Correction to: Nature Medicine https://doi.org/10.1038/nm.3867, published online 25 May 2015.

In the version of the article initially published, three pairs of micrographs (in Fig. 5i and Supplementary Figs. 3a and c) inadvertently contained overlapping areas. These figures have been amended with new micrographs and are available as Supplementary Information with this notice.