Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
and JavaScript.
Permissive regulations in a few regions of the world are dictating where human embryonic stem (hES) cell research is taking place, but this could change as numerous countries are still formulating policy.