Human stem cells can integrate into developing pig embryos, a finding that could lead to new ways of growing human organs and studying early human development.

John Wu et al./Cell

Previous attempts to engraft human stem cells into developing mice have met with limited success. Juan Carlos Izpisua Belmonte at the Salk Institute for Biological Studies in La Jolla, California, and his colleagues instead worked with embryos of pigs, which are biologically more similar to humans. They injected various types of human pluripotent stem cell which can develop into any cell type into balls of cells called blastocysts that become embryos. Early-stage human pluripotent stem cells integrated into the blastocysts, but only stem cells injected at an intermediate stage of maturity went on to form later-stage embryonic chimaeras, which contained appreciable numbers of cells from both species.

The researchers also grew rat stem cells (pictured in red) into organs in mouse embryos by eliminating the development of certain mouse organs a technique that could be applied to humanpig chimaeras to generate human organs in the future.

Cell 168, 473486 (2017)

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