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The Siglec-sialic acid-axis is a target for innate immunotherapy of glioblastoma

ABSTRACT: 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 microglia (MG) or monocyte-derived cells (MdCs). Here, we aim at defining the role of inhibitory Siglec-9 in human and its mouse homologue Siglec-E in innate-centered immunotherapy against GBM. 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). Using a CT-2A orthotopic GBM mouse model with MG-specific spatio-temporal deletion of Siglece (Sall1CreERT2 x Sigleceflox), we observed high MG-proliferation upon Siglece knockout (Ki-67+ MG 14.8% in Creneg vs. 34.9% in Crepos, p < 0.0001) accompanied by an enhanced microglial GBM-cell uptake (5.6% in Creneg vs. 12.3% in Crepos, p < 0.001). By extending the Siglece knockout to the MdC compartment (Cx3cr1CreERT2 x Sigleceflox) we observed a significantly prolonged survival in the Crepos population (21d in Creneg vs. 27d post-tumor injection in Crepos, p = 0.018), which could be further promoted by combining Siglece knockout with CD47 blockade (11% long-term remission in Crepos + anti-CD47). Proteomics analysis revealed increased antigen processing and presentation capabilities of SigleceKO MdCs which was confirmed by ex-vivo OT-1 cross-presentation assays. This increased T cell priming upon MdC SigleceKO was further boosted by addition of anti-PD1 antibody to the SigleceKO + anti-CD47 combination. Resulting in 23% of animals experiencing long-term remission in the triple treatment arm, even after tumor re-challenge. Genetic targeting of sialic acids, the ligand for Siglec receptors, on CT-2A cells (GNE-KO), resulted in increased GBM-cell phagocytosis by MG and MdCs and less exhausted tumor-infiltrating CD8+ T cells (14.8% in WT vs. 5.9% in GNE-KO, p = 0.003). In a translational approach, we are currently testing anti-Siglec-9 treatment regimens in patient GBM explants, cultured for 5 days in perfusion bioreactors.

ORGANISM(S): Mus musculus

PROVIDER: GSE212616 | GEO | 2023/06/14

REPOSITORIES: GEO

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Project description:A significant challenge for chimeric antigen receptor (CAR) T cell therapy against glioblastoma (GBM) is its immunosuppressive tumor microenvironment (TME), which is densely populated and supported by protumoral glioma-associated microglia and macrophages (GAMs). Targeting CD47, a don't-eat-me signal overexpressed by tumor cells, disrupts the CD47-SIRPalpha axis and induces GAM phagocytic function. However, antibody-mediated CD47 blockade monotherapy is associated with toxicity and low bioavailability in solid tumors. To overcome these limitations, we combined local CAR T cell therapy with paracrine GAM modulation to effectively eliminate GBM. To this end, we engineered a new CAR T cell against epidermal growth factor receptor variant III (EGFRvIII) that constitutively secretes a signal regulatory protein gamma (SIRPgamma)-related protein (SGRP) with high affinity to CD47. Anti-EGFRvIII-SGRP CAR T cells eliminated EGFRvIII+ GBM in a dose-dependent manner in vitro and eradicated orthotopically xenografted EGFRvIII-mosaic GBM by locoregional application in vivo. This resulted in significant tumor-free long-term survival, followed by partial tumor control upon tumor re-challenge. Combining anti-CD47 antibodies with anti-EGFRvIII CAR T cells failed to achieve a similar therapeutic effect, underscoring the importance of sustained paracrine GAM modulation. Multidimensional brain immunofluorescence microscopy and in-depth spectral flow cytometry on GBM-xenografted brains showed that anti-EGFRvIII-SGRP CAR T cells accelerated GBM clearance, increased CD68+ cell trafficking to tumor scar sites and promoted GAM-mediated tumor cell uptake. In a peripheral lymphoma mouse xenograft model, anti-CD19-SGRP CAR T cells had superior efficacy to conventional anti-CD19 CAR T cells. Validation on human GBM explants revealed that anti-EGFRvIII-SGRP CAR T cells had a similar tumor-killing capacity to anti-EGFRvIII CAR monotherapy but showed a slight improvement in the maintenance of tumor-infiltrated CD14+ cells. Thus, local anti-EGFRvIII-SGRP CAR T cell therapy combines the potent antitumor effect of engineered T cells with the modulation of the surrounding innate immune TME. This results in the additive elimination of bystander EGFRvIII- tumor cells in a manner that overcomes the main mechanisms of CAR T cell therapy resistance, including tumor innate immune suppression and antigen escape.

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The Siglec-sialic acid-axis is a target for innate immunotherapy of glioblastoma

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