Kasey Nguyen

Background:  Glioblastoma (GBM) is a World Health Organization grade IV astrocytoma and the most aggressive primary brain tumor in adults. Despite maximal safe surgical resection, radiation, and chemotherapy with temozolomide, median survival remains 12–15 months. GBM’s poor prognosis is largely attributed to its infiltrative growth, treatment resistance, and profound heterogeneity. The tumor microenvironment (TME) in GBM is highly immunosuppressive, dominated by tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), and inhibitory cytokines like interleukin-10 (IL-10), which promote T-cell exhaustion and immune evasion.¹⁻³ This immune landscape limits the efficacy of traditional immunotherapies, including checkpoint inhibitors and conventional chimeric antigen receptor (CAR) T-cell therapies. SynNotch-CAR T cells, which require a tumor-specific “priming” antigen to trigger CAR expression against a secondary target, offer a novel logic-gated approach to improve specificity and persistence in targeting GBM.⁴

Objective:This review aimed to investigate the mechanisms by which GBM induces immune suppression and evaluate SynNotch-CAR T cells’ therapeutic potential in overcoming barriers such as antigen heterogeneity and T-cell dysfunction.

Search Methods:  A comprehensive literature search was conducted using PubMed for articles published between 2017 and 2024. Search terms included “glioblastoma,” “CAR T cells,” “SynNotch,” “immune suppression,” “tumor microenvironment,” and “T-cell exhaustion.” MeSH terms and keywords were used to identify primary studies, preclinical trials, and clinical data on immunotherapy in GBM.

Results:  GBM reshapes its TME by epigenetically reprogramming glioma stem cells to adopt myeloid-like transcriptional profiles, promoting TAM recruitment via Ccl2 and Ccl9.² IL-10 secreted by TAMs and MDSCs induces CD8⁺ T-cell exhaustion, as demonstrated by their spatial co-localization and suppressed cytotoxic profiles.³ JAK/STAT pathway inhibition restored T-cell activity in ex vivo human GBM models and in vivo murine studies.³ SynNotch-CAR T cells activate only after encountering a priming antigen like EGFRvIII or MOG, leading to subsequent CAR expression against IL13Rα2 or EphA2—common GBM markers.⁴ Preclinical studies showed that SynNotch-CARs reduced off-tumor toxicity, resisted exhaustion, and achieved better tumor clearance than conventional CARs.⁴ Complementing these preclinical insights, a Phase I trial using IL13Rα2-targeting CAR T cells showed clinical benefit and safety in patients with recurrent high-grade glioma, particularly with dual intratumoral and intracerebroventricular delivery.⁵

Conclusion: GBM’s immunosuppressive TME, driven by TAMs, IL-10, and antigenic diversity, poses major challenges to conventional immunotherapy. SynNotch-CAR T cells address these barriers by integrating multi-antigen recognition and conditional activation, enhancing specificity while preserving T-cell potency. Future strategies may involve combining SynNotch-CARs with JAK/STAT inhibitors or myeloid-targeting agents to synergistically restore immune function. Further clinical trials are needed to validate these findings and determine optimal therapeutic sequencing. SynNotch-based platforms represent a promising frontier in precision immunotherapy for GBM.

Works Cited:

1. Yeo AT, Rawal S, Delcuze B, et al. Single-cell RNA sequencing reveals evolution of immune landscape during glioblastoma progression. Nat Immunol. 2022;23(6):971-984. doi:10.1038/s41590-022-01187-2
2. Gangoso E, Southgate B, Bradley L, et al. Glioblastomas acquire myeloid-affiliated transcriptional programs via epigenetic immunoediting to elicit immune evasion. Cell. 2021;184(9):2454-2470.e26. doi:10.1016/j.cell.2021.03.028
3. Ravi VM, Neidert N, Will P, et al. T-cell dysfunction in the glioblastoma microenvironment is mediated by myeloid cells releasing interleukin-10. Nat Commun. 2022;13(1):925. doi:10.1038/s41467-022-28565-4
4. Choe JH, Watchmaker PB, Simic MS, et al. SynNotch-CAR T cells overcome challenges of specificity, heterogeneity, and persistence in treating glioblastoma. Sci Transl Med. 2021;13(591):eabe7378. doi:10.1126/scitranslmed.abe7378
5. Brown CE, Hibbard JC, Alizadeh D, et al. Locoregional delivery of IL-13Rα2-targeting CAR-T cells in recurrent high-grade glioma: a phase 1 trial. Nat Med. 2024;30(4):1001-1012. doi:10.1038/s41591-024-02958-4