1. Vaccine Development Laboratory, Department of Vaccine, National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki, Finland
2. Institut für Mikrobiologie und Molecularbiologie, Ernst-Moritz-Arndt-Universität Greifswald, F.-L.-Jahn-str. 15, D-17487 Greifswald, Germany
3. Institute of Biotechnology, University of Helsinki, Viikki Biocenter, PO Box 56, FIN-00014, University of Helsinki, Finland