Advanced human cerebral organoids as a model for investigating glioma stem cell interactions with microglia and vascular cells and response to radiotherapy

ABSTRACT The recent development of human brain organoids from induced pluripotent stem cells (IPSCs) enables the modeling of brain biology and pathophysiology, such as gliomas. However, most models lack vascular and/or immune systems, both of which play essential roles in maintaining brain health and in pathophysiological mechanisms. We have established a new method for generating vascularized complex cerebral organoids (CCOs) containing microglial cells (brain-resident macrophages) by incorporating bipotent hematopoietic/endothelial progenitors derived from the same IPSC lines during the early stages of development. This approach led to the formation of extensive vascular-like structures with blood-brain barrier characteristics, which were perfused upon transplantation into immunodeficient mice. Additionally, microglial cells exhibiting typical phenotypes and functionalities also developed within the CCOs. By coculturing CCOs with glioma stem cells, we demonstrated that this model effectively recapitulates the tumor niche of glioblastoma, showing vascular co-option, reprogramming of microglia into tumor-associated macrophages, and recurrence after radiotherapy. In conclusion, our vascularized and immunocompetent CCO model will be invaluable for understanding human brain development, exploring how this process is disrupted in diseases like gliomas, and discovering new therapeutic strategies.