1. Experimental Transplantation and Immunology Branch, National Cancer Institute, Bethesda, MD 20892, USA.
2. Experimental Immunology Branch, National Cancer Institute, Bethesda, MD 20892-1360, USA.
3. Intramural Research Support Program and
4. Protein Chemistry Laboratory, Science Applications International Corporation, Frederick, MD 21702, USA.
5. Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
6. Laboratory of Molecular Immunoregulation, NCI, Frederick, MD 21702, USA.