Abstract 5203: Discovery and development of SLD2435, a novel humanized IgG1 bispecific antibody simultaneously targeting human TIGIT and PVRIG for cancer immunotherapy

Abstract Despite dramatic success for immune checkpoint inhibition in treating certain patient subsets, there remains high unmet medical need for the treatment of patients who are refractory to or relapse following treatment with current checkpoint inhibitors. TIGIT and PVRIG, are exciting novel targets for immune-oncology which function as immune inhibitory receptors expressed on both T and NK cells and have been reported to inhibit anti-tumor activity. SLD2435, a novel humanized IgG1 bispecific antibody simultaneously targeting human TIGIT and PVRIG that synergistically enhances both NK and T cell functions, demonstrates significant preclinical anti-tumor efficacy. Here, we reported the discovery, development and characterization of SLD2435 for potential use in cancer patients. Anti-human TIGIT mAb was generated from mouse hybridoma whereas anti-human PVRIG Ab was discovered from Alpaca as single-domain antibody (sdAb). Both Abs were identified based on the ability to block the interaction of TIGIT or PVRIG with their cognate ligands (PVR or PVRL2 respectively) and for the ability to enhance primary human NK cytotoxicity over tumor cell lines as well as to promote the function of antigen-specific CD8+ T cells. Lead anti-human PVRIG sdAb was then selected and fused to the N-terminal of lead anti-human TIGIT mAb with a peptide linker for SLD2435 construction followed by subsequent testing in multiple abovementioned assays. SLD2435 simultaneously bound to human TIGIT and PVRIG with sub-nanomolar affinity and showed cross-reactivity to respective cynomolgus targets together with strong avidity mediated receptor-ligand interaction blocking at both protein and cellular levels. In vitro functional studies revealed that SLD2435 induced potent primary human NK cell mediated cytotoxicity over WiDr tumor cells better than the combination of anti-PVRIG and anti-TIGIT mAbs. It could also trigger preferential depletion of TIGIT+/TIGIT+PVRIG+ Treg via ADCC. In addition, SLD2435 enhanced IFN-γ production of CMV antigen-specific CD8+ T cells culturing with PVR+PVRL2+HLA matched Colo205 tumor cells and had synergistic effect on T cell activation when further combined with an anti-PD-L1 mAb. In consistent with in vitro results, SLD2435 displayed significant anti-tumor efficacy in vivo in a HuPBMC A375 xenograft model. At last, SLD2435 demonstrated great developability profile under various stress tests. Taken together, these data support the further development of SLD2435 as a potential novel therapeutic agent for the treatment of cancer patients. Citation Format: Xiaofeng Zhao, Yayuan Fu, Xiaoqing Liu, Fengli Shan, Zhenna Gao, Mengyu Wang, Huiming Xu, Hai Huang, Yang Liu, Wenqing Yang, Zhuoxiao Cao, Renhong Tang. Discovery and development of SLD2435, a novel humanized IgG1 bispecific antibody simultaneously targeting human TIGIT and PVRIG for cancer immunotherapy [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 5203.