1. Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021.
2. Progenics Pharmaceuticals, Inc. Tarrytown, New York 10591.
3. Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.
4. Henry M. Jackson Foundation, Rockville, Maryland 20850.
5. Present address: Advanced BioScience Laboratories Inc., Kensington, Maryland 20895.