Nat. Med. 21, 628–637 (2015); published online 18 May 2015; corrected after print 12 August 2015

In the version of this article initially published, the labels to the left of the two micrographs in Figure 2c are reversed. Also, in Figure 4g, MKi67, used as a cell proliferation marker, is misspelled. The errors have been corrected in the HTML and PDF versions of the article.