A new report on the ethics of crossing species boundaries by inserting human cells into nonhuman animals—research surrounded by debate—makes recommendations clarifying the ethical issues and calling for improved oversight of this work. Advances in human stem cell science and gene editing enable scientists to insert human cells more extensively and precisely into nonhuman animals, creating “chimeric” animals, embryos, and other organisms that contain a mix of human and nonhuman cells. Many people hope that this research will yield enormous benefits, including better models of human disease, inexpensive sources of human eggs and embryos for research, and sources of tissues and organs suitable for transplantation into humans. But there are ethical concerns about this type of research, which raise questions such as whether the moral status of nonhuman animals is altered by the insertion of human stem cells… (READ MORE)

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