Plasma IL-8 and ICOSLG as prognostic biomarkers in glioblastoma

Abstract

Background: CNS immune privilege has been challenged in recent years. Glioblastoma (GBM) immune dysfunction includes complex interactions with the immune system outside the CNS. The aim of this study was to determine diagnostic and prognostic potential of immune-related proteins in plasma in GBM and interrogate biomarker presence in the brain tumor microenvironment (TME).

Methods: One hundred and fifty-eight patients with glioma WHO grade II-IV were included. Plasma collected at surgery was screened for 92 proteins using proximity extension assay technology and related to clinical outcome. Secretion and expression of candidate prognostic biomarkers were subsequently analyzed in 8 GBM cell lines and public RNAseq data.

Results: Plasma levels of 20 out of 92 screened proteins were significantly different in patients with GBM compared to patients with astrocytoma WHO grade II-III. High plasma interleukin-8 (IL-8) (hazard ratio [HR] = 1.52; P = .0077) and low CD244 (HR = 0.36; P = .0004) were associated with short progression-free survival and high plasma IL-8 (HR = 1.40; P = .044) and low ICOS ligand (ICOSLG) (HR = 0.17; P = .0003) were associated with short overall survival (OS) in newly diagnosed patients with GBM. A similar trend was found for ICOSLG (HR = 0.34; P = .053) in recurrent GBM. IL-8 was mostly secreted and expressed by mesenchymal GBM cell lines and expressed by vascular cells and immune cells in the TME. This was also the case for ICOSLG, although less consistent, and with additional expression in tumor-associated oligodendrocytes.

Conclusions: High plasma IL-8 and low ICOSLG at surgery are associated with short OS in newly diagnosed GBM. Source of plasma ICOSLG may be found outside the TME.

Keywords: ICOS ligand; IL-8; circulating biomarkers; glioblastoma.

Figure 1.

Paired plasma IL-8 (A) and ICOSLG (B) values from initial GBM surgery and recurrence (n = 11). One-unit increase in NPX corresponds to a 2-fold increase in protein abundance. GBM, glioblastoma; ICOSLG, ICOS ligand; IL-8, interleukin-8; LOD, limit of detection; NPX, Normalized Protein Expression.

Figure 2.

IL-8 and ICOSLG levels in patient plasma and cell line conditioned media from 8 patients and paired cell lines are shown in (A) and (B). In (C) association between CXCL8, ICOSLG RNA expression and OS in TCGA LGG and GBM datasets are illustrated using Cox proportional hazards regression. Cell line CXCL8 and ICOSLG RNA expression in (D). (E) depicts RNA expression of CXCL8 and ICOSLG in GBM single cells and (F) depicts RNA expression of CXCL8 in purified cells from human brain. In (F) astrocytes include mature astrocytes, fetal astrocytes, and astrocytes from sclerotic hippocampi and GBM. One-unit increase in NPX corresponds to a 2-fold increase in protein abundance. CM, conditioned media; CXCL8, C-X-C Motif Chemokine Ligand 8; GBM, glioblastoma; ICOSLG, ICOS ligand; IL-8, interleukin-8; LGG, low-grade glioma; LOD, limit of detection; NPX, Normalized Protein Expression; OS, overall survival.