Main Inclusion Criteria: All subjects must meet ALL of the following inclusion criteria to
be enrolled.

   1. Male and female subjects aged 18 years or older.

   2. Meet revised 2016 World Health Organization (WHO) criteria for the diagnosis of
   polycythemia vera.

   3. Records of all phlebotomies performed for at least 28 weeks (preferably up to 52
   weeks) before dosing are available.

   4. 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 due to cytoreductive therapy.

   5. 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 and with no planned change in dose.

Main Exclusion Criteria: Subjects must meet NONE of the following exclusion criteria to be
enrolled:

   1. Active or chronic bleeding within 4 weeks of screening.

   2. Meets the criteria for post-PCV myelofibrosis as defined by the International Working
   Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT).

   3. Known primary or secondary immunodeficiency.

   4. Any surgical procedure requiring general anesthesia within 1 month prior to screening
   or planned elective surgery during the study.