Nat. Med. 23, 815–817 (2017); published online 12 June 2017; corrected after print 20 July 2017

In the version of this article initially published, in the “Polymer/lipid-based formulation of mRNA” section of the Online Methods, the text incorrectly stated that mRNA was in 190 ml rather than 190 ml of cold DMEM. The error has been corrected in the HTML and PDF versions of the article.