Abstract 4205: Staged anti-PD-1 therapy with intratumoral recombinant calreticulin improves anti-tumor immunity and survival in glioblastoma mouse models

Background: Glioblastoma (GBM), the most common and lethal primary brain tumor, has a median survival of a mere 15 months and leads to approximately 12,000 deaths in the US annually. Targeted and combinatorial-based clinical trial therapies have shown poor efficacy in GBM treatment, partly due to the restrictive nature of the blood-brain barrier, an immunosuppressive tumor microenvironment, GBM’s heterogeneity and adaptability, and GBM’s ability to metastasize and invade critical regions of the brain. However, promising recent literature has indicated that neoadjuvant anti-PD-1 checkpoint-inhibition immunotherapy - i.e., starting it right before surgery for recurrence - improves survival outcomes in human GBM patients. Results: Here, we demonstrate a proposed mechanism of action wherein localized intratumoral danger-associated molecular pattern (DAMP, a known immunogenic driver) injection of calreticulin - used to mimic natural DAMP release from necrotic cells during surgery - combined with neoadjuvant anti-PD-1 immunotherapy leads to better survival outcomes in both orthotopic mouse CT2A and CT2A-Luc GBM models. This survival benefit is also seen in a more aggressive (larger tumor inoculation size) orthotopic CT2A-Luc GBM model. Flow cytometry indicates increased microglia cell counts and activation marker expression, and increased myeloid activation marker expression in mice brains treated with our combination immunotherapy in a CT2A GBM model. Additionally, in vivo treatment with our combination immunotherapy led to increases in the local T and NK cell numbers, the CD8:CD4 ratio, and the proliferation of CD4 T cells in mice brains of a CT2A GBM model. In vitro results suggest that co-culture with CT2A cells increased PD-1 expression in macrophages and microglia and that our combination treatment of calreticulin and anti-PD-1 immunotherapy reduces the viability of mouse GBM cells when mixed with macrophages. Significance: This project paves the path for a novel immunotherapeutic approach to tackle GBM and other cancers. Future studies could incorporate relevant DAMP’s into nanoparticles for sustained release after intratumoral injection and possibly viral delivery of DAMP’s that are constitutively secreted, thereby prolonging an anticipated immune response. Citation Format: Suchet Taori, Breanna Noffsinger, Charlotte A. Miller, Aizhen Xiao, Laryssa Manigat, Qing Zhong, Tajie Harris, Benjamin Purow. Staged anti-PD-1 therapy with intratumoral recombinant c