Correction to: Nature Immunology https://doi.org/10.1038/s41590-018-0051-0 (2018); published online 12 February 2018.

In the version of this article initially published, the Supplementary Note was missing. The Supplementary Note has now been provided online and is cited in the Methods section of the article. The error has been corrected in the HTML and PDF version of the article.