EMBRONIC AND INDUCED PLURIPOTENT STEM CELLS
Janet Rossant, PhD, senior scientist, chief of research, and Lombard Chair in Paediatric Research at the Research Institute,
The Hospital for Sick Children.
BioPharm: What are the advantages to studying these types of stem cells, and where do you see them fitting in to the regenerative medicine
Rossant: Human embryonic stem cells (ESCs) have been with us for quite a few years. They have been derived from early human embryos
derived from in vitro fertilization clinics. These are embryos that would not be used for reproductive purposes. When couples have finished with
their fertility treatments, the remaining frozen embryos can be either destroyed or, with the donor's consent, can be used
for research. ESCs have been extremely important in showing us the power of these pluripotent cells to generate many different
kinds of cells in culture, opening up the possibility that, in the long run, some of those cell types might be used to treat
neurodegenerative diseases or traumatic injuries.
There are some issues with ESCs: obviously, there are the ethical concerns about the origins of those cells. Beyond that,
given a small bank of ESCs, would we be able to identify a matched patient who required a graft? Obviously not. The new technology
of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka and colleagues in 2006 has changed the game in many ways (2).
Obviously, the ethical concerns are much less, and now you have the potential to make many different iPSCs from individual
patients. In the long run, the hope is that iPSCs could be sources of cells for patient-matched stem-cell therapies. In terms
of therapy, however, are pluripotent cells really going to be the future source of stem cells for regenerative medicine? The
answer is in some areas yes, and in other areas no. There are already some clinical trials underway with cells derived from
ESCs for spinal cord repair and for macular degeneration. There are trials being conducted now, so they can and will be used
for certain situations. But for other situations that people are interested in, such as neurodegenerative diseases, I think
we're quite a way off from being able to take embryonic stem cells and directly use them as cells to treat patients.
The other exciting aspect of iPSCs is not their direct use for therapies, but their use as models to study the disease process.
Because you can take skin cells from a patient who had any kind of disease and make iPSCs from that patient, you now have
the ability to model that disease in a dish. For example, if you have a patient with a neurodegenerative disease, and you
can make nerve cells from that patient's iPSCs in the dish, you can study the progression of the disease in those nerve cells,
and really start to understand what goes wrong in the disease. You can then perhaps develop drugs to treat the disease based
on stem cells. I would call that stem cell-related therapies, where you're not actually using the cells themselves as therapy
but they become a very important tool to develop treatments for many diseases. That's the advantgage of iPSCs over ESCs. People
work on human ESCs to drive their differentiation into different pathways, because they're still the best understood pluripotent
cells. With iPSCs, there seems to be more variablity between cell lines when they're made by the induced pluripotent route.
We haven't completely nailed the process of reprogramming in those cells, so that we can be sure that they behave like early
embryonic cells. There's still a need to keep working with embryonic stem cells. But the two side-by-side become a very powerful