Immunophenotyping of Newly Diagnosed and Recurrent Glioblastoma Defines Distinct Immune Exhaustion Profiles in Peripheral and Tumor-infiltrating Lymphocytes

Purpose: Immunotherapeutic treatment strategies for glioblastoma (GBM) are under investigation in clinical trials. However, our understanding of the immune phenotype of GBM-infiltrating T-cells (TILs) and changes during disease progression is limited. Deeper insight is urgently needed to therapeutically overcome tumor-induced immune exhaustion. Experimental Design: We used flow-cytometry and cytokine assays to profile TILs and blood lymphocytes (PBL) from GBM patients, comparing newly diagnosed or recurrent GBM to long-term survivors (LTS) and healthy donors. TCR sequencing was performed on paired samples of newly diagnosed and recurrent GBM. Results: We identified a clear immune signature of exhaustion and clonal restriction in the TIL of patients with GBM. Exhaustion of CD8+ TILs was defined by an increased prevalence of PD-1+, CD39+, Tim-3+, CD45RO+, HLA-DR+ marker expression and exhibition of an effector-/transitional memory differentiation phenotype, whereas KLRG1 and CD57 were underrepresented. Immune signatures were similar in primary and recurrent tumors, however, restricted TCR repertoire clonality and a more activated memory phenotype were observed in TIL from recurrent tumors. Moreover, a reduced cytokine response to PHA stimulation in the blood compartment indicates a dysfunctional peripheral T-cell response in GBM patients. LTS displayed a distinct profile, with abundant naïve and less exhausted CD8+ T-cells. Conclusions: TILs and PBLs exhibit contrasting immune profiles, with a distinct exhaustion signature present in TILs. While the exhaustion profiles of primary and recurrent GBM are comparable, TCR sequencing demonstrated a contracted repertoire in recurrent GBM, concomitant with an increased frequency of activated memory T-cells in recurrent tumors.

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