Eunsil Sung,^1,6 Minkyung Ko,^2,6 Ju-young Won,³ Yunju Jo,^2,4 Eunyoung Park,¹ Hyunjoo Kim,¹ Eunji Choi,³ Ui-jung Jung,¹ Jaehyoung Jeon,¹ Youngkwang Kim,¹ Hyejin Ahn,³ Da-som Choi,³ Seunghyun Choi,² Youngeun Hong,¹ Hyeyoung Park,¹ Hanbyul Lee,¹ Yong-Gyu Son,¹ Kyeongsu Park,¹ Jonghwa Won,¹ Soo Jin Oh,³ Seonmin Lee,⁵ Kyu-pyo Kim,⁵ Changhoon Yoo,⁵ Hyun Kyu Song,⁴ Hyung-seung Jin,³ Jaeho Jung,¹ and Yoon Park^2,7

¹ABL Bio Inc., Seongnam 13488, South Korea; ²Theragnosis Center, Biomedical Research Institute, Korea Institute of Science and Technology (KIST), Seoul 02792, South Korea; ³Department of Convergence Medicine, Asan Institute for Life Sciences, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, South Korea; ⁴Department of Life Sciences, Korea University, Seoul 02481, South Korea; ⁵Department of Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, South Korea ⁶These authors contributed equally. ⁷Lead contact

Correspondence: Hyung-seung Jin, Jaeho Jung, Yoon Park

Several preclinical studies demonstrate that antitumor efficacy of programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) blockade can be improved by combination with other checkpoint inhibitors. Lymphocyte-activation gene 3 (LAG-3) is an inhibitory checkpoint receptor involved in T cell exhaustion and tumor immune escape. Here, we describe ABL501, a bispecific antibody targeting LAG-3 and PD-L1 in modulating immune cell responses against tumors. ABL501 that efficiently inhibits both LAG-3 and PD-L1 pathways enhances the activation of effector CD4⁺ and CD8⁺ T cells with a higher degree than a combination of single anti-LAG-3 and anti-PD-L1. The augmented effector T cell responses by ABL501 resulted in mitigating regulatory-T-cell-mediated immunosuppression. Mechanistically, the simultaneous binding of ABL501 to LAG-3 and PD-L1 promotes dendritic cell (DC) activation and tumor cell conjugation with T cells that subsequently mounts effective CD8⁺ T cell responses. ABL501 demonstrates its potent in vivo antitumor efficacy in a humanized xenograft model and with knockin mice expressing human orthologs. The immune profiling analysis of peripheral blood reveals an increased abundance of LAG-3^hiPD-1^hi memory CD4⁺ T cell subset in relapsed cholangiocarcinoma patients after gemcitabine plus cisplatin therapy, which are more responsive to ABL501. This study supports the clinical evaluation of ABL501 as a novel cancer immunotherapeutic, and a first-in-human trial has started (NCT05101109).