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Optic pathway gliomas (OPGs) are low grade gliomas intrinsic to the visual pathway, frequently associated with Neurofibromatosis Type 1 (NF-1). Bilateral OPGs without chiasmatic involvement are almost pathognomonic for NF-1. We report an unusual case of bilateral optic nerve glioma without chiasmatic involvement in a 17-month old male patient with craniosynostosis and Crouzon Syndrome, an autosomal dominant disorder caused by activating FGFR2 mutations associated with craniosynostosis and optic atrophy. The patient’s c.1032 G>A pathogenic variant in FGFR2 is a variant known to affect splicing and results in a protein that lacks part of an important domain involved in ligand binding. Although FGFR1 mutations have been implicated in low-grade glioma through MAPK activation, FGFR2 mutations have not yet been described in OPGs, although they have been described in epileptogenic low-grade gliomas and mixed neuronal-glial tumors. Our patient presented with worsening vision in the setting of known Crouzon Syndrome. An eye examination revealed bilateral primary optic atrophy. Brain and orbital MRIs demonstrated fusiform dilation and STIR hyperintensity of the intraorbital segments of the optic nerves bilaterally with normal pre-chiasmatic optic segments. There were no other radiographic or physical stigmata suggestive of NF-1. Next generation sequencing and copy number analysis from peripheral blood were negative for variants in NF1. RNA based studies for NF1 aberrations are pending. Although follow up MRI scans demonstrated stable size of his OPGs, the risk of further visual deficit was considered significant due to his pre-existing optic atrophy and poor baseline visual acuity. Therefore, he was started on vincristine and carboplatin chemotherapy according to A9952, and induction therapy has been well tolerated. To our knowledge, this is the first patient with Crouzon Syndrome who has developed bilateral optic pathway gliomas. Orbital MRIs should be considered for these patients with worsening visual acuity not explained by other causes.

Viral vectors and electroporation (EP)-mediated gene transfers are efficient means of inducing somatic mosaicism in mice, but they lack the exquisite control over transgene copy number, gene zygosity, and genomic-locus speci-ficity that genetically engineered mouse models (GEMMs) provide. Here, we develop and demonstrate a simple and generalizable in vivo method, mosaic analysis by dual recombinase-mediated cassette exchange (MADR). MADR allows for stable labeling of mutant cells express transgenic elements from a precisely-defined chromosomal locus. To test our method, we generated reporter-labeled lineages from stem and progenitor cells in a well-defined Rosa26mTmG mouse. We demonstrate the power and versatility of MADR by creating novel glioma models with mixed, reporter-defined zygosity or with “personalized,” H3.3-containing driver mutation signatures from pediatric glioma-each manipulation altering the profile of resulting tumors. Thus, MADR provides a high-throughput genetic platform for the dissection of development and disease, and this rapid method can be applied to the thousands of existing gene-trap mice.

Pediatric gliomas, a type of brain tumor which arises from uncontrolled growth of glial cells, are the most common type of CNS tumor in children. As the list of putative driver mutations in glioma grows, we are just beginning to elucidate the combined effects of unhinged signaling pathways on the transformation of CNS cells. While the oncogenic role of ETV5 in various cancers is well-established, its role in high-grade pediatric gliomas has yet to be elucidated. We have created a mosaic, autochthonous, glioma model that captures the first hours and days of gliomagenesis in more resolution than conventional mouse models of cancer. Our various models of pediatric glioma have indicated a fundamental role for Etv5 in tumor cells. We show that ETV5 is highly expressed in our glioma models and primary pediatric glioma cells. We are currently pursuing an omics approach to identifying the mechanisms regulating ETV5 in high-grade glioma. Additionally, we are employing a novel single-site conditional system to identify ETV5 genomic targets in patient tumors and to explore the results of ETV5 manipulation on cell fate. Taken together, we provide evidence that Etv5 is necessary for tumor initiation and regulates the exuberant gliogenesis observed in these tumors.

We have been investigating the effects of immune system modulation on brain tumor survival in animal models of pediatric malignancies. For example, TGF-β is produced by various tumor types and dampens the response of the immune system, preventing recognition of tumor cells. Thus, we crossed mice with T-cell-specific TGF-β blockade (CD4-TGFβRII-DNR) with a mouse model of medulloblastoma (SmoA1 transgenic mice) and analyzed offspring. We noted dramatic infiltration of T cells into the tumor and coincident improvement in survival of these mice. Furthermore, there was a striking change in T cell phenotype—notably a large increase in memory T cells in double transgenic mice, which are in principle able to mount anti-tumor immunity. We've been employing a novel piggyBac model of forebrain glioma to rapidly generate tumors from patient driver genes. Interestingly, using genome-wide analysis, many members of the TGF-β ligand family are upregulated by tumor cells and these secreted ligands appear to be the principle immunosuppressive molecules expressed by the tumor propagating population. Given the survival-promoting role of T cell TGF-β signaling blockade in our medulloblastoma model, we have generated de novo tumors in CD4-TGFβRII-DNR mice using our in vivo piggyBac system and are investigating the applicability of this strategy in pediatric forebrain glioma.