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. 2021 Oct 29;6:71. doi: 10.1038/s41536-021-00182-8

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a Number of publications per year. b World map with a color scale indicating the number of papers published in each country (image adapted from Freepik.com). c–f Pie charts of features of publications related to MSC source (c), time of administration (d), delivery route (e), and modifications (f). g Distribution of quality scores. h Percentages of studies meeting each quality score criterion. i Risk of bias: percentages of low risk (green), unclear risk (yellow), and high risk (red) for each category.