 - Male or female, 18 to 60 years old, with sickle cell disease hemoglobin SS, HbSβ0thalassemia, HbSβthalassemia, or HbSC not requiring chronic blood transfusion therapy; without hospitalization in 30 days before screening or receiving blood transfusion within 30 days before screening; subjects are allowed concomitant use of hydroxyurea if the dose has been stable for the 3 months prior to screening. 