“…One pioneering study injected human PSCs into pig blastocysts, but found limited contribution to chimeras (Wu et al, 2017); this may be due to the poor quality of human (primate) iPSCs or simply because of the large evolutionary distance between humans and pigs that are estimated to have diverged $91 million years ago (Jørgensen et al, 2005). In addition, due to ethical concerns, the injection of human iPSCs into primate embryos is limited to in vitro experiments only (Tan et al, 2021). Moreover, while under certain circumstances it is ethical to transplant human PSCs into rodent and pig blastocysts (Wu et al, 2016;Suchy and Nakauchi, 2017), it is currently ethically impermissible to inject them into NHP embryos and transplant the chimeric embryos into a female NHP recipient (Suchy and Nakauchi, 2017;Hermere ´n, 2015;Tan et al, 2021), and therefore we did not inject human iPSCs into the rhesus blastocysts.…”