Abstract 3243: A CTLA4 antibody with enhanced properties
Authors: Weinberger Leehee , Stanhill Ariel , Boim Aviv , Meyer Karin , Leitner Orith , Hamawi Hedva , Navon Ami 
Published: August 2019

Background: Immune therapy has been viewed in recent years as a major new path in oncology greatly due to the pioneering success in clinical practice of Yervoy (Ipilimumab), a CTLA-4 monoclonal antibody. To date, only a handful of immune modulator antibodies are U.S. FDA approved. CTLA-4 antibody mechanism of action of is not fully resolved and addresses Fc dependent elimination of tumor associated T regulatory cells as well as blocking of CTLA4-CD80/CD86 ligand interaction. We present a new CTLA-4 monoclonal antibody (TikAb) that demonstrates superior properties both in-vitro and in-vivo.

Methods: Based on the crystal structure of CTLA-4:CD80 and CTLA-4:CD86, a mimitope (a synthetic mimetic of the CTLA-4 surface interacting with CD80/CD86) was synthesized and used to immunize humanized mice. Known procedures for fusion and monoclonal antibody generation were performed and clones were selected based on FACS binding to CTLA-4 and CD80/86 interaction blocking. Functional T cell activation was performed and human CTLA-4 knock-in mice were used in a MC38 colon tumor model to evaluate TikAb efficacy in-vivo.

Results: TikAb, a full human antibody, demonstrates high binding affinity towards CTLA-4 expressing cells of 6-8-fold increased affinity over Ipilimumab, as was determined by cell-based assay (FACS) and by SPR (Biacore). Blocking of CTLA-4 ligands CD80 and CD86 was also significantly increased relative to Ipilimumab. TikAb binding towards endogenous CTLA-4 expressing cells (activated CD4+ T-cells) was also observed and was improved compared with ipilimumab. CTLA-4 epitope for TikAb binding differs from the reported epitope of Ipilimumab on CTLA-4, by the differential binding of TikAb towards CTLA-4 of different species. The same difference in the binding epitope was also observed following a comparison to numerous other pre-clinical and early stage CTLA-4 antibodies. Synergetic activation of T-cell activation is observed upon a combined treatment of PBMC cells with TikAb and Nivolumab (a PD-1 monoclonal Ab). In-vivo tumor models of MC-38 colon cells in CTLAh/h mice showed a dose dependent reduction of tumor size and greater reduction of tumor size and a significant increase in survival rates compared with Ipilimumab. Re-challenge of TikAb surviving mice with tumor cells showed immunological memory and complete recovery without further treatment.

Conclusions: We present TikAb - a new full human CTLA4 antibody with enhanced properties in values determined in-vitro and in-vivo. These observation support further examination of TikAb as a therapeutic candidate to treat cancer which may allow a lower treatment dose with an improved efficacy to peers.

Citation Format: Leehee Weinberger, Ariel Stanhill, Aviv Boim, Karin Meyer, Orith Leitner, Hedva Hamawi, Ami Navon. A CTLA4 antibody with enhanced properties [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 3243.