This Synthetic Bone Implant Could Replace Painful Marrow Transplants

Lab-engineered bone (the outer layer) with functional bone marrow (the inner layer). Image: Varghese Lab at UC San Diego
Lab-engineered bone (the outer layer) with functional bone marrow (the inner layer). Image: Varghese Lab at UC San Diego

Thanks to advances in medicine, bone marrow transplants are no longer the last resorts they once were. Every year, thousands of marrow transplants are performed, a common treatment for ailments from bone marrow disease to leukemia. But because they first require a patient undergo radiation to kill off any existing bone marrow stem cells, marrow transplants remain incredibly hard on a patient.

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Now, engineers at the University of California San Diego have developed a synthetic bone implant with functional marrow able to produce its own blood cells. So far, researchers revealed in a paper published in the Proceedings of the National Academy of Sciences this week, they have successfully tested the engineered bone tissues in mice. But one day, those biomimetic bone tissues could provide new bone marrow for human patients in need of transplants, too.

The implant does away with the need for radiation by giving donor cells their own space in the body to grow. Inside the implant, there is no threat of those cells being overtaken by the body’s native stem cells.

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In mice, the researchers implanted the synthetic bone tissues with functional marrow under the skin. After six months, those donor cells were still alive and had begun supplying the mice with new blood cells.

The implants were designed to replicate the long bones in the body, with an outer bone compartment containing calcium phosphate minerals to build bone cells, and an inner area for donor stem cells that produce blood cells.

When implanted, they grew into bone tissues with working blood vessel network and functional bone marrow that supplied the body new blood cells. After 24 weeks, researchers found a mix of host and donor blood cells was still circulating in the bloodstream of the mice.

A treatment based on this technology would only work for patients with non-malignant bone marrow diseases, like aplastic anemia, a condition where the body can’t make enough platelets and blood cells. That’s because while the technique can replenish types of cells that are lacking, it can’t doing anything to fight off cells that have mutated and are spreading. Cancer patients would still need need to undergo radiation therapy to have their cancerous cells wiped out.

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Much more research is needed, of course, before these implants are ready to make their way into human patients. But what’s exciting here is that the synthetic bone tissues were not only functional, they allowed donor marrow to grow and survive for many weeks in the presence of host cells, and for the products of that marrow to make their way into the body’s circulatory system. Pretty neat.

Senior Writer, Gizmodo.

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DISCUSSION

Dr Emilio Lizardo

This article does not make a lot of sense.

Bone marrow transplants are rarely done these days. Most of the transplants are done with peripheral stem cells which are easier to collect and are richer in the desired stem cells anyway so the procedure tends to be more effective with less toxicity. This is a somewhat pedantic point that has little bearing on the actual article.

What does matter is that the point to stem cell transplant (or bone marrow transplant is one of two thing. Most commonly it allows a patient to receive very high doses of chemotherapy and radiation to treat the underlying disease. The doses are so large that they would carry very high risk of death through long term or even permanent damage to the bone marrow causing very low blood counts which could result in infection, bleeding, or heart attack. Stem cells are given back (either the patient’s own or another person’s) and take root in the bone marrow where they reconstitute the patient’s ability to make blood cells and prevent those complications. Hence the more formal name of “high dose therapy with stem cell rescue.” The theory is that if you can just give enough treatment you can cure anything. This is very not true, but fits into the basic oncology myth that if a little is good, more must be better. Stem cell transplant has its place, but still can’t cure most things.

The other goal of a stem cell transplant is to use somebody else’s cells (allogeneic transplant) to get a “graft vs tumor effect.” People who get allogeneic transplants are at risk for “graft vs host” which is where the donated cells create an immune system that recognizes the host’s tissues as “not self” and creates antibodies against them. It is the flipside of a person “rejecting” a solid organ transplant like a kidney. It usually requires immunosuppressive medications to prevent serious side effects and people have to remain on those drugs for their whole lives, which causes other potential problems including infection and other cancers. However, if you can get that donated immune system to attack the disease that you are treating (most often lymphoma or leukemia), that can be quite effective in controlling the disease.

The thing about this article is that I see no way at all that artificial bone marrow changes any of what I just said. It might be very useful for a rarer condition called myelofibrosis where the bone marow gets scarred for reasons that are not well understood and there is no room to make blood cells. But there are drugs in development that are starting to show promise reversing fibrosis in a few people.