The world’s first ever PERV-inactivated (porcine endogenous retroviruses) pigs have been cloned, addressing the concern of risks in pig organs for transplants into humans, scientists from China, the U.S., and Denmark recently announced, Economic Information Daily reported.

The research result has been published in the journal Science.

Harvard geneticist George Church called the clones a milestone in xenotransplantation, as the most important safety issue has been solved and the xenotransplantation is expected to be made available for clinical application in 2 years, bringing great hope to patients around the world.

In the research, the scientists modified the pigs’ genes using a gene-editing technique known as CRISPR to inactivate the PERVs, created PERV-inactivated pig embryos, and transferred them into surrogate sows to produce clones.

Earlier this year, 37 such clones were produced. Today, 15 are still alive with ages ranging from one to four months, appearing quite healthy, said Wei Hongjiang, a professor with Yunnan Agricultural University.

Currently, the scientists try to make pig organs less prone to attack by their human recipients’ immune systems using gene-editing techniques, in order to achieve clinical application of xenotransplantation as soon as possible, geneticist Luhan Yang, co-founder and chief scientific officer of eGenesis, disclosed.

There are more than 2 million patients worldwide who need organ transplants each year, while the supply is way below the demand.

Pig organs are considered the most feasible for xenogeneic transplantation, as they are similar to humans in both size and function.

However, pigs have PERVs embedded in their genome. These viruses are able to jump from a pig cell to a human one when mixed in the lab and then be passed to fresh human cells from the infected one. This standing block has now been cleared owing to the scientists’ efforts.