Abstract 4045: Collagen binding enhances anti-CTLA4 therapy in recurrent glioblastoma

Abstract Recurrent glioblastoma (rGBM) is an aggressive malignant brain tumor, with a median survival of 6 months. rGBM establishes an immunosuppressive tumor microenvironment (TME) driven by regulatory T cells (Treg) and exhausted T cells (Tex). Since both Treg and Tex highly express CTLA4, antagonistic CTLA4 antibodies (αCTLA4) were considered promising therapeutic agents. Despite this rationale, clinical trials showed no survival benefit in rGBM, likely due to poor tumor penetration of αCTLA4. Therefore, technology to enhance αCTLA4 delivery in rGBM tissue is critically needed. rGBM acquires treatment resistance through alteration of extracellular matrix (ECM) proteins in the tumor microenvironment (TME). Our lab proposes utilizing this ECM change as a reservoir to accumulate αCTLA4. We focused on COL I & III, which are minimally expressed in the normal brain but highly upregulated in rGBM. We created CBD-αCTLA4 by fusing αCTLA4 with the collagen-binding domain (CBD) of von Willebrand factor (vWF), leveraging vWF's selective binding to COL I & III at sites of vascular disruption, inflammation, and tumors while sparing normal organs with COLI&III high expression. In syngeneic rGBM murine models, CBD-αCTLA4 showed greater accumulation than αCTLA4 using confocal microscopy and biodistribution assay. Single-cell RNAseq showed CBD-αCTLA4 reduced Treg and Tex populations within rGBM tumors, thereby transforming the immunosuppressive TME and facilitating the recruitment of type 1 conventional dendritic cells (cDC1s) into the tumor. Survival analysis in our models revealed CBD-αCTLA4 treatment (100μg i.v., twice) prolonged survival by 140% with a 14% CR rate in rGBM mice models, while αCTLA4 (non-CBD) treatment showed no survival extension. For clinical translation, we developed a humanized CBD-αCTLA4 (CBD-Ipilimumab) and validated its efficacy in 3D human GBM slice cultures, demonstrating decreased Treg cells in human tumor tissue. Furthermore, CBD-ipilimumab significantly prolonged survival in peripheral blood mononuclear cell (PBMC)-humanized mice bearing human rGBM tumors. Collagen-binding αCTLA4 achieved enhanced intratumoral accumulation, reversed the immunosuppressive profile, and elicited potent antitumor effects in rGBM. Our results suggest that CBD-αCTLA4 holds significant promise as an innovative immunotherapy for rGBM. Moreover, this collagen-targeting platform has broad implications, as it can be extended to other antibody-based therapeutics for brain tumors. Citation Format: Lewis Barr, Jun Takei, Chuyi Wang, Opeyemi Iwaloye, Ken Furudate, Haruka Ichie, Shunsuke Tsuzuki, Jun Ishihara, Satoru Osuka. Collagen binding enhances anti-CTLA4 therapy in recurrent glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4045.