1. Novartis Vaccines, Cambridge, MA 02139;
2. Novartis Vaccines, 53100 Siena, Italy;
3. Novartis Institutes for Biomedical Research, Emeryville, CA 94608;
4. Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138; and
5. Department of Cell Biology, Harvard Medical School, Boston, MA 02115