Specific Targeting of Tumour-Associated Sialic Acids using Chimeric Switch Receptors (CSRs) based on the Novel (Sialo)-Checkpoint Molecule Siglec-9

Cancer exploits different mechanisms to escape T-cells immunosurveillance. These include for
example the overexpression of checkpoint ligands (such as PDL1) but also aberrant glycosylation.
Indeed, cancer aberrant sialylation was early documented and shown to dampen the anti-tumor
immunity. Herein we were able to identify that IFNγ, a potent immune modulator secreted in TME,
induces a2,6-hypersialylation in multiple cancer cell lines derived from various solid histologies.
Additionally, we show that T-cells can express a receptor for sialic acid moieties known as Siglec9.
We demonstrate that Siglec-9+ population display exhaustive immunophenotype and impaired
effector functions. We speculate that Siglec-9 is a novel checkpoint molecule, similarly to PD-1. Using
the CRISPR/Cas9 technology, we also demonstrated that the KO of Siglec-9 in primary human T cells
alleviates exhaustive immunophenotype and enhance their functionality. Finally, we aimed at
augmenting cancer-specific T cell activity by taking an advantage of tumor hypersialylation. To this
end, we elaborated different Siglec-9-based Chimeric Switch Receptors (CSRs) which included the
intracellular moiety derived from costimulatory molecules (CD28 and 41BB). T-cells co-expressing
these with tumor specific TCR or CAR displayed higher cytokine secretion and activation profiles
following co-culture with tumor cells. Moreover, T-cells equipped with specific Siglec9 chimeric
receptors could mediate considerable tumor regressions in a xenograft model of human tumors.
Overall, this work shed light on additional tumor evasion mechanisms mediated by sialylated
residues and provide to an approach to improve engineered T-cell based cancer treatment.