Combining the RCAS/tv-a retrovirus and CRISPR/Cas9 gene editing systems to generate primary mouse models of diffuse midline glioma

Diffuse midline gliomas (DMGs) are lethal brain tumors that arise in children and young adults, resulting in a median survival of less than two years. Genetically engineered mouse models (GEMMs) are critical to studying tumorigenesis and tumor-immune interactions, which may inform new treatment approaches. However, current midline glioma GEMM approaches are limited in their ability to multiplex perturbations and/or target specific cell lineages in the brain for genetic manipulation. Here, we combined the RCAS/tv-a avian retrovirus system and CRISPR/Cas9 genetic engineering to drive midline glioma formation in mice. CRISPR/Cas9-based disruption of Trp53, a tumor suppressor that is frequently disrupted in midline gliomas, along with the oncogene PDGF-B resulted in high grade tumor formation with moderate latency (median time to tumor formation of 12 weeks). We confirmed CRISPR-mediated Trp53 disruption using next-generation sequencing (NGS) and immunohistochemistry (IHC). Next, we disrupted multiple midline glioma tumor suppressor genes (Trp53, Pten, Atm, Cdkn2a) in individual mouse brains. These mini-pooled in vivo experiments generated primary midline gliomas with decreased tumor latency (median time to tumor formation of 3.6 weeks, P < 0.0001, log-rank test compared to single-plex gRNA). Quantification of gRNA barcodes and CRISPR editing events revealed that all tumors contained cells with various disruptions of all target genes and suggested a multiclonal origin for the tumors as well as stronger selection for Trp53 disruption compared to disruption of the other genes. This mouse modeling approach will streamline midline glioma research and enable complex experiments to understand tumor evolution and therapeutics.