President Obama has removed the limits on federal funding of research on human embryonic stem cells (ESCs), allowing for researchers to go from having a small number of cell lines eligible for federal funding to having at least a few hundred.

ESCs can develop into any other cell type found in the body, and so have huge potential for use in medicine, to repair lost or damaged tissues. But some people object to their use on moral grounds because the creation of an ESC line usually involves the destruction of a pre-implantation embryo, just a few days old.