Scientists have inched closer to creating a human-animal hybrid as they reported growing human cells inside pig embryos.

The feat may eventually lead to growing livers and other human organs in animals that could alleviate the shortage of donated organs for transplant patients.

Growing Human Cells Inside Body Of Animals

The process involves generating stem cells from the skin of a patient. The stem cells will be used to grow the desired new organ in a large animal such as pigs. The organ is then harvested to be transplanted back into the patient's body. Because the organ is made of the patient's own cells, the risk of immune rejection is little.

For their study, the researchers injected pig embryos with three to 10 of human stem cells each and implanted these embryos into sows. After three to four weeks of development, researchers removed and examined 186 embryos and saw human cells after four weeks of development.

The cells generated the precursors of heart, muscles, pancreas, liver, and spinal cord tissue in the animal embryos.

"Interspecies blastocyst complementation enables organ-specific enrichment of xenogenic pluripotent stem cell (PSC) derivative," the researchers wrote in their study.

"Interspecies blastocyst complementation might allow human organ generation in animals whose organ size, anatomy, and physiology are closer to humans."

Possibility Of Humanizing Animals

The researchers said that they plan to conduct tests that would focus the human cells to produce specific tissues that would avoid any contribution to the brain, eggs, and sperm will human cells.

Among the issues that hamper the creation of chimeras, particularly those that use human cells, is the possibility that animals could be humanized in unintended ways. Human cells that get incorporated into the pig's brain may endow the animal with human qualities. Human cells that come to compose the reproductive tissues of an animal may also result in undesirable outcomes.

Life-Saving Importance Of Creating Human-Animal Hybrids

Despite concerns, the ability to grow human cells in animals also has life-saving implications particularly among organ transplant patients.

Human organ transplants tend to be complicated medical procedures that usually results in the patient's body rejecting the donated organ. Because of organ shortage, some patients also die before an organ becomes available.

Figures from the U.S. Department of Health and Human Services show that more than 119,000 individuals are on the national waiting for an organ transplant. Twenty-two of those waiting for transplant die every day.

Researchers Jason Wu, from the Salk Institute in La, Jolla, California, and colleagues, whose experiment was reported in Cell on Thursday, hope to eventually take human cells from individuals in need of transplant and grow the cells in an animal embryo to be later transplanted back into the patient without being rejected.

"There isn't a need to get into a debate about moral humanization if scientists target the organs where the human cells will go," said Insoo Hyun, from Case Western Reserve University. "Scientists are not making chimeras just for fun — it's to relieve the dire shortage of transplantable organs."

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