A number of diverse lines of research and development will lead to new technologies that replace or repair organs. The present list looks much as follows:
- Electromechanical and blended biological-electromechanical systems: artificial hearts, prosthetic limbs and eyes, dialysis machines that contain cultured kidney tissue, and so forth.
- Repair of organs in situ using transplanted stem cells or stem cell signaling to spur regrowth that otherwise would not happen.
- Engineering of complete organs from a patient's own cells, such as through bioprinting.
- Decellularization to replace the cells in human donor tissue and organs in order to form patient-matched transplants.
- Xenotransplantation: the use of decellularized organs and tissues from animals, which provide the structure and chemical cues to allow repopulation with the patient's human cells.
A recent article at the Scientist looks at a couple of these lines of work - organ engineering versus xenotransplantation, both of which draw heavily upon the comparatively new techniques of decellularization in order to achieve new and better results, both in the laboratory and for patients in trials:
Today, the organ shortage is an even bigger problem than it was in the 1980s. ... he supply has stagnated despite well-funded attempts to encourage donations, and demand is growing, especially as the organs of a longer-lived population wear out.
Faced with this common problem, Vacanti and Cooper have championed very different solutions. Cooper thinks that the best hope of providing more organs lies in xenotransplantation - the act of replacing a human organ with an animal one. From his time in Cape Town to his current position at the University of Pittsburgh, he has been trying to solve the many problems that occur when pig organs enter human bodies, from immune rejection to blood clots. Vacanti, now at Massachusetts General Hospital, has instead been developing technology to create genetically tailored organs out of a patient's own cells, abolishing compatibility issues. "I said to myself: why can't we just make an organ?" he recalls.
In the race to solve the organ shortage, xenotransplantation is like the slow and steady tortoise, still taking small steps after a long run-up, while organ engineering is more like a sprinting hare, racing towards a still-distant finish line. Most of those betting on the race are backing the hare. Industry support has dried up for xenotransplantation after years of slow progress, leaving public funders to pick up the expensive tab. Stem cells, meanwhile, continue to draw attention and investment. But both fields have made important advances in recent years, and the likely winner of their race - or whether it will result in a draw - is far from clear.
Xenotransplants will always have to deal with an immune clash of some degree, so growing an organ that is perfectly matched to a patient would be preferable. The question is whether tissue-engineering technologies will reach that point before genetic engineering enables the first transgenic pig hearts or kidneys to be successfully installed in patients. Sachs says, "I consider xenotransplantation still the nearest-term, best hope for solving the organ shortage, but in the long run, I think tissue engineering will replace it."
There is also the matter of scale. Platt thinks that organ engineering is too costly to meet the needs of everyone waiting for a transplant. "You'd have to turn over the entire GDP of a country to accomplish that," he says. On the other hand, "I could get a pig for a couple of hundred dollars." But Macchiarini argues that organ engineering is in its infancy, and every advance improves efficiency and lowers cost. "What we did in 2008 in 6 months, we can now do in a few weeks," he says. "We do care about getting this to every patient." Vacanti adds that mass-producing artificial scaffolds will make organ engineering even more cost-effective. "When you scale them up, the bulk materials and manufacturing tech are extremely cheap," he says. "I think it's going to be cheaper than growing lots of pigs."
We shall see. The only sure thing in my book is that vigorous competition is good for both speeding progress and producing higher quality solutions. That is just as true in medicine as for every other field of human endeavor.