[1] Katholieke Univ Leuven, Stem Cell Inst, B-3000 Louvain, Belgium
[2] Univ Minnesota, Stem Cell Inst, Minneapolis, MN 55455 USA
[3] Tech Univ Munich, Dept Internal Med, D-8000 Munich, Germany
[4] Erasmus Univ, Dept Cell Biol & Genet, NL-3000 DR Rotterdam, Netherlands