low-middle income counties.

Autophagy inhibition is the next step in the treatment of glioblastoma patients following the Stupp era

It has now been nearly 15 years since the last major advance in the treatment of patients with glioma. "The addition of temozolomide to radiotherapy for newly diagnosed glioblastoma resulted in a clinically meaningful and statistically significant survival benefit with minimal additional toxicity". Autophagy is primarily a survival pathway, literally self-eating, that is utilized in response to stress (such as radiation and chemotherapy), enabling clearance of effete protein aggregates and multimolecular assemblies. Promising results have been observed in patients with glioma for over a decade now when autophagy inhibition with chloroquine derivatives coupled with conventional therapy. The application of autophagy inhibitors, the role of immune cell-induced autophagy, and the potential role of novel cellular and gene therapies, should now be considered for development as part of this well-established regimen.

Characterization of systemic immunosuppression by IDH mutant glioma small extracellular vesicles

BACKGROUND

Gliomas are the most common primary brain tumors and are universally fatal. Mutations in the isocitrate dehydrogenase genes (IDH1 and IDH2) define a distinct glioma subtype associated with an immunosuppressive tumor microenvironment. Mechanisms underlying systemic immunosuppression in IDH mutant (mutIDH) gliomas are largely unknown. Here, we define genotype-specific local and systemic tumor immunomodulatory functions of tumor-derived glioma exosomes (TEX).

METHODS

TEX produced by human and murine wildtype and mutant IDH glioma cells (wtIDH and mutIDH, respectively) were isolated by size exclusion chromatography (SEC). TEX morphology, size, quantity, molecular profiles and biodistribution were characterized. TEX were injected into naive and tumor-bearing mice, and the local and systemic immune microenvironment composition was characterized.

RESULTS

Using in vitro and in vivo glioma models, we show that mutIDH TEX are more numerous, possess distinct morphological features and are more immunosuppressive than wtIDH TEX. mutIDH TEX cargo mimics their parental cells, and induces systemic immune suppression in naive and tumor-bearing mice. TEX derived from mutIDH gliomas and injected into wtIDH tumor-bearing mice reduce tumor-infiltrating effector lymphocytes, dendritic cells and macrophages, and increase circulating monocytes. Astonishingly, mutIDH TEX injected into brain tumor-bearing syngeneic mice accelerate tumor growth and increase mortality compared with wtIDH TEX.

CONCLUSIONS

Targeting of mutIDH TEX represents a novel therapeutic approach in gliomas.

TIGIT and PD-1 Immune Checkpoint Pathways Are Associated With Patient Outcome and Anti-Tumor Immunity in Glioblastoma

Glioblastoma (GBM) remains an aggressive brain tumor with a high rate of mortality. Immune checkpoint (IC) molecules are expressed on tumor infiltrating lymphocytes (TILs) and promote T cell exhaustion upon binding to IC ligands expressed by the tumor cells. Interfering with IC pathways with immunotherapy has promoted reactivation of anti-tumor immunity and led to success in several malignancies. However, IC inhibitors have achieved limited success in GBM patients, suggesting that other checkpoint molecules may be involved with suppressing TIL responses. Numerous IC pathways have been described, with current testing of inhibitors underway in multiple clinical trials. Identification of the most promising checkpoint pathways may be useful to guide the future trials for GBM. Here, we analyzed the The Cancer Genome Atlas (TCGA) transcriptomic database and identified PD1 and TIGIT as top putative targets for GBM immunotherapy. Additionally, dual blockade of PD1 and TIGIT improved survival and augmented CD8⁺ TIL accumulation and functions in a murine GBM model compared with either single agent alone. Furthermore, we demonstrated that this combination immunotherapy affected granulocytic/polymorphonuclear (PMN) myeloid derived suppressor cells (MDSCs) but not monocytic (Mo) MDSCs in in our murine gliomas. Importantly, we showed that suppressive myeloid cells express PD1, PD-L1, and TIGIT-ligands in human GBM tissue, and demonstrated that antigen specific T cell proliferation that is inhibited by immunosuppressive myeloid cells can be restored by TIGIT/PD1 blockade. Our data provide new insights into mechanisms of GBM αPD1/αTIGIT immunotherapy.

Blockade of Cell Volume Regulatory Protein NKCC1 Increases TMZ-Induced Glioma Apoptosis and Reduces Astrogliosis

Glioma is one of the most common primary malignant tumors of the central nervous system accounting for approximately 40% of all intracranial tumors. Temozolomide is a conventional chemotherapy drug for adjuvant treatment of patients with high-risk gliomas, including grade II to grade IV. Our bioinformatic analysis of The Cancer Genome Atlas and Chinese Glioma Genome Atlas datasets and immunoblotting assay show that SLC12A2 gene and its encoded Na⁺-K⁺-2Cl^- cotransporter isoform 1 (NKCC1) protein are abundantly expressed in grade II-IV gliomas. NKCC1 regulates cell volume and intracellular Cl^- concentration, which promotes glioma cell migration, resistance to temozolomide, and tumor-related epilepsy in experimental glioma models. Using mouse syngeneic glioma models with intracranial transplantation of two different glioma cell lines (GL26 and SB28), we show that NKCC1 protein in glioma tumor cells as well as in tumor-associated reactive astrocytes was significantly upregulated in response to temozolomide monotherapy. Combination therapy of temozolomide with the potent NKCC1 inhibitor bumetanide reduced tumor proliferation, potentiated the cytotoxic effects of temozolomide, decreased tumor-associated reactive astrogliosis, and restored astrocytic GLT-1 and GLAST glutamate transporter expression. The combinatorial therapy also led to suppressed tumor growth and prolonged survival of mice bearing GL26 glioma cells. Taken together, these results demonstrate that NKCC1 protein plays multifaceted roles in the pathogenesis of glioma tumors and presents as a therapeutic target for reducing temozolomide-mediated resistance and tumor-associated astrogliosis.

Long-Term Survivorship Following Stereotactic Radiosurgery Alone for Brain Metastases: Risk of Intracranial Failure and Implications for Surveillance and Counseling

BACKGROUND

Historically, survival for even highly select cohorts of brain metastasis patients selected for SRS alone is <2 yr; thus, limited literature on risks of recurrence exists beyond 2 yr.

OBJECTIVE

To investigate the possibility that for subsets of patients the risk of intracranial failure beyond 2 yr is less than the commonly quoted 50% to 60%, wherein less frequent screening may be appropriate.

METHODS

As a part of our institutional radiosurgery database, we identified 132 patients treated initially with stereotactic radiosurgery (SRS) alone (± pre-SRS surgical resection) with at least 2 yr of survival and follow-up from SRS. Primary study endpoints were rates of actuarial intracranial progression beyond 2 yr, calculated using the Kaplan-Meier and Cox regression methods.

RESULTS

The median follow-up from the first course of SRS was 3.5 yr. Significant predictors of intracranial failure beyond 2 yr included intracranial failure before 2 yr (52% vs 25%, P < .01) and total SRS tumor volume ≥5 cc (51% vs 25%, P < .01). On parsimonious multivariate analysis, failure before 2 yr (HR = 2.2, 95% CI: 1.2-4.3, P = .01) and total SRS tumor volume ≥5 cc (HR = 2.3, 95% CI: 1.2-4.3, P = .01) remained significant predictors of intracranial relapse beyond 2 yr.

CONCLUSION

Relapse rates beyond 2 yr following SRS alone for brain metastases are low in patients who do not suffer intracranial relapse within the first 2 yr and with low-volume brain metastases, supporting a practice of less frequent screening beyond 2 yr. For remaining patients, frequent (every 3-4 mo) screening remains prudent, as the risk of intracranial failure after 2 yr remains high.

Stereotactic body radiation therapy for benign spine tumors: is dose de-escalation appropriate?

OBJECTIVE Akin to the nonoperative management of benign intracranial tumors, stereotactic body radiation therapy (SBRT) has emerged as a nonoperative treatment option for noninfiltrative primary spine tumors such as meningioma and schwannoma. The majority of initial series used higher doses of 16-24 Gy in 1-3 fractions. The authors hypothesized that lower doses (such as 12-13 Gy in 1 fraction) might provide an efficacy similar to that found with the dose de-escalation commonly used for intracranial radiosurgery to treat acoustic neuroma or meningioma and with a lower risk of toxicity. METHODS The authors identified 38 patients in a prospectively maintained institutional radiosurgery database who were treated with definitive SBRT for a total of 47 benign primary spine tumors between 2004 and 2016. SBRT consisted of 9-21 Gy in 1-3 fractions using the CyberKnife (n = 11 [23%]), Synergy S (n = 21 [45%]), or TrueBeam (n = 15 [32%]) radiosurgery platform. For a comparison of SBRT doses, patients were dichotomized into 1 of 2 groups (low-dose or high-dose SBRT) using a cutoff biologically effective dose (BED_10Gy) of 30 Gy. Tumor control was calculated from the date of SBRT to the last follow-up using Kaplan-Meier survival analysis, with comparisons between groups completed using a log-rank method. To account for potential indication bias, a propensity score analysis was completed based on the conditional probabilities of SBRT dose selection. Toxicity was graded using Common Terminology Criteria for Adverse Events version 4.0 with a focus on grade 3+ toxicity and the incidence of pain flare. RESULTS For the 38 patients, the most common histological findings were meningioma (15 patients), schwannoma (13 patients), and hemangioblastoma (7 patients). The median age at SBRT was 58 years (range 25-91 years). The 47 treated lesions were located in the cervical (n = 18), thoracic (n = 19), or lumbosacral (n = 10) spine. Five (11%) lesions were lost to follow-up after SBRT. The median follow-up duration for the remaining 42 lesions was 54 months (range 1.2-133 months). Six (16%) patients (with a total of 8 lesions) experienced pain flare after SBRT; no significant predictor of pain flare was identified. No grade 3+ acute- or late-onset complication was noted. The 5-year local control rate was 76% (95% CI 61%-91%). No significant difference in local control according to dose, fractionation, previous radiation, surgery, tumor histology, age, treatment platform, planning target volume, or spine level treated was found. The 5-year local control rates for low- and high-dose treatments were 73% (95% CI 53%-93%) and 83% (95% CI 61%-100%) (p = 0.52). In propensity score-adjusted multivariable analysis, no difference in local control was identified (HR 0.30, 95% CI 0.02-5.40; p = 0.41). CONCLUSIONS Long-term follow-up of patients treated with SBRT for benign spinal lesions revealed no significant difference between low-dose (BED_10Gy ≤ 30) and high-dose SBRT in local control, pain-flare rate, or long-term toxicity.

Single-cell profiling of human gliomas reveals macrophage ontogeny as a basis for regional differences in macrophage activation in the tumor microenvironment

Background

Tumor-associated macrophages (TAMs) are abundant in gliomas and immunosuppressive TAMs are a barrier to emerging immunotherapies. It is unknown to what extent macrophages derived from peripheral blood adopt the phenotype of brain-resident microglia in pre-treatment gliomas. The relative proportions of blood-derived macrophages and microglia have been poorly quantified in clinical samples due to a paucity of markers that distinguish these cell types in malignant tissue.

Results

We perform single-cell RNA-sequencing of human gliomas and identify phenotypic differences in TAMs of distinct lineages. We isolate TAMs from patient biopsies and compare them with macrophages from non-malignant human tissue, glioma atlases, and murine glioma models. We present a novel signature that distinguishes TAMs by ontogeny in human gliomas. Blood-derived TAMs upregulate immunosuppressive cytokines and show an altered metabolism compared to microglial TAMs. They are also enriched in perivascular and necrotic regions. The gene signature of blood-derived TAMs, but not microglial TAMs, correlates with significantly inferior survival in low-grade glioma. Surprisingly, TAMs frequently co-express canonical pro-inflammatory (M1) and alternatively activated (M2) genes in individual cells.

Conclusions

We conclude that blood-derived TAMs significantly infiltrate pre-treatment gliomas, to a degree that varies by glioma subtype and tumor compartment. Blood-derived TAMs do not universally conform to the phenotype of microglia, but preferentially express immunosuppressive cytokines and show an altered metabolism. Our results argue against status quo therapeutic strategies that target TAMs indiscriminately and in favor of strategies that specifically target immunosuppressive blood-derived TAMs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-017-1362-4) contains supplementary material, which is available to authorized users.

Mutant IDH1 regulates the tumor-associated immune system in gliomas

Amankulor et al. created a syngeneic pair mouse model for mutant IDH1 (muIDH1) and wild-type IDH1 (wtIDH1) gliomas and demonstrated that IDH1 mutations caused down-regulation of leukocyte chemotaxis, resulting in repression of the tumor-associated immune system.

Gliomas harboring mutations in isocitrate dehydrogenase 1/2 (IDH1/2) have the CpG island methylator phenotype (CIMP) and significantly longer patient survival time than wild-type IDH1/2 (wtIDH1/2) tumors. Although there are many factors underlying the differences in survival between these two tumor types, immune-related differences in cell content are potentially important contributors. In order to investigate the role of IDH mutations in immune response, we created a syngeneic pair mouse model for mutant IDH1 (muIDH1) and wtIDH1 gliomas and demonstrated that muIDH1 mice showed many molecular and clinical similarities to muIDH1 human gliomas, including a 100-fold higher concentration of 2-hydroxygluratate (2-HG), longer survival time, and higher CpG methylation compared with wtIDH1. Also, we showed that IDH1 mutations caused down-regulation of leukocyte chemotaxis, resulting in repression of the tumor-associated immune system. Given that significant infiltration of immune cells such as macrophages, microglia, monocytes, and neutrophils is linked to poor prognosis in many cancer types, these reduced immune infiltrates in muIDH1 glioma tumors may contribute in part to the differences in aggressiveness of the two glioma types.

Targeted next-generation sequencing panel (GlioSeq) provides comprehensive genetic profiling of central nervous system tumors

BACKGROUND

Identification of genetic changes in CNS tumors is important for the appropriate clinical management of patients. Our objective was to develop a next-generation sequencing (NGS) assay for simultaneously detecting the various types of genetic alterations characteristic for adult and pediatric CNS tumors that can be applied to small brain biopsies.

METHODS

We report an amplification-based targeted NGS assay (GlioSeq) that analyzes 30 genes for single nucleotide variants (SNVs) and indels, 24 genes for copy number variations (CNVs), and 14 types of structural alterations in BRAF, EGFR, and FGFR3 genes in a single workflow. GlioSeq performance was evaluated in 54 adult and pediatric CNS tumors, and the results were compared with fluorescence in-situ hybridization, Sanger sequencing, and reverse transcription PCR.

RESULTS

GlioSeq correctly identified 71/71 (100%) genetic alterations known to be present by conventional techniques, including 56 SNVs/indels, 9 CNVs, 3 EGFRvIII, and 3 KIAA1549-BRAF fusions. Only 20 ng of DNA and 10 ng of RNA were required for successful sequencing of 100% frozen and 96% formalin-fixed, paraffin-embedded tissue specimens. The assay sensitivity was 3%-5% of mutant alleles for SNVs and 1%-5% for gene fusions. The most commonly detected alterations were IDH1, TP53, TERT, ATRX. CDKN2A, and PTEN in high-grade gliomas, followed by BRAF fusions in low-grade gliomas and H3F3A mutations in pediatric gliomas.

CONCLUSIONS

GlioSeq NGS assay offers accurate and sensitive detection of a wide range of genetic alterations in a single workflow. It allows rapid and cost-effective profiling of brain tumor specimens and thus provides valuable information for patient management.

Tumor bed radiosurgery following resection and prior stereotactic radiosurgery for locally persistent brain metastasis

PURPOSE

Despite advances in multimodality management of brain metastases, local progression following stereotactic radiosurgery (SRS) can occur. Often, surgical resection is favored, as it frequently provides immediate symptom relief as well as pathological characterization of any residual tumor. Should the pathological specimen contain viable tumor cells, further radiation therapy is an option to sterilize the tumor bed. We evaluated the use of repeat SRS (rSRS) in lieu of whole-brain radiation therapy (WBRT) as a means of improving local control (LC) while minimizing potential toxicity and dose to the normal brain.

MATERIALS/METHODS

A retrospective review was performed to identify patients with brain metastases who underwent SRS and then surgical resection for locally recurrent or persistent disease. From 2004 to 2014, 13 consecutive patients or 15 lesions were treated with rSRS after resection, either post-operatively to the tumor bed (n = 10, 66.6%) or after a second local recurrence (n = 5, 33.3%). LC, distant brain failure (DBF), and radiation toxicity were determined using patient records, RECIST criteria v1.1, and CTCAE v4.03.

RESULTS

At a median follow-up interval of 9.0 months (range 1.8-54.9 months) from time of rSRS, five patients remain alive. Following rSRS, 13 of the 15 (86.6%) lesions were locally controlled with an estimated 100% LC at 6 months and 75% LC at 1 year. However, 11 of the 15 (73.3%) treated lesions developed DBF after rSRS with 3 of 13 patients proceeding to WBRT. Two of 15 (13.3%) resulted in either grade 2 radionecrosis with grade 3 seizures or grade 3 radionecrosis.

CONCLUSION

Repeat SRS represents a potential salvage therapy for patients with locally recurrent brain metastases, providing additional tumor control with acceptable toxicity, even in the setting of prior SRS and surgical resection. rSRS may be reasonable to use as an alternative to WBRT in this setting.

Osteopontin-CD44 signaling in the glioma perivascular niche enhances cancer stem cell phenotypes and promotes aggressive tumor growth

Stem-like glioma cells reside within a perivascular niche and display hallmark radiation resistance. An understanding of the mechanisms underlying these properties will be vital for the development of effective therapies. Here, we show that the stem cell marker CD44 promotes cancer stem cell phenotypes and radiation resistance. In a mouse model of glioma, Cd44(-/-) and Cd44(+/-) animals showed improved survival compared to controls. The CD44 ligand osteopontin shared a perivascular expression pattern with CD44 and promoted glioma stem cell-like phenotypes. These effects were mediated via the γ-secretase-regulated intracellular domain of CD44, which promoted aggressive glioma growth in vivo and stem cell-like phenotypes via CBP/p300-dependent enhancement of HIF-2α activity. In human glioblastoma multiforme, expression of CD44 correlated with hypoxia-induced gene signatures and poor survival. Altogether, these data suggest that in the glioma perivascular niche, osteopontin promotes stem cell-like properties and radiation resistance in adjacent tumor cells via activation of CD44 signaling.

The incidence and patterns of hardware failure after separation surgery in patients with spinal metastatic tumors

BACKGROUND CONTEXT

Spine metastases occur frequently in patients with cancer. A variety of surgical approaches, including anterior transcavitary, lateral extracavitary, posterolateral, and/or combined techniques are used for spinal cord decompression and restoration of spinal stability. The incidence of symptomatic hardware failure is unknown for the majority of these approaches.

PURPOSE

The purpose of this study was to determine the incidence of symptomatic hardware failure and the associated risk factors in patients with metastatic epidural spinal cord compression (MESCC).

STUDY DESIGN/SETTING

This was a retrospective study.

PATIENT SAMPLE

The current series analyzes a cohort of 318 patients who underwent separation surgery, which involves single-stage posterolateral decompression and posterior segmental instrumentation for MESCC.

OUTCOME MEASURES

The event of interest was hardware failure; the competing event was death resulting from any cause. All patients were monitored for survival analysis. A competing risk analysis was conducted to examine univariately a number of potential risk factors associated with hardware failure, including junctional level, gender, construct length, and the presence or absence of prior chest wall resection.

METHODS

A retrospective analysis and chart review were performed for 318 consecutive patients who underwent posterolateral decompression and posterior screw-rod fixation without supplemental anterior fixation from March 2004 to June 2011 at our institution. The median follow-up time for survivors without hardware failure was 399 days (range, 9-2,828), with a mean operative time of 3 hours. A total of 78% of patients died during the 7-year study period.

RESULTS

Of the 318 patients, nine (2.8%) exhibited signs and symptoms of hardware failure and required revision of the instrumentation. Patients with chest wall resection and those with initial construct length greater than six contiguous spinal levels exhibited a statistically significantly higher risk of symptomatic hardware failure than their counterparts. We observed a trend toward an increased risk of failure in women compared with men (p=.09).

CONCLUSIONS

The incidence of hardware failure is low in patients with MESCC who undergo posterolateral decompression and posterior screw-rod instrumentation. Moreover, the short operative time and low morbidity profile associated with this approach make it a reliable and acceptable method for the surgical treatment of MESCC. Patients with constructs spanning six or more levels or those with prior chest wall resection are at higher risk for instrumentation failure.

Resection of glioma in an fMRI-defined "split" Broca's area

Gross total resection of gliomas can be limited by the involvement of tumor in eloquent areas. Moreover, lesions can impart cortical reorganization and make the precise determination of hemispheric dominance and localization of language function even more difficult. Preoperative mapping with functional magnetic resonance imaging (fMRI), intraoperative imaging modalities, and intraoperative direct cortical stimulation enable surgeons to map the functional topography of the brain in relation to the tumor and perform a safe maximal resection. In this report, we present a patient with left frontal glioma of complex morphology, wherein the tumor was enveloped by Broca's area on fMRI. Intraoperative mapping and intraoperative magnetic resonance imaging (iMRI) allowed gross total resection of the tumor with preservation of language function and illustrate the utility of multiple contemporary modalities in the surgical management of low-grade gliomas located in eloquent cortices.

Stereotactic laser induced thermotherapy (LITT): a novel treatment for brain lesions regrowing after radiosurgery

Since the inception of radiosurgery, the management of brain metastases has become a common problem for neurosurgeons. Although the use of stereotactic radiosurgery and/or whole brain radiation therapy serves to control the majority of disease burden, patients who survive longer than 6-8 months sometimes face the problem of symptomatic radiographically regrowing lesions with few treatment options. Here we investigate the feasibility of use of MRI-guided stereotactic laser induced thermotherapy (LITT) as a novel treatment option for these lesions. Six patients who had previously undergone gamma knife stereotactic radiosurgery for brain metastases were selected. All patients had an initial favorable response to radiosurgery but subsequently developed regrowth of at least one lesion associated with recurrent edema and progressive neurological symptoms requiring ongoing steroids for symptom control. All lesions were evaluated for craniotomy, but were deemed unresectable due to deep location or patient's comorbidities. Stereotactic biopsies were performed prior to the thermotherapy procedure in all cases. LITT was performed using the Visualase system and follow-up MRI imaging was used to determine treatment response. In all six patients biopsy results were negative for tumor and consistent with adverse radiation effects also known as radiation necrosis. Patients tolerated the procedure well and were discharged from the hospital within 48 h of the procedure. In 4/6 cases there was durable improvement of neurological symptoms until death. In all cases steroids were weaned off within 2 months. One patient died from systemic causes related to his cancer a month after the procedure. One patient had regrowth of the lesion 3 months after the procedure and required re-initiation of steroids and standard craniotomy for surgical resection. There were no complications directly related to the thermocoagulation procedure. Stereotactic laser induced thermotherapy is a feasible alternative for the treatment of symptomatic regrowing metastatic lesions after radiosurgery. The procedure carries minimal morbidity and, in this small series, shows some effectiveness in the symptomatic relief of edema and neurological symptoms paralleled by radiographic lesional control. Further studies are necessary to elucidate the safety of this technology.

Astrocyte-specific expression patterns associated with the PDGF-induced glioma microenvironment

BACKGROUND

The tumor microenvironment contains normal, non-neoplastic cells that may contribute to tumor growth and maintenance. Within PDGF-driven murine gliomas, tumor-associated astrocytes (TAAs) are a large component of the tumor microenvironment. The function of non-neoplastic astrocytes in the glioma microenvironment has not been fully elucidated; moreover, the differences between these astrocytes and normal astrocytes are unknown. We therefore sought to identify genes and pathways that are increased in TAAs relative to normal astrocytes and also to determine whether expression of these genes correlates with glioma behavior.

METHODOLOGY/PRINCIPAL FINDINGS

We compared the gene expression profiles of TAAs to normal astrocytes and found the Antigen Presentation Pathway to be significantly increased in TAAs. We then identified a gene signature for glioblastoma (GBM) TAAs and validated the expression of some of those genes within the tumor. We also show that TAAs are derived from the non-tumor, stromal environment, in contrast to the Olig2+ tumor cells that constitute the neoplastic elements in our model. Finally, we validate this GBM TAA signature in patients and show that a TAA-derived gene signature predicts survival specifically in the human proneural subtype of glioma.

CONCLUSIONS/SIGNIFICANCE

Our data identifies unique gene expression patterns between populations of TAAs and suggests potential roles for stromal astrocytes within the glioma microenvironment. We show that certain stromal astrocytes in the tumor microenvironment express a GBM-specific gene signature and that the majority of these stromal astrocyte genes can predict survival in the human disease.

Cerebrovascular disease associated with Aarskog-Scott syndrome

Faciogenital dysplasia, also known as Aarskog-Scott syndrome (AAS), is an X-linked dominant congenital disorder characterized by multiple facial, musculoskeletal, dental, neurological and urogenital abnormalities, ocular manifestations, congenital heart defects, low IQ and behavioral problems. Here we describe an unusual presentation of dysplastic carotid artery, basilar artery malformation or occlusion and posterior circulation aneurysm in a 13-year-old male with AAS.

Krev1 interaction trapped-1/cerebral cavernous malformation-1 protein expression during early angiogenesis

OBJECT

Molecular genetic studies of cerebral cavernous malformation (CCM) have identified three loci, CCM1-3, that can lead to CCM when mutated. Examination of the CCM1 locus established KRIT1 (Krev1 Interaction Trapped genre 1) as the CCM1 gene. Despite the identification of KRIT1 as the gene mutated in CCM1, little has been learned regarding its function. The authors recently demonstrated specific KRIT1 expression in endothelial cells. Based on this result and the fact that the CCM phenotype features defects in microvasculature, we hypothesized that KRIT1 may take an active part in normal angiogenesis.

METHODS

In this study, the authors investigated the spatial and temporal expression of KRIT1 during normal vessel development and maturation by examining KRIT1 protein in both in vitro and in vivo angiogenic systems with the use of postconfluent endothelial cell cultures along with placental tissues from different developmental stages.

CONCLUSIONS

The results demonstrate that KRIT1 is expressed during capillary-like tube formation in the early stages of angiogenesis in vitro. Histological examination of placental tissue, a well-established in vivo model of angiogenesis, shows KRIT1 expression in active angiogenic and vasculogenic areas of the immature placental villi. As the placenta matures, KRIT1 expression is restricted to microvascular and small arterial endothelial cells with little or no expression seen in the intima of large vessels. It can therefore be concluded that KRIT1 is expressed during early angiogenesis by endothelial cells and may play a key role in vessel formation and/or development.

KRIT1/cerebral cavernous malformation 1 protein localizes to vascular endothelium, astrocytes, and pyramidal cells of the adult human cerebral cortex

OBJECTIVE

Mutations in KRIT1 cause familial cerebral cavernous malformation, an autosomal dominant disorder affecting primarily the central nervous system vasculature. Although recent studies have suggested that Krev-1 interaction trapped 1 (KRIT1) is a microtubule-associated protein that interacts with integrin cytoplasmic domain-associated protein-1alpha, the function of KRIT1 remains elusive.

METHODS

We used Western blotting and immunohistochemistry with specific KRIT1 polyclonal antibodies to investigate KRIT1 protein expression in diverse cerebral and extracerebral tissues.

RESULTS

Immunostaining demonstrates that although KRIT1 is expressed in a broad variety of human organs, it localizes to the vascular endothelium of each, specifically to capillaries and arterioles. KRIT1 antibody fails to stain fenestrated capillaries in the kidney, the liver, or the red pulp of the spleen, where endothelial cells do not to adhere to one another. In contrast, intense staining is observed in the thymus and the white pulp of the spleen, where specialized blood-organ barriers are formed. Other cell types, including various epithelia, cardiac myocytes, and hepatocytes, also stain with KRIT1.

CONCLUSION

Although KRIT1 expression is seen in every endothelium studied, cerebral cavernous malformation lesions are seen almost exclusively in the central nervous system, suggesting that additional cell type(s) contribute to the pathophysiology of cerebral cavernous malformations. Here, we demonstrate that KRIT1 is also present in cells and structures integral to the cerebral angiogenesis and formation of the blood-brain barrier, namely, endothelial cells and astrocytic foot processes, as well as pyramidal neurons in the cerebral cortex.