Biotheus' 4-1BB agonist is a humanized VHH that targets a unique membrane-proximal epitope on 4-1BB situated on the CRD4 domain to maintain agonist activity but in turn reduce toxicity risk. Activation of 4-1BB can improve immune effector function and memory. By pairing with an anti-CLDN18.2 binder, PM1032 activates 4-1BB in CLDN18.2-enriched tumours. Fc function has been depleted to minimize FcR-mediated crosslinking. In preclinical studies, single-agent activity has been observed, and PM1032 may be used to treat CLDN18.2+ solid tumours such as gastric and pancreatic cancer.