Abstract 6326: Discovery & preclinical evaluation of BPB-101: A novel triple functional bi-specific antibody targeting GARP-TGFβ complex/SLC, free TGF-β and PD-L1
Authors: Xu Wenxin , Xu Jieying , Xu Deyu , Cheng Hongjie , Zhang Li , Zheng Huan , Ye Siyuan , Jiang Mengshi , Wang Jiabing , Ding Lieming 
Published: June 2023

Abstract
Background: Recent studies on tumor microenvironment (TME) have been conferred considerable attention, especially the transforming growth factor-β (TGF-β) signal axis and the PD-L1/PD-1 signal axis. TGF-β is a crucial enforcer in promoting tumor cells angiogenesis, plasticity, fibrosis, and in regulating immune homeostasis and tolerance. The TGF-β signaling controls innate and adaptive immunity in TME by inhibiting the activity of natural killer (NK) cells and effector T cells, while promoting the expansion of regulatory T cells (Tregs). Many studies have revealed that free TGF-β mainly released from glycoprotein A repetitions predominant (GARP)-TGFβ complex at the surface of activated Tregs, B, NK, and tumor cells. Existing antibodies or fusion proteins targeting TGF-β cannot simultaneously block the TGF-β releasing and naturalized free TGF-β in TME, thus limiting the anti-tumor effect. Herein, we designed a bi-specific antibody named as BPB-101 with triple functions: specifically target GARP-TGFβ complex and/or small latent complex (SLC), free TGF-β, and PD-L1. BPB-101 can stop tumor expansion and recruitment, and may enhance the immune effector cells to eliminate the tumor.
Methods: An anti-GARP mAb was discovered using a hybridoma platform and selected for binding with GARP-TGFβ complex/SLC and free TGF-β. An anti-PD-L1 nAb was screened out by VHH library and optimized in tumor-bearing mice. After humanizing, these two antibodies were successfully assembled to form a unique bi-specific antibody, BPB-101. The binding affinity of BPB-101 to GARP-TGFβ complex/SLC, free TGF-β and PD-L1 was determined by ELISA, FACS and SPR/BLI. Report gene assay was utilized to detect the blocking activity of BPB-101. The TGF-β secretion from activated Tregs was also analyzed. Finally, the anti-tumor efficacy of BPB-101 was assessed with a transgenic mouse model (B6-hLRRC32). To address the biosafety risks, the nonclinical safety profile was also evaluated in cynomolgus monkeys.
Results and Conclusion: BPB-101 is a high-affinity antibody aims to reverse immunosuppressive TME by triple-targeting functions. The blocking ability of TGF-β in not only latent form but also free form makes our BPB-101 distinct from M7824, any other existing anti-TGF-β mAbs and anti-GARP mAbs. In a MC38-hPD-L1 tumor-bearing B6-hLRRC32 model, BPB-101 showed significant tumor growth inhibition of 93 % at the dose of 5 mg/kg (p&lt;0.001), showing superior efficacy to monoclonal antibody alone or in combination with anti-PD-L1 nAb. In addition, BPB-101 showed durable responsiveness and a splendid safety profile with manageable adverse events. These striking results support the clinical development potential of our trifunctional agent as a monotherapy and in combination with other immunotherapies.
Citation Format: Wenxin Xu, Jieying Xu, Deyu Xu, Hongjie Cheng, Li Zhang, Huan Zheng, Siyuan Ye, Mengshi Jiang, Jiabing Wang, Lieming Ding. Discovery & preclinical evaluation of BPB-101: A novel triple functional bi-specific antibody targeting GARP-TGFβ complex/SLC, free TGF-β and PD-L1 [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 6326.