Chinese scientists have successfully modified a gene in pigs that enables the pigs to produce human serum albumin, a protein made by the liver.

The breakthrough was published on Thursday by Scientific Reports, an online open-access journal from the publishers of Nature.

The scientists used a precise genome modification tool called CRISPR/Cas9 to insert a human albumin coding sequence into the pig gene.

"The pig albumin shares about 80 percent of its characteristics with human albumin at the amino acid level, but the 20 percent difference means we cannot use it directly in patients," said Zhang Pumin, a co-author of the paper and a researcher at Beijing Proteome Research Center.

Human serum albumin plays a critical role in keeping people healthy. It is used to treat a number of conditions, including liver diseases and traumatic shock.

Previous attempts at using pig genes to produce human albumin were unable to overcome the problem that the pigs generate both pig albumin and human albumin simultaneously, and they are difficult to separate.

Zhang's team, however, adopted a new method to solve the problem. This time, the human albumin sequence was placed precisely in the pig albumin gene locus in fertilized pig eggs, a technique called a "knock-in". The result was the production of human albumin and the suppression of pig albumin.

The modified eggs were then implanted into the wombs of female pigs for development. The pigs produced in this way and their offspring now carry human albumin in their blood.

"The next step is to industrialize the product," Zhang said. "If we can use pigs as a factory for human albumin, it will provide an infinite amount for medical use."

Since albumin is extracted from human blood, which is always in short supply in China, the supply is inadequate.

Earlier reporting in People's Political Consultative Daily said the market gap of human albumin was 3 million bottles a year.

"The commercial prospect is promising," said Zhao Jianguo, a researcher at the Institute of Zoology of the Chinese Academy of Sciences.

The government's guiding price for human albumin in medicine is about 40 yuan ($6.30) per gram, which means a pig could produce almost 10,000 yuan worth of human albumin every year by donating blood once a month.

"Using pigs as a reactor to produce an essential substance for medical use is a field full of possibilities," Zhao said.

chengyingqi@chinadaily.com.cn