by Chris Kamel
In Britain, a young boy is currently recovering from a remarkable surgery to replace his windpipe. Tissue transplantation itself is hardly a routine thing, but there are a couple of things that make this case, reported in the British Medical Journal, particularly interesting.
Avoiding immune response
First, the trachea being transplanted is being grown by the boy's own cells. Stem cells, isolated from bone marrow, were used to grow a new windpipe on scaffolding from a donor trachea, stripped down to a decellularized collagen scaffold.
Traditional tissue transplant requires careful donor-recipient matching and a potential lifetime of immunosuppressant drugs to prevent immune response and tissue rejection. By regrowing a trachea using his own cells, this patient will avoid that risk.
This alone is pretty exciting, but in fact isn't the first time a trachea transplant has been done in the absence of anti-rejection drugs. In June 2008, a Columbian woman, Claudia Castillo, successfully received a transplanted trachea grown from her own stem cells, without the need for immunosuppressants. Again, a donor scaffold was produced and was then seeded with Castillo's mesenchymal stem-cell-derived chondrocytes and epithelial respiratory cells and left to grow in a special bioreactor for several days before transplant.The body as an incubator
While Castillo's trachea was safely transplanted without drugs, it took several months to expand the stem cells before seeding the donor scaffold, and the new tissue growth required highly specialized equipment before transplant. The whole process was an expensive, multi-centre affair, and almost didn't happen due to issues transporting the stem cells from Bristol, where they were grown, to Barcelona, where the surgery took place.In another operation, a Belgian woman, Linda De Croock, received a donor windpipe which was prepared for transplant by first implanting it in her arm. This allowed revascularization and progressive replacement of donor tissue with the patient's own. Because De Croock herself was used as the tissue incubator, it eliminated the need for special tools to incubate or grow the tissue. But again, this took several months, though the procedure allowed her to return to a normal life without the need for the usual course of drugs.
Part of what makes the British case unique is that the tissue is being grown in situ. Stem cells were isolated and ready for use within hours of extraction and surgery was performed with the new tissue being grown in the boy's body, in the correct anatomical location. This is not insignificant. It means that this or similar procedures become accessible to hospitals that may not have the facilities to grow new tissues and organs. It also reduces the wait for surgery since the tissue doesn't have to be grown beforehand. The fact that the tissue is being regrown in the body also suggests possible usefulness as a 'patch kit' for damaged tissue rather than replacing whole organs, as touched upon in a previous post.
The obvious hope is to eventually perform similar procedures with other tissues, not only reducing the risk but also donor shortages. Researchers are already working on ways to grow more complex organs. At the University of Minnesota, scientists have managed to reconstitute a partially functional rat heart using similar methods.
While growing yourself a fresh kidney for transplant is still some ways off, these are exciting steps towards rejection-free, non-donor organs thanks to stem cell-based regenerative medicine.