Cellular Allies Against Glioblastoma: Therapeutic Potential of Macrophages and Mesenchymal Stromal Cells

Background/Objectives: Glioblastoma (GBM) remains the most aggressive primary brain tumor in adults, with limited therapeutic options and poor prognosis despite maximal surgery, radiotherapy, and chemotherapy. The complex and immunosuppressive tumor microenvironment, pronounced intratumoral heterogeneity, and the presence of the blood–brain barrier (BBB) severely restrict the efficacy of conventional and emerging therapies. In this context, cell-based strategies leveraging macrophages, mesenchymal stromal cells (MSCs), and their derivatives have gained attention as “cellular allies” capable of modulating the GBM microenvironment and acting as targeted delivery platforms. Methods: This review systematically analyzes preclinical and early clinical literature on macrophage- and MSC-based therapeutic strategies in GBM, including engineered cells, extracellular vesicles (EVs), membrane-coated nanoparticles, and hybrid biomimetic systems. Studies were selected based on relevance to GBM biology, delivery across or bypass of the BBB, microenvironmental modulation, and translational potential. Evidence from in vitro models, orthotopic and syngeneic in vivo models, and available clinical trials was critically evaluated, with emphasis on efficacy endpoints, biodistribution, safety, and manufacturing considerations. Results: The reviewed evidence demonstrates that macrophages and MSCs can function as active therapeutic agents or delivery vehicles, enabling localized oncolysis, immune reprogramming, stromal and vascular remodeling, and enhanced delivery of viral, genetic, and nanotherapeutic payloads. EVs and membrane-based biomimetic platforms further extend these capabilities while reducing cellular risks. However, therapeutic efficacy is highly context-dependent, influenced by tumor heterogeneity, BBB integrity, delivery route, and microenvironmental dynamics. Clinical translation remains limited, with most approaches at preclinical or early-phase clinical stages. Conclusions: Cell-based and cell-derived platforms represent a promising but still evolving therapeutic paradigm for GBM. Their successful translation will require rigorous biomarker-driven patient selection, improved models that capture invasive GBM biology, scalable GMP-compliant manufacturing, and rational combination strategies to overcome adaptive resistance mechanisms.