The regenerative capabilities of stem cells are a big draw for researchers trying to use them to cure diseases. But there are many hurdles to be crossed to translate scientific euphoria into economically feasible reality.
A blind pastor in Mountain View, North Carolina, regains 20/20 sight in one eye. A Korean woman who has not walked in 20 years because of a spinal cord injury walks with the aid of a walker. Every fourth person in India has reason to hope that damage wrought by a sweet tooth can be corrected. Have these people found the elixir of life?
Not quite, yet. They have found what stem cells can do.
The story begins with an egg and a sperm. Three to five days after a sperm and an egg get together in fertilisation, an early embryo (called blastocyst) is formed. Blastocyst is a microscopic ball of cells at the top with a hollow middle and a clump of 30 cells or so within, at one end.
All cells of tissues and organs such as the heart, lung, liver, kidney and skin of the growing foetus stem from these cells. Hence their name, stem cells - embryonic stem cells, to be precise.
As stem cells, however, they cannot pump blood though the body like a heart muscle cell or fire electromagnetic signals to other cells like nerve cells. They do not have the tissue-specific structures that make them specialise as a heart, nerve, kidney, lung or a skin cell. When they receive the right signals, however, they spontaneously develop into cells of a specific tissue or organ. This process is called differentiation.
Stem cells renew themselves without inhibition. They multiply through the same process of cell division that all cells in our body do but with a difference - they can keep going for ever. This is called proliferation. Embryonic stem cells have known to multiply for over a year in culture dishes in laboratories, faithfully reproducing stem cells that retain their integrity. A starting population of stem cells that proliferates for many months in the laboratory can yield many millions of stem cells.
Years of research on mice and other animals has led scientists to get at these stem cells - precursors to every organ in the human body. If they can get them to proliferate in the laboratory under controlled conditions, if they can decipher the signals that push these cells into an area of specialty such as a heart or a lung cell, if they can transplant these cells into a patient to replace the cells that are not functioning well, and if they can make sure the immune system of the patient will not reject their carefully prepared transplant - the "ifs" are plenty, which, in itself, is a lure for scientists.
But the potential use of stem cells and their regenerative capabilities is a big draw for such eminent researchers as Dr. Philip Schwartz, Director of the National Human Neural Stem Cell Resource at the Children's Hospital, Orange County, California, and Dr. Hwang Woo-Suk of Seoul National University, Korea.
Although work on human embryonic stem cells is relatively new, for over 30 years they have been used in treating cancer. These are stem cells present in the bone marrow of adults, the origin of which is still contested. They may be remnants of embryonic stem cells but are not found in all tissues or organs. While embryonic stem cells grow as a compact colony, adult stem cells are individual cells residing alongside specialised cells of the tissue.
For long, it was believed that adult stem cells could only be found in the bone marrow and the skin acting as cell reserves in the tissue, primarily replenishing dead, non-functional or diseased cells. Now, adult stem cells have been found in several other tissues such as the brain, the peripheral blood vessels, the skeletal muscle, the skin, the intestines and the liver.
There are only a few of them in each tissue. They are less easily swayed into becoming cell-types of tissues other than the ones in which they reside. Of late, scientists have discovered some flexibility in adult stem cells too. Blood-forming stem cells in the bone marrow can become brain and heart muscle cells, liver stem cells can be made to produce insulin, and so on. This "plasticity" has raised hopes in researchers of using adult stem cell transplants to cure diseases.
The obvious advantage is if the stem cells come from the patients themselves, chances of the body rejecting a transplant are slim to non-existent. On the flip side, there are not that many stem cells in mature tissues and growing them in the laboratory without letting them specialise is difficult. Not to mention prodding them into a cell type that you want.
Despite this or because of it, adult stem cell research is a happening field these days. Especially considering that embryonic stem cell research has run into stormy weather.
Embryos are good sites for stem cell harvesting, especially multi-potent (or as they say in the field, pluripotent) ones. But, getting at these stem cells was a challenge until 1988 when Dr. James Thomson from the University of Wisconsin, Madison, succeeded in isolating and culturing human embryonic stem cells.
To get these stem cells, embryos are needed. They are not derived from eggs fertilised in a woman's body. To get embryos, the source is a fertility clinic. In-vitro fertilisation has long been used to overcome infertility issues. In-vitro, literally, means "in glass".
"The egg and the sperm are joined together in a culture dish and in specific, careful, culture conditions, cell division is allowed to take place and the embryo develops," explains Schwartz. Embryonic stem cells are found within the blastocyst, a three-to-five-day-old embryo. These embryos, when not used, are donated for research purposes with the informed consent of the donors.
"The inner cell mass from the hollow (of the blastocyst) is removed and then cultured. And that removal, of course, kills the embryo. The embryo is no longer viable after that," points Schwartz.
This is where the battle-lines are drawn. There is stiff opposition, especially in the West to the idea of killing an embryo, since these embryos are fully viable and would lead to foetuses and children if left unmolested. There is an embryo-adoption programme in the United States called the Snow Flakes programme. They have some 75-100 babies born from embryos adopted from in-vitro fertilisation clinics.
"And one of the things that it clearly shows is that those embryos can make babies. They are not just a ball of cells - they are cute little people. So, advocates of human embryonic stem cell research have to pause to consider closely what these people are talking about because they are faced with such graphic examples of these little kids running around," says Schwartz.
In Schwarz's opinion it is unfortunate that the issue has divided people into two camps at the opposite ends of the spectrum. He thinks that there is a lot of middle ground. Those advocating embryonic stem cell research need to be sensitive to emotions of people who find killing embryos objectionable. At the same time, Schwartz thinks people on the other side of the line should be better educated about the research programme and what it can do.
WHAT can embryonic stem cell research do?Today, every newspaper has advertisement space for patients seeking organ and tissue donors. Solicitations appear on television and radio too. Donated organs and tissues are used to replace ailing or destroyed tissue, but the supply is much too limited and the demand skyrocketing. If embryonic stem cells can be successfully directed into forming cells of specific tissues, they offer a source of replacement cells and tissues to treat diseases such as Parkinson's, Alzheimer's, spinal cord injury, stroke, heart disease and diabetes.
Researchers like Schwartz, are also looking at using stem cell transplants to cure metabolic diseases. These diseases are rare but definitely in the realm of what stem cells can cure.
Metabolic defects and diseases are caused by the body's inability to process some bio-molecules. Canavan's and Krabbe diseases are examples of this and are fearsome because they strike very young. In a child with Canavan's disease, the brain cells stop producing an enzyme called myelin, which is essential for the brain to function properly.
"If you can just imagine the brain as made up of a bunch of wires and if the insulator is missing, all the wires will short-circuit. And that is exactly what the myelin does - it acts as an insulator of these wires and in the absence of that, the brain works poorly, if at all," explains Schwartz. One idea to cure this is to make new myelin-producing cells to simply wrap the wires that the brain has, he adds.
Krabbe disease is another such affliction, especially in kids. It is a nasty disease in which children miss an enzyme critical to forming the myelin sheath. Though born looking normal they have this rapid down-hill course when they start to lose all cognitive and motor functions and die by two years of age. Research done by Dr. Joanne Kurtzberg and her colleagues at Duke University, North Carolina, U.S., has shown that stem cell transplants can certainly help these kids.
There is growing evidence that stem cell transplants can save children with more than 45 such fatal diseases that are caused by the deficiency of a specific enzyme.
All this is exciting, but immortality is elusive. Several kinks have to be straightened, processes understood, and technology invented to translate scientific euphoria into economic feasibility.
How to get the stem cells out of embryos (obtained from in-vitro fertilisations) has been worked out. How to make them multiply in petri dishes has been figured out barring some issues with contamination from animal cells and components needed to do the culture. How to direct the millions of stem cells you have generated into doing what you want them to do? This is work in progress.
How do you mimic the signals the body uses to direct stem cell differentiation? What are those signals? There is a set of in-house instructions for cells - a section of the DNA code that defines the role of any given cell. Then there are intra-cell communications too that define the specific action of a cell. Are these signals tissue-specific?
"Our understanding of those very early processes of differentiation is still pretty little and so is our research to figure out what signals trigger off a particular differentiation path," says Schwartz. "The human embryo develops from a single cell and develops in three-dimensional space. The whole process is driven to form a human being with all its body parts and what we are doing is taking out a group of those cells and popping it in a culture dish under abnormal growing conditions in a two-dimensional shape and we are trying to get it to do the same thing. And, this is very difficult".
If you do get the stem cells to take on identities you want them to, how do you transplant them? Transplant rejections are not uncommon. It is the body's own defence mechanism, after all - the immune system rejecting foreign cells. How does one get around this? Hwang managed to do just that.
He took cells (skin cells from skin biopsies) from the patients themselves and removed the nucleus from them (enucleating). The nucleus in a cell contains the genetic material - a blue-print of the patient's body. This nucleus is then put into an enucleated egg from a donor. By electrical and chemical prodding of this egg, he got it to divide and turn into an early human embryo. This is the process of cloning - therapeutic cloning through nuclear transfer.
The first time he tried this, last year in February, Hwang worked through 242 eggs to create one line of embryonic stem cells. "This time, with marked improvement, we needed 16.8 oocytes (eggs) for one stem cell line," he says. "The number," he is confident, "can be further reduced in future studies." Hwang has used cells from patients of different demographic types - children, men, women, and so on and has been able to generate 11 different stem cell lines in this process.
Since the stem cells generated this way contain the patient's genetic material in them, the risk of transplant-rejection is minimal to non-existent.
That problem is taken care of. It is one down, but how many more to go? Or yet to come?
IN February last year, Hwang and his colleagues in Seoul University first published their work in Science. Appreciation of a scientific breakthrough in this field of embryonic stem cell research was buried under vehement protests on moral and ethical grounds, primarily from the West. A man declared a scientific hero in Korea, Hwang has been chastised for his work by several prominent people in the West, President Bush included.
For people who consider harvesting embryos immoral, creating them in the first place is akin to playing God. Hwang disagrees. "Our experiment is generating stem cells to cure patients with incurable diseases," he says.
If the stem cells are not removed (thus killing the embryo), is this embryo capable of forming a human being? "Our experiment is to create stem cells. Please do not say `killing of embryo'. We are generating nuclear transfer constructs, not embryos. Our experiment focusses on generating embryonic stem cells," replies Hwang. An exercise in semantics or spoken like a true scientist?
But, one cannot wear blinders, according to Schwartz. "Clearly the people that are for embryonic stem cell research need to recognise that the embryo is in fact being killed to make the stem cells and need to recognise that there is a significant number of people that find that objectionable. Simply dismissing it or casting it afloat so that you get 51 per cent of the vote that says you can, may not be an appropriate way of doing this in these important issues. Perspective is really important."
Apart from moral and ethical concerns, there may be other practical problems to deal with. To clone embryos, you need eggs. To get these eggs, you need women who are willing to subject themselves to oval stimulation and surgical manipulation. "Let us say you can create one embryonic stem cell line off 10 eggs, which is about the average for one woman with one of these cycles of oval stimulation. And that is only for one patient. In this country (the U.S.), it is estimated that there can be between 10-15 million people that can benefit by stem cell treatments. Where will all the women come from?" asks Schwartz.
In the U.S., young women in college have been recruited and paid $2,000-3,000 to step through the procedure to donate eggs. "Need money, have eggs," may make business sense to poor women in the U.S. and the world over. Stem cell treatments, with current science and technology limitations, may well be for the rich because, "if you look at how much it is going to cost to set up a custom-made embryonic cell and then to do the transplant and the typical processes involved in that - it will be quarter of a million dollars," says Schwartz.
This may also be a cultural issue. In Korea, which is fast becoming a hub of embryonic stem cell activity, thanks to Hwang, eggs were donated without payment and donors are informed before hand about this. Women do not think it wrong to donate their eggs for curing diseases. In an interview with The Korea Times, Hwang said: "If I were a woman, I would definitely donate my eggs to scientific research without hesitation."
Ask him about the costs involved and he replies like a scientist, "I don't want to estimate cost. I will do my work."
Plenty of work there is to do. To stem or not to stem may well be answered by how well science can decipher the secrets of a tiny embryo.
