Perenostobart is a human IgG4-kappa monoclonal antibody that targets ectonucleoside triphosphate diphosphohydrolase-1 (ENTPD1), commonly known as CD39. As an IgG4 isotype, it is engineered to minimize effector functions (e.g., antibody-dependent cellular cytotoxicity) and focus on modulating enzymatic activity. CD39 is an ectoenzyme that hydrolyzes extracellular ATP to ADP and ultimately to AMP, which is then converted by CD73 into immunosuppressive adenosine.