## 4 Discussion
However, this anti-tumor activity is paradoxically coupled with promoting glioma cell differentiation, suggesting a dual role for mast cells in glioma progression [76]. Another paradoxical function of immune cells is related to NKT cells, a unique subset of T lymphocytes. NKT cells can initiate an immune response through cytokine production while simultaneously promoting an immunosuppressive environment [77]. While inflammation can potentially target GBM and GSCs, it can also have paradoxical outcomes. GBM reshapes its microenvironment, leading to a shutdown of the immune response by recruiting various immunosuppressive cells, such as Tregs, MDSCs, and TAMs. These cells can modulate other immune cells through direct cell-cell contact and the release of several immunomododulatory factors [78; 79]. This intricate balance between pro- and anti-inflammatory responses highlights the complexity of the GBM microenvironment and underscores the potential role of GPRC5A in shaping the immune microenvironment. A small animal model, such as a xenograft or orthotopic mouse model, can be effectively utilized to study the cellular composition associated with GPRC5A. By implanting GBM cell lines with high and low GPRC5A expression directly into the brains of immunocompetent mouse models, the tumor-associated immune landscape can be assessed within a living organism. Then, to evaluate the cellular profiles, several techniques can be employed: flow cytometry to analyze circulating immune cells, immunofluorescence or immunohistochemistry (IHC) to examine immune cell distribution within tissue, in vivo imaging to monitor tumor progression over time, and enzyme-linked immunosorbent assays (ELISA) to measure cytokine and chemokine secretion. These methods can collectively provide a comprehensive view of how GPRC5A influences the immune microenvironment and tumor dynamics in GBM. The cellular composition of the GBM microenvironment is also enriched with stromal cells that play a critical role in creating a favorable niche for GBM progression. [PERSON] et al. demonstrated that the enrichment of ECM in the GBM environment is supported by several stroma cells, including perivascular fibroblasts, pericytes, and SMCs. Each of these cells plays a substantial role in GBM pathogenesis. For instance, the perivascular fibroblasts are correlated with poor prognosis and resistance to immunotherapy. These cells support GBM by recruiting TAMs and promoting stemness properties [33]. Moreover, pericytes are also crucial for GBM vasculature, stabilizing blood vessels and controlling immune infiltration, thereby modulating immune surveillance [80]. It was shown that an increased proportion of pericytes is associated with tumor recurrence and poor prognosis. Moreover, pericytes aid in the repair of DNA damage caused by therapy through the secretion of CCL5 chemokine, which binds to the CCR5 receptor on GBM cells, thus increasing tumor resistance [81]. Interestingly, pericytes can originate from MES-GSC differentiation to maintain vasculature, and targeting these GSC-derived pericytes has been shown to reduce tumor growth [82]. Similarly, SMCs can also be generated from CD133+ GSCs to maintain vascular integrity and promote angiogenesis, which is critical for tumor progression [83; 84; 85]. Experimental validations will be important to validate whether CD133+/GPRC5A+ can generate diverse stroma cells, such as SMCs or pericytes and assess the therapeutic potential of targeting GPRC5A in GBM. [PERSON] et al., through a spatial transcriptomic investigation, showed that CAFs are enriched in perivascular niches, close to pericytes, MES-GSCs, endothelial cells, and TAMs. Mechanistically, CAFs are recruited to tumor sites via the secretion of PDGF and TGF-\(\beta\) by GSCs, which migrate to the GSC niche to recruit and promote the polarization of macrophages [34]. Altogether, these findings suggest that GPRC5A is associated with highly vascular niches, a histopathology characteristic of GBM tumorigenesis [86].