Agonistic antibodies directed to immunostimulatory receptors are a currently untapped source for immunotherapy. Whereas checkpoint blockers have translated into the clinic, the rules for agonistic antibodies have been more difficult to discern and these reagents await further optimization. Here we discuss the salient properties of monoclonal antibodies (mAb) required to strongly agonize these receptors and discuss potential strategies for the future. We show that immunostimulatory mAb (ISA) can agonize key stimulatory receptors on the cell surface—many of which are from the TNFR family—and highlight the importance of isotype. Using CD40 mAb as a paradigm, we show that receptor clustering is key for ISA responses—probably mimicking ligand. This clustering can be achieved via Fc gamma receptor (FcgR) engagement or independently with the hIgG2(B) isotype. For CD40 this is highly epitope dependent, showing that epitope, isotype, and domain location all interact to drive mAb agonism. Finally, we show that isotype engineering can overcome “weak” epitopes. This can be completely independent of FcgR interaction in the case of hIgG2B, which may be of use in humans where the FcgR profile within the tumor microenvironment may vary.

Citation Format: Xiaojie Yu, Anne White, Martin Glennie, Ivo Tews, Hayden Fisher, Chris Orr, Ruth French, Stephen Beers, Aymen Al'Shamkhani, Osman Dadas, Ali Roghanian, Jane Willoughby, Mark S. Cragg. Optimizing immunostimulatory antibodies for cancer immunotherapy [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr IA03.