IMMU-86. Dynamic Treg-myeloid crosstalk dictates glioblastoma progression

Abstract Glioblastoma (GBM) remains a highly aggressive brain tumor with limited therapeutic options and significant immune evasion. Tumor-associated regulatory T cells (Tregs) and macrophages (TAMs) are central orchestrators of the GBM immune microenvironment; however, the dynamics and subtype-specific interactions between these populations during disease progression are still poorly understood. In this study, we utilized complementary mesenchymal and proneural murine GBM models to examine the differentiation trajectories and functional crosstalk of Tregs at single-cell resolution. Single-cell RNA sequencing (scRNA-seq) of tumor-infiltrating Tregs revealed that mesenchymal GBM promoted the expansion of an immunosuppressive Treg population characterized by elevated CCR8 (C-C chemokine receptor type 8), GITR (Glucocorticoid-Induced TNFR-Related protein), and IL1R2 (Interleukin 1 Receptor Type 2), which was less pronounced in proneural GBM. Trajectory analysis uncovered enhanced proneural-to-mesenchymal transition signatures, indicating dynamic Treg adaptation to evolving tumor states. Validation in human spatial transcriptomic GBM datasets revealed that the murine tumor Treg signature was enriched within mesenchymal regions and closely associated with myeloid-dense microenvironments. By leveraging a time-course scRNA-seq dataset from the mesenchymal GBM model, we observed a progressive expansion of the mesenchymal-like Treg signature paralleling tumor evolution and mesenchymal transition. Notably, CellChat-based cell–cell communication analysis demonstrated that Treg–myeloid interactions were not only enhanced over time but also that Treg subsets differentially engaged with immunosuppressive TAMs through unique ligand–receptor pairs, underscoring the dynamic and reciprocal adaptation between regulatory and myeloid compartments. Collectively, our study delineates a model in which GBM progression is shaped by the evolving interplay of Treg and myeloid programs, providing a framework for targeting context-specific immunosuppressive circuits in future immunotherapeutic strategies.