Targeting hypoxia-driven histone lactylation in myeloid cells synergizes with CD137 agonism to expand effector-like exhausted CD8+ T cells in glioblastoma.

BACKGROUND: Overwhelming presence of immunoregulatory myeloid cells and dysfunctional T cells is a major barrier to effective immunotherapies in glioblastoma (GBM). Therapeutic strategies that simultaneously address myeloid-driven immunosuppression and impaired T cell function are therefore needed to restore antitumor immunity in GBM.

METHODS: We employed single-cell RNA sequencing, immunophenotyping, and functional analyses in an orthotopic murine GBM model (SB28) to investigate how hypoxia shapes the tumor immune microenvironment and limits CD8+ T cell responses. Pharmacologic hypoxia modulation using low-dose axitinib was combined with therapeutic intervention targeting CD137 in two GBM models (SB28, CT2A).

RESULTS: Monocyte-derived macrophages (MDMs) and neutrophils constitute the most abundant and functionally immunosuppressive myeloid subsets within the GBM TME. Hypoxia reprogrammed MDMs and neutrophils into immunosuppressive cells, limiting the expansion of CD8+ T cells. Low-dose axitinib reduced intratumoral hypoxia, leading to altered glucose uptake and histone lactylation in MDMs and neutrophils, thereby impairing their immunosuppressive function and promoting the expansion of intratumoral PD-1+CD137+CD8+ T cells, specifically in the SB28 model. CD137 is largely expressed by effector-like exhausted CD8+ T cell subsets (EX-eff). Agonistic targeting of CD137, in combination with axitinib, robustly expanded EX-eff, which was accompanied by durable tumor regression, immunological memory, and long-term survival. Additionally, the abundance of PD-1+CD137+CD8+ T cells correlated with improved disease-free survival in patients with GBM.

CONCLUSION: Together, these findings establish a rationale for a combinatorial strategy that couples myeloid cells targeting and CD8+ T cell activation to overcome immunotherapy resistance in GBM.