(a)Sickle Cell Anemia having history of one or more of the following despite treatment with standard therapies such as hydroxyurea: i) 2 or more episodes of acute chest syndrome since age 13 years ii) pulmonary hypertension as measured by tricuspid regurgitant jet velocity of greater than 2.5m/s iii) 2 or more painful crisis per year requiring medical care and analgesia in excess of what is needed at baseline.