Judging by the volume of news over the past few weeks, we've entered the period in which a wave of early adult stem cell research is starting to produce results. As is usual in a young field of medicine, it looks fairly confusing and there's a lot of contradictory information out there - especially from the anti-abortion groups who are hyping adult stem cell research (as an alternative to embryonic stem cell research) for ideological reasons.
Let's start with the bad news: a Swedish group claims that adult stem cells are indeed limited in their regenerative powers:
There is little, if any, evidence that adult stem cells can build other cells in an adult organism than those formed in the organs they themselves come from. At any rate, blood stem cells do not convert to heart muscle cells in a damaged heart, which was previously hoped. This has been shown by a research team from the Stem Cell Center at Lund University in Sweden in an article in Nature Medicine.
During the end of the 1990s and early 2000s scientists nourished great hopes that adult stem cells would be able to develop into all sorts of cells. If so, it would not be necessary to use the ethically more problematic embryonic stem cells. However, newer studies have shown that while adult stem cells are very good at producing different types of cells in their own respective organs, they have little or no ability to form cells in other organs.
"Both we and two American research teams have used various methods to replicate a study from three years ago that appeared in Nature. It was about transplanting blood stem cells to create new heart muscle cells to repair a heart after a heart attack. But all of our results univocally indicate that this is not possible," says Jens Nygren. He is a doctoral student and part of research team headed by Professor Sten Eirik Jacobsen at the Stem Cell Center.
This raises questions - given that recent human trials have shown that adult stem cells have an impressive regenerative effect when combined with bypass surgery for heart disease.
Perin, in collaboration with Hans F.R. Dohmann at Hospital Procardiaco in Rio de Janeiro, Brazil, has already tested the treatment on 14 patients in Brazil. That study, published last year in Circulation, showed that the procedure is safe and significantly improves heart function.
"We saw significant improvements in exercise capacity," says Perin. "This is measured in terms of peak oxygen capacity, which went from 17 percent to 24 percent in treated patients."
So how does this therapy work? Do stem cells release chemical signals causing existing tissue to regenerate? Do they fuse with muscle cells? Both? Neither? These are questions that remain unanswered - more research is needed.
Meanwhile, other scientists are demonstrating all sorts of impressive regenerative techniques in petri dishes and laboratory mice, performed on the way to fully understanding stem cell biochemistry. One might almost call this the barnstorming era of stem cell science. For example, while serious work is being done in the UK on regenerating teeth from stem cells, a research team in the US has found that dental pulp-derived stem cells can protect and promote the survival of some types of brain cells.
In people with Parkinson's disease, a shortage of the neurotransmitter dopamine causes symptoms such as muscle rigidity, tremors, difficulty walking and problems with balance and coordination. Previous studies in animals and humans have focused on other sources of stem cells, however, most of those cells die when grafted into the brain.
The major advantage to using dental pulp-derived stem cells is that they are more robust than other stem cells. The dental pulp cells also express glial cell-line neurotrophic factors, which work to support dying nerve cells and replace dead cells. And the cells could be extracted from patients to be treated, avoiding immune complications from foreign donors.
While some scientists are figuring out how to craft therapies from stem cells, others are working on improving basic methods and knowledge - just as important, given our still limited knowledge regarding stem cell biochemistry, differentiation and other matters more arcane. It was recently shown that, for at least some uses, adult stem cells derived from fat are as effective as adult stem cells derived from bone marrow:
For the first time, stem cells purified from fat have been used to heal an injury in a living animal. Michael Longaker of Stanford University in California and his team showed in mouse experiments that so-called adipose-derived adult stromal (ADAS) cells purified from a rodent's belly fat could be coaxed to heal a skull fracture too large to mend by itself.
If the same technique works in humans, these cells could be coaxed to mend broken bones and correct other defects in tens of thousands of surgical procedures each year in which bone grafts and prosthetics are now necessary.
This is indeed a big improvement - fat is far more easily extracted than bone marrow. We might see the start of "therapeutic liposuction!"
Other US researchers are making progress in understanding stem cell biochemistry, step by step.
The discovery of a molecule that stops stem cells from replicating could enhance the ability of stem cells to fight cancer and other diseases. By defining the molecular switch that hinders stem cell replication, researcher Tao Cheng and colleagues from the University of Pittsburgh School of Medicine in Pennsylvania may have overcome a major hurdle to growing stem cells in the laboratory.
Stem cells can even be a delivery method for some cancer therapies. Killing cancer cells isn't hard - there are many methodologies available that will accomplish this - but ensuring that the only cells killed are cancer cells is hard. This is why delivery mechanisms are so important in the search for cancer therapies.
A mechanism has been discovered that allows some stem cells to track brain tumors, a finding that could be used to deliver targeted cancer treatments. Researchers at Cedars-Sinai's Maxine Dunitz Neurosurgical Institute in Los Angeles, California say that neural stem cells - immature cells that can differentiate into any central nervous system cell - could be used to deliver cancer-killing genes to deadly brain tumors.
"We have previously demonstrated the uncanny ability of neural stem cells to seek out and destroy satellites of tumor cells in the brain," says John S. Yu, a senior author of the study. "Now we know at least one component of tumor cells that is attracting neural stem cells toward them. With this knowledge, we hope to expedite the translation of this powerful and novel strategy for the clinical benefit of patients with brain tumors."
It is understanding the mechanisms - the chemical pathways, the biochemistry - of stem cells that will lead to further advances and medical application. Knowledge is the fastest pathway to results. The stem cell therapies we see in trials now are merely the first of the first, the best we can do with our present level of knowledge. It's impressive - very impressive when it comes improving the condition of heart failure patients - but still crude compared to what we will eventually be able to accomplish.