Medical Student Stanford University School of Medicine
Introduction: Toll-like receptor 9 (TLR9) agonists are a promising immunotherapy for glioblastoma (GBM), but delivery of these agents is currently limited to intratumoral administration. To enable efficient payload delivery to GBM tumors following systemic administration, a tumor-targeting peptide (PIP) delivery system was utilized. This study examined the impact of systemically-delivered tumor-targeted CpG (“PIP-CpG V3”) for promoting antigen presentation in brain tumors.
Methods: Syngeneic murine glioma cells (GL261) were orthotopically implanted in 6–8-week-old female C57BL/6J mice. For PIP localization, 1.5 nmol AF680-conjugated PIP (PIP-AF680) was intraperitoneally injected in tumor-bearing and non-tumor-bearing mice with organs dissected 2 hours later for ex vivo fluorescence imaging. To assess antigen processing and presentation, DQ-ovalbumin assays were employed on mouse brains 14 days post-tumor implantation with flow cytometric analysis 24 hours later. Mice were treated on post-implantation days 10, 12, and 14 with either 200 uL vehicle, 200 ug anti-PD1, 250 ug PIP-CpG V3, or the combination of anti-PD1 and PIP-CpG V3.
Results: Mice systemically injected with PIP-AF680 exhibited fluorescence signal within implanted brain tumors but not in non-tumor-bearing brain. Flow cytometry revealed increased DQ+ immune cell representation in the tumor microenvironment (TME) with PIP-CpG V3 treatment. This effect was most pronounced in the DQ+CD11b+CD11c+ dendritic cell population, both in terms of the number of cells (PIP-CpG V3: p = 0.0221, combination: p = 0.0366) and as a proportion of DQ+ CD45+ immune cells (PIP-CpG V3: p = 0.0448, combination: p = 0.0038).
Conclusion : PIP effectively traffics to orthotopic brain tumors in a murine model. The higher presence of DQ+ immune cells in the TME suggests PIP-CpG V3 may increase antigen processing by myeloid cells, particularly CD11b+CD11c+ dendritic cells.
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