1. Department of Haematology, University of Cambridge, Hills Road, Cambridge CB2 2QH, United Kingdom; MRC Centre for Protein Engineering, Hills Road, Cambridge CB2 2QH, United Kingdom
2. MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom
3. Department of Haematology, University of Cambridge, Hills Road, Cambridge CB2 2QH, United Kingdom
4. MRC Centre for Protein Engineering, Hills Road, Cambridge CB2 2QH, United Kingdom; MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom