173P First-in-human study to evaluate the safety and clinical activity of FS222: A tetravalent bispecific antibody targeting PD-L1 and CD137, in patients with advanced solid tumors

FS222 is a novel tetravalent bispecific antibody targeting PD-L1 and CD137 that aims to overcome the limitations of current PD-(L)1 and CD137 (4-1BB) monotherapies via a unique mechanism of action that elicits PD-L1-dependent CD137 activation. This has the potential to deliver strong antitumor clinical activity, even in PD-L1 low conditions as seen in preclinical models, with good tolerability.