1. Division of Cellular Immunology (G0100), Tumor Immunology Program, German Cancer Research Center, Im Neuenheimer Feld 280, D69120 Heidelberg, Germany
2. Department of Immunology and Cell Biology, University of Muenster, Roentgenstr. 21, D-48149 Muenster, Germany
3. INSERM U412, Ecole Normale S périeure de Lyon, 69367 Lyon, Cedex 07, France
4. Division of Cellular Immunology (G0100), Tumor Immunology Program, German Cancer Research Center, Im Neuenheimer Feld 280, D69120 Heidelberg, Germany; 4Department of Cancer Immunology and AIDS, Dana Farber Cancer Institute, Boston, MA 02115, U.S.A.