Since the 2016 WHO grading system of CNS tumors(Wesseling and Capper, 2018) was established, glioma grading has been reclassified not only using traditional tissue morphology but also by focusing on the status of IDH1, IDH2 mutants and 1p/19p codeletion to identify gliomas according to genomics. Then, the newest-edition WHO classification of gliomas in 2021(Louis et al., 2021) further included ATRX loss, TP53 wt., TERT promoter mutation, and CDKN2A/B homozygous deletion as pathological diagnostic markers that can be used to distinguish different grades of malignancy of gliomas. Finally, diffuse gliomas were divided into 5 subgroups as follows: 1.) anaplastic oligodendroglioma, IDH-mutant and 1p/19q-codeleted, WHO Gr. III; 2.) anaplastic astrocytoma, IDH-mutant, WHO Gr. III; 3.) glioblastoma, IDH-mutant, WHO Gr. IV; 4.) anaplastic astrocytoma, IDH-wildtype, WHO Gr. III; 5.)glioblastoma, IDH-wildtype, WHO Gr. IV.
Compelling evidence indicates that aggressive tumor resection provides disease survival benefits for newly diagnosed GBM patients. The volume of residual GBM tumors as determined from postoperative images is a highly important factor affecting the disease-free time and median survival for GBM patients.(Keles et al., 1999) However, maximal resection of newly diagnosed Gr. III gliomas is recommended even if there is no clear evidence of a benefit on survival, but most expert consensus agrees with this aim for the tumor operation.(Keles et al., 2006) Adjuvant treatments of both Gr. III and Gr. IV gliomas include CCRT with different chemo-regimens, either TMZ or PVC. TMZ plays a more specific therapeutic role in GBM. However, there is a predominant disparity in disease survival between Gr. III and Gr. IV glioma patients. To our knowledge, we present a unique approach for differentiating Gr. III and Gr. IV glioma patients.
CXCL8 (C-X-C motif chemokine ligand 8) is also named interleukin 8 (IL8). Previous studies correlating IL8 and the prognosis of cancers include studies of colorectal cancer (CRC),(Cui et al., 2022; Ichikawa et al., 2022; Schimek et al., 2022) breast cancer,(Abou Shousha et al., 2022; Al-Kharashi et al., 2022) pancreatic cancer,(Li et al., 2022a) gastric cancer(Lin et al., 2022) and glioblastoma.(Chen et al., 2022) Based on our findings, IL8 could have an important impact on the prognosis of Gr. III and Gr. IV glioma patients. In addition, IL8 levels could be used to further differentiate GBM from high-grade glioma.
Immunotherapy has been considered one indication for curing cancers. IL8 can be produced by several immune cells and shows a close relationship with the tumor immune microenvironment. IL8-associated neutrophil recruitment modulates the immune microenvironment of CRC cells.(Schimek et al., 2022) Elevation of IL8 levels induces upregulation of PD-1 presentation in CD8-positive T cells to cause immunosuppression in stomach cancer.(Li et al., 2022b) From those studies, IL8 has been associated with immune cells, including in malignant tumors of the colorectum and stomach and GBM.
Recently, a series of studies related to GBM and IL8 have been conducted that have investigated IL8 expression in tumors, plasma IL8 levels of GBM patients, and treatment-induced IL8 expression. Data regarding GBM has indicated that Annexin-1, as an oncogene, promotes GBM cell escape from immune attack via IL8, which indirectly upregulates the expression of markers associated with the migration of dendritic cells.(Chen et al., 2022) In other clinical studies of plasma IL8 levels and GBM, the plasma levels in 158 patients with Gr. II-IV gliomas whose samples were collected during surgery and the levels of 20 proteins as candidate markers for GBM were significantly different from those with GBM. Finally, a higher level of IL8 in plasma was associated with a lower OS in GBM patients.(Holst et al., 2021) IL8 levels can discriminate GBM from Gr. III glioma and is a prognostic biomarker associated with poor PFS of GBM patients in TCGA dataset, and an indicator of poor prognosis regarding OS in GBM patients exists in the CGGA cohort.
As a common alkylating agent of adjuvant chemotherapy in GBM, TMZ is indicated to upregulate the activity of the IL8-dependent CXCL2/CXCR2 axis to promote angiogenesis and the production of tumor-associated macrophages. At the same time, combination therapy with TMZ and an antagonist of CXCR2 overcomes therapeutic resistance induced by TMZ.(Urbantat et al., 2021) In our study, IL8 expression was associated with higher levels of immune cells, including macrophages and neutrophils. Increased IL8 expression was also highly correlated with the levels of the immune infiltration of M2 macrophages in primary and recurrent GBM.
In conclusion, even though our study provides a well-known biomarker, IL8, to classify high-grade glioma, IL8 has multiple effects on disease prognosis, tumor immunity and recurrent gliomas. IL8-associated M2 macrophage infiltration could provide both prognostic and recurrent biomarkers to differentiate Gr. III and GBM.
In the future, immunohistochemical staining of high-grade glioma and survival analysis based on IL8 expression in clinical patients might provide further proof that IL8 is a unique factor and therapeutic target of GBM.