Pig-Monkey Hybrids Created to Eventually Generate Human Organs in Pigs

Researchers injected D-ESCs (embryonic stem cells) into porcine blastocysts (pig pre-embyros) to obtain neonatal interspecies chimeras. The D-ESCs differentiated into all three germ layers in the pig fetuses, consistent with a previous study reporting human/pig chimeras. The human/pig fetuses survived only 28-days, and it was not possible to observe whether the chimeric human ESCs could develop into mature functional cells in pigs for ethical issues. In this study, they confirmed that monkey/pig chimeras can form functional hepatocytes and renal cells in neonatal pigs. These functional cells could be isolated for further research and future clinical application.

The findings could pave the way toward overcoming the obstacles in the re-engineering of heterogeneous organs and achieve the ultimate goal of human organ reconstruction in a large animal.

Interspecies chimerism has been most successful in rodents, and these studies typically achieve a high proportion of chimerism and generate xenogeneic organs. The pluripotency levels of rodent PSCs are the highest known, as they are genuine naïve cells, and they can produce live offspring by tetraploid complementation, which is the most stringent test of pluripotency.

cmESCs (chimeric stem cells mixed into different species) explore the possibility of interspecies chimerism in the development of late embryonic stage pigs. By optimizing the medium in which the cmESCs and injected blastocysts were cultured, we observed an increase in the anti-apoptotic ability of cmESCs and in the extent of chimeric embryo development, resulting in the successful incorporation of xenogenous cmESC grafts into multiple tissues of the neonatal pigs. This work will enable developments in xenogeneic organogenesis towards producing tissue-specific functional cells and organs in large animal models via interspecies blastocyst complementation.

Blastocyst complementation by pluripotent stem cell (PSC) injection is believed to be the most promising method to generate xenogeneic organs. However, ethical issues prevent the study of human chimeras in the late embryonic stage of development. Primate embryonic stem cells (ESCs), which have similar pluripotency to human ESCs, are a good model for studying interspecies chimerism and organ generation. However, whether primate ESCs can be used in xenogenous grafts remains unclear. In this study, we evaluated the chimeric ability of cynomolgus monkey (Macaca fascicularis) ESCs (cmESCs) in pigs, which are excellent hosts because of their many similarities to humans. We report an optimized culture medium that enhanced the anti-apoptotic ability of cmESCs and improved the development of chimeric embryos, in which domesticated cmESCs (D-ESCs) injected into pig blastocysts differentiated into cells of all three germ layers. In addition, we obtained two neonatal interspecies chimeras, in which we observed tissue-specific D-ESC differentiation. Taken together, the results demonstrate the capability of D-ESCs to integrate and differentiate into functional cells in a porcine model, with a chimeric ratio of 0.001–0.0001 in different neonate tissues. We believe this work will facilitate future developments in xenogeneic organogenesis, bringing us one step closer to producing tissue-specific functional cells and organs in a large animal model through interspecies blastocyst complementation.

Protein & Cell – Domesticated cynomolgus monkey embryonic stem cells allow the generation of neonatal interspecies chimeric pigs

46 thoughts on “Pig-Monkey Hybrids Created to Eventually Generate Human Organs in Pigs”

  1. The disconnection in a printed organ is much less severe than in a cut, and there is work in scarless healing.

  2. What I meant with the partially cured polymer analogy is that the monomers are disconnected, same as the wood particles in particle wood. Whereas in a fully cured polymer, the monomers are connected properly, as are wood “particles” in hardwood.

    If you consider a cut injury, there is also a disruption of the extracellular matrix and a physical disconnection between neighboring cells – much worse than what you get out of a printer. Yet the body is capable of healing it, and restoring proper connection.

  3. > They’re cells embedded in an intercellular matrix, built in different developmental phases, components of which have been created by different tissues and transported there over time, etc.

    At the end of all that process, it’s still just different types of cells embedded in a protein network (extracellular matrix) and forming various microstructures (vessels, layers, etc). Given enough resolution and a good library of bioinks, all of that can be printed.

    Alignment is indeed a challenge, but carbon fiber (and other composites’) 3D printers face a similar challenge. It is being solved as we write here.

    With enough resolution, I imagine even gap junctions could eventually be printed by applying the right “glue” and signaling molecules between individual cells. The “glue” would provide the initial connection, and the signaling molecules would coax the cells to finish the job. But this would be an advanced feature, that we are still far from.

    Microvasculature isn’t static once an organ is formed. It can grow and adapt to demand, and does so all the time in response to exercise and other stimuli. There are known signaling molecules that encourage vasculature formation. I suspect cell alignment can adapt too.

    The first printed organs surely won’t be perfect, but if they last a few years, the next version will be better. Transplants don’t last forever either.

    > Will they just figure this stuff out on their own once we place them down?

    We can embed signal molecules to help.

  4. No, this is not like a partially cured polymer versus a fully cured one. I used the wood analogy for a reason. These are two different construction and adhesion methods, not just different stages of cooking for the same method.

    I guess I’m not sure why you think chimeric research is in the early phases. I mean, they’ve already created complete mouse kidneys in rats. The biggest problem is working out the best source of (induced or otherwise) human stem cells, which is a common problem with the 3D printing technology.

  5. The replacement of intercellular matrix with “collagen, etc” is exactly what I’m talking about. There’s no way that will have the same properties. You might get something which works well enough to avoid dying, but that’s a low bar.

  6. Organs aren’t just a bunch of mature cells. They’re cells embedded in an intercellular matrix, built in different developmental phases, components of which have been created by different tissues and transported there over time, etc.

    They are cells with specific connections to some, but not all, neighbors, like gap junctions, and specific alignment properties. A heart won’t pump if the cells aren’t aligned properly. If you have them “roughly” aligned (that is, you Somehow coax them to come out of the printer pointing the right direction), they still won’t have optimal microalignment with each neighbor. You’d lose half the contractile energy.

    Cells are arranged around a microvasculature that developed according to demand in a real world scenario, not something placed down according to a model. Small differences in demand versus capacity could cause pockets of microvasculature to collapse or bias the distribution of nutrients, causing different tissue layers or cell types to develop out of whack with one another.

    Will they just figure this stuff out on their own once we place them down? Why should we expect them to? They’ve never had to do that in the past.

    I expect that even once we get these to “work”, they will continue to develop problems over time. Inefficiencies in ion transport will cause kidneys to develop calcification issues, hearts will hypertrophy and see stiffening valves, etc. I guess we could just keep replacing them and learn as we go.

  7. > basically particle board compared to real wood

    The chemical analogy would be a partially cured polymer (or worst case, just a mix of monomers) vs a fully cured one. Luckily, we have live cells on our side to finish the curing process and turn that particle board to hardwood.

    > I think it will take a long time.

    IMO pigs will take longer. The research there is still in early stages, especially with the chimera approach. And then there are regulatory roadblocks.

  8. You don’t print with undifferentiated stem cells. You print with more or less mature cells plus collagen etc, with the goal of getting as close as possible to the macroscopic and microscopic structure of a mature organ. From there, the cells only need to bridge the gap of what the printer can’t do. Which is somewhat similar to just the final stages of maturation, or maybe healing an injury.

    In principle, we can coax the cells to do the right thing by embedding the right signaling molecules. But we may need more research to find the correct ones (and more engineering to embed them well enough).

  9. > with the 3D printing stuff, they’re at the point of making little blobs of cells that wiggle.

    They’re somewhat further along than that: https://www.sciencealert.com/researchers-have-just-3d-printed-a-mini-heart-using-human-tissue

    Separate but related: https://www.sciencedaily.com/releases/2019/08/190801142542.htm

    Multi-material 3D printers exist, so combining different tissues is already possible. I think the biggest technical challenges at the moment are resolution and combining a large enough library of bio-inks. There are many different cell types even in a single organ, there’s the extracellular matrix, and then there are signaling molecules such as various growth factors. That’s a lot of inks.

    Of course, there are also bio-engineering challenges – which inks to use and how to use them to get a functional organ of good enough quality.

  10. But with the 3D printing stuff, they’re at the point of making little blobs of cells that wiggle. Even when they one day get it to the right shape and size and manage to merge different tissue types in, it’s basically particle board compared to real wood.

    Eventually, we can probably engineer cell lines which are meant to be 3D printed to begin with, and optimize our way to high performance organs/tissues. We won’t need the pigs forever. But I think it will take a long time.

  11. The problem is that the maturation phase evolved to take place over time, starting from a few cells from different tissue layers operating in concert with one another, also including other cells that migrate to the site over time, and receiving biochemical signals from surrounding (and sometimes distant) cells during a specific sequence of embryonic and juvenile growth phases.

    3D printing just won’t include that, and neither does letting it mature a bit in a patient. Organs don’t have a development path which includes filling in a scaffold straight to adult form. The cool thing about the chimera is that the incubator grows with the organ, using all the same programs that the cells evolved to use. When this route is cracked, you will have an organ every bit as good as the original.

  12. 2. Depends how many pig cells there are. If there are too many, it can make the organ useless.
    4. My impression is that organ 3D printing closer, and making faster progress. There was a demo mini-heart printed a few months ago. But I agree that there are still challenges to solve.
    Btw, one may do a hybrid approach: 3D print the best you can with appropriate growth factors etc, then let it mature in an bio-incubator (or maybe inside the patient, if it’s not a vital organ).

  13. 1. Much faster than the current wait lists.

    2. Why not just let the immune system clear the few remaining pig cells?

    3. George church is on it, but there are reasons our immune system uses this rejection method so it’s better to match it to your immune system and preserve immunosurveillance capacities.

    4. 3D printing of organs is so, so far away from being useable. Even when we get there, they will likely be inferior. Growing in an animal is how the whole tissue differentiation/organization/orientation/strengthening program is built. It’s not easy to hack this.

  14. George Church is doing all sorts of genetic engineering, so it’s quite possible that he’s working on this too. Or at least is familiar with someone else’s work.

    Different colored eyes is most likely heterochromia. Same set of genes, but different activation. Chimerism is when there are different sets of genes.

  15. Wasn’t George Church at Harvard saying something about gene-engineered pigs that could produce organs for humans that won’t be rejected and that, as a bonus, they were also being altered so that the organs could be frozen and thawed without harm, so that hospitals could keep a ready supply on hand?

    So far as ethics and morality? Until everyone becomes morally outraged about eating bacon and ham, it shouldn’t be an issue.

    As far as creating chimeras? That’s a non-issue as far I’m concerned. I’m probably a chimera myself (different colored eyes) and darn glad of it, since one of them sees great while the other is getting worse all the time.

  16. 1. Pigs take a while to grow.
    2. Even if the stem cells are from the patient, there will likely be pig tissue mixed in, so will still need anti-rejection drugs (which makes 1 a moot point, I suppose).
    3. May be simpler and probably more reliable to genetically-engineer the pigs to remove rejection markers.
    4. By the time this tech is ready for application, we will likely have organ 3D printing, which would be faster and doable with the patient’s own stem cells.

  17. Well, it keeps the Catholic sur-PETA creeps from firebombing the research facilities on a regular basis … there’s that.  Not as much primal empathy for bacon-monkey hybridization to try out thousands, … millions, of highly educated (i.e. arguably more likely to have useful results) guesses in random shot mutation evaluation. Harder with pig-human hybrids. … … … until the punkey business delivers a reliable, extraordinarily useful, life-saving and perchance life-improving grunting parts-factory result.  

    Just Saying,
    GoatGuy ✓

  18. More like once they’ve done enough groundwork it’ll be worth everyone’s time to argue the ethical case of doing it with humans cells. But yeah, by “ethical issues” they mean “regulatory issues”.

  19. the existing technology of using human stems cells to create human organs needs only to be improved.

    That’s what this study is about though. Currently chimerism is the best technology for incubating human stem cells to create human organs. And in a world where people eat meat every day, I can’t understand the objection.

  20. This is sickening, cruel and beyond unethical. PETA and every other animal protection agency needs to get involved. The focus of this study is completely flawed also, as the existing technology of using human stems cells to create human organs needs only to be improved. Why should animals have to suffer like this and put public safety at risk in the process? How was this study ever given the green light? Doesn’t it make sense that if we want to ensure our own survival, as well as that of other species, that future studies like this should be completely illegal?

  21. One big attraction of this approach is that the xeno-transplants can be (at least in theory) developed to not produce rejection issues.

    Whereas a transplant from some desperate guy in Bangladesh (even if he is healthy and disease free) still means you need to spend the rest of your life on a cocktail of anti-rejection and immune suppression drugs.

    Also, while you can bribe the poor guy for a kidney (not an iPad, but maybe enough cash to make a dowry for his daughter to get married or something) it is a lot less likely he’ll be willing to lose a liver, or his heart.

  22. “So once they prove it can be done then the “ethical issues” mysteriously evaporate?”
    I have no doubt about that.
    But it is probably going to be too expensive as long as it is possible to gift an I Pad to some poor fellow in Bangladesh in exchange for a kidney.

  23. However, ethical issues prevent the study of human chimeras in the late embryonic stage of development.

    So what is the purpose of this work? If it is unethical to actually do it with human cells?

    OR does the “ethics” depend on how commercially viable it is? So once they prove it can be done then the “ethical issues” mysteriously evaporate?

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