Neoplastic and non-neoplastic astrocyte states converge on mesenchymal and injury-response programs during glioblastoma recurrence.

Glioblastomas initially respond to radiotherapy but invariably recur, often within high-dose radiation treatment fields. Although stromal radiation responses are incompletely understood, evidence suggests that the tumor microenvironment becomes tumor-supportive after therapy. Using a genetically engineered glioblastoma mouse model, we profiled healthy brain, primary tumors, and post-radiotherapy recurrences with single-cell and spatial transcriptomics and immunofluorescence. Across 13 non-neoplastic cell types and 10 tumor cell states, we mapped transcriptional adaptations accompanying progression from healthy brain to primary and recurrent glioblastoma. We find distinct astrocyte states linked to disease stage, including reactive, non-neoplastic astrocytes and tumor cells adopting reactive astrocyte-like phenotypes. Reactive astrocyte-like tumor cells with mesenchymal and injury-response signatures are enriched after radiotherapy and persist in recurrent tumors. Receptor-ligand interactions between reactive astrocytes and tumor cells include known and putative drivers of aggressiveness. These findings highlight convergent reactive astrocyte programs in astrocytes and tumor cells as potential mediators of glioblastoma radioresistance.