​These questions require a yes answer to qualify.​

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• Are you at least 18 years of age?

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• Are resistant to or intolerant of Hydroxyurea, that is, fulfilling at least 1 of the following criteria:

1.  Platelet count > 600× 109/L after 3 months of at least 2 g/day of HU (2.5 g/day in subjects with a body weight over 80 kg) OR at the subject's maximally tolerated dose if that dose is < 2 g/day.

2.  Platelet count > 400 × 109/L and WBC count < 2.5 × 109/L or hemoglobin (Hgb) < 10 g/dl at any dose of HU.

3.  Presence of leg ulcers or other unacceptable muco-cutaneous manifestations at any dose of HU.

4.  HU-related fever.

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• Platelet count > 650 × 109/L at screening

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• WBC > 11.0 × 109/L at screening.