How far is it from the fact that gene editing helps "Bajie" cross-border debut with xenogeneic organ transplantation
Tao Yuxiang reporter Shengli
When it comes to the value of pigs, we often think of it as a source of meat, but in fact, the value of pigs is much more than that. In the hands of scientists, pigs have become a scientific tool that can carry out human organ transplants and save the lives of patients with organ failure.
In order to promote more transformation and application of pigs in medicine, in June this year, the first domestic medical mini-pig production, research and breeding base was settled in the Sichuan Neijiang National Agricultural Science and Technology Park. The base covers an area of about 100 acres. 10 mu has been built, including various functional areas for miniature pig breeding, operating rooms, laboratories, etc. It is a high-standard medical pig test base and organ donor factory. "After gene editing, the'Ba Jie' will also possess the 72 transforming abilities like the great brother Sun Wukong, transforming multiple tissues or organs of itself for human use." The lead unit of the base, Chengdu Zhongke Aoge Pan Dengke, chief scientist of Biotechnology Co., Ltd., said that the base will be dedicated to the new industrial field of breeding, research and application transformation of domestic medical pigs and organ transplant donor gene-edited mini-pigs, and establish medical pig systems and standards for organ transplantation and biology. Medicine makes a contribution.
Why can pigs become the preferred donor for xenotransplantation? What is the bottleneck for xenotransplantation to enter clinical application? How will the medical application of pigs develop in the future? A reporter from Science and Technology Daily conducted an interview on this.
Severe donor shortage pigs are recognized by the scientific community as the most ideal heterogeneous donor
Organ transplantation is the first choice for the treatment of organ failure in end-stage cancer patients. However, in China, the ratio of waiting for organ transplantation and obtaining organ transplantation can reach 30:1. Every year, hundreds of thousands of patients die because they cannot wait for organ transplantation. . "The bottleneck of organ transplantation lies in the serious shortage of donors, and the most feasible, effective and quickest way to solve this problem is xenotransplantation." Pandenko said. The advantage of xenotransplantation lies in the abundant source of organ donors. It can be mass-produced and factory-produced, and the number of transplanted organs is not only in short supply, but also may come from patients at the end of the disease, and the organ quality cannot be guaranteed.
Then why choose pigs as the donor for xenotransplantation?
"Humans are primates. Although they are similar in physiological anatomy and metabolism to other primates such as monkeys and orangutans, primates have a long generation gap, low reproduction rate, and high feeding costs, which are difficult to satisfy. Human organ transplantation needs; and most primates are protected animals internationally, which is not conducive to clinical promotion.” Pan Dengke said that pigs are not only very similar to humans in organ size, anatomical characteristics, and physiological and biochemical characteristics, but also have a shorter growth cycle. With a high reproduction rate, it is recognized by the scientific community as an ideal donor for xenotransplantation.
However, there is a saying in the folks that "mutton can't stick to a dog", and the difficulty of xenotransplantation is exactly the same. "Although pigs are the most ideal donor for xenogeneic organ transplantation, a variety of immune rejection reactions will occur after pig organs are transplanted into humans, especially hyperacute rejection reactions that make the transplanted organs lose function in a short time." Pandenko said. This is the most natural defense for species to maintain the continuity of the germ line. Even the organs between human relatives may not be matched successfully, let alone pigs and humans.
To allow pig organs to be transplanted into the human body and make people willing to accept this "foreign visitor", the problem of rejection of xenotransplantation must first be solved, which has become a major technical challenge.
Knockout key gene pig kidney transplantation has clinical trial basis
How do pig organs differ from human organs? By finding these differences and then eliminating them, can the organs of pigs work normally in the human body? With this line of thinking, scientists have discovered that the main reason for rejection is that natural antibodies in the human body can recognize α-galactosidase (α-gal) and β-galactosidase (β-galactosidase) on the surface of pig cells. gal) and N-acetylneuraminic acid hydroxylase (Neu5Gc protein), these three proteins are synthesized by GGTA1, B4GalNT2 and CMAH genes, respectively. "These are the 3 genes that are most likely to trigger immune rejection in pigs. If these genes are knocked out, won't the problem be solved?" Pan Dengke said. The current study found that only the above 3 genes can be knocked out. After pig organs are transplanted to humans, there will be almost no major rejection, and they have the basis for entering clinical trials.
In recent years, Pandenke’s team has bred knockout pigs without α-gal and bred more than 6 generations; bred knockout pigs without α-gal and β-gal; and without α-gal and Neu5Gc genes Knock out the pig. In June of this year, the research team used one-time gene editing to construct a knockout vector for the pig B4GalNT2 and CMAH genes, and completed the knockout of the other two genes on the GGTA1 knockout pig somatic cells prepared by the team in the early stage, and then knocked out The cells of these genes are put into the eggs, the eggs are activated by electrofusion, and then the activated embryos that develop normally are transplanted into the sows, and the sows are conceived until the cloned pigs with the 3 genes knocked out are born.
At present, this genetically modified pig is 75 days old. Researchers fused its cells with human serum and found that the combination of heterologous antigen-antibody combination and
Complement-mediated immune rejection is significantly reduced, and my country's pig xenotransplantation has taken a big step towards clinical trials.
How to ensure the safety of pig organ transplantation into human body? Before medical products enter human clinical trials, they must undergo preclinical trials on monkeys that are very close to humans. “We transplant the organs to monkeys first, observe and record the survival time and response status of the monkeys, and only if the safety and effectiveness standards of organ transplantation can be met, can we apply for clinical trials.” Pan Dengke said.
In 2019, Pandengke’s team transplanted pig kidneys without α-gal and highly expressing human complement activation inhibitor CD55 into non-human primate rhesus monkeys, completely using human clinical immunosuppressants, rhesus monkey kidneys The survival time after transplantation reached 32 days, reaching the longest survival record of xenogeneic kidney transplantation in the world with the same immunization program (that is, using the same human clinical immunosuppressive agent). Pan Dengke said that the success of this pig-monkey kidney transplantation marks that the genetically modified donor pigs for xenogeneic kidney transplantation in China have reached the international level of similar research.
From agriculture to medical use to create future biomaterials and organ factories
Internationally, it has been studying pig xenotransplantation since 1995, and has accumulated more than 20 years of experience. At present, tissue engineering products such as porcine cornea and heart valves have been widely used in human clinical trials. Porcine pancreatic islet cells and skin xenotransplantation have entered the stage of human clinical trials, and porcine kidney xenotransplantation has also completed preclinical Trials have the basis for conducting human clinical trials. According to a report in Science magazine this year, pig kidney xenotransplantation will enter human clinical trials within this year.
With the gradual realization of preclinical trials and clinical trials of pig xenotransplantation, the transformation and application of pigs in medicine has received more attention. The Neijiang Gene-edited Pig Industry-University-Research Collaborative Innovation Base currently has more than 10 species of more than 200 genetically modified pigs.
"The medical pig test base is a very important support link for the application of translational medicine, but the previous lack of relevant base construction in China has become a bottleneck restricting the application of pig translational medicine." Pan Dengke said that the establishment of a medical gene-editing mini-pig test base, It is to take advantage of good hardware and software to carry out gene-edited mini-pig breeding, research and application transformation, to build a batch production factory of biological materials and organ donors, and to benefit more patients.
"The agricultural value of pigs is well known. In the field of biomedicine, pigs are more precious. In addition to being an ideal donor for xenotransplantation, they can also provide biological materials and products to simulate human diseases." Pan Dengke introduced, along with pigs. There are more and more medical applications in China. In the future, “special pigs for medical biomaterials” bases will be established in China to realize domestic procurement of traceable pig-sourced biological materials; “ultra-clean pigs” bases will be established to serve as experimental units, Colleges and universities provide experimental pigs to provide hospitals with safe and clean organ transplantation donor pigs in batches; it will also be used as a research model to simulate human diseases, carry out small-pig evaluation of medical devices, and establish a preclinical large-animal test platform for drugs. "To maximize the medical value of pigs, this is a thing that benefits all mankind." Pan Dengke said.