Abstract 2287: Bispecific anti-PD1 checkpoint inhibitors antibodies (BiCKI), an optimized platform designed to tackle anti-PD-(L)1 primary and secondary resistance mechanisms

Abstract Although Anti PD(L)1 therapy lead to impressive therapeutic responses by reinvigorating T cells, primary and secondary resistances occur de novo or during treatment impeding the full efficacy of the drug. To tackle this resistance mechanisms and reduced the immunotoxicity of combination therapy, we designed a 2nd generation of anti-PD1 antibody by fusing immune protein to the Fc portion of the antibody, named BiCKI®. The anti PD1 will more selectively drive the immune active drug on antigen-experienced (PD1+) T cells, through cis-targeting mechanism. These bifunctional molecules were designed with an optimized anti-PD1 backbone for bispecific format, fused to an active protein domain to the C-ter of heavy and/or light chains. Different protein candidate were successfully fused to the optimized anti-PD1, such as cytokines, costimulatory molecules, or dominant negative receptors with PD1/PDL1 full antagonistic activity. In contrast to combination, BiCKI® antibodies enable the simultaneous dual-binding specificity in a single drug allowing a synergistic activation. Each BiCKI® is selected on its synergistic capacity to re-activate of anti-tumor T cell responses or TCR signaling in cell-based assays. Bispecific antibody development in clinic has been hampered by difficult manufacturing process, reduced pharmacokinetic (PK) and drug exposure. Both anti PD-1 CDRs and VH/VL framework sequences were carefully selected and optimized for bioproductivity and biostability of the molecule. A 2 to 15-fold increased productivity in mammalian cells was observed versus the non-optimized anti-PD1 antibody or other anti-PD-1 bispecific backbones as Pembrolizumab or Nivolumab. We also evaluated the impact of the Fc isotype,linker flexibility and affinity of the fused compound on the PK profile of different bispecifics fused to costimulatory molecules or cytokines. The IgG isotype with reduced FcgR binding property, of the anti-PD-1 backbone was associated with a better PK profile with some exceptions for cytokine. The presence or length of a linker between Fc domain and the fused protein has a small impact the PK and drug efficacy. More importantly, the affinity of the fused compound has an impact the PK profile of BiCKI® For example, the anti-PD-1 fused to wild-type IL-7 cytokine possesses a high affinity for the CD127/CD132 receptors but display a reduced drug exposure both in mouse and cynomolgus. This potential difficulty was solved with further improved products including IL-7 mutants having reduced affinity for CD127 and/or CD132. While significant correlation between IL7 affinity and PK has been observed, increased PK and drug exposure could be achieved using optimized combination of Fc isotype a linker length design and BiCKI-IL7 mutants retaining significant IL7R signaling. Conclusion: Our BICKI® platform was designed to overcome major hurdles of bispecific antibody development, we improved its manufacturability and drug exposure by selectively designing the structure of bispecific antibodies. By fusing costimulatory molecule, cytokines or dominant negative receptor to the anti PD-1 blocking antibody, we can generate and select various efficient bispecific molecules acting in synergy to counteract primary and secondary resistance mechanisms of anti-PD(L)1 therapies. Citation Format: Caroline Mary, Aurore Morello, Virginie Thepenier, Géraldine Teppaz, Justine Durand, Nicolas Poirier. Bispecific anti-PD1 checkpoint inhibitors antibodies (BiCKI), an optimized platform designed to tackle anti-PD-(L)1 primary and secondary resistance mechanisms [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 2287.