FS222

FS222 is a next-generation, tetravalent bispecific antibody designed to target both programmed death-ligand 1 (PD-L1) and CD137 (also known as 4-1BB). Its unique structure enables potent, PD-L1-dependent activation of CD137, providing selective agonism within the tumor microenvironment. This dual mechanism allows for simultaneous inhibition of the PD-L1 immune checkpoint and activation of T-cell mediated anti-tumor responses. Preclinical studies demonstrated that FS222 induces robust T-cell activation and antitumor activity with a favorable safety profile. In phase 1 clinical trials involving patients with advanced solid tumors—including those refractory to prior immunotherapy—FS222 has shown promising antitumor activity, particularly in metastatic cutaneous melanoma, non-small cell lung cancer, ovarian cancer, triple-negative breast cancer, liposarcoma, colon cancer, mesothelioma, and others. The drug is administered intravenously every four weeks. Adverse events are generally manageable and reversible; common side effects include elevated liver enzymes (AST/ALT), pyrexia, thrombocytopenia, asthenia, neutropenia and cytokine release syndrome[1][5][6][8][10].

Other names

FS222 mAb²