Exhausted status and anti-PD-1 response of tumor-infiltrating $CD8^+$ T cells in patients with glioblastoma

Abstract

Glioblastoma(GBM) is the most common and aggressive primary malignant brain tumor and has a poor prognosis. Recently, Immune checkpoint inhibitors (ICIs) are used for the treatment of various cancers, but clinical trials of anti-PD-1 with recurrent GBM patients have failed to show clinical benefits. Several factors may limit the efficacy of ICIs, including the exhaustion status of tumor-infiltrating lymphocytes (TILs). Therefore, in this study, we examined the differentiation status of $CD8^+$ TILs from primary GBM patients and their reinvigoration by ICIs to understand the nature of T-cell exhaustion in GBM. I isolated TILs from 98 patients with newly diagnosed GBM and found that $CD8^+$ TILs had significantly increased expression of immune checkpoint receptors, compared to peripheral blood $CD8^+$ T cells. Among $CD8^+$ TILs, $PD-1^+$ cells exhibited more terminally differentiated phenotypes than PD-1- cells. Evaluating the anti-PD-1-induced reinvigoration of $CD8^+$ TILs after ex vivo stimulation with anti-CD3 and anti-PD-1, I found that reinvigoration inversely correlated with the percentage of $Eomes^{hi} T-bet^{lo}$ cells among $PD-1^+CD8^+$ TILs. When anti-CTLA-4 was used in combination with anti-PD-1, an additional increase in $CD8^+$ TIL proliferation was not observed in patients who did not respond to anti-PD-1. Therefore, in primary GBM, the differentiation status of $CD8^+$ TILs determines their reinvigoration ability upon ICI treatment. To explore the possibility of novel strategy, I combined anti-PD-1 with galunisertib, one of the promising TGF-$\beta$ blockers. Galunisertib could reinvigorate $CD8^+$ TILs regardless of the response to anti-PD-1. In addition, the reinvigoration effect of combined anti-PD-1 with galunisertib was more prominent in the ‘low responding TILs’ group compared to the ‘high responding TILs’ group. The present study may provide the rationale and evidence for establishing optimal strategies for combinational ICI treatment in patients with GBM.