In Stem Cell Therapies Today, we saw how stem cells
are being used to treat diseases such as leukemia. Stem cell transplant procedures
also show promise for treating neurological disorders such as Parkinson's disease.
What does the future hold for stem cell therapies?
Researchers and physicians are working to design stem cell therapies that
- Are more effective, and
- Reduce the invasiveness and the risk to patients
Today's stem cell therapies usually rely on cells that are donated by another person.
This raises the possibility of donor cell rejection by the patient's immune system. In the
future, it may be possible for a person to use a sample of his or her own stem cells to
regenerate tissue, which would reduce or even eliminate the danger of rejection. How might
this be done? Some possibilities include:
- Collecting healthy adult stem cells from a patient and manipulating them in the laboratory to
create new tissue. The tissue would be re-transplanted back into the patient's body, where it
would work to restore a lost function.
- Therapeutic cloning, as described in Creating Stem Cells for Research, might enable the creation
of embryonic stem cells that are genetically identical to the patient.
- One less invasive way to achieve this goal would be to manipulate existing stem cells within
the body to perform therapeutic tasks. For example, scientists might design a drug that would direct
a certain type of stem cell to restore a lost function inside the patient's body. This approach would
eliminate the need for invasive surgical procedures to harvest and transplant stem cells.
On the surface, the possibilities for stem cell therapy seem limitless. Couldn't we use stem
cell technologies to replace any diseased or damaged tissue in the body? To answer this question,
researchers must figure out the true potential and limitations of stem cells. Some questions
currently being addressed include:
How long will a stem cell therapy last?
- The reason we age is because our cells do. If adult stem cells are used in
therapies, will the tissues created from those cells age and malfunction more quickly?
Scientists don't yet know how long different stem cell treatments might last.
Can we ensure that stem cell therapies won't form tumors in the body?
- Embryonic stem cells are naturally programmed to divide continuously and remain
undifferentiated. To be used successfully in therapies, embryonic stem cells must be
directed to differentiate into the desired type of tissue and ultimately stop dividing.
Any undifferentiated embryonic stem cells that are placed in the body might continue to
divide in an uncontrolled manner, forming tumors.
Avoiding tumor growth is crucial to the success of stem cell therapies. Let's look at
this in more detail.
In both embryonic and adult stem cells, improper regulation of genes can lead to
uncontrolled cell division and tumor formation. This is a special concern with cells
that have been cultured in the laboratory for a period of time, because they may regulate
their genes differently than they would in the body.
Why does this happen? Because most cells in our bodies are not meant to divide indefinitely,
and none of them are meant to grow in lab dishes. Many tissues, such as blood and skin, rely on
a renewal process that directs cells to stop dividing, differentiate and even die after a period
of time. Proper direction comes in the form of signals from neighboring cells and the environment
in which the cells live.
To make cells grow indefinitely in lab dishes, this process must somehow be put on hold. This
is accomplished by feeding the cells with a liquid medium containing nutrients and growth factor
proteins, which cause the cells to activate genes that promote cell division. In most cases, the
regular signals provided by the cells' normal environment are not all present.
Not all cells respond well to this new living situation. Some will die, leaving only the ones
that are better suited to an environment where indefinite growth is encouraged. After many rounds
of division in a lab dish, the surviving cells may have changed so much that they are unable to
respond to the signals in the body's normal environment. They may even have permanent changes in
their DNA. Putting these cells back into the body is a risky proposal, because they are conditioned
to continue growing rather than differentiating, possibly forming tumors. This is sort of like
taking an animal that had spent its entire life in captivity and returning it to the wild. Would
you expect the animal to know how to act in its new surroundings?
Simulating the body's normal environments in the laboratory is one of the major challenges in
stem cell research, and it is the focus of intensive research efforts around the world. Future
therapies will rely on our ability to manipulate stem cells in a way that will be accepted as
normal by the body.
Supported by a Science Education Partnership
Award (SEPA) [No. 1 R25 RR16291-01] from the National Center for Research Resources, a component of the
National Institutes of Health, Department of Health and Human Services. The contents provided
here are solely the responsibility of the authors and do not necessarily represent the official
views of NCRR or NIH.
Can our cells switch identities?
Recent research has shown that cells originating in one organ can travel to
another and assume the identity of cells at their new location. This phenomenon,
called plasticity, has been demonstrated in model organisms such as mice and rats,
as well as in humans. Types of cells that show plasticity include:
- Bone marrow cells, which have been shown to become liver or kidney
- Brain cells, which have been shown to become blood or muscle
Someday it may become possible to use this plasticity in creating new stem cell
therapies. Right now, however, it is still not clear whether cells that show plasticity
are entirely at home in their new locations. Although they might look like their new
neighbors, scientists don't know whether the traveling cells are truly acting like
cells at their new location.