Abstract 172: Targeting the poliovirus receptor to activate T cells and induce myeloid-derived suppressor cells to differentiate to M1-like macrophages via the IFNγ-pSTAT1-IRF8 axis in cancer therapy
Authors: Feng Mingyang , Tan Sirui , Ma Qizhi , Zhang Benxia , Chen Yue , Li Qiu , Wang Yongsheng 
Published: March 2024

Abstract
T cell immunoglobulin and ITIM domain (TIGIT) is one of the most important immune checkpoints expressed on lymphocytes, and poliovirus receptor (PVR, also CD155) serves as the most crucial ligand for TIGIT, harboring an important function in cancer cells and influencing the tumor microenvironment (TME). While it's well-established that TIGIT blockade could reverse immunosuppression, the question of whether direct inhibition of PVR yields comparable results remains to be fully elucidated. In this study, we generated a mouse gene Pvr knock out (KO) Lewis lung cancer (LLC) cell line and found that the Pvr-KO tumors tended to develop a pro-inflammatory TME, as reflected by a downregulation of monocytic-myeloid derived suppressor cells (M-MDSCs) and an upregulation of CD8+ central memory T cells. Through bulk RNA-seq and multi-cytokines measurement, we quantified the transcription and protein levels of immunostimulatory cytokines and chemokines and found they were significantly upregulated in Pvr-KO TME, including GM-CSF, IFN-γ, TNF-α, IL-2/4/6/10, CCLs (including CCL2/3/4/5) and CXCLs (including CXCL1/2/5). We further employed single-cell RNA sequencing (scRNA-seq) on 20,026 intra-tumoral CD45+ immune cells. Using a conserved MDSCs gene set and the 'AddModuleScore' function of Seurat package, we identified the clusters of MDSCs and found the differentiation ability of M-MDSCs in Pvr-KO TME was enhanced. Through pseudo-temporal ordering, we found the M-MDSCs in the Pvr-KO TME have a trend to differentiate towards M1-like macrophages, which could play an essential positive role in anti-tumor immunity. We further focused on the scRNA-seq of T cell subsets and found the enhanced function of cytotoxic CD8+ T cells, leading to increased production of IFN-γ. In the intercellular communications analysis, a significant upregulation of the IFNG-IFNR signal between T cells: MDSCs in the Pvr-KO group was observed. Moreover, we found that Irf8, a key factor in myeloid cell differentiation, was significantly upregulated in the M-MDSCs of Pvr-KO tumor. We then employed CUT & Tag sequencing and confirmed that IFN-γ induces phosphate Stat1, which then binds on the promoter of Irf8. These findings suggest that the IFN-γ-Stat1-Irf8 axis plays a crucial role in MDSCs differentiation and may be a potential target for therapeutic intervention in cancer. Next, an anti-PVR nanobody was synthesized and its efficacy was evaluated in the context of LLC and 4T1 tumor grafts. When in combination with anti-PD-1 therapy, anti-PVR exhibited a remarkable capacity to reduce tumor size in both tumor models with no notable indications of toxicity observed. Our findings provide new insights into the role of PVR in modulating the TME and offer potential strategies for enhancing the effectiveness of immunotherapy.
Citation Format: Mingyang Feng, Sirui Tan, Qizhi Ma, Benxia Zhang, Yue Chen, Qiu Li, Yongsheng Wang. Targeting the poliovirus receptor to activate T cells and induce myeloid-derived suppressor cells to differentiate to M1-like macrophages via the IFNγ-pSTAT1-IRF8 axis in cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 172.