Background: In the last years, the transmembrane proteoglycan NG2 has gained interest as a therapeutic target for the treatment of diverse tumor types, including gliomas, because increases of its expression correlate with dismal prognosis. NG2 has been shown to function as a co-receptor for PDGF ligands whose aberrant expression is common in gliomas. We have recently generated a glioma model based on the overexpression of PDGF-B in neural progenitors and here we investigated the possible relevance of NG2 during PDGF-driven gliomagenesis. Methods: The survival curves of NG2-KO mice overexpressing PDGF-B were compared to controls by using a Log-rank test. The characteristics of tumors induced in NG2-KO were compared to those of tumors induced in wild type mice by immunostaining for different cell lineage markers and by transplantation assays in adult mice. Results: We showed that the lack of NG2 does not appreciably affect any of the characterized steps of PDGF-driven brain tumorigenesis, such as oligodendrocyte progenitor cells (OPC) induction, the recruitment of bystander OPCs and the progression to full malignancy, which take place as in wild type animals. Conclusions: Our analysis, using both NG2-KO mice and a miRNA based silencing approach, clearly demonstrates that NG2 is not required for PDGF-B to efficiently induce and maintain gliomas from neural progenitors. On the basis of the data obtained, we therefore suggest that the role of NG2 as a target molecule for glioma treatment should be carefully reconsidered.

Glioblastoma is a lethal primary brain tumor lacking effective therapy. The secluded onset site, combined with the infiltrative properties of this tumor, require novel targeted therapies. In this scenario, the use of oncolytic viruses retargeted to glioblastoma cells and able to spread across the tumor cells represent an intriguing treatment strategy. Here, we tested the specificity, safety and efficacy of R-613, the first oncolytic HSV fully retargeted to EGFRvIII, a variant of the epidermal growth factor receptor carrying a mutation typically found in glioblastoma. An early treatment with R-613 on orthotopically transplanted EGFRvIII-expressing human glioblastoma significantly increased the median survival time of mice. In this setting, the growth of human glioblastoma xenotransplants was monitored by a secreted luciferase reporter and showed that R-613 is able to substantially delay the development of the tumor masses. When administered as late treatment to a well-established glioblastomas, R-613 appeared to be less effective. Notably the uninfected tumor cells derived from the explanted tumor masses were still susceptible to R-613 infection ex vivo, thus suggesting that multiple treatments could enhance R-613 therapeutic efficacy, making R-613 a promising oncolytic HSV candidate for glioblastoma treatment.

Gliomas are aggressive brain tumors that progressively acquire a profound immune-evasive phenotype during malignant evolution. However, the mechanisms driving this transition from immune surveillance to immune tolerance are only partially understood. We used a PDGF-B-driven murine model in which sequential low- and high-grade stages of gliomagenesis can be experimentally identified, allowing us to investigate how immune suppression emerges during malignant progression. In vivo lymphocyte depletion experiments were performed in mice bearing immunogenic low-grade glioma transplants to assess the role of specific immune populations. Transcriptomic profiling and flow cytometry were conducted to characterize tumor–immune interactions and cellular dynamics within the tumor microenvironment were evaluated. Depletion experiments demonstrated that CD4⁺ lymphocytes are essential for initiating immune surveillance and promoting the recruitment of cytotoxic CD8⁺ T cells. Transcriptomic analyses revealed that high-grade glioma cells extensively reprogram surrounding immune populations, inducing a shift toward an immunosuppressive transcriptional state characterized by reduced expression of MHC-II-related genes and attenuated interferon signaling. This remodeling was associated with a marked loss of cytotoxic CD8⁺ T lymphocytes and NK cells, driven by contact-dependent interactions with high-grade glioma cells. Strikingly, high-grade glioma cells also enabled the in vivo engraftment of otherwise non-tumorigenic, immunostimulatory low-grade glioma cells, indicating an active reshaping of the immune microenvironment to enforce tolerance. Overall, our findings suggest that the progression to high-grade glioma relies less on cell-autonomous “stealth” mechanisms and more on the ability to tame and reprogram the immune microenvironment, thereby creating a tolerant, tumor-permissive niche.