Blood-brain barrier and blood-tumoral barrier formation in glioblastoma: endothelial cells and glioblastoma stem cells at the immune-brain crossroad.

Glioblastoma (GBM) is the most aggressive primary brain tumor characterized by significant cellular and molecular complexity. Central to this complexity are glioma stem cells (GSCs) and the perivascular niche, a specialized microenvironment that integrates signals from the systemic circulation with cues arising from tumor development. Acting as a regulatory hub, the perivascular niche influences GSC proliferation, migration, and resistance to therapy through multiple interactions among vascular, immune, and tumor cell populations. In this review, we focus on GSCs and examine the cellular composition and molecular mechanisms operating within the perivascular niche, highlighting key modes of crosstalk that sustain tumor progression. We furthermore critically evaluate experimental strategies used to study this compartment, including 2D and 3D cell cultures, organoids, and in vivo models, discussing their respective strengths and limitations for testing intercellular interactions and therapeutic approaches. A comprehensive understanding of tumor heterogeneity and the interactions between different tumor cell populations, combined with well-characterized experimental models, is essential for deriving mechanistic insights and informing the development of more effective targeted therapies for GBM, ultimately advancing our knowledge of how tumor-microenvironment interactions drive GBM progression.