PL02.2.A Microglia-specific disruption of sialic acid-Siglec-9/E interactions. A novel immunotherapy against glioblastoma?. (5th September 2022)

• Record Type: Journal Article
• Authors: Schmassmann, P; Roux, J; Martins, T A; Ritz, M; Shekarian, T; McDaid, M; Hutter, H Läubli G
• Is Part Of: Neuro-oncology. Volume 24(2022)Supplement 2
• Page Start: ii2
• Page End: ii2
• Publication Date: 2022-09-05
• Subjects: Brain Neoplasms -- Periodicals; Brain -- Tumors -- Periodicals; Brain -- Cancer -- Periodicals; Nervous system -- Cancer -- Periodicals; 616.99481
• DOI: 10.1093/neuonc/noac174.005
• Languages: English
• ISSNs: 1522-8517

Abstract

Abstract: Background: Recently, 'don't eat me'-signals like CD47 have emerged as novel innate immune checkpoints, enabling cancer cells to evade clearance by phagocytes such as monocyte-derived macrophages (MdM) or microglia (MG). Here, we aim at defining the role of inhibitory Siglec-9 in human and its mouse homologue Siglec-E in MG-centered immunotherapy against GBM. Material and Methods: We employed a CT-2A orthotopic GBM mouse model with MG specific ( Sall1 CreERT2 x Siglece flox ) and whole innate-compartment ( Cx3cr1 CreERT2 x Siglece flox ) spatio-temporal deletion of Siglece. We applied multi-color flow cytometry, transcriptomics and proteomics analysis to decipher the immune response upon Siglece knockout. Results: TCGA RNA-sequencing data revealed a significant correlation between high expression of immunoinhibitory SIGLEC9 and poor survival in GBM patients (log-rank p = 0.02). Siglec-E blockade increased murine MG mediated GBM cell in vitro phagocytosis (normalized phagocytosis of 1.00 in isotype vs. 1.76 in anti-Siglec-E antibody, p < 0.001). In the MG specific spatio-temporal deletion of Siglece ( Sall1 CreERT2 x Siglece flox ), we observed high MG-proliferation upon Siglec-E knockout (Ki-67 + MG 14.8% in Cre - vs. 34.9% in Cre +, p < 0.0001) accompanied by an enhanced microglial GBM-cell uptake (5.6% in Cre - vs. 12.3% in Cre +, p < 0.001). By extending the Siglece knockout to the MdM compartment in our glioma mouse model ( Cx3cr1 CreERT2 x Siglece flox ) we observed a significantly prolonged survival in the Cx3cr1 Cre+ population (21d in Cre - vs. 27d post-tumor injection in Cre +, p = 0.018), which could be further promoted by combining Siglece knockout with CD47 blockade (30d post-tumor injection in Cre + + anti-CD47). Unbiased proteomics analysis revealed increased antigen processing and presentation capabilities of Siglece knockout MdMs which was confirmed by ex-vivo OT-1 cross-presentation assays. This bridging of innate and adaptive responses with increased T cell priming upon MdM Siglece knockout was further promoted by addition of anti-PD1 antibody to the combined Siglece knockout and anti-CD47 treatment arm. Animals harboring CT-2A tumors, exhibited a sustained survival benefit under the triple therapy, with 23% of animals experiencing long-term remission, even after tumor re-challenge into the contra-lateral hemisphere. By genetically targeting sialic acids, the ligand for Siglec receptors, on CT-2A cells (GNE-KO), we observed a strong innate and adaptive immune response with increased GBM-cell phagocytosis by MG and MdMs and less exhausted tumor-infiltrating CD8 + T-cells (14.8% in WT vs. 5.9% in GNE-KO, p = 0.003). Conclusion: These data identify the sialic-acid-Siglec-E pathway as an anti-phagocytic signal in a pre-clinical GBM model, and demonstrate its therapeutic potential in GBM immunotherapy.