1. Cellular and Molecular Therapeutics Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
2. Sickle Cell Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
3. Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.