Main Session
Sep
28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology
Presenter(s)
Jinyi Lang, MD, PhD - Sichuan Cancer Hosiptal and Institute, Chengdu, Sichuan
M. Chen1, Z. Fang2, and J. Lang2; 1Department of Radiation Oncology, Precision Radiation in Oncology Key Laboratory of Sichuan Province, Chengdu, Sichuan, China, 2Department of Radiation Oncology, Radiation Oncology Key Laboratory of Sichuan Province, Sichuan Clinical Research Center for Cancer, Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, University of Electronic Science and Technology of China, Chengdu, Sichuan, China
Purpose/Objective(s):
Minibeam radiation therapy (MBRT) combined with bevacizumab has been shown to normalize tumor vasculature and enhance CD8+ T cell infiltration. However, whether this combination can fully reprogram the immunosuppressive tumor microenvironment (TME) remains unknown. This study aims to comprehensively investigate the compositional and spatial remodeling of the TME induced by MBRT plus bevacizumab.Materials/Methods:
Female BALB/c mice bearing orthotopic 4T1 breast tumors were randomly assigned to four groups: Control, MBRT alone, bevacizumab (Bev) alone, and MBRT+Bev combination. Tumors were harvested on day 7 post-treatment. We performed multiplex immunofluorescence (mIF) staining to simultaneously visualize and quantify: Tumor vasculature (CD31) and endothelial activation (ICAM1); Cytotoxic T cells (CD8) and their exhaustion status; Regulatory T cells (Foxp3); Myeloid-derived suppressor cells (Gr1). Key spatial parameters analyzed included: density of CD8+ T cells in the tumor parenchyma vs. stroma; proximity analysis of CD8+ T cells to Foxp3+ Tregs; colocalization of CD8+ T cells with ICAM1+ vessels.Results:
Combination therapy with MBRT+Bev significantly suppressed tumor growth and prolonged survival compared to monotherapies. mIF analysis revealed profound remodeling of the TME at both compositional and spatial levels. Consistent with our previous findings, MBRT+Bev upregulated endothelial ICAM1 expression and increased total CD8+ T cell infiltration by approximately 2-fold. Critically, spatial analysis showed that these CD8+ T cells were predominantly localized within the tumor parenchyma (p<0.01 vs. control), whereas in untreated tumors, CD8+ T cells remained largely trapped in the perivascular stroma. Beyond increasing infiltration, the combination therapy significantly reduced the fraction of CD8+ T cells co-expressing exhaustion markers PD-1 and TIM-3 (p<0.01 vs. control), indicating a functional rejuvenation of effector T cells. MBRT+Bev drastically reduced the intratumoral density of Foxp3+ Tregs and Gr1+ MDSCs. More importantly, proximity analysis revealed that in the combination group, the remaining CD8+ T cells were significantly less likely to be found in close proximity (<20µm) to Foxp3+ Tregs, effectively disrupting the formation of localized immunosuppressive niches that impair T cell function.Conclusion:
This study provides the first spatial evidence that MBRT combined with bevacizumab does more than simply open the vascular gate for T cell entry. The combination therapy actively reconstructs the tumor immune ecosystem by: (i) facilitating the penetration of CD8+ T cells into the tumor parenchyma, (ii) alleviating their exhaustion status, and (iii) physically separating them from suppressive Tregs. This comprehensive spatial reprogramming of the TME offers a strong rationale for integrating MBRT with vascular normalization strategies to overcome immunotherapy resistance and achieve durable antitumor responses.