gms | German Medical Science

Objective: 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.

Methods: We used flow-cytometry and cytokine assays to profile TILs and blood lymphocytes (PBL) from GBM patients (n=36), comparing newly diagnosed or recurrent GBM to long-term survivors (LTS, n=5)) and healthy donors (n=18). 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 (all p<0.01). Moreover, a significantly reduced cytokine response upon T-cell stimulation in the peripheral compartment reflected the inability of GBM patients to mount an efficient T-cell response (p<0.05). LTS displayed a distinct profile, with abundant naïve and less exhausted CD8+ T-cells.

Conclusion: 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.