Nat. Immunol. 18, 541–551 (2017); published 13 March 2017; corrected after print 17 April 2017; corrected after print 18 May 2017

In the version of this article initially published, the vertical axis of Figure 5j was incorrectly labeled 'PC1 (22.56%)'. The correct label is 'PC3 (6.47%)'. The error has been corrected in the HTML and PDF versions of this article.