For the first
time, scientists have coaxed human embryonic stem cells into becoming three-dimensional
tissue structures, a breakthrough that could pave the way for regenerating
organs and tissues to replace those damaged by disease.
The research
has stirred up excitement among tissue-engineering scientists that likely
will spill over to biotechnology companies seeking to capitalize on the
organ and tissue replacement market, which by some estimates could exceed
$25 billion worldwide.
A method of
regenerating damaged organs and tissues would be invaluable not only for
patients but also for reducing healthcare costs. Surgical transplantation
-- the current standard method of repairing failing organs and tissues
-- accounts for nearly half of total healthcare expenditures, amounting
to more than $400 billion per year in the United States alone, according
to some estimates.
Embryonic stem
cells hold great promise as a source of new organs and tissues because
they have the unique ability to develop into all the different tissues
in the body -- at least in a lab dish. But scientists have found it difficult
to induce the cells to develop into specific 3-D structures, such as the
heart and liver.
The new research,
which was published this week in the online edition of the Proceedings
of the National Academy of Sciences, helps overcome those problems and
shows it is possible to channel the development of the stem cells into
3-D structures of interest.
Using carefully
constructed scaffolds for the stem cells to grow on, a team led by Robert
Langer of the Massachusetts Institute of Technology in Cambridge succeeded
in forming liver, cartilage, nerve and blood vessels. The tissues also
appeared to function normally when implanted under the skin of mice, although
they were not used to replace damaged tissues.
"This is the
first time people have been able to make 3-D tissue structures using human
stem cells and polymer scaffolding," Langer told United Press International.
"It's great,"
Jennifer Elisseeff, an assistant professor of biomedical engineering at
Johns Hopkins University in Baltimore, said of the study. "This is really
what the field of tissue engineering needs to move forward," she told UPI.
Elisseeff noted
tissue-engineering scientists "are really excited about this." Numerous
studies were presented on this topic at a recent biomedical engineering
meeting and forthcoming research will describe using scaffolding and stem
cells to generate tissues that could prove useful for treating diabetes,
she said.
The composition
of the scaffolding material is essential to ensure the correct development
of the cells. The material cannot induce an immune reaction by the body
because the goal is to transplant the structures into patients, so the
substance has to degrade in an appropriate way as the cells grow and fill
in structures.
Langer's team
used 3-D scaffolding composed of biodegradable polymers and placed growth
factors in the structures to cue the human stem cells to develop into the
desired tissues. Growth factors are substances produced by the body that
help guide tissue development. Each tissue or organ has its own unique
set of growth factors.
After two weeks,
the primitive tissues were then transplanted under the skin of mice where
they continued to develop and integrate with blood vessels, suggesting
the technique could be used to give rise to tissues that will function
inside the body, Langer said.
Langer hopes
the scaffolding will lead the way to using stem cells to grow replaceable
organs, but he noted longer studies will be needed in advanced animal models,
such as pigs and primates, to ensure the organs are safe and functional.
"It's still early and there's a lot of research we need to do," he said.
Robert Spiro,
vice president of research and development at Isto Technologies -- a St.
Louis biotech company focused on developing products that can regenerate
human tissues -- said there is "a coming wave from industry" in the next
3-5 years of tissues grown from stem cells and scaffolding.
The first applications
will be bone and skin because these tissues already have inherent regeneration
capabilities, "so it's a little easier to stimulate or augment," Spiro
told UPI.
Growing entire
organs outside of the body is "still pretty far away," Spiro said. "Most
of the push is implanting these tissues and getting the regeneration to
occur at the site inside the body," he said.
David Mooney,
a tissue-engineering professor at the University of Michigan in Ann Arbor,
called the study "an important advance." The work may not lead immediately
to growing whole organs outside the body, but it could help scientists
learn how to generate parts of organs or tissues, which may be beneficial
as well, Mooney told UPI.
Growing entire
organs is "the grand slam home run in the bottom of the ninth inning" in
the field of tissue engineering, he said, but there are many steps in between
that will have benefit, such as regenerating heart valves, blood vessels
or portions of bone.
"You don't need
to recreate the entire organ," Mooney said. "If you can regenerate a portion
of it, that would make a difference in saving lives." In addition, the
ability to regenerate tissues in the lab could give scientists insight
into the mechanisms and biology involved in that process. This, in turn,
could lead to new therapies, he said.
--
Copyright 2003 by United
Press International.
All rights reserved.
|
