An alternative to stem cell transplants in regenerative medicine is the manipulation of existing cell populations in the body: using biochemical signals to direct these cells to rebuild damaged tissue. This has proven effective in the laboratory in recent years, spurring significant regeneration that would not normally have happened. Here is one example:

Researchers are reporting they have successfully persuaded damaged joints to regrow cartilage and bone, using a novel "cell homing" approach. The experiments, conducted in rabbits, are a proof of concept of a method that may one day replace artificial joint transplants in humans ... The method uses a carefully constructed "bioscaffold," impregnated with a growth factor that causes precursor cells to migrate to the site and become cartilage and bone cells

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Animals treated with the method fully recovered weight-bearing and locomotion within a month, and the regenerated tissue was similar to naturally occurring cartilage and bone, the researchers said.

The research report is online at the Lancet. This general approach to regenerative medicine has both advantages and drawbacks: on the one hand using a patient's own cells removes the need to source cells for transplant, thus hopefully leading to a leaner and less costly technology platform. On the other hand, a person's stem cell populations decline in effectiveness with advancing age. It is still an open question as to whether the cause of this decline is that signalling mechanisms become age-damaged, that the population shrinks with age, or that the cells themselves become too damaged to function well. All three many be the case to some degree or another, or only important for some groups of stem cells in the body. A number of research groups are working hard on uncovering the truth of it, but the central problem remains: if you want to command the stem cells already present in a body to get to work, they have to be up to the job.

The most important potential applications of regenerative therapies apply to the old: restoring worn organs, and repairing the damage caused by aging. So broader development of these therapies will have to lead to some consideration of how to restore aged stem cell populations to youthful effectiveness along the way. I am optimistic that we will see progress on this front over the next decade, as the next wave of therapies are tested and evolved in the course of medical tourism, and their shortcomings for older people are better categorized and understood.