by Julie Fidler, Natural Society:
For many years, some members of the scientific community have been absolutely engrossed in trying to solve one of the biggest health conundrums in the United States: how to get more people to donate their organs. And if that can’t happen on a grand scale, well, scientists are turning to cloned pigs for organs.
In 2016, there were just 33,600 organ transplants, while there were 116,800 patients on transplant waiting lists. Since you can’t force people to become organ donors, scientists figure the only other option is to look elsewhere for organs. Now, through gene-editing and cloned some pigs, scientists have come a step closer to solving the problem, but the process is risky. 
You can’t transplant pig organs into humans because the body would assuredly reject them. There is also a concern that pig retroviruses could spread to human cells. With the help of pig cloning and CRISPR-Cas9 gene-editing technology, researchers have been able to solve the latter problem. 
The CRISPR-Cas9 is a medical and scientific advancement like no other that holds the potential to eradicate genetic diseases and create transplantable organs for humans. However, the technology is still relatively new and hasn’t been around long enough for scientists to know if gene-editing could cause serious, irreversible damage to animals and the environment.
(One recent study by researchers at Columbia University found that while CRISPR-Cas9 did correct blindness in mice, using the technique also resulted in unintentional mutations in more than 1,000 other genes.)
Humans, Organs, and Pigs
Researchers took cells from the pigs, then snipped the viral DNA from their genomes using CRISPR technology. 
Each pig cell was restored to its earliest developmental stage and then placed in an egg, giving it the genetic material to allow the egg to develop into an embryo. The embryos, now genetically identical to the pig that supplied the initial cell, were implanted in sows, who eventually gave birth to the piglets.
Most of the cloned piglets died shortly after birth, but 15 of them lived, and the oldest is now 4 months old. Scientists will monitor the genetically-modified piglets throughout their lives looking for any long-term adverse effects from the procedure.