Clinical trials have shown limited efficacy of anti–PD-1 treatment for glioblastoma (GBM). In this study, we examined the expression of TGFβ type I receptor (TGFβRI) in GBM-infiltrating CD8⁺ T cells and the characteristics of TGFβRI⁺CD8⁺ T cells. We examined the ex vivo effects of the co-blockade of PD-1 and TGFβ on the functions of GBM-infiltrating CD8⁺ T cells.

Using flow cytometry, we examined the phenotypes of tumor-infiltrating CD8⁺ T cells from newly diagnosed patients with GBM. We performed single-cell RNA/T-cell receptor sequencing to characterize the tumor-infiltrating TGFβRI⁺CD8⁺ T cells. We also examined the effects of co-blockade of PD-1 and TGFβ on the functions of tumor-infiltrating CD8⁺ T cells in ex vivo assays.

GBM-infiltrating CD8⁺ T cells expressed significantly increased levels of TGFβRI compared with peripheral blood CD8⁺ T cells. Among tumor-infiltrating CD8⁺ T cells, TGFβRI⁺CD8⁺ T cells exhibited increased expression of immune checkpoint inhibitory receptors, and tumor antigen–specific cells were enriched in TGFβRI⁺CD8⁺ T cells. Single-cell profiling revealed that tumor-infiltrating TGFBR1⁺CD8⁺ T cells demonstrated more clonal expansion and upregulation of T-cell receptor signaling genes compared with TGFBR1⁻CD8⁺ T cells. In vitro, anti-CD3 stimulation upregulated TGFβRI expression on CD8⁺ T cells. Patients with GBM with a high frequency of TGFβRI⁺CD8⁺ T cells presented with increased TGFβ signaling intensity. Importantly, combined blockade of PD-1 and TGFβ significantly enhanced the functions of tumor-infiltrating CD8⁺ T cells ex vivo.

Our findings provide a basis for further investigation of the co-blockade of PD-1 and TGFβ for the treatment of patients with GBM.