Abstract 4110: Identification of PD1 B cell mimotopes with functional PD1-PDL1 blocking capacity: New strategy for cancer immunotherapy
Authors: Tobias Joshua , Battin Claire , Linhares Annika De Sousa , Karin Baier , AMbroye Katharina , Drinic Mirjana , Garner-Spitzer Erika , Zielinski Christoph , Kundi Michael , Steinberger Peter , Wiedermann Ursula 
Published: August 2019

Abstract
Immune checkpoint (ICP) blockade has become a major focus in cancer immunotherapy, and the application of monoclonal antibodies (mAbs) as ICP inhibitors shows impressive results in the therapy against cancers like melanoma, renal cell carcinoma or non-small cell lung cancer. Active immunization with B cell epitopes/mimotopes of ICP inhibitors rather than application of the corresponding mAbs for passive immunotherapy may, however, provide advantages such as induction of antibodies by the patient’s own immune system and overcoming the costly treatment of the mAbs.
Applying a platform for bacterial surface-display of overlapping peptides spanning the extracellular domains of human PD1 (hPD1) and mouse PD1 (mPD1), as well as in vitro solid phase-based ELISA assay and cellular-based assays involving human Jurkat T cells expressing human/mouse PD1 and/or PDL1, B cell epitopes/mimotopes of Nivolumab and an anti-mPD1 mAb (with a blocking capacity) were identified. The mimotopes were not only shown to inhibit the binding of the corresponding mAbs but also to revert the PD1-PDL1 blocking inhibitory capacity of the respective mAbs. More importantly, to proof the antitumor activity of antibodies against PD1 mimotopes in vivo, rabbits were immunized with the mimotope of anti-mPD1 mAb to generate mimotope-specific IgGs. The specific IgGs not only inhibited the interaction of mPD1 and mPDL1 in vitro, but also significantly reduced tumor growth in a syngeneic model of mice grafted with cells expressing the breast cancer-associated tumor antigen Her-2/neu.
Our results show systematic identification and characterization of mimotopes of anti-PD1 ICP inhibitor B cell mimotopes conferring in vivo anti-tumor activity, and also indicate the potential of such mimotopes for active immunization in cancer therapy. Based on the results, enhancement of our second generation of anti-Her-2/neu vaccine (HerVAXX; Tobias et al, 2017*) by combining with mimotopes of ICP inhibitors is also proposed, which may potentially pave the way to a paradigm change in active immunotherapy against Her-2/neu overexpressing cancers using an effective multi-level vaccine.
The study is granted by Imugene Limited, Australia, and Medical University of Vienna.
* Tobias J. et al. BMC Cancer, 2017, 17:118.
Citation Format: Joshua Tobias, Claire Battin, Annika De Sousa Linhares, Baier Karin, Katharina AMbroye, Mirjana Drinic, Erika Garner-Spitzer, Christoph Zielinski, Michael Kundi, Peter Steinberger, Ursula Wiedermann. Identification of PD1 B cell mimotopes with functional PD1-PDL1 blocking capacity: New strategy for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4110.