1. Fox Chase Cancer Center, Philadelphia, Pennsylvania 191111;
2. Department of Microbiology, Parasitology, and Pathology, North Carolina State University, Raleigh, North Carolina 270662;
3. Infectious Diseases Laboratories, Institute of Medical and Veterinary Science, and Department of Microbiology and Immunology, University of Adelaide, Adelaide, SA 5000, Australia3
4. Triangle Pharmaceuticals, Inc., Durham, North Carolina 277074; and