TMOD-08. Modeling low-grade astrocytoma by genetic engineering of brain organoids

Monoallelic mutations in IDH1 or IDH2 are hallmarks of low-grade gliomas. Subsequent loss-of-function mutations in TP53 and ATRX are defining genetic events in the development of low-grade astrocytoma (LGA). However, efforts to isolate and culture LGA cells in vitro have been unsuccessful, and a reliable experimental system for dissecting the roles of IDH and other genetic alterations remains unavailable. Our objective is to generate efficient LGA models to overcome these challenges. We derived neural progenitor cells and brain organoids from induced pluripotent stem cells (iPSCs). We first introduced genetic alterations, including IDH1 R132H, TP53 knockdown (TP53-KD), and ATRX knockdown (ATRX-KD), into the neural progenitor cells. We observed that the IDH1 R132H mutation alone, or in combination with TP53-KD and ATRX-KD, caused growth arrest in neural progenitor cells. In contrast, introducing these mutations into brain organoids yielded different results. The IDH1 R132H mutation alone inhibited brain organoid growth. However, the combination of IDH1 R132H and TP53-KD promoted brain organoid growth in vitro but failed to induce tumor formation after orthotopic transplantation into mouse brains. Interestingly, brain organoid cells harboring all three alterations (IDH1 R132H, TP53-KD, and ATRX-KD) formed LGA-like glial tumors upon transplantation into mouse brains. The growth and pathological features of these xenograft tumors closely resembled human LGA. These findings suggest that brain organoids, which are miniature brain-like structures containing organized neurons, neural progenitor cells, astrocytes, and oligodendrocytes, may provide a permissive microenvironment for glioma formation. Thus, we have developed brain organoid-based LGA models that enable both in vitro and in vivo studies of LGA gliomagenesis.