A Study to Evaluate Safety, Pharmacokinetic, and Biological Activity of INCB059872 in Subjects With Sickle Cell Disease

Inclusion Criteria: * Diagnosis of SCD (sickle cell SS) confirmed through hemoglobin electrophoresis. * Must be red blood cell (RBC) transfusion-independent (not currently on regularly scheduled transfusions) for ≥ 3 months from the time of first dose of study drug. * No RBC transfusion within 30 days of first dose of study drug. * Hydroxyurea (HU) refractory -Must not have received HU therapy during the 3 months before receiving study drug. * Creatinine clearance ≥ 60 mL/min based on the institutional formula. * Willingness to avoid pregnancy or fathering children. Exclusion Criteria: * Any unresolved toxicity ≥ Grade 2 from previous therapy except for stable chronic toxicities not expected to resolve. * Pregnant or nursing women or participants expecting to conceive or father children within the projected duration of the study, starting with screening visit through completion of safety follow-up. * Received an investigational study drug within 28 days or 5 half-lives (whichever is longer) before receiving the first dose of study drug (requirement may be waived with medical monitor approval). * Chronic or current active infectious disease requiring systemic antibiotics, antifungal, or antiviral treatment. * Prior receipt of LSD1 inhibitor therapy for any indication.