171 Characterisation of macrophage and microglial phenotype within resected glioblastoma tissue and potential for re-polarisation using precision cut human tissue slices

Abstract

Glioblastoma is the most common and most aggressive primary brain tumour in adults, representing one of the most formidable challenges in oncology. Despite surgical resection, radiotherapy and chemotherapy, median survival rates are low (12-18 months) with fewer than 10% of patients surviving beyond five years. These stark statistics highlight the clear unmet therapeutic need. A defining feature of glioblastomas is the profound immunosuppressive tumour microenvironment that hampers anti-tumour immune activity. To interrogate this environment, we have used high-parameter flow-cytometry (21 markers in total) to comprehensively characterise immune cell populations within freshly resected ‘near in vivo’ glioblastoma tumour tissue, with a particular focus on macrophage and microglial populations. Our analysis revealed that macrophages and microglia dominated the CD45+ immune cell infiltrate within glioblastoma albeit with inter-patient heterogeneity in ratios of macrophage-like (CD11b+, TMEM119-) vs microglial-like (CD11b+, TMEM119+). In general, skewing towards an immunosuppressive ‘M2-like’ phenotype was judged by expression of CD163 and/or CD206 yet their profiles did not necessarily fit a traditional ‘M1 vs M2’ dichotomy, highlighting the limitations of oversimplified classification frameworks in this disease context. Surprisingly in some donors, toll-like receptor agonism only exerted limited phenotypic reprogramming in macrophages and microglia, which suggests intrinsic resistance to innate immune activation. In contrast, exogenous pro-inflammatory cytokines more profoundly tilted the balance towards ‘M1-like’ phenotypes, revealing an underappreciated capacity for functional plasticity within these cells. The predominance of macrophages and microglia within the glioblastoma microenvironment positions them as potentially critical effectors for immuno-therapies. Our findings further highlight both the complexity and therapeutic malleability of these myeloid populations, strengthening the rationale for strategies that re-educate tumour-associated macrophages and microglia, shifting them from immunosuppressive accomplices to pro-inflammatory anti-tumour effectors.