Nat. Biotechnol. 30, 1217–1224 (2012); published online 18 November 2012; corrected after print 30 May 2013

In the version of this article initially published, the description of mice in the first paragraph of Online Methods was incomplete. Female SJL/J mice should have been described as SJL/JCrHsD; female BALB/c mice, as BALB/cJ mice; TCR transgenic mice expressing a TCR on the SJL/J background, expressed it on the SJL/JCrHsD background. Marco−/− mice, described as “on the BALB/c background,” should have been described as backcrossed to the BALB/cAncrl (Charles River) background. The errors have been corrected in the HTML and PDF versions of the article