Tonic Signaling Shaped by Epitope Targeting Governs CAR-T Cell Fitness and Antitumor Activity in Diffuse Midline Glioma [RNA-Seq]

We systematically evaluated B7-H3–targeting CAR-T cells derived from three monoclonal antibodies (376.96, MGA271, and Hu8H9) in diffuse midline glioma (DMG or DIPG), a fatal pediatric brain tumor. Among these, 376.96 CAR-T cells had markedly lower tonic signaling, diminished expression of exhaustion markers, and enhanced tumor killing, cytokine production, and persistence. Transcriptomic and epigenomic profiling revealed a restrained activation state with reduced tonic signaling pathways and elevated stemness properties, oxidative metabolism, and innate immune sensing in these cells. In patient-derived spheroids and orthotopic DIPG xenografts, mRNA-based 376.96 CAR-T cells achieved robust tumor control and extended survival. By leveraging epitope selection, we reveal a mechanistic link between tonic signaling and CAR-T cell exhaustion, and provide a rational framework for optimizing CAR-T cell design to achieve improved efficacy and durability in pediatric brain tumor therapy.