Nat. Med. 10, 1208–1215 (2004)

In the process of following up the findings reported in this study, we were unable to reproduce the original results. By carefully examining the first author's notebook, we found that some of the primary data were erroneously or artificially presented in the paper. Under these circumstances, all authors unanimously wish to retract this paper as soon as possible. We deeply apologize to the readers for any inconvenience caused by this retraction.