Seongju Jeong,¹ Eunyoung Park,² Hyung-Don Kim,^1,3 Eunsil Sung,² Hyunjoo Kim,² Jaehyoung Jeon,² Youngkwang Kim,² Ui-jung Jung,² Yong-Gyu Son,² Youngeun Hong,² Hanbyul Lee,² Shinai Lee,² Yangmi Lim,² Jonghwa Won,² Minwoo Jeon,¹ Shin Hwang,⁴ Lei Fang,⁵ Wenqing Jiang,⁵ Zhengyi Wang,⁵ Eui-Cheol Shin,¹ Su-Hyung Park,^1,* Jaeho Jung^2,*

¹Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea
²ABL Bio Inc, Seongnam, Korea
³Department of Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Seoul, Korea
⁴Department of Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Seoul, Korea
⁵I-Mab Biopharma, Shanghai, China

SJ, EP and H-DK are joint first authors.
S-HP and JJ are joint senior authors.

^*Correspondence to Dr Su-Hyung Park; Dr Jaeho Jung;

Background 
Stimulation of 4-1BB with agonistic antibodies is a promising strategy for improving the therapeutic efficacy of immune checkpoint inhibitors (ICIs) or for overcoming resistance to ICIs. However, dose-dependent hepatotoxicity was observed in clinical trials with monoclonal anti-4-1BB agonistic antibodies due to the activation of 4-1BB signaling in liver resident Kupffer cells.

Methods 
To avoid this on-target liver toxicity, we developed a novel bispecific antibody (4-1BB×PD-L1 bispecific antibody, termed “ABL503”) uniquely designed to activate 4-1BB signaling only in the context of PD-L1, while also blocking PD-1/PD-L1 signaling.

Results 
Functional evaluation using effector cells expressing both 4-1BB and PD-1 revealed superior biological activity of ABL503 compared with the combination of each monoclonal antibody. ABL503 also augmented T-cell activation in in vitro assays and further enhanced the anti-PD-L1-mediated reinvigoration of tumor-infiltrating CD8+ T cells from patients with cancer. Furthermore, in humanized PD-L1/4-1BB transgenic mice challenged with huPD-L1-expressing tumor cells, ABL503 induced superior anti-tumor activity and maintained an anti-tumor response against tumor rechallenge. ABL503 was well tolerated, with normal liver function in monkeys.

Conclusion 
The novel anti-4-1BB×PD-L1 bispecific antibody may exert a strong anti-tumor therapeutic efficacy with a low risk of liver toxicity through the restriction of 4-1BB stimulation in tumors.