According to reports, recently, the University of Maryland School of Medicine in the United States completed the world's first pig heart transplant, and the 57-year-old patient is currently in good condition. Why would scientists and doctors choose a pig's heart as a donor?
Professor Zhao Qiang, Vice President of Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine and an expert in cardiac surgery, will answer your questions.
Professor Griffith (left) with Bennett (right) (Credit: University of Maryland School of Medicine)
The current shortage of donors for heart transplants
Source: University of Maryland School of Medicine
Professor Zhao Qiang said that at present, there is a serious shortage of transplanted organs around the world, and people are dying in waiting every day. In China, there are as many as 1.5 million patients with advanced heart failure every year, but about 500 to 600 patients can really receive transplants.
Heart transplantation is basically not difficult in terms of surgical techniques, the success rate of surgery is more than 95%, and the survival rate of one year after surgery is 94 to 95%. The first heart transplant in China, and the first in Asia, was completed at Ruijin Hospital in 1978. Since then, heart transplants have been carried out continuously in China, and there have been reports of patients surviving for more than 20 years after transplantation.
Therefore, the difficulty of heart transplantation is still a big contradiction between the shortage of heart transplant donors and the large number of patients with advanced heart failure who need to receive heart transplantation.
Professor Zhao Qiang said that in order to solve the dilemma of the shortage of transplanted organs, scientists have turned their attention to animal organs. However, the rejection response of xenotransplantation between different species is stronger than that of all-species transplantation, so scientists have adopted the method of genetic modification.
Close in size, few zoonotic diseases, fast reproduction...
All are the reasons for choosing a pig heart
Why choose a pig heart? Zhao Qiang said that the size of the pig's heart and the human heart is close. From the perspective of the origin of species, it is far from humans, so there are fewer zoonotic diseases, with the development of gene editing technology, scientists can cut off the gene expression of pigs, transfer human genes to the heart of pigs, so that after the heart of the pig is transplanted into the human body, the rejection response will be reduced.
It is reported that 10 genes of the pigs used in the operation have been modified, of which 3 genes will trigger the rejection of the human immune system; in addition, in order to prevent the overgrowth of the pig heart tissue after transplantation, the growth genes of the pig have also been inactivated; 6 human genes have been implanted into the genome of the pig to enhance the tolerance of the pig organs to the human immune system.
Moreover, pigs can reproduce quickly, so it is more appropriate for doctors to choose pigs as a source of xenosis for donors.
In order to improve the success rate of surgery, the scientific team has previously tried to transplant the hearts of pigs into 50 baboons for experiments to study the response to postoperative reactions such as immunosuppression, hypotension, and obstruction of blood clotting.
Before the pig heart transplant, in October last year, American researchers successfully transplanted the genetically modified pig kidney to the thigh of a brain-dead patient with renal insufficiency, although the in vitro observation experiment lasted only three days, but there was no rejection reaction.
Does this mean that the xenograft was successful?
Professor Zhao Qiang said that once this technology is successful, it will bring new dawn to heart transplantation, kidney transplantation and liver transplantation and solve the problem of donor shortage. However, xenotransplantation still has multiple ethical and technical problems, which need to be further studied and discussed.
For example: Is there more rejection than all-in-one transplantation? After the pig's tissue is transplanted into the human body, will it form a chimera with the human immune system, will it be passed on to the offspring, or will it have a negative impact on human evolution? Ethically, how does the recipient of a pig's heart identify with himself? What does society think of him? These issues require our attention.
Of course, the pinnacle of the development of transplant technology, in the case of heart transplantation, is to use the patient's own cells to create an artificial, flesh-and-blood heart through laboratory culture, such a heart is theoretically a perfect donor. In terms of genomics and immunotechnology, China is closely following the international frontier, but we have not made progress in tissue cultivation.
Whether genetically modified organ transplantation is for the benefit of mankind or opens a Pandora's box, which requires continuous discussion and improvement in ethics, laws and regulations.
Source: CCTV