Abstract 959: Immune signatures of GD2 CAR T cell activity in H3K27M+ diffuse midline glioma patients

Abstract Introduction: H3K27M-mutated diffuse intrinsic pontine glioma (DIPG) and spinal cord diffuse midline glioma (DMG) are universally lethal central nervous system (CNS) tumors in children and young adults. We previously demonstrated safety and activity of GD2.41BB.z chimeric antigen receptor T cells (CAR-Ts) at dose level 1, 1x106 GD2 CAR-T/kg (Majzner/Ramakrishna et al. Nature 2022) and reported results of dose level 2, 3x106 GD2 CAR-T/kg (Majzner et al. AACR 2022). Here, we present in depth high-dimensional analyses to define the immune states that contribute to CAR-T activity in patients. Methods: Thirteen patients (10 DIPG/3 spinal DMG; 4-30 years old; 7F/6M) were enrolled in this GD2 CAR-T phase 1 clinical trial (NCT04196413). GD2 CAR-Ts were administered to 12/13 enrolled patients. In the first cohort, CAR-Ts were administered initially intravenously (IV), followed by serial intracerebroventricular infusions (ICV; range 0-11 infusions/patient). Patient GD2 CAR-T product, peripheral blood, and cerebrospinal fluid (CSF) samples were evaluated for CAR-T expansion (qPCR; flow cytometry), cytokine signatures (Multiplex Luminex), and immune cell profiles (single cell RNA-sequencing). Data were analyzed in the context of clinical trajectory and patient response. Results: 10/12 infused subjects demonstrated clinical and/or radiographic benefit, with less systemic toxicity following ICV compared to IV infusion. CAR-T expansion was noted in the periphery and CSF of all treated patients and following serial ICV infusions. In peripheral blood, cytokine concentrations, including IFN-gamma, IL6, and CXCL9, were higher after IV compared to ICV CAR-T infusions, correlating with increased systemic inflammation. Conversely in CSF, cytokine concentrations, such as CCL2 and CXCL9, were higher following ICV compared to IV CAR-T infusions. Transcriptomic analysis was conducted on 576,199 single cells from 91 samples, including GD2 CAR-T products and patient CSF. This is the largest CAR-T dataset in CNS tumors. Patient CSF samples were dominated by T cell and myeloid populations. After IV CAR-T infusion, patient CSF exhibited an increased fraction of regulatory T cells and suppressive myeloid populations from baseline. These immune suppressive cells reduced after ICV infusion. Ongoing analyses are underway to explore the relation of these immune populations to patient response. Conclusions: H3K27M-mutated DIPG/DMG patients demonstrate continued clinical response with serial ICV GD2 CAR-T infusions, with heterogeneity in the durability of response across patients. In-depth correlative analyses profile distinct immune populations and demonstrate population shifts depending on route of administration and over the course of treatment. Key findings from these data will allow for iterative improvement in CAR-T therapies for H3K27M+ DIPG/DMG patients, providing hope to shift the paradigm of this fatal disease. Citation Format: Sneha Ramakrishna, Zinaida Good, Moksha Desai, Daniel Zamler, Rebecca Mancusi, Jasia Mahdi, Robbie Majzner, Liora Schultz, Rebecca Richards, Jennifer Kamens, Valentin Barsan, Cynthia Campen, Sonia Partap, Zachary Ehlinger, Warren Reynolds, Yiyun Chen, Mark P. Hamilton, Jennifer Moon, Christina Baggott, Michael Kunicki, Michelle Fujimoto, Amy Li, Sneha Jariwala, Sharon Mavroukakis, Emily Egeler, Ashley Jacobs, Courtney Erickson, Karen Yamabe-Kwong, Snehit Prabhu, Kara Davis, Steve Feldman, Bita Sahaf, Crystal L. Mackall, Michelle Monje. Immune signatures of GD2 CAR T cell activity in H3K27M+ diffuse midline glioma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 959.