Less than 0.001 percent human -- the rest pig. Scientists create the first human-pig chimera embryos by injecting human stem cells to pig embryos. These human-animal chimeras would be useful for studying early stages of human development. It also provides a more realistic platform for drug testing before doing human clinical trials. However, the final aim is to generate human organs or tissues from animals.
Previously, scientists revealed the hybrid of mice and rats. Rat-grown mouse pancreas were transplanted in mice with diabetes and given immunosuppressive therapy to prevent rejection. Diabetes was reversed in the mice recipients. The same principle might apply to humans if scientists can generate organs that can match humans in larger animals like pigs.
"The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that." Juan Carlos Izpisua Belmonte lead researcher of the study said according to Science Daily. He added that growing fully functional human cells is very difficult, let alone tissues or organs. "This is an important first step," he added.
In a study published in the journal, Cell, on Thursday, Jan. 26, researchers revealed how they created the human-pig chimera embryos. Pigs were chosen as hosts because their organs more closely resemble that of humans, however, the study proved to be more challenging. The first challenge is finding human stem cell that would survive in pig embryos. To finish the research, they studied about 1,500 embryos for a period of four years.
The researchers also needed to find the perfect timing to introduce the human cells. The developmental stages of pigs and humans are far different. Pigs only need less than four months in the womb compared to nine months for humans. Belmonte compared it to entering a freeway with faster speed. "If you have different speeds, you will have accidents," he said.
Different forms of human stem cells were injected to embryos to find which will survive longer. Another concern in the study is the human-pig chimera might be too human. The scientists doesn't want the human stem cells to contribute in the development of the brain. The embryos were also only allowed to develop for about three to four weeks. The researchers said it is enough to understand how human cells mix with pig cells without raising ethical concerns.