1. Gene Therapy Program, University of Pennsylvania, Philadelphia, PA 19104, USA.
2. Special Pathogens Program, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba R3E 3R2, Canada.
3. Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba R3E 0J9, Canada.
4. Center for Vaccine Research, University of Pittsburgh, Pittsburgh, PA 15261, USA.
5. Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, PA 15261, USA.
6. Department of Immunology, University of Manitoba, Winnipeg, Manitoba R3E 0T5, Canada.