Cord Blood Cells Proven to Differentiate Into Heart Muscle and Brain Cells
DURHAM, N.C. -- Scientists at the Duke Comprehensive Cancer
Center have scientifically validated for the first time
that stem cells in umbilical cord blood can
infiltrate damaged heart tissue and transform themselves into
the kind of heart cells needed to halt further damage.
Clinical proof of this principle has existed for a decade,
as Duke physicians have used cord blood to correct heart, brain
and liver defects in children with rare metabolic diseases. But
until now they lacked the molecular evidence to prove that cord
blood stem cells were the root of a cure.
Now, the Duke team has dissected heart tissue to confirm the
presence of donor stem cells in heart tissue. Moreover, they
showed that donor stem cells had differentiated into heart
muscle cells called myocytes, which then produced the critical
enzyme needed to halt the progressive heart damage, said
Kirsten Crapnell, Ph.D., a research fellow at Duke.
Crapnell will present the team's findings at the
International Association of Bone Marrow Transplantation
Research meeting Feb. 12-17 in Orlando, Fla.
"We've had convincing clinical evidence that stem cells from
umbilical cord blood extended much farther than the
blood-forming and immune systems, and that they can
differentiate themselves into brain, heart, liver and bone
cells," said Joanne Kurtzberg, M.D., director of the Duke
Pediatric Bone Marrow and Stem Cell Transplant Program. "But
now we have examined heart tissue on a cellular level and
proven that donor cells are not only present in heart tissue,
but they have become heart muscle cells."
To validate the stem cells' activities, Crapnell dissected
and analyzed heart tissue from a 4-year-old boy whose
transplant was successful, but who later died of an infection
before his immune system was strong enough to fight it. The boy
had suffered from a rare metabolic disease called Sanfilippo
Syndrome B, in which the body is missing a critical enzyme
needed to break down complex sugars in various cells. As sugar
byproducts accumulate in vital organs such as the liver, heart
and brain, cells become damaged and die.
Duke physicians had observed that children with these rare
metabolic diseases tended to regain organ function more rapidly
when given cord blood rather than traditional bone marrow. They
theorized that cord blood stem cells, being less mature than
stem cells in adult bone marrow, could more easily adapt to
their new surroundings and respond to signals that
differentiate them into the needed kind of cell.
Indeed, it appears that donor stem cells inexplicably home
in on defective tissue and establish themselves there, as
though they are missionaries recruited to rescue cells in need,
the scientists said. Proof of this principle has come from
various imaging studies which demonstrate that certain organs
regain function after cord blood transplants. But no one had
shown that cord blood cells were actually present in these
organs and the reason behind the improvements -- until now.
Crapnell proved the presence of donor stem cells in the
young boy's heart by searching for aberrant female stem cells
(from his baby girl donor) amid his largely male heart cells.
She used two fluorescent stains to label heart cells as either
male or female. The red stain would be attracted to female X
chromosomes and the green stain would be attracted to male Y
chromosomes. The fluorescent colors would easily illuminate the
gender of each cell.
Crapnell then used two additional antibody stains to test
for cell surface "markers" -- sites on the surfaces of cells --
that indicate what type of cell it is. The first stain had an
affinity for troponin, a protein on the surface of heart cells.
The second stain had an affinity for myosin, a protein on the
surface of muscle cells. Again, she could easily label each
cell as a heart muscle cell or one of another origin.
She found that, although few in number, the female heart
cells were clearly illuminated amid a larger pool of male heart
cells (called myocytes). Just a few donor stem cells are enough
to provide a wide swath of damaged tissue with the enzyme
necessary to restore function, the researchers believe.
CORD BLOOD STEM CELLS DIFFERENTIATE INTO BRAIN CELLS
The same phenomenon is likely at work in brain tissue as
well, said Jennifer Hall, MD, a research fellow at Duke who is
also presenting at the International Association of Bone Marrow
Transplantation Research meeting.
Cord blood transplants appear to halt or slow the
progressive brain damage that is caused by metabolic diseases
such as Sanfilippo Syndrome, Krabbe Disease and Hurler's
Syndrome. Yet precious time is lost as the stem cells traverse
their way from the bloodstream into the brain, where they
eventually engraft and differentiate into the needed types of
brain cells. Meanwhile, children may miss a critical
therapeutic window of treatment.
If scientists could somehow nudge stem cells toward becoming
the needed brain cells, then deliver them directly to the
patient's brain in their differentiated state, doctors could
theoretically spare some patients irreversible brain
So Hall tested the potential of hematopoietic stem cells to
differentiate inside a test tube into specific kinds of brain
cells, called oligodendroctyes. These brain cells are targeted
for destruction in children with metabolic diseases.
Hall cultured a unit of cord blood stem cells in a flask
together with growth factors, hormones and other compounds that
direct stem cells toward the oligodendroctye lineage. One month
later, Hall analyzed the cells under a microscope and found
that 60 percent of them appeared to resemble cells of an
Hall validated her observations by staining the cells with
various antibodies that only bind to and illuminate proteins
unique to oligodendrocytes precursor cells. Similarly, she
stained the cells with antibodies for a host of other cell
types. The presence of unique proteins in a given cell confirms
that it is actively producing that protein, not just that its
genetic code is capable of doing so, said Hall. In this case,
the oligodendrocytes were producing the needed protein or
"The therapeutic goal is to rapidly produce oligodendrocytes
in the lab, and then infuse them into patients soon after
transplant," said Hall. "Delivering cells directly to the brain
could hasten engraftment of the cells and could ultimately
result in repairing of neurologic tissue."
Hall said the potential also exists for repairing spinal
cord injuries and multiple sclerosis, which -- like the
metabolic "leukodystrophies" -- result from deterioration of
the myelin sheath that coats nerve cells.