Abstract 2332: VSTM2A modulation of immune response in colorectal cancer through abrogating PD-L1 and PD-1 interaction
Authors: Dong Yujuan , Zhou Yunfei , Wong Nathalie , Yu Jun , Ng Siu Man Simon 
Published: April 2023

Abstract
Background: Checkpoint immunotherapy using humanized antibody is a new therapeutic strategy against advanced colorectal cancer (CRC). Nonetheless, it shows low tumor penetration due to the large molecule size. Therefore, small immune regulatory molecules are actively sought. Our previous study showed that a small secretory protein VSTM2A suppressed Wnt signalling pathway through inducing LRP6 lysosome dependent degradation. However, its role in immune modulation is largely unknown.
Methods: Clinicopathological features were analyzed using CRC patient cohort. Functional biology of VSTM2A was investigated using T cell-antigen presenting cell (APC) co-culture models and knockout mice model. Liquid chromatography with tandem mass spectrometry (LC-MS) was carried out for mechanistic investigation.
Results: Gene ontology analysis of colon RNA-seq dataset from TCGA/GTEx revealed significant enrichment of adaptive immune response and lymphocyte activation with high VSTM2A expression. CRC patients with inferior VSTM2A expressions were associated with lower immunoscores in both early and late stages of CRC. In addition, our immunohistochemical examinations of 208 in-house CRC cases further pinpoints to a considerable fraction of VSTM2A-negative cases showing avoidance of spontaneous CD8a+ cells infiltration (Pearson's chi-squared test P &lt; 0.001, φ = 0.24) and worse clinical outcome.
LC-MS assay followed by reciprocal immunoprecipitation revealed that VSTM2A interacted with the IgV motif of immune checkpoint protein programmed cell death 1 ligand 1 (PD-L1). We further found that VSTM2A recognized PD-L1 with a dissociation constant (Kd) of 2.6 nM. Recombinant VSTM2A dose dependently suppressed the interaction of PD-L1 and PD-1 with IC50 of 4.51 nM, indicating VSTM2A is a potential intrinsic PD-L1 antagonist. Moreover, our in-vitro mechanistic studies revealed that VSTM2A protein could block the interaction of PD-1/PD-L1, and induced NFAT-RE luciferase activity dose-dependently using a bioluminescent cell-based PD-1/PD-L1 blockade bioassay. VSTM2A could dramatically activate the interleukin-2 production from DO11.10 T cell in the presence non-T cell spherocyte isolated from BALB/c mice and OVA323-339 peptide.
Furthermore, our in-vivo study revealed that VSTM2A triggered a distinct increase in CD45+CD3+ T cells infiltration in the syngeneic MC38 mouse model. Vstm2a+/- knockout mice challenged with azoxymethane and dextran sodium sulfate showed significantly high CRC incidence and tumor burden in comparison to wild-type littermates. Tumor from Vstm2a+/- mice showed significantly less CD8+ T cell infiltration.
Conclusions: our study demonstrate the tumor extrinsic role of VSTM2A in modulation of microenvironment through abrogating PD-L1/PD-1 interaction. Silencing of VSTM2A in CRC could suppress T cell activation and infiltration in the tumor sites.
Citation Format: Yujuan Dong, Yunfei Zhou, Nathalie Wong, Jun Yu, Siu Man Simon Ng. VSTM2A modulation of immune response in colorectal cancer through abrogating PD-L1 and PD-1 interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2332.