The “cybrid” or hybrid human-animal embryos are created in the laboratory by Somatic Cell Nuclear Transplantation, using emptied eggs from animals and the nuclear and cellular DNA from humans.. We know that there are currently experiments on-going with the human embryos made using emptied cow eggs (more on the “ease” of making these embryos, here), and now the British have authorized the development of pig-human embryos.
The experimenters admit that the problem will be achieving embryos and embryonic stem cells that do not contain DNA left from the egg. Proving the purity and “human-ness” of the stem cells will be a complication that I do not believe they will be able to overcome, at least for transplantation into humans, except possibly in the case of severe, last-hope disease and trauma.
The ethical debates about xeno-transplants and treatments using living organs, cells and tissues from animals carry the risks of transmitting animal diseases that humans have no immunity for and the development of new strains of disease that cross species lines. Ethicists have predicted that at least the early patients will have to live their lives in isolation at the worst, and have life-long surveillance at the best. (more on the debate, here and here.)
However, the researchers will probably be able to develop other uses, such as the early warning chemical weapon detection systems that are being developed by our own military, using human embryonic stem cells.
Rather than humanitarian and medical hope, I believe that time will show us that the research is the result of pure greed, with each lab hoping to come up with a product that can be patented and sold. I’m disappointed that the courts and “ethics” bodies in the US and UK have allowed these patents of human organisms. The drive to “create” new human cells and artifacts using human DNA is the logical outcome.