1. Program in Cancer Biology, Cancer Institute, Institute for Stem Cell Biology and Regenerative Medicine, and Ludwig Center, Stanford University School of Medicine, Palo Alto, CA 94305, USA.
2. Department of Bioengineering and Howard Hughes Medical Institute, Stanford University School of Medicine, Palo Alto, CA 94305, USA.
3. MRC Molecular Haematology Unit and Department of Haematology, Weatherall Institute of Molecular Medicine, and University of Oxford and Oxford University Hospitals NHS Trust, Oxford OX3 9DS, UK.
4. Division of Hematology, Department of Internal Medicine, Stanford University School of Medicine, Palo Alto, CA 94305, USA.