Medulloblastoma (MB) groups 3 and 4 arise from human-specific developmental contexts that remain experimentally inaccessible, limiting mechanistic insight into tumor initiation. We generated cerebellar organoids (CbOs) from expanded potential stem cells (EPSCs) and performed integrated single-cell transcriptomic and DNA methylation analyses, revealing discrete human rhombic lip progenitor populations whose developmental programs align with group 3- and group 4-associated lineages. Using c- MYC overexpression as an initiating oncogenic event, we demonstrated that these lineage-restricted progenitors are susceptible to neoplastic transformation, generating tumors with group 3 MB molecular features in vitro and in vivo. We further established a CbO-MB coculture system that preserves malignant and nonmalignant cellular compartments, hence enabling interrogation of tumor–microenvironment interactions and providing simultaneous readouts of antitumor efficacy and cerebellar toxicity upon drug treatment. Receptor–ligand modeling in this system identifies TGFβ paracrine signaling as a microenvironmental pathway supporting MB growth, which we validated pharmacologically. Further analyses of cocultured MB cells revealed a myogenic differentiation program enriched in MYC -driven MB and recurrent disease, which is associated with poorer prognosis. Together, this work establishes a collection of CbO models for studying group 3/4 MB initiation, growth, and microenvironmental dependencies and provides a tractable platform for further mechanistic and therapeutic investigation of these tumors.
Willott et al. (Wed,) studied this question.