Has science gone too far or is this just the beginning?
Scientists from the University of California, Davis (UC Davis), in the US, are in the process of researching methods to overcome the worldwide shortage of organ transplants.
Currently they are experimenting with injecting human stem cells into pig embryos and calling them human-pig embryo chimeras.
A genetic chimera is a single organism composed of cells from different zygotes, and can result in male and female organs, two blood types or subtle variations in form.
Chimeric embryo development
Developing chimeric embryos starts in a laboratory under a microscope. The procedure involves two steps.
The first step of the procedure uses CRISPR gene editing, which involves the removal of DNA from a newly fertilised pig embryo with the gene responsible to grow the organ needed in the transplant, (University of California, Davis is using the pancreas in its experiment), creating a genetic void.
Human pluripotent (iPS) stem cells are then injected into the pig embryo. The iPS stem cells come from embryos that are three to five days old and can divide into more stem cells or develop into any type of cell in the body.
Once the stem cells are implanted into the embryo, it's then surgically inserted into the womb of an adult pig.
UC Davis researchers hope the injected stem cells will fill the genetic void in the pig embryo and result in the foetus growing the human organ needed for transplant.
Last year, the National Institute of Health postponed funding on the experiment until it knew more about the implications.
The NIH's main concern is the human cells might shift into the developing pig's brain and result in it having human characteristics.
Pablo Ross, a reproductive biologist and the head of the research at UC Davis, says this is unlikely, but a key reason why the research is proceeding with such caution: "We think there is very low potential for a human brain to grow, but this is something we will be investigating."
Ross's team previously attempted injecting the stem cells into pig embryos. However, they hadn't created a genetic void. The researcher has admitted to finding human cells in several areas of the developing foetus but said they "struggled to compete" with the pig cells.
His team hopes that by leaving the genetic void, the pancreas will be more successful in creating a human like pancreas.
Aside from Ross's team, other scientists have created human-pig chimeric embryos but the foetuses were terminated before they could be born.
A professor in the department of neurosurgery, Walter Low, from the University of Minnesota, has said that pig bodies are the ideal "biological incubator" for growing human organs, and could potentially be used to create corneas, lungs, hearts and kidneys if the pancreas is successful.
The embryos still have a long way to go before an organ transplant could take place.
The embryos are in the process of undergoing testing but they have to be terminated after 28 days.
Currently, scientists are not sure what the end result will be, but they continue to research and experiment.
Following 28 days, the embryo will be removed from the womb and the tissue growth is analysed. The goal is to further the scientific understanding of the process.
Previously, pigs were used in the creation of tissue valves and they can last 15-20 years. They also don't use the long term use of medication. However, if the patient undergoing surgery is very young, they may need additional surgery in the future or a valve replacement later in life.