Functional Characterization Of A Novel Gene In The Antigen Presentation Pathway Allows Specific Immunotherapeutic Targeting Of Glioblastoma Cancer Stem Cells

Glioblastoma is the most prevalent and aggressive primary brain tumor in adults, and conventional treatment strategies have made minimal progress in prolonging overall survival. Cancer stem cells are critical for tumor initiation, growth, and maintenance, and are able to co-opt complex host mechanisms to evade immune recognition. Immune checkpoint inhibition has proven revolutionary for the treatment of several types of solid tumors, but has largely failed in attempts to improve outcomes in glioblastoma. Developing a deeper understanding of the functional immunomodulatory role of genes unique to glioma stem cells (GSCs) may help to elucidate this enigma, and inform more specific immunotherapeutic targeting. To better understand the ability of GSCs to promote immunosuppression and self-tolerance in the tumor niche, we interrogated RNA-seq data from GSCs and differentiated glioma cells (DGCs) and identified a novel gene in the antigen presentation pathway (APP). In vitro targeting of this gene increased sensitivity to CD8+ T cell killing and reduced expression of other T-cell inhibitory ligands in GSCs alone, decreasing tumor-mediated immunosuppression. Compared to DGCs, GSCs were found to be key promoters of immune self-tolerance and evasion, with unaltered GSCs exhibiting minimal peptide binding to MHC Class I and, therefore, decreased antigen presentation. Specific targeting of the identified APP gene led to a reversal of this interaction, with increased binding capacity and, correspondingly, tumor antigen recognition. In vivo administration of a specific APP gene targeting agent in human GSC xenograft mice displayed decreased tumor burden and a striking prolongation of overall survival compared to both controls and mice treated with known immune checkpoint inhibitors. High expression of the APP gene is associated with poor clinical prognosis, supporting the clinical relevance of this discovery. Thus, novel targeting of the antigen-presenting pathway may provide a therapeutic vulnerability unique to glioblastoma cancer stem cells. Citation Format: Reilly L. Kidwell, Xiqing Li, Jeremy N. Rich. Functional characterization of a novel gene in the antigen presentation pathway allows specific immunotherapeutic targeting of glioblastoma cancer stem cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6611.