Many advances in the biological sciences rely on using cunning and deceit to cause an organism to react in a certain way. By using some clever tricks, researchers at U of T have produced bone marrow by enticing blood-borne stem cells to grow inside cozy cellular homes that resemble the interior of actual bones. More than just lab trickery though, this finding points to an alternative to that of traditional bone marrow transplants–a procedure that is difficult and painful, with only a partial rate of success.
Biomaterials seeded with bone cells provided the needed deception, and the whole experiment was carried out inside “nude” mice. These critters differ from their furry kin in that they are genetically engineered such that their immune systems are unable to mount an effective response.
The tricksters were Prof. John Davies and Dr. David Lickorish of the Institute for Biomaterials and Biomedical Engineering (IBBME), as well as several colleagues at Tsurumi University in Japan.
This is the first time that bone marrow has developed inside a so-called biodegradable implant, which acts much like the dissolvable stitches you get after oral surgery: they allow the cells to regrow, and dissolve afterwards, leaving normal tissue.
Bones are not exactly hollow. The humerus (upper arm) and femur (thigh) for instance, both contain trabecular bone, a foam-like material shielded by a load-bearing layer on the outside. Bone marrow cells attach to the walls of the spongy interiors, where they differentiate into many of the commodities that your body needs to survive, such as red blood cells.
Davies’ team seeded bone cells onto a scaffold that resembled the trabecular bone. The scaffold is about the size of a Q-tip, made of a biodegradable material, and interspersed with calcium minerals also found in real bones. After the bone cells were implanted in the scaffold, they were implanted in nude mice.
Nude mice lack effective immune systems, and so there is no risk that they might reject the implant. Implant rejection is a common problem when transplanting human organs, because the recipient’s body recognizes the organ as foreign and will not accept it.
Stem cells in the blood streams of the nude mice were attracted to the bone sites, where bone marrow is usually found, and began to attach there and grow.
“Not only does the scaffold support bone growth,” said Davies, “but the host animal sees the implant as a normal trabecular bone.”
Davies believes this technology could one day be used to regenerate human bone marrow, by implanting humans with scaffolds seeded with their own bone cells. It might provide a less invasive alternative to the current marrow transplant procedure, in which a donor’s bone is smashed open and marrow scraped out.
Only about 30 per cent of those who need transplants are compatible with a kin donor, according to Beverly Campbell, the director of the donor registry at Canadian Blood Services. At any given time, about 250 Canadians await a marrow transplant from an unrelated donor.
