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Stem Cells Offers New Hope In Various Forms

Posted on: Tuesday, 2 June 2009, 11:43 CDT

The human body is a mosaic of specialized cells that come together like pieces of a puzzle to create a beating heart, a conscious brain, sensuous nerves and the other tissues and organs. Amidst all of these specialized cells exist stem cells – each a blank slate full of potential for developing into pieces of the puzzle that is the human body.

Fundamental properties

All stem cells have three fundamental properties. They are capable of renewing themselves, are unspecialized and can give rise to specialized cells. As stem cells divide to renew themselves (proliferate), they remain unspecialized. Stem cells are not “precut” to fit any specific puzzle (unspecialized). Therefore they cannot work in concert with specialized cells.

However, under the right circumstances, a dividing stem cell can become a specialized human puzzle piece. While this characteristic is common to all stem cells, there are differences that allow us to distinguish between three major classes of stem cells: embryonic stem cells, adult stem cells and cancer stem cells. All three classes of stem cells are being studied at the Baylor College of Medicine STaR (Stem Cells and Regenerative Medicine) Center directed by Margaret Goodell, Ph.D., who is also an associate professor in the BCM department of pediatrics.
Embryonic stem cells
Embryonic stem cells are found in blastocysts, which originate a few days after fertilization. This hollow structure consists of an outer and an inner layer of cells. The inner layer of cells can be harvested to give rise to a line of laboratory-grown embryonic stem cells.

Microscopic image of a blastocysts, Copyright International Society for Stem Cell Research
Once isolated from the blastocyst, the inner layer of cells can be grown continuously in a cell culture dish. Under the right growth conditions, these cells will continue to proliferate and remain unspecialized. After months of continuous proliferation, an embryonic stem cell line is established. These cells are capable of evolving into any specialized cell type existing within the human body (pluripotent). By changing the growth conditions, embryonic stem cells can be coaxed into specializing into other cell types like blood cells, heart muscle cells, nerve cells, etc.

Promise of hope

Daniel Lacorazza, Ph.D
The promise of such work gives hope to individuals with devastating disorders. Embryonic stem cells are considered by many to have the potential to transform “someone who cannot move and breathe to someone who can move and breathe,” said Daniel Lacorazza, Ph.D., assistant professor of pathology and immunology and a member of the STaR Center at BCM.

The use of embryonic stem cells in research in the United States has been controversial from the beginning. On Aug. 9, 2001, then President George W. Bush, by executive order, limited federal spending to a limited number of already established embryonic stem cell lines. Advocates for people with diseases and disorders such as spinal cord injury, amyotrophic lateral sclerosis (ALS) and Parkinson’s disease have lobbied for a change, and recently President Barak Obama announced a change in the executive stance that should loosen restrictions. In some states, including Texas, legislators are attempting to reinstitute bans locally.

Adult stem cells

Like embryonic stem cells, adult stem cells are also unspecialized and capable of becoming specialized cells . However, significant differences exist.

Adult stem cells in very limited numbers are found amongst specialized cells within already developed tissues or organs. For example, stem cells for the hematopoietic (or blood) system can be found in circulating blood and in the bone marrow, but only in small numbers.

Adult stem cells reside in very specific areas of each tissue and do not divide until triggered by disease or damage. In the event of disease or tissue damage, adult stem cells will become specialized cells of their host tissue. In effect, they are a safety net allowing the body to replace damaged or dead tissue cells.

Unlike embryonic stem cells, adult stem cells are much more difficult to maintain in cell culture for extended periods of time and therefore are more challenging to study.

Different kinds of adult stem cells

Not only do adult and embryonic stem cells differ in source and proliferative capabilities, they also differ in the types of cell each can potentially become. Embryonic stem cells can become almost any cell type in the human body, but most adult stem cells are limited to becoming cell types similar to those in the tissue where they reside. Examples of normal adult stem cell specialization include:

Hematopoietic stem cells (blood stem cells found in the bone marrow) give rise to all types of blood cells
Epithelial stem cells of the digestive tract give rise to several cell types found in the digestive tract
Skin stem cells give rise to keratinocytes, the cells that make up most of our skin
Bone marrow transplant
Treatment with adult stem cells is limited to the tissues from which they are derived. For example, bone marrow transplants are the most established and successful stem cell treatment. They involve adult stem cells found in the bone marrow and have been used successfully for more than 25 years to treat conditions like leukemia.

Cancer stem cells

Just as every tissue is thought to retain its own adult stem cell source, several scientists have come to the controversial conclusion that even cancers possess their own stem cells. Cancer stem cells are “found in pockets inside the tumor,” said William Brinkley, Ph.D., Distinguished Service Professor in the BCM department of molecular and cellular biology and dean of the BCM Graduate School of Biomedical Sciences. Cancers were originally thought to arise from cells that had mutations causing uncontrolled growth. The discovery of the cancer stem cell suggests that it is mutated stem cells capable of uncontrolled growth and specialization that lead to the development of cancer.

The cancer stem cell is one that can become any cell type within that cancer. Many cancer treatments target active cells that have already become or are in the process of becoming specialized cancer cells. The inactive or unspecialized cancer stem cell is more resistant to chemotherapy and can lead to relapse of disease after treatment. Since the first cancer stem cell (from blood cancer) was identified in 1997, cancer stem cells have been found in many forms of cancer including, but not limited to, brain, breast, ovary, prostate, colon, lung and bladder cancers.

By studying cancer stem cells scientists will learn more about where these cells come from and how they are different from other specialized cancer cells. This information could allow medical experts to be more precise in their diagnosis by determining the differences between easily treatable cancers and those that are more aggressive. Scientists could also identify new cancer treatments targeted to kill cancer stem cells and prevent relapse of disease.

Stem cell controversy

Stem cell treatment is considered one of the most hopeful strategies for treating debilitating diseases like spinal cord injury, multiple sclerosis, Parkinson’s, Alzheimer’s and much more. Researchers hope that by introducing new stem cells to the damaged or diseased area that they can encourage growth of new specialized cells of the afflicted tissue, effectively regenerating healthy and functional tissue. Most research in the U.S. has focused on treatments using adult stem cells, but will soon expand to treatments using embryonic stem cells. While there is much furor over the latest move to make federal funds available for studying embryonic stem cells, Brinkley said the promise is real and that hope cannot be denied.

“Until you’ve walked in the shoes of these patients, you can’t understand the impacts these breakthroughs could make,” he said.

The topic of embryonic stem cell research is one filled with controversy and compromise, and has been ongoing in the U.S. since the mid-1990s, when it first became possible to grow such cells in culture. Supporters feel this research could greatly enhance medical treatment for several currently incurable debilitating diseases, while those opposed believe it immoral to destroy the inner layer of cells from an embryo capable of becoming a human life.

Studying embryonic stem cells requires that the blastocyst development be halted and redirected from becoming a human life to establishing a cell line. Opponents feel that life begins at fertilization and the destruction of a 5-day-old blastocyst is the equivalent of murder. However, some scientists disagree because, without implantation into a woman’s uterus, a young blastocyst alone is incapable of becoming a human life. This is not a question answerable by science, and whether one supports embryonic stem cell research or not is ultimately a personal and private decision.

Many in the field of science and those who advocate for patients with deadly diseases see embryonic stem cells as offering an important avenue of promise for treatments and even cures.

Political history

The U.S. political stance on stem cell research began when President Clinton signed the Dickey Amendment to the Labor, Health and Human Services, and Education Act of 1996 banning the use of federal funds for research that would create, damage or destroy human embryos for research purposes. In 2001, President George W. Bush restricted federally funded research to the use of existing embryonic stem cell lines. During his presidency, the House and Senate passed bills that would have loosened those restrictions, but Bush vetoed them. The recent Executive Order by President Barak Obama loosens restrictions even further, but the limits of the Dickey Amendment continue to stymie research.

Adult stem cells have promise in many fields and there are no restrictions on the use of federal funds for studying them. However, many in the field feel that the limits of adult stem cells make it imperative that embryonic stem cells be studied as well.

President Obama’s Executive Order to rescind the ban on federal funding for embryonic stem cell research is the first step in moving embryonic stem cell research forward in the U.S. The late Michael E. DeBakey, M.D., no stranger to controversy himself, believed that as soon as there’s a breakthrough in stem cell research, the controversy will die away.

President Obama is a supporter and co-sponsor of the Stem Cell Research Enhancement Act of 2007. This Act would support research of human embryonic stem cells from embryos donated from in vitro fertilization clinics that may otherwise be discarded. The criteria for using these embryos for research would include gaining informed consent from patients to whom the embryos belong and ensuring the embryos are deemed in excess and were created solely for the purpose of fertility treatment.

The Stem Cell Research Enhancement Act would reach yet another compromise by allowing researchers in the U.S. to expand embryonic stem cell research while prohibiting scientists from creating or cloning embryos for research purposes. Under the current administration, scientists may finally have the chance to dissolve the controversy with breakthroughs in treatments using stem cells.


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