ET and PV are rare, chronic myeloproliferative neoplasms characterised by abnormal blood cell production and limited long-term treatment options. The investigational biologic is designed to target disease-driving immune mechanisms and is intended to address disease progression rather than only symptom control. The Orphan Drug Designation is granted to therapies intended to treat rare diseases affecting fewer than 200,000 patients in the United States. Patients with ET and PV typically require lifelong treatment. According to the companies, the monoclonal antibody targets an immune-evasion pathway implicated in the underlying biology of myeloproliferative neoplasms.