[1] Univ Cambridge, Cambridge Inst Med Res, Dept Pathol, Cambridge CB2 0XY, England
[2] Univ Southampton, Fac Med, Southampton SO16 6YD, Hants, England
[3] Univ Southampton, Inst Life Sci, Southampton SO16 6YD, Hants, England
[4] Univ Tubingen, Inst Cell Biol, Dept Immunol, D-72076 Tubingen, Germany
[5] Univ Cambridge, Cambridge Inst Med Res, Dept Haematol, Cambridge CB2 0XY, England