Jun 15 2010

Growing New Livers

A team as Mass General has published the results of their preliminary research into growing new livers from hepatocyte stem cells. The work is encouraging – but to put it into perspective, it is still a long way away from growing fully functional transplantable organs.

What the team did was take rat livers and wash away all of the liver cells leaving behind just the connective tissue. They used this connective tissue as a scaffold on which to grow a new liver with hepatocytes. They then transplanted the new liver into rats. They report that the artificial livers survived for a few hours.

This is obviously a long way away from an artificial liver. First, the new livers had only hepatocytes, but not the other kinds of cells that make up a normal liver. So even if this technique worked completely, it would only create a partially functioning liver.

Another obstacle to overcome is creating a liver that has something approaching a normal infrastructure, including blood vessels and bile ducts. It’s not enough to have a mass of cells, they have to have the proper structure to function. This is not a trivial obstacle.

In fact the liver may be a deceptively difficult organ to grow in this manner. Other teams have had success using essentially the same technique with hearts – using a scaffold on which to grow new heart cells. Heart cells have the advantage of synchronizing themselves as they grow, so they beat together. The challenge is growing the internal electrical system of the heart, but this can be bypassed by using a pacemaker.

Other organs will be of varying complexity. A pancreas doesn’t seem as difficult as a lung or liver, while kidneys have a complex internal structure.

The questions is – how much potential is there in the scaffolding approach to growing organs? This seems like a stop-gap measure – a partial solution to the problem of how to grow organs. It may be useful for a couple of different kinds of organs, likes hearts, and for some other body parts – a trachea was transplanted using this method. But it seems unlikely, without further major breakthroughs, that this approach will be the ultimate solution to growing organs.

Growing new organs from scratch – from an embryonic state – may be the only way to get the full infrastructure and cellular organization. The problem here is that it takes time. An adult organ may take a decade to grow. For some organs an adult organ, or close to it, would be necessary – like heart and lungs. For others, even a several year old organ may suffice. A small liver or kidney would still provide significant function, and may continue to grow as the recipient ages.

There is also the  question of what to grow the new organs in. Ideally we would grow them in vats – some completely artificial environment. But this will likely be a huge technological hurdle. There are insurmountable ethical problems to growing them in people – clones that would serve as organ banks (like in the movie, The Island). It is interesting to consider the public reaction to other human options, such as growing them in headless torsos – just a formless mass of cloned human tissue full of organs being fed intravenously.

There is also the option of genetically engineering animals to grow cloned human organs, and then sacrificing them when the organs are needed. Perhaps they can be engineered to be immunologically naked, and then matched to the recipient when it comes time to harvest the organ.

There are two significant advantages to growing organs. The first is that we have a shortage of donated organs – people die waiting for organs to be transplanted. The second is the issue of tissue rejection. Getting a transplant even from a compatible donor requires a lifetime of immunosuppressant drugs and the risk of rejection. A transplant of  your own cloned tissue, however, would be 100% compatible and therefore not require drugs or risk rejection. This is a huge advantage, which would revolutionize organ transplants.

Conclusion

This latest study is a baby step forward in one technique which is likely to be very useful, but ultimately limited, in terms of a final solution for organ transplants. But it’s a step. We need another 50 baby steps or so before we reach our goal, but there are useful milestone along the way. I think we will see in the next decade grown hearts for transplant, and maybe even grown livers and pancreases. Skin is another organ that will likely occur sooner than later. But such predictions are inherently unreliable – there remains major obstacles to overcome and they cannot be predicted in the short term.

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