TIGIT Is Positively Associated with Advanced Human Glioma and Displays an Immunosuppressive Microenvironment

Abstract

Background: Diffuse glioma is a malignant human brain cancer that is hard to overcome. This represents a high risk of mortality. The current challenge is limited to the control of tumor progression and survival improvement. Immunotherapy consists of stimulating the immune system in order to eliminate the non-self-elements that damage the human body, including cancer cells. However, in human glioma, the current immunotherapeutic targets did not show significant benefit. In this study, we aimed at evaluating the expression and potential role of a new immunosuppressive molecule, TIGIT in glioma patients. Methods: A cohort of 667 patients from the TCGA database along with a cohort of 53 Moroccan patients, were analyzed in order to assess the role of TIGIT in human glioma progression and to estimate whether blocking this immune checkpoint molecule would be of a potential therapeutic benefit. Real time RT-PCR from fresh human biopsies and RNAseq data analysis were performed in this study. Results: Our results showed that high expression of TIGIT had prognostic value with some known clinical glioma risk factors such as sex, age and IDH mutation status. High expression of TIGIT was positively associated with advanced grades of glioma. Interestingly, elevated rates of TIGIT were significantly associated to elevated levels of other inhibitory immune checkpoint molecules (PD-1, VISTA and Tim-3) in human glioma patients, also TIGIT showed strong association with Treg cell-secreted cytokines (TGF-beta and IL-10), indicating the high potential involvement of TIGIT in immunosuppression in human glioma. Moreover, we reported that high TIGIT expressing CD8 T-cells displayed more surface inhibitory molecules and, elevated levels of Treg cells and FoxP3 were linked to higher rates of TIGIT, supporting the likely involvement of TIGIT in the suppression of the intra-tumoral immune cells. Finally, high expression of TIGIT was significantly linked to advanced histological subtypes of glioma and was associated with poor overall survival in human glioma. Conclusion: TIGIT blockade might be of valuable therapeutic benefit in patients with advanced glioma.