We evaluated the safety, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of intravenous (IV) inclacumab, a fully human IgG4 anti–P-selectin monoclonal antibody in development for the treatment of sickle cell disease, at doses up to and exceeding those previously tested in healthy individuals. The gene discussed is SELP; the disease is sickle cell disease.