Stem Cells Abroad

by Margaret Wahl on Tue, 2009-09-01 11:21

Why you probably should resist the lure of cures in faraway lands

Stem cells are a legitimate and exciting area of ALS research, and MDA is actively exploring the potential of these cells.

Stem cells that are too undifferentiated (immature) can be unpredicatable and dangerous, while those that are too differentiated (mature) are no longer able to engraft. Bottom line for the medical consumer: Buyer beware.

As of fall 2009, there are no stem cell-based treatments for ALS that are known to be either safe or effective. Unfortunately, that doesn’t stop foreign clinics from offering them.

You don’t have to do much searching these days to find advertisements for treatments using stem cells in India, China and Eastern Europe. Some even mention ALS specifically. It’s hard to resist the lure of a possible treatment or even cure for a disease as devastating as ALS, but there are some questions you should ask before packing your bags.

What kind of stem cells are they using?

The first question to ask is, what does the clinic mean by “stem cells”?

The answer may not be clear, and it may not be entirely truthful.

Even in the United States and Western Europe, the definition of stem cell is unclear. Mature, fully developed, specialized cells, such as those of the nervous system, muscles, liver, skin, etc., come from (“stem” from) less developed, less specialized cells. The term “stem cell” has been used to describe cells in various stages of development, from the most primitive and flexible cells to cells that are well along the path of becoming a specific kind of cell.

Human embryonic stem cells, taken from human embryos at a very early stage of development, are completely undifferentiated, meaning they have the potential to become any type of cell. That’s logical, because an embryo is formed from only two, merged cells — an egg from a woman and a sperm cell from a man — but every tissue subsequently develops from it.

Cells with the suffix “blast” are generally well advanced in the process of differentiating into specific types of cells. Myoblasts are well on their way toward becoming muscle, osteoblasts toward becoming bone, and lymphoblasts toward becoming blood cells known as lymphocytes.

Stemlike cells appear to exist along a continuum of development. For instance, the satellite cells that lie near muscle fibers are less differentiated than myoblasts but more differentiated than embryonic cells. Under certain circumstances, such as when muscle repairs are needed, these satellite cells divide into two cells, one remaining a satellite and the other differentiating into a myoblast.

Until recently, scientists thought the human body harbored no precursors to nerve cells (the main type of cell affected in ALS) after the initial development of the nervous system. Today, we know that’s not true. However, stemlike cells in the nervous system are extremely rare.

A cell that’s too far along in its journey toward becoming, say, a motor neuron (a nerve cell that controls muscle), probably won’t integrate into existing tissue. On the other hand, one that’s not mature enough may not develop into the desired tissue type.

For obvious reasons, a cell that’s on its way to becoming a type of tissue that’s not desired (bone, for instance, instead of nerve) could be a disaster.

Scientists don’t yet fully understand what signals are needed to coax cells to become what they want them to become, although a lot of progress has been made in this area.

What are the risks of stem cell treatments?

Treatment failure: The most likely outcome is simply that the treatment won’t help. If you don’t mind spending many thousands of dollars and doing a lot of traveling without any therapeutic benefit, that may be an acceptable risk. However, you might enjoy a trip to China more without the treatment, while avoiding more serious possible outcomes.

Tumor formation: Malignant tumors come from cells that are incompletely differentiated and lack the regulatory controls on growth that mature, fully differentiated cells possess. Tumor formation is a definite risk when transplanting undifferentiated cells into a patient.

Quality control varies in foreign clinics.

Immune system rejection: If the cells being transplanted come from another person or another species, there’s a strong possibility that the immune system of the recipient will reject them. At best, that means the cells won’t survive, and time, money and effort will have been wasted. At worst, a life-threatening immune response (such as what people allergic to bees experience when stung) could occur. In between are other types of harm, such as development of a chronic autoimmune response to the new cells and the tissues in which they reside.

Infection: It's highly possible for cells used for transplantation to carry viruses or other pathogens from their human or animal sources or to acquire them while they’re being grown in a laboratory where less-than-stringent procedures are in place. A recipient of contaminated cells faces the possibility of serious disease or even death. Also, any surgical procedure, in and of itself, always carries a small risk of infection.

Why are conditions like spinal cord injury and bone marrow cancers better candidates for stem cell treatments than ALS?

Lack of understanding of the disease: Unfortunately, the ALS disease process still is not well understood. It’s unknown whether transplanted cells would meet the same fate as the patient’s original nerve cells. Spinal cord injury and bone marrow cancers are well understood compared to ALS.

ALS affects a larger area: Despite the devastating effects of spinal cord injuries, the area of tissue damage in most injuries is extremely small compared to that in ALS. It’s easier to patch a small defect like a spinal cord injury than to repopulate multiple areas of the central nervous system with new cells, as would be needed to correct the ravages of ALS.

Intricate, extensive connections: In addition to its sheer size, the connections in the motor nervous system between nerve cells and other nerve cells, muscle fibers, and support cells (glia) are specific and complex. There’s some speculation that certain types of stem cells may “know” how to connect to other cells once they’re in the right place, but that’s far from clear.

These types of connections also are important in repair of spinal cord injury, but there aren’t anywhere near as many of them to make. In other conditions, such as bone marrow cancers, these connections aren’t relevant.

What is MDA doing about developing therapies for ALS using stem cells?

MDA’s Venture Philanthropy (MVP) program is consulting experts in this field, with the goal of developing clear guidelines for judging which stem cells proposed by various biotechnology companies have the best therapeutic potential for ALS.

The anticipated guidelines will include criteria for judging laboratory data on the efficacy and safety of the proposed therapy; criteria for assessing the proposed methods of manufacturing, expanding and purifying the stem cells; and the safety and feasibility of conducting clinical trials using the proposed cells.

Margaret Wahl
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