Abstract 3444: Spatial profiling of recurrent glioblastoma in a Phase I clinical trial reveals favorable immune remodeling induced by intracerebroventricular CAR T therapy

Abstract Recurrent glioblastoma (rGBM) is an aggressive brain tumor with median survival under one year after standard chemoradiation. Antigen heterogeneity, immune exclusion, and a suppressive tumor microenvironment (TME) limit responses to immunotherapy. A first-in-human phase 1 trial of intracerebroventricular EGFR/IL13Rα2 CAR T cells (CART-EGFR-IL13Rα2) in EGFR-amplified rGBM was feasible, produced manageable neurotoxicity, and induced radiographic tumor regressions in a subset of patients (NCT05168423).To understand how this therapy reshapes the local TME, we analyzed paired tumor resections from 6 patients enrolled in the phase 1 trial, with specimens obtained from the primary intracranial disease site at trial enrollment (pre-treatment) and at radiographic progression after CART-EGFR-IL13Rα2 infusion. Multimodal spatial profiling included regional transcriptomic and protein mapping (GeoMx), single-cell whole-transcriptome imaging (CosMx), and high-resolution spatial transcriptomics (Visium HD). We annotated tumor, myeloid, lymphoid, and stromal compartments and derived composite scores for stemness, invasion, cell death, and immune regulation. Neighborhood- and interaction-based analyses were used to compare cellular states and cell-cell communication.Across patients, post-treatment samples showed reduced expression of CAR target antigen and a shift in tumor-intrinsic programs toward less stem-like, less migratory, and more apoptotic states, despite radiographic progression. The post-treatment TME was remodeled, with fewer suppressive myeloid- and B-cell-rich niches and increases in interferon-responsive and T cell-associated activation programs. Spatial interaction analyses indicated that pre-treatment rGBM contained dense networks of myeloid-tumor and myeloid-T-cell contacts consistent with impaired antigen presentation and effector function. Post-treatment specimens, in contrast, showed partial disruption of these suppressive circuits and the emergence of microenvironments more permissive to T-cell infiltration and activity.In the parent phase 1 trial, CART-EGFR-IL13Rα2 was feasible Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3444.