Correction to: Nature Biotechnology https://doi.org/10.1038/s41587-020-0446-y, published online 2 March 2020.

This paper was originally published under standard Springer Nature copyright (© The Author(s), under exclusive licence to Springer Nature America, Inc.). It is now available as an open-access paper under a Creative Commons Attribution 4.0 International license. The error has been corrected in the HTML and PDF versions of the article.