IMMU-69. Immune-Mediated Recurrent Glioblastoma Growth: Insights from a Novel Murine Model

Abstract Glioblastoma (GBM) is the most common primary brain malignancy, with ~15 months median overall survival (OS). Recurrent GBM (rGBM) is more aggressive with survival typically <10 months, believed due to chemoradiation selectivity. Re-resection offers limited benefit for rGBM. Although immune infiltrates are known to promote GBM progression, xenograft preclinical models of recurrent tumors lack immune components. We sought to elucidate the immune microenvironment’s role in rGBM via a novel murine rGBM model. To create the model, CT-2A or SB28 glioma cells were implanted into C57BL/6J mice with subsequent near total resection (>75%) on day 8 and recurrent tumor cell harvest on day 15. To confirm increased aggressiveness, naïve mice were implanted with rGBM and control lines. Immune profiling was performed via flow cytometry post-resection. Lymphoid (CD45+CD11b-) and myeloid (CD45+CD11b+) cells isolated from the tumors were analyzed for their effects on tumor proliferation via MTT assay using both transwells and co-cultures. rGBM lines showed significantly higher proliferation (p<0.0001) and shorter OS (24 vs. 30 days). CD45+CD11b- and CD45+CD11b-CD4- lymphoid cells promoted the proliferation of recurrent gliomas (p<0.01) but not primary gliomas. Myeloid cells via co-culture but not transwell decreased proliferation in recurrent gliomas (p<0.01) but not primary gliomas. At 3 days post-resection, Ki67+ lymphoid cells were elevated diffusely in the brain (p=0.004) and by day 5 in the peripheral blood (p=0.033). Co-implantation of rGBM with lymphoid cells worsened OS (19 vs. 29 days, p=0.167), and with myeloid cells improved OS (38 vs. 29 days, p=0.019). The novel syngeneic rGBM model highlights that recurrent tumor aggressiveness is not solely driven by chemoradiation selectivity. Lymphoid cells markedly enhance recurrent glioma proliferation, likely via cytokine receptor upregulation. Myeloid cells significantly decrease proliferation likely by direct-cell-to-cell interaction. Increased lymphoid proliferation in the brain and periphery post-resection underscores their critical role in rGBM progression.