"Now that it has been proven that species barriers can be broken down and cell competition has failed in mice, the next step is to start with pigs."
Looking at the mouse experiment records in front of him, Huang Qin couldn't help but smile as he thought that he was about to face the piglets he was most familiar with.
Ding Mian's face was not so pretty. He stared at the several lines of numbers on the report and fell into deep thought.
"The overall chimerism rate under genetic modification only reaches 22%, which does not seem to be an ideal number."
Huang Qin said indifferently: "That's for sure. Research on heterogeneous chimeras is not as easy as everyone thinks."
"Mainly, human stem cells do not match the development of mouse embryos. Human cells and mouse cells cannot interact well, so the survival rate is so low."
"Besides, the development speed of heterogeneous cells is inconsistent, and the development programs are also different. Even if the overall embryonic chimerism is increased, some tissues will have very low or no chimerism."
"Generally speaking, the chimerism rate in organs such as the heart, muscles, and pancreas is relatively high. The content of human cells in the tissues is very high, but there are quite few in blood vessels, brains, limbs, and bones."
“So if it is evenly divided, it can reach more than 20%, which is already very amazing.”
"When there was cell competition before, the chimerism rate was only one in 10,000, or even one in 100,000. We have improved it by a factor of two thousand. It is simply a qualitative leap."
"Do you want a 100% chimerism rate? How is that possible?"
"Even the overall chimerism between rats and mice only reaches 20%-30%."
"Although through complementation, their chimerism in some organs can reach more than 90%. But that is also because rats and mice are two similar species, both belong to rodents, and their development programs are relatively similar, just like humans and mice. Gorillas have the same relationship.”
"But the evolutionary relationship between humans and mice is very far away. Normally, human cells may not receive compatible development signals during mouse embryonic development."
"I know, I'm just a little disappointed with the role of cell competition." Ding Mian said seriously.
"The genetic similarity between humans and mice is even higher than that of pigs, so the number of future human-pig chimeras may not be as high."
"What we need to do next, in addition to testing the overall chimerism, is the most important thing is the chimerism in some important organs."
"I hope they can also reach satisfactory figures of 90%."
Huang Qin said in surprise: "You are too optimistic."
"Even with complementation between rats and mice, the only organ that has been successful so far is the pancreas."
"Other organs, such as kidneys, although there are reports that mouse stem cells can generate kidneys in rat embryos, the size of the organs is smaller than that of rat kidneys at the same time, and their functions have not been fully tested."
"All this shows that this field is still in the exploratory stage and is still far away from clinical application."
"But they didn't solve the problem of cell competition. But we have solved it."
Ding Mian said matter-of-factly: "So we will definitely be able to successfully enter the clinic. You have to have confidence in me."
Huang Qin was silent for a moment, and then he said, "Then what exactly do you plan to do?"
As soon as he mentioned his plan, Ding Mian immediately became excited and sat upright, no longer the previous lazy posture.
He seemed to be well prepared and laid out his plan with confidence.
"From chimera research to the eventual realization of organ transplantation, in general, there should be such a road map."
"The first step is to solve the technical problem of low overall embryonic chimerism rate, and how to make cross-species pluripotent stem cells more effectively enter the early developing embryos of another species and participate in the early development of various organs."
"If this problem is solved, the next step is how to control it, especially to prevent human embryonic stem cells from entering organs we don't want them to enter. This is an ethical issue, and it is also a technical issue."
"The third point is whether the functionality of xenochimeric organs is similar to human organs. This may require some transplant experiments."
"Of course, in the early stage of this stage, monkeys may be used for testing, and human organs from pigs may be transplanted into monkeys and other primates. After verification, everything is fine, and then applied to human clinical trials."
"The fourth and final point is to create a complete organ."
"Because even if the chimerism of some organs is as high as 90%, the created organ is not a complete organ. For example, some of the blood vessels, nerves and interstitial cells are still from the host."
"After these tissues enter the human body, as foreign cells, immune rejection will still occur."
Huang Qin asked curiously: "Isn't it possible to replace these things with human ones?"
Ding Mian reluctantly shook his head and sighed.
"It's difficult. Even if we knock out the genes related to the pig's kidney or pancreas, artificially create an empty niche, and then use human stem cells to fill the gap, there is still no way to control the specific development process of this organ in the embryo. .”
"An important reason is that the embryos of different animals develop at different speeds. As primates, it takes ten months for our embryos to fully develop."
"But it only takes 3 months for pigs and 20 days for mice. Can humans catch up with this speed of cell differentiation?"
"In short, the rate of cell differentiation is much slower in human cells than in mouse, rat and pig cells."
"Not to mention the size factor. Even if organs made of human cells grow in mice, can you transplant pancreatic islets that are as small as soybeans?"
"However, in terms of body shape, pigs are still better. The size of the internal organs is not much different from that of humans. Moreover, the internal organs need to grow to maturity before they can be used for transplantation. The growth genes can also be modified to a certain extent. Considering all aspects, they are considered the most suitable animals. .”
"That's why we chose pigs."
"Well, why do you sound so pessimistic?" Huang Qin said disapprovingly: "I think it's fine. I just need to learn from nature and make do with it."
Ding Mian laughed and said, "That's right. If we can get to the fourth step, it means we are one step away from success."
"Don't worry about it until then. The first priority is to take care of the first three steps."
After confirming the work plan, the two of them suddenly became energetic.
When they came to the laboratory, they took out the prepared pig embryos and injected them with genetically modified human pluripotent stem cells.
This batch of human pluripotent stem cells was added with the fluorescent protein GFP, which can track the traces of cells and their offspring.
Subsequently, the cell culture fluids of the two were mixed together to increase the adaptability of human stem cells in pig embryos.
In this way, human-pig chimeric embryos were finally successfully cultured while suppressing competition between heterogeneous cells.
Since the first test was only to test the overall chimerism, there were ethical considerations, such as concerns about human cells entering the reproductive system and brain, or developing parts similar to humans.
The embryo only develops in the pig's body for 3 to 4 weeks before the pregnancy is terminated.
The final results showed that the human-pig chimera did not show obvious cell competition, and the overall chimerism reached 28%, which was 6 percentage points higher than the human-mouse chimera.
The degree of chimerism in different tissues and organs also varies greatly, just like in mice.
For example, the chimerism of heart and muscle is significantly higher than that of other tissues, and the chimerism of pancreas and kidney is also higher than that of lung and liver.
Looking at the entire embryo, there are approximately 20,000 human cells for every 100,000 pig cells.
And after testing, the human cells in the pig liver and kidneys have certain functionality.
This result is surprising enough.
If it were possible to concentrate these human cells in several locations including the heart, lungs, liver, and kidneys...
Just thinking about it made the two of them feel excited at the prospect.
"The first step was achieved, with a chimerism of up to 28%, which is not much different from the same species."
"The second step is to make human cells concentrate on certain organs, then we need to start creating niches for corresponding organs in pigs."
Ding Mian said with a smile, with a hint of excitement in his voice.
Huang Qin nodded, patted his chest, and said, "The next step is up to me. Genetic modification of pig egg cells is my specialty."
"Heart, kidneys, liver, pancreas, let's start with these four."
Ding Mian said thoughtfully: "Make a batch of pig egg cells, about 100, in groups of 20. Each of the four groups will knock out the relevant genes of one organ to create a niche."
"Don't move the remaining group and keep it as the control group."
"Five days after fertilization, a blastocyst will be formed, and then human pluripotent stem cells will be injected, and then placed into the sow for development."
"After waiting 3 to 4 weeks, you can observe the early development of the embryo and know whether it can be successful."
"Got it." Huang Qin responded without saying much. The people in his department are experienced and can do this kind of work with ease, and there is no need to explain too many details.
The first batch of samples is just to test whether this method is useful and to what extent it can be achieved.
If it succeeds, that's great. If it fails, it's appropriate to learn from the experience and make another batch.
There are not so many scientific research achievements that can be achieved overnight. Only through constant failures, summarizing and moving forward can we reach the end.
The development period of human-pig chimera embryos like this is too long, and the chance of growing up smoothly is not very high. He is mentally prepared to inject thousands of pig blastocysts.
However, the experimental results greatly exceeded his expectations.
Of the 80 chimeric embryos that created organ niches, only half miscarried.
The remaining 40 human-pig chimeras were born alive from the sows, and a third died within a week.
In the end, about 20 piglets survived for more than one month and were determined to be human-pig chimeras through PCR sequence inspection.
"The first batch of samples had a 25% survival rate, which is really surprising."
Looking at this result, Huang Qin couldn't help but be overjoyed.
Ding Mian raised his eyebrows, stood in front of the cage, looked at the lively little piglet inside, and couldn't help but be moved by it.
These piglets look no different from normal pigs, but inside their bodies there are human hearts beating, human kidneys undergoing dialysis, or human livers detoxifying.
It is this ordinary appearance that forms a sharp contrast with the miracle happening under the skin, which makes people marvel.
"This is the miracle of life, so why is it not what my heart desires."
He murmured to himself: "Is xenotransplantation finally going to be successful?"
"Am I the one destined to complete this great mission?"
When Huang Qin heard this, his face suddenly darkened. He turned around and reminded him kindly: "Brother, don't forget, there is still me, Xiao Huang."
"Haha, I just said it casually." Ding Mian laughed and avoided the other party's eyes with a guilty conscience.
Not long after, the results of the internal organ biopsy of the chimera came out.
Almost all of the 20 piglets generated a human organ, but the chimerism of the organs generated in each pig was different, which is related to their ontogeny.
The chimerism of human organs in some pigs is as high as 92%, while in others it is only over 80%.
The lowest is about 79%, which is a very impressive number.
In addition, traces of human cells also appeared in other tissues of these piglets, but the number was not large, about one in 10,000.
Overall, the program of artificially creating organ niches to grow human organs has been very successful.
"By the way, I forgot to tell you." Huang Qin patted his head and reminded: "It's been one month now, and primate transplants can be performed on macaques or baboons in about two months."
"Because some organs of pigs are larger than those of monkeys, pigs cannot be allowed to grow too large. Young pigs of about 2 months are most suitable."
"We will test the organ function after transplantation. If it can be used normally, it means that the research has entered the third step."
"Okay." Ding Mian nodded, looked at Huang Qin's face, and couldn't help but joke.
"Why, before you saw human cells on mice, you felt creepy. Why did you not react when you saw pigs growing human organs?"
Huang Qin smiled naively and said, "Don't they all say that I think too much?"
"Actually, you are right. We are all biologists. We should understand that everyone has an independent consciousness composed of cells. From a macro perspective, everyone is unique."
"But on a microscopic level, the human body is also a community of cells that have co-evolved and developed together. Human-pig chimeras are no more weird and disgusting than the symbiotic bacteria that populate our intestines."
"Now that I've realized this, I've become more comfortable with being a chimera between anyone and any other animal."
"Of course," he paused, and then added: "My cells and genes must never appear in any mice, pigs, or cows. I can't stand it anyway."
Ding Mian was speechless for a moment: "You are very honest and forthright. You are so typical."
"There is a classic famous saying, what is it said?" Huang Qin laughed and said boldly.
“Engineers have an instinct to build, biologists have an instinct to cultivate.”
"Humans, on the other hand, have the instinct to have double standards! Hahaha~"
Ding Mian's eyes became confused: "Which celebrity said this? Why haven't I heard of it?"
Huang Qin patted his chest and said loudly: "Of course I, Mr. Huang, said it."
"We have achieved organ xenotransplantation. I, Huang, will definitely enter the halls of human science and become a great scientist, leaving a name in history."
"What I say are naturally famous quotes." (End of Chapter)
