The techniques pioneered by the winners of this year's Nobel Prize in medicine, John B. Gurdon and Shinya Yamanaka, have already allowed scientists to generate stem cells and clone animals.
But it is the potential these discoveries hold that truly boggles the mind. If stem cells – the primitive cells that develop into tissue like skin, blood, nerves, muscle and bone – can be harnessed, the belief is they can be used as a repair kit for the body.
In theory, a few skin cells could be harvested to rebuild a spinal cord damaged by trauma, to replace brain cells destroyed by dementia, to rebuild heart muscle damaged by a heart attack or to grow a new limb ravaged by diabetes. It is the stuff of science fiction, so close we can taste it.
But these dreams of miracle cures must be tempered with a strong dose of realism.
Despite billions of dollars in investment in research, from government agencies and biotech companies, there is little evidence that stem cell therapies work.
Yes, some hearing has been restored in gerbils and there have been modest improvements in paralyzed lab rats using stem cell treatments, but these are baby steps. In humans, the gains have been far more modest.
We can treat some forms of cancer, like leukemia and multiple myeloma, with stem cell transplants. But this is simply a refinement of an earlier technique, bone marrow transplant. And to perform such a transplant, the immune system must, for all intents and purposes, be destroyed – a punishing regime with a significant mortality rate.
It is a far cry from the notion of an injection of magic stem cells that allow people to walk again or restore their memories.
The International Society for Stem Cell Research says that while there are hundreds of conditions that can purportedly be treated with stem cells, the treatments that have actually been shown to be beneficial are "extremely limited." Aside from the cancer treatments mentioned above, some bone, skin and corneal conditions have been treated by grafting stem cells, growing them in the lab and transplanting them.
But in all these cases, the stem cells are tissue-specific, meaning the cells are carrying out a function they were designed to do. This is very different from the notion that undifferentiated stem cells can be used to treat a broad range of conditions.(And we won't delve into potential problems, such as rejection and the concern that stem cells could grow out of control and cause cancerous tumours.)
Where stem cells have been used in this manner, as an elixir if you will, the reports are all anecdotal and dubious. This includes high-profile cases like that of star football player Peyton Manning, whose neck injury was treated (in a manner that is not clear) with stem cells, and so-called stem cell tourists who travel to China in hopes their paralysis will be cured.
The reality is we've been talking about the promise of stem cells since 1962, when Prof. Gurdon cloned a tadpole from a modified frog embryo. The conversation was jacked up a notch when, in 2006, Dr. Yamanaka was able to produce mouse stem cells from mouse skin cells (thus avoiding the thorny issue of using embryonic stem cells).
Since then, the progress has been significant in the lab and modest in the clinical world. But real progress in science is slow and sometimes hard to see. This does not mean we should lose hope. The promise, the excitement at the potential of stem cells, is greater than ever. We should celebrate the Nobel winners for their very real achievements – allow ourselves to dream of revolutionary possibilities even – while being careful to not succumb to the hype.
André Picard