Abstract A030: A deeper understanding of tumor microenvironment modulation induced by IL13Ra2 CAR T cells in a patient with grade 3 ependymoma

Abstract Grade 3 ependymoma is classified as a fast-growing solid tumor that often occurs in the base of the brain with a median survival of less than two years. Despite aggressive standard treatments (surgery, radiation therapy and chemotherapy), grade 3 ependymoma remains uniformly fatal, especially if the tumor cannot be completely removed or if it spreads to other areas of the central nervous system (CNS). Achieving a responsive therapy with chimeric antigen receptor (CAR) T cell therapy has been a significant challenge due to evasive tumor microenvironment, specifically utilized by slid tumors, to resist therapy. Recent studies have highlighted the substantial role of glioma-associated stromal cells in solid tumors by depositing various collagen subunits, including COL1A1, within the extracellular matrix (ECM). This collagen deposition leads to increased ECM stiffness, modulating the tumor microenvironment, inducing immune suppression (e.g. SPP1 overexpression), and hindering T cell trafficking, ultimately worsening clinical outcomes and patient survival. To gain a better understanding of the role of the tumor microenvironment in CAR T persistence and efficacy, we designed and performed ultra-high plex immunofluorescent staining on tissue biopsies obtained from a patient with grade 3 ependymoma before and after treatment with IL13Ra2 CAR T cells. The patient has been received three CAR T infusions at weekly intervals. The tissues were stained for CD3, CD19 (CAR T cells), CD68, CD163, HLA-DR (macrophages), CD3, CD8 (endogenous T cells), SOX2 (stem cells), SPP1 (suppression) and COL1A1 (extracellular matrix). The presence of CAR T cells in tissue biopsies indicated persistence of IL13Ra2 CAR T cells for more than a year. Our preliminary analysis revealed an increase in the number of HLA-DR+ CD163+ macrophages within cellular neighborhoods associated with CAR T cells (around 50% of CD163+ express HLA-DR after treatment) as compared to baseline tumors, which suggests a dynamic interaction between myeloid subsets and CAR T cells within the tumor microenvironment. Ongoing experiments are currently investigating the presence of antigen presenting natural killer cells (CD56, HLA-DR), proliferative T cells (CD3, Ki67) and inflammatory macrophages and/or T cells (IFNg) to gain a better understanding of IL13Ra2 persistence in brain tumor patients. Citation Format: Maryam Aftabizadeh, Brenda Aguilar, Massimo D'Apuzzo, Behnam Badie, Christine E Brown. A deeper understanding of tumor microenvironment modulation induced by IL13Ra2 CAR T cells in a patient with grade 3 ependymoma [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr A030.