Abstract 5526: AK131, an anti-PD1/CD73 bispecific antibody for cancer immune therapy
Authors: Huang Zhaoliang , Pang Xinghua , Zhong Tingting , Jin Chunshan , Chen Na , Xia Dennis , Zhang Peng , Wang Max , Xia Michelle , Li Baiyong 
Published: June 2022

Background: AK131 is a bispecific antibody derived from AK105 (the Akeso PD-1 antibody) and AK119 (the Akeso CD73 antibody). AK119 is a dual mechanism antibody (2021SITC poster #750) that blocks the generation of adenosine and stimulates antigen specific B cell activation. Adenosine is a key immune suppressive molecule thought to contribute to resistance to PD-1 antibody therapy. Both CD73 and PD-1 are targets with high expression in the tumor microenvironment. Moreover, a growing body of literature evidence supports an important role B cells play in tumor immunity. Thus we developed a bispecific PD-1/CD73 antibody with the capacity to relive immune checkpoint control of T cells, activate B cells, and eliminate immune suppression by adenosine, for immune therapy of cancer.

Method: Binding assays of AK131 to antigens, and antigen expressing cells were performed by using ELISA, Fortebio, and FACS assays. In-vitro bioactivity assays of AK131 including the investigation of neutralizing activity to PD-1 by reporter gene assay, activation of T cells by detecting secretion of IFN-γ and IL-2 by ELISA, inhibition of CD73 enzymatic activity by cell-based enzyme assay, activation of B cells by measuring CD69, CD83, HLA-DR and IgM expression, as well as endocytosis of CD73 by cellular assay. In-vivo anti-tumor activity of AK131 was further confirmed by C57BL/6-hPD-1/hPD-L1/hCD73 transgenic mouse MC38-hPDL1-hCD73 tumor syngeneic model.

Result: AK131 effectively bound to human PD-1 and CD73 with high affinity. The interaction between PD-1 and its ligand PD-L1 was blocked by AK131 in reporter gene assay. In cellular assays, AK131 effectively promoted the secretion of IFN-γ and IL-2 by T cells in co-culture of PBMCs and Raji-PDL1 cells. Moreover, AK131 inhibited CD73 enzymatic activity and induced endocytosis of CD73. AK131 enhanced the expression of CD69, CD83, HLA-DR and IgM which are the activation marker of B cell, in a adenosine-independent manner. In in-vivo assay, AK131 successfully inhibited tumor growth in C57BL/6-hPD-1/hPD-L1/hCD73 transgenic mouse MC38-hPDL1-hCD73 tumor syngeneic model.

Conclusion: AK131 is a bi-specific antibody targeting both PD-1 and CD73. In pre-clinical studies, AK131 showed potent in-vitro and in-vivo activities. In summary, AK131 effectively blocked PD-1/PDL-1 interaction, promoted the activation of T cells and B cells, inhibited the CD73 enzymatic activity, and induced CD73 endocytosis. AK131 also demonstrated robust in-vivo anti-tumor activity in mouse model. These observations, addition to other preclinical study results, supports the development of AK131 as an anti-tumor agent in the clinic.

Citation Format: Zhaoliang Huang, Xinghua Pang, Tingting Zhong, Chunshan Jin, Na Chen, Dennis Xia, Peng Zhang, Max Wang, Michelle Xia, Baiyong Li. AK131, an anti-PD1/CD73 bispecific antibody for cancer immune therapy [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 5526.