Distinctive features of the tumor and immune microenvironment in glioblastoma

Immune checkpoint inhibitors (ICI) have improved outcomes for asymptomatic patients with melanoma brain metastases (MBM) but have delivered limited benefit in glioblastoma (GBM). Defining context-dependent features of ICI response is critical for tailoring effective therapeutic strategies and improving GBM patient outcomes. Multiparameter flow cytometry analyses of immune composition and activation status were performed on 110 tumor cell suspensions obtained from cavitron ultrasonic surgical aspirates (CUSA) specimens (n = 40), and surgically resected GBM (n = 21) and MBM (n = 49) tumors. GBM tumors exhibited marked phenotypic heterogeneity, frequently co-expressing stem-like and differentiation markers. GBM stemness correlated with increased macrophage infiltration and reduced T cell abundance, implicating plasticity in the establishment of an immunosuppressive microenvironment. Compared to MBM, GBM showed a marked paucity of T cells, an enrichment of myeloid cells, downregulated MHC-I, and elevated PD-L2 expression on tumor cells. Multiplex immunostaining performed on a subset of GBM samples, confirmed myeloid predominance and indicated pronounced spatial heterogeneity. However, the presence of antigen-experienced T cells and preserved IFNγ signaling indicates a latent potential for immune engagement. These findings provide a rationale for ICI-based combinations designed to restore effective anti-tumor immunity in GBM.