Nature 542, 115–118 (2017); doi:10.1038/nature21056

In the Acknowledgements section of this Letter, the sentence: “This study was supported by the Baxter Foundation, California Institute for Regenerative Medicine (CIRM) grants TT3-05501 and RB5-07469 and US National Institutes of Health (NIH) grants AG044815, AG009521, NS089533, AR063963 and AG020961 (H.M.B.)” should have read: “This study was supported by funding from the Baxter Foundation to H.M.B.” Furthermore, the last line of the Acknowledgements section should have read: “In addition, this work was supported by a National Institutes of Health (NIH) National Center for Advancing Translational Science Clinical and Translational Science Award (UL1 TR001085). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.” The original Letter has been corrected online.