Microglia Reprogramming in Glioblastoma: Stem Cell-Derived Factors as Emerging Immunomodulators

Glioblastoma (GBM) remains one of the most challenging forms of cancer to treat, despite that extensive molecular profiling is now available. Indeed, intratumoral cellular heterogeneity, receptor redundancy, and adaptive resistance through compensatory signaling limit the impact of targeted therapies. Moreover, immunotherapies also underperform: checkpoint blockade and vaccine strategies did not obtain consistent benefits in a low mutational burden, poorly immunogenic tumor microenvironment (TME) dominated by immunosuppressive myeloid cells. In this article, we provide evidence that tumor-associated macrophages (TAMs), a form of CNS resident microglia and infiltrating macrophage, derived from bone marrow, adopt a spatially and transcriptionally distinct, non-binary continuum, shaped by tumor-derived signals and niche constraints, allowing glioma cells to resist to immune and pharmaceutical therapeutics. Metabolic rewiring, including hypoxia-linked glycolytic pressure, lactate signaling, and lipid-associated programs, determine immunosuppressive outputs and restrict plasticity, while epigenetic imprinting (DNA methylation, histone modifications, and chromatin regulators) stabilizes these programs and limits access to inflammatory loci. We discuss how stem cell secretome, and extracellular vesicles (EVs) and their cargo may act as tunable autocrine/paracrine inputs that may bias microglial regulatory control. Finally, we highlight major translational confounders, including EV operational definitions, blood-brain barrier (BBB) permeability and regional exposure, inconsistent dosing units, mixed myeloid compartments, and manufacturing dependent variability. Therefore, an exposure-aware framework that integrates product identity, delivery evidence, state-sensitive potency assays, and functional endpoints would be highly desirable.