Patients around the world face terrifying waitlists for organ transplants. In the US, the wait time for a liver transplant averages 26 months; for a lung, it can be nearly three years. To make matters worse, even if a donor becomes available, there is still a risk that the transplant will be rejected.
The ability to bioengineer organs would solve both of these problems. An organ fabricated from the recipient's own cells could be made to order and would not face the risk of immune rejection. “These organs would be available on demand and thereby overcome donor organ shortage,” says Harvard Medical School's Harald Ott, lead author of a paper published in this issue of Nature Medicine detailing lab-grown lungs (page 927).
In recent years, replicating complex three-dimensional tissue structures has become more feasible thanks to a technique called decellularization. In this process, cells are washed away from an organ with special detergents, leaving behind the extracellular matrix of collagen. This matrix serves as the scaffold on which a transplant is grown, and it doesn't provoke an immune response because the donor's collagen is similar to the recipient's.
In humans, the technique has been used successfully to make transplants of simple, hollow organs such as the bladder or trachea. Other lab-grown organs are still years away from becoming available, but scientists have taken the important first steps by creating whole functioning organs in rats. Here are some recent successes:
Heart: One of the earliest demonstrations of the scaffolding strategy came from Ott and his colleagues, who grew a rat heart that beat when given an electric current (Nat. Med. 14, 213–221, 2008).
Lungs: Ott's team again used the decellularization technique to create a complete set of rat lungs. After transplantion, the rats could breathe for up to six hours with the engineered organs (Nat. Med. 16, 927–933, 2010). This study comes on the heels of work from a team at Yale University in New Haven, Connecticut that used a similar technique, but in that study the rats survived for only two hours (Science doi:10.1126/science.1189345, 2010).
Liver: Replicating the liver's intricate vascular structure has proven particularly challenging, but successful liver grafts were grown and transplanted into rats at Massachusetts General Hospital in Boston, as reported last month in Nature Medicine (16, 814–820, 2010).
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Palmer, R. Lab-grown organs seen as remedy for long donor waitlists. Nat Med 16, 834 (2010). https://doi.org/10.1038/nm0810-834b