Cbl-b-IN-2 is an orally active biological compound that inhibits the E3 enzyme Casitas b lineage lymphoma proto-oncogene b (Cbl-b) in the ubiquitin proteasome pathway and can be used in the study of diseases that modulate the immune system and are susceptible to regulation by the immune system. Cbl-b-IN-2 can also be used in cancer research alone or in combination with one or more immune checkpoint inhibitors, antitumour agents and radiopharmaceuticals.