1,9 1Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA; 2Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA; 3Center for Regenerative Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA; 4Harvard Stem Cell Institute, Cambridge, Massachusetts 02138, USA; 5Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, Massachusetts 02138, USA; 6Division of Infectious Diseases,...