Link to Research Paper: http://www.cell.com/cell/fulltext/S0092-8674(16)31752-4
A new breakthrough occurred during a study where pig embryos containing human cells were formed. These embryos are a step in growing animals that contain human organs. These could be used for organ transplants. However, it will likely be a long time before this becomes a reality. The pig embryos contained very few human cells. In addition, pig embryonic cells and human embryonic cells grow at different rates, making it difficult to place both cells into a single embryo. Lastly, there are ethical concerns surrounding this process. For example, there is a concern over the pigs developing a human brain, and thus being sentient.
I was quite surprised by this article. I didn't think it was possible to have embryos with cells from multiple species. However, I do have ethical concerns over growing animals just for organ transplants. I personally think that it would be better to find a different way to grow them.