Nat. Biotechnol. 25, 238–243 (2007); published online 21 Jan 2007; corrected after print 7 February 2008

In the version of this article initially published, the y-axes of Figures 1e, 2c and 2d are labeled incorrectly. They should be labeled “% CD45.2 in PB,” and not “% CD45.1 in PB” as labeled originally and in a subsequent corrigendum in August 2007. The error has been corrected in the HTML and PDF versions of the article.