BEIJING — Chinese scientists have, for the first time, cultivated a beating heart structure with human cells in a pig embryo, reporting that the heart continued to beat for 21 days unaided.
The study, led by Lai Liangxue's team from the Guangzhou Institutes of Biomedicine and Health under the Chinese Academy of Sciences, was announced at the International Society for Stem Cell Research's annual meeting in Hong Kong on June 12.
Previously, the team had cultivated human kidneys in pigs for up to 28 days.
According to a report in Nature on June 13, the team reprogrammed human stem cells by introducing genes to prevent cell death and improve their survival in pigs.
At the early blastocyst stage - early in pregnancy when a ball of cells forms - they implanted pre-modified human stem cells into pig embryos, which were then transferred to surrogate sows.
Researchers observed embryonic hearts growing to a human-equivalent size, comparable to a fingertip, at the same developmental stage - and still beating, according to the Nature report.
Using prelabelled luminescent biomarkers, the researchers reported detecting light from human cells coinciding with an embryonic heartbeat.
Nature quoted Lai as saying that modified embryos developed typically sized beating hearts, but the report did not say what proportion of the hearts were human cells.
The embryos survived only 21 days. Lai suggested at the meeting, "human cells may disrupt pig heart function".
Photo: South China Morning Post
In September 2023, Lai's team generated early human kidneys in pig embryos with 70 per cent human cells, in a study featured as a cover story in Cell Stem Cell.
Their technology could revolutionise organ transplants. However, clinical applications may take years to develop.
At the same conference, a research team led by Shen Xiling from the University of Texas MD Anderson Cancer Centre announced it had integrated human cells into mouse embryo intestines, livers and even brains.
Unlike the technical approach used by Lai's team, the Anderson Cancer Centre team first reprogrammed human stem cells and directly cultivated organoids - or miniature versions of organs grown from stem cells - of the intestine, liver and brain in culture dishes.
One month post-birth, around 10% of mice had human intestinal cells; incorporation into the liver and brain was lower.
Transplants treat organ failure, but accessibility is limited by a shortage of donor organs.
Pigs are suitable donors because they have anatomical similarities to humans, but immune responses that cause human rejection prevent their direct use. Growing human organs in pigs offers a potential solution.
This research direction is known as human-animal chimeras, referring to the combination of human and animal cells or tissues within a single organism. However, research on human-animal chimeras has sparked ethical controversies.
China introduced regulations last year, stating that human cell transplants into non-human animals for research purposes could only be conducted when other methods could not resolve the research issues.
At the conference, Stanford University's Hiromitsu Nakauchi urged further analysis to confirm human origin of the cells in the pig embryo experiment, noting that the localisation of fluorescent cells in the heart made integration with pig cells unclear.
Hideki Masaki of the Institute of Science Tokyo added: "For transplantable hearts, organs must be exclusively human to prevent immune rejection."
On June 16, Nature published commentary that alluded to prospects in the field: "Human-animal chimeras are an exciting yet challenging area of research. Human cells are coaxed to grow in animal embryos, allowing researchers to study human tissue development. The long-term goal is to grow human organs that can be harvested for transplantation."