1. Department of Virology, Haartman Institute, University of Helsinki, and HUSLAB, Helsinki University Central Hospital, Haartmaninkatu 3 (POB 21), FIN-00014 Helsinki, Finland
2. Cancer Gene Therapy Group, Molecular Cancer Biology Program and Transplantation Laboratory, University of Helsinki, and HUSLAB, Helsinki University Central Hospital, FIN-00014 Helsinki, Finland
3. Institute of Medical Technology and Tampere University Hospital, University of Tampere, FIN-33014 Tampere, Finland
4. Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California 94143