Abstract LB-153: KY1055, a novel ICOS-PD-L1 bispecific antibody, efficiently enhances T cell activation and delivers a potent anti-tumour response in vivo

Abstract

Abstract Antibodies blocking the PD-1/PD-L1 axis present significant breakthroughs in the treatment of hitherto untreatable cancers. However, despite the highly encouraging progress that has been made, multiple tumour types demonstrate limited response to these therapies. The emerging picture is that combination with other therapies is required to improve response rates and/or the durability of response. Additional benefit could be achieved by combining an anti-PD-L1 approach with another modulator of T cell activation. ICOS is a co-stimulatory molecule expressed on activated T cells such as TEff and TReg cells present in the tumour microenvironment (TME). ICOS agonism has been demonstrated to improve TEff cell survival and IFNγ release, resulting in the activation of T cell-dependent eradication of the tumour. In addition, the high expression of ICOS observed on TReg cells in the TME allows these highly immunosuppressive cells to be selectively depleted when using the appropriate antibody format. With the aim of targeting both ICOS and PD-L1, we have developed a bispecific mAb² (KY1055) as a human IgG1 format that consists of fully human Fab arms targeting ICOS and a modified Fc (Fcab) containing binding sites to PD-L1. We demonstrate potent (single digit nM) binding to ICOS via the Fab and to PD-L1 via the Fcab. Furthermore, in vitro studies reveal that KY1055 can bridge together ICOS- and PD-L1-expressing cells and can activate ICOS signalling through this cross-presentation. Functionality of the Fcab was validated by demonstrating that it blocks the PD-1-PD-L1 inhibitory pathway, resulting in the up-regulation of IFNγ in monocyte:T cell co-culture assays. We also demonstrate the ability of KY1055 to deplete ICOShigh cells in vitro by ADCC. In vivo, we confirm the anti-tumour efficacy of KY1055 in several syngeneic models that are poorly responsive to the respective monotherapies and further demonstrate improved anti-tumour efficacy when combined with anti-CTLA4 and anti-PD-1 in vivo. Finally, we demonstrate that KY1055 depletes TRegs and improves the TEff : TReg ratio in vivo in a CT26 model of tumour growth. Altogether, these data warrant further development of KY1055 for the treatment of solid tumours. Citation Format: Richard C. Sainson, Nahida Parveen, Gwenoline Borhis, Miha Kosmac, Tracey OKell, Emma Taggart, Joana Carvalho, Matthew McCourt, Hanif Ali, Hannah Craig, Aksana Labokha. KY1055, a novel ICOS-PD-L1 bispecific antibody, efficiently enhances T cell activation and delivers a potent anti-tumour response in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-153.