Correction to: Nature Immunology https://doi.org/10.1038/s41590-018-0111-5 (2018), published online 18 May 2018.

In the version of this article initially published, a source of funding was not included in the Acknowledgements section. That section should include the following: P.J.M.O. was supported by EU FP7 PREPARE project 602525. The error has been corrected in the HTML and PDF version of the article.