1. From the Department of Cell and Molecular Biology, Perelman School of Medicine (S.B., X.S.), Department of Pharmacology, Perelman School of Medicine (M.P.), and Department of Pathology and Laboratory Medicine (D.L.F., P.G.), University of Pennsylvania, Philadelphia; and Center for Cellular and Molecular Therapeutics (S.B., X.S., D.L.F., P.G.) and Division of Hematology (M.P.), Children’s Hospital of Philadelphia, PA.