Inclusion Criteria: 

• Male and female subjects aged 18 years or older.
• Meet revised 2016 World Health Organization (WHO) criteria for the diagnosis of PV.
• Hematocrit < 45% before dosing.
• Phlebotomy requiring defined as:
  • Regularly spaced phlebotomies over at least 28 weeks prior to dosing;
  • At least 3 phlebotomies during the 28 weeks prior to dosing;
  • Last phlebotomy within approximately 12 weeks before Screening.
• Records of all phlebotomies performed for at least 28 weeks (preferably up to 52 weeks) before dosing.
• Eastern Cooperative Oncology Group (ECOG) performance status 0, 1 or 2.
• Women of childbearing potential and men agree to use medically acceptable contraception (< 1% annual failure rate) during the study and for 90 days after the last dose of study drug.
• Subject understands the study procedures, is willing and able to adhere to study requirements and agrees to participate in the study by giving written informed consent.
• Subjects who are not receiving cytoreductive therapy must have been discontinued from any prior cytoreductive therapy for at least 24 weeks before Screening and have recovered from any adverse events (AEs) due to cytoreductive therapy.
• Subjects receiving cytoreductive therapy with hydroxyurea, interferon, or ruxolitinib must have received cytoreductive therapy for at least 24 weeks and be on a stable dose or have a decreasing dose (Medical Monitor approval required) for at least 8 weeks before dosing with no planned change in dose.

Exclusion Criteria:

• Clinically meaningful laboratory abnormalities at Screening including, but not limited to:
  • Absolute neutrophil count 1.5 × ULN;
  • Platelet count 1.5 × ULN;
  • Estimated Glomerular Filtration Rate (eGFR) <40 mL/min/1.73 m^2;
  • Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≥ 2.5 × upper limit of normal (ULN) or direct bilirubin > 1.5 × ULN.
• Pregnant or lactating females.
• Clinically significant thrombosis (e.g., deep vein thrombosis or splenic vein thrombosis) within 1 month of Screening.
• Active or chronic bleeding within 4 weeks of Screening.
• Meets the criteria for post-PV myelofibrosis as defined by the International Working GroupMyeloproliferative Neoplasms Research and Treatment (IWG-MRT).
• Infection requiring hospitalization or intravenous antimicrobial therapy, or opportunistic infection within 3 months of dosing; any infection requiring antimicrobial therapy within 4 weeks of dosing. Prophylactic antibiotics are allowed.
• Any serious or unstable medical or psychiatric condition that would prevent, (as judged by the Investigator) the subject from properly providing informed consent or any condition which would jeopardize compliance with the study.
• Known primary or secondary immunodeficiency.
• Positive for hepatitis B or hepatitis C or known human immunodeficiency virus (HIV) infection.
• Any surgical procedure requiring general anesthesia within 1 month prior to Screening or planned elective surgery during the study.
• History of invasive malignancies within the last 5 years, except localized cured prostate cancer, cervical cancer, and ductal carcinoma in situ (DCIS).
• Current or recent history of alcohol dependence or illicit drug use within 1 year prior to Screening.
• Subject is unable to give informed consent.
• Receipt of an investigational agent within 30 days of Screening.

Eligibility last updated 1/4/22. Questions regarding updates should be directed to the study team contact.