1. Wellcome – MRC Stem Cell Institute, University of Cambridge 1 , Cambridge CB2 0AW , United Kingdom
2. University of Cambridge 2 Department of Haematology , , Cambridge CB2 0AW , UK
3. Microsoft Research 3 , 21 Station Road, Cambridge CB1 2FB , UK
4. University of Cambridge 4 Department of Biochemistry , , Cambridge CB2 1QR , UK