165TiP A first-in-human phase I study of FS222, a CD137/PD-L1 tetravalent bispecific antibody, in patients with advanced malignancies

Abstract

Checkpoint Inhibitor (CPI) therapy is standard of care in a range of tumor types but many patients fail to gain long term clinical benefit. Agonist antibodies targeting the T cell costimulatory receptor CD137 (4-1BB) have shown immune-stimulatory effects, but hepatotoxicity significantly hindered development. FS222, a novel tetravalent bispecific antibody, incorporates two CD137 binding sites in the Fc-region (Fcab) and anti-PD-L1 Fabs in a natural human IgG1 antibody with silenced FcyR activity.