CNSC-69. TUMOR EXTRACELLULAR VESICLES PROMOTE IMMUNOSUPPRESSIVE MONOCYTE INDUCTION VIA THE TIGIT/CD155 AXIS, DAMPENING NLRP3-MEDIATED INFLAMMATORY RESPONSE IN GLIOBLASTOMA

Abstract Glioblastoma (GBM), the most aggressive primary brain tumor in adults, is marked by profound immune suppression. Tumor-derived extracellular vesicles (TEVs) are increasingly recognized as key mediators of this immunosuppressive environment. In this study, we examined the tumor-immune microenvironment using ultrasonic aspirate samples from GBM patients (n = 14). Several immune checkpoint molecules, including PDL1, B7-H3, and VISTA, were notably elevated. TIGIT, a receptor typically associated with T cells, was widely expressed across multiple myeloid subsets, including monocytic myeloid-derived suppressor cells (mMDSCs; 64.27 ± 7.99%) and non-classical monocytes (NCM; 39.8 ± 4.37%). Co-culture of healthy donor monocytes (n=10) with TEVs replicated similar effects (control 11.69±1.87 vs EV treated 23.32±2.0). We found CD155, the primary TIGIT ligand, to be heavily enriched in TEVs and co-expressed with TIGIT in co-culture, suggesting the TIGIT/CD155 axis may be involved in promoting immune suppression. Additionally, induced MDSCs significantly inhibit T cell proliferation (30.65±5.97% proliferation, v/s control 86.47±2.94, p=0.0001), concomitant with a surge in Th2 immune responses via TIGIT+ monocytes along with an increase in NLRP3 and IL-1β expressing cells. Interestingly, TIGIT knockdown did not affect NLRP3 expression but did restore T cell proliferation (64.13 ± 1.33%; p = 0.02) and pro-inflammatory cytokine production. However, the restoration of T cell proliferation was lost when NLRP3 was also silenced, indicating its essential role in mediating immune rescue. Overall, our findings highlight a crucial role of TIGIT in driving myeloid-mediated immune suppression in GBM. Furthermore, TIGIT inhibition may unmask NLRP3 function, potentially contributing to immune rescue.