Abstract 522: Optimization of novel anti-4-1BB antibodies on Biocytogen's in vivo drug screening platform

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Abstract 4-1BB (CD137, tumor necrosis factor receptor superfamily 9) is an inducible costimulatory receptor expressed on activated T and natural killer (NK) cells. 4-1BB ligation on T cells triggers a signaling cascade that results in upregulation of anti-apoptotic molecules, cytokine secretion, and enhanced effector function. In dysfunctional T cells that have a decreased cytotoxic capacity, 4-1BB ligation demonstrates a potent ability to restore effector functions. On NK cells, 4-1BB signaling can increase antibody-dependent cell-mediated cytotoxicity. Agonistic monoclonal antibodies targeting 4-1BB have been developed to harness 4-1BB signaling for cancer immunotherapy. We have interests in developing novel 4-1BB antibodies for boosting cancer patients' own immunity in light of other successful immune checkpoint modulators. We developed a cohort of 4-1BB specific antibodies using the classic hybridoma technology. Then, we took the advantages of Biocytogen's humanized mice and screened the purified antibodies in B-h4-1BB mice bearing MC-38 tumor cells. We found some antibodies that are as potent as Urelumab in vivo. We then humanized the antibody to obtain YH004. To determine the subtype of the antibody, we grafted the antigen-binding domain onto various human Fc backbones. Interestingly, we found that the human IgG1 isotype was more effective against tumors than the other isotypes in B-4-1BB mice with MC38 tumors and Treg depletion were noted in tumor-infiltrating lymphocyte analysis using the same murine model. In addition, we proved that the synergistic anti-tumor activity of YH004 in combination with pembrolizumab in B-hPD-1/h4-1BB mice. In brief, the 4-1BB antibody was validated in humanized mice to provide a favorable reference for future clinical evaluation. Citation Format: Chaoshe Guo, Yu Zhu, Yunyun Chen, Yi Yang, Zhihong Li. Optimization of novel anti-4-1BB antibodies on Biocytogen's in vivo drug screening platform [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 522.