1. Contribution from the Transplantation Research, Novartis Pharma AG, S-507.312, CH-4002 Basel, Switzerland, Centro de Investigación Lilly S. A., Avda. de la Industria 30, 28108 Alcobendas, Madrid, Spain, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K., and Glaciology Center, University of Bristol, Bristol BS8 1SS, U.K.