Abstract 5527: A novel fully human anti-TIGIT and PVRIG bispecific antibody that elicits potent anti-tumor efficacy in pre-clinical studies

Abstract Background: TIGIT (T-cell immunoglobulin and ITIM domain), which is primarily expressed on activated and 'exhausted' T and NK cells, is one of the promising 'next generation' immune checkpoint molecules. Engagement of TIGIT to its ligands (i.e., PVR and PVRL2) leads to inhibitory signaling in T cells, promoting functional exhaustion of tumor-infiltrating T lymphocytes. Anti-TIGIT monoclonal antibodies have shown clinical benefit when combined with anti-PD-L1 agents in NSCLC. However, the single-agent efficacy of anti-TIGIT therapies have been limited. PVRIG (PVR-related immunoglobulin domain containing), which is another coinhibitory receptor of the DNAM/TIGIT/CD96 nectin family, binds with high affinity to PVRL2 and suppresses T-cell function, and shows nonredundant inhibitory effects alongside the TIGIT/PVR/PVRL2 axis. Here, we report a fully-human anti-TIGIT × PVRIG bispecific antibody (anti-TIGIT × PVRIG biAb), which blocks both the PVRIG/PVRL2 and TIGIT/PVR/PVRL2 pathways, that maintains the efficacy of the combination of the two mono-agents. The anti-TIGIT × PVRIG biAb is also highly efficacious when combined with PD1/PD-L1 inhibitors in mouse tumor models. Methods: An anti-TIGIT × PVRIG biAb was generated through the fusing of a fully-human IgG targeting TIGIT with a wild type G1-Fc to a fully-human scFv at the c-terminus targeting PVRIG. Binding affinity and specificity analyses were studied by flow cytometry and biolayer interferometry. The co-binding of the anti-TIGIT × PVRIG biAb to TIGIT and PVRIG was detected by ELISA. The immunomodulatory functions of the anti-TIGIT × PVRIG biAb were evaluated using a luciferase reporter cell assay in vitro and human PBMC-based tumor models in vivo. Results: The anti-TIGIT × PVRIG biAb binds with high affinity to the extracellular domain of human TIGIT/PVRIG and can bind to TIGIT and PVRIG simultaneously. In a competition assay, the anti-TIGIT × PVRIG biAb efficiently blocked the interaction between TIGIT and PVR/PVRRL2, and PVRIG with PVRL2. In a luciferase reporter cell system, the anti-TIGIT × PVRIG biAb induced high levels of luciferase activity compared with the anti-TIGIT or anti-PVRIG mAbs alone. In vivo, the anti-TIGIT × PVRIG biAb demonstrated stronger anti-tumor efficacy than the anti-TIGIT and anti-PVRIG mAbs as monotherapies or combined with anti-PD-1 mAb. Conclusion: Our anti-TIGIT × PVRIG biAb, a fully human bispecific antibody, either alone or in combination with anti-PD-1 mAb promotes immune cell activation both in vitro and in vivo, supporting its clinical development for the treatment of human cancers. The molecule is currently under GLP-toxicity evaluation in NHP, and a first-in-human study is expected to begin in 2022. Citation Format: Shuang Dai, Weifeng Huang, Zhijun Yuan, Shaogang Peng, Jiayi Si, Chao Wang, Xiaoniu Miao, Yingda Xu, Joanne Sun, Xiaolin Liu, Andy Tsun, Tianhang Zhai. A novel fully human anti-TIGIT and PVRIG bispecific antibody that elicits potent anti-tumor efficacy in pre-clinical studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5527.