Author: MacKenzie Rachelle Coon, Justin Geise, Judith Noemi Rivera, Matthew L. Scarpelli, Jessica Leigh Veenstra, Chandler Zaugg 👨🔬
Affiliation: Purdue University, Indiana University 🌍
Purpose: Glioblastoma (GBM) is among the most aggressive and treatment-resistant cancers due to its immunosuppressive tumor microenvironment. Immunotherapy holds promise for GBM treatment, but its efficacy is constrained by limited immune activity within the tumor. This study investigates how radiation therapy (RT) modulates immune cell populations in the GBM microenvironment to identify RT regimens that prime the tumor for adoptive immunotherapy. By elucidating immune response timing, we aim to establish optimal conditions for combining RT with immunotherapy to improve clinical outcomes.
Methods: Thirty-four mice (18 female, 16 male) were orthotopically injected with GL-261 glioma cells to establish a GBM model. Immune cells were evaluated in female mice across three time points (24, 72, and 144 hours) post-RT. Male mice were assessed at 72 hours post-RT. Immune cells were quantified using immunohistochemistry and included natural killer cells (CD335+), neutrophils (Ly6G+), T-cells (CD3+), and macrophages (CD68+). Pairwise comparisons assessed RT-induced immune cell changes relative to control cohorts without RT.
Results: In female mice, macrophage populations increased significantly at 72 hours (p=0.01) and 144 hours (p=0.002) after a 20-Gy radiation dose, suggesting a central role in immune priming. T-cells significantly decreased at 24 hours after 20-Gy (p=0.03), indicating potential early immunosuppression of these cells, but recovered by 144 hours. In contrast, natural killer cells and neutrophils showed no significant changes, highlighting cell-specific responses to RT. In male mice, macrophage populations increased significantly at 72 hours after 20-Gy (p=0.04), while other immune populations showed no significant changes.
Conclusion: This study demonstrates RT's potential to modulate immune populations and create a therapeutic window for adoptive immunotherapy in GBM. Of note were significant increases in macrophage populations 72 hours post-RT, indicative of a potential target for combination immunotherapy. By identifying optimal time points for immune infiltration, this work provides a framework for designing synergistic RT-immunotherapy regimens.