Sweet Success Embryonic Stem Cells and the Treatment of

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					Sweet Success? Embryonic Stem Cells and the Treatment of Type I (Insulin Dependent)
                               Diabetes Mellitus

                                     By Gordon Burke

                                    December 23, 2004


       One of the great scourges of the twenty-first century is Type 1 (insulin dependent)

diabetes mellitus (IDDM). Around one million Americans suffer from this disease

(Spiegel, 2003) and the incidence has increased sharply in the western world since 1950

(The Rise, 2003). The only established treatment for IDDM, exogenous insulin delivered

by injections or pump, is imperfect and does not reliably prevent complications and

premature death (Spiegel, 2003; Diabetes Myths, 2003). Many of the sufferers are babies

and children. In the hope of reversing this terrible human toll, researchers funded by the

Juvenile Diabetes Research Foundation and other groups have been searching for a

means of prevention and cure. One of the most promising avenues is through human

embryonic stem (hES) cells, which can theoretically be manipulated to produce any cell

in the body and therefore replace the patient’s own cells which have been destroyed by

accident or disease. Stem cell researchers believe that IDDM offers an excellent prospect

for the “holy grail,” the cure of a human disease through hES cells, because the disease is

caused by the death of a single cell type, the β-cell (Shaw 2004). In theory, these cells

could be replaced by new β-cells grown from hES cells. However, there are serious

obstacles to this outcome, including the scientific, political, and financial. This paper

will review the biology of IDDM, its possible causes and prevention, the current status of

hES research in the United States, political activism by the IDDM community on behalf
of hES research, and recent studies shedding light on the potential of hES cells to cure

this devastating disease.

        IDDM results when the immune system of the body attacks and destroys its own

pancreatic beta cells, the cells that produce endogenous insulin. Without these cells, the

patient is unable to metabolize carbohydrates, including sugar; sugar builds up in the

tissues, and the untreated patient will die of the disease. Although taking insulin will

keep the person alive, it doesn’t cure IDDM, nor does it necessarily prevent

complications (Diabetes Myths, 2003), including retinopathy leading to blindness,

amputations due to circulatory problems, kidney disease, and neuropathy affecting

various systems of the body (Diabetes Complications, 2003). Some patients, called

“brittle diabetics,” never achieve good blood glucose control despite strict adherence to a

treatment regimen (Diabetes Myths, 2003). Could patients live with donor transplant

cells? Cadaveric islet cell transplantation, the so-called “Edmonton Protocol,” has thus

far achieved mixed results. Around 100 diabetics are now living free of insulin injections

thanks to these transplanted cells, but they are required to take immunosuppressive drugs

with serious side effects of their own; also, there is a shortage of islet cells available for

transplant (Diabetes Myths, 2003; Spiegel, 2003). Clearly, more research is needed to

find better treatments and hopefully a cure.

   One investigative strategy is to search for the causes of IDDM in the hope that better

understanding may lead to more effective therapy. This has proven to be challenging

because the causes are complex, both genetic and environmental. Unlike some human

illnesses potentially treated by hES cells, such as muscular dystrophy, IDDM isn’t caused

by a single gene (Researchers Find, 2003; Shaw, 2004). “Instead, around 19
chromosomal regions are associated with the risk for developing diabetes, and within

these regions, only two types of genes had been identified with confidence” (Researchers

Find, 2003). IDDM and other autoimmune illnesses tend to cluster in families. Based on

this knowledge, John Todd and his research team searched for a susceptibility gene by

analyzing the DNA from a large number of autoimmune patients, humans without

autoimmune illnesses, and mice suffering from the “mouse model” of IDDM. In diabetic

humans and mice, there was a variant in “the gene that encodes the CTLA4 protein”

(Researchers Find, 2003). Without sufficient levels of this protein, the immune response

will attack the body’s own tissues. To learn more about the genetic factors in IDDM,

researchers are collecting genetic material from a database of 7,500 families (Spiegel,

2003). Genetic factors aren’t the only cause—there are sets of identical twins where only

one develops IDDM (Shaw, 2004).

   Environmental “triggers” are also under investigation. The incidence of IDDM has

been rising since 1950 in populations without any major genetic change, which is

evidence that some recent environmental influence may be a causal factor. These factors

must begin acting on patients early in life. Among the possible environmental causes are

more rapid childhood growth, early exposure to cow’s milk, and improved hygiene,

which leads to a lower rate of childhood infections and, at least in theory, to a less

“mature” and discriminating immune response. There is evidence in both human and

mouse models to support this still unproven “hygiene hypothesis” (The Rise, 2003). To

tease out the relative importance of genetic and environmental causes, two longitudinal

studies are ongoing, TEDDY (The Environmental Determinants of Diabetes in the

Young) and TRIGR (Trial to Reduce the Incidence of Type 1 Diabetes in the Genetically-
at-Risk). TEDDY is following a group of infants born with high genetic risk of IDDM to

see whether environmental factors correlate with development of the disease; TRIGR

focuses on dietary factors in high-risk babies. At this time, non-genetic causes remain

poorly understood despite their obviously high importance for development of the

disease.

   What about efforts to prevent IDDM? Ideally, it wouldn’t be necessary to restore

blood glucose control, because the immune response could be stopped from destroying β-

cells in the first place. Unfortunately, there are ethical problems with prevention trials.

Thus far, no preventive treatment is known to be free of side effects, nor is it possible to

be certain who will actually come down with the disease. Also, targets of preventive

efforts would be children who would be exposed to potentially risky preventive therapy

over time (Diabetes Prevention, 2003). Not surprisingly, no surefire preventive strategy

has been developed for IDDM. Current trials focus on identifying people who are at high

risk and/or may have already starting losing β -cells although they are as yet symptom-

free. These patients are treated with low-dose insulin, sometimes administered orally or

nasally. This approach has yet to achieve definitive results (Diabetes Prevention, 2003).

As part of TRIGR, a study group of infants is receiving an experimental formula to

investigate whether avoiding exposure to cow’s milk proteins can prevent the disease

(Diabetes Prevention, 2003). At this time, no method is known to prevent the onset of

IDDM.

   With its uncertain cause, devastating consequences, inadequate treatment, and non-

existent preventive strategies, Type 1 Diabetes cries out for a breakthrough therapy and

cure. Many in the IDDM community have placed their hopes in the hES research to
provide the functioning β-cells that would restore normal glucose control and thus cure

the disease. Embryonic stem cells have two main sources: 1) week-old human embryos

discarded by in vitro fertilization clinics, and 2) somatic cell nuclear transfer (SCNT) or

“therapeutic cloning,” in which an unfertilized egg is injected with the intended

recipient’s DNA to create immune-compatible transplant cells (Kessler, 2004; Brown,

2004). In both cases, harvesting stem cells destroys the embryo or clone. “Pro-life”

activists object to the use of embryonic stem cells because they believe that destruction of

an embryo is the same as killing a person; they also think that therapeutic cloning is

“playing God” and destroying a potential life (Kessler, 2004; Brown, 2004; Wills, 2004).

Supporters of stem cell research counter-argue that “actual human life begins in the

womb or at certain stages of reproduction, but not in a Petri dish at eight or 12 days,” in

the words of Illinois State Senator Kirk Dillard, explaining his vote in favor of a proposal

that would endorse embryonic stem cell research in Illinois under certain guidelines

(Wills 2004).

   In August 2001, President Bush weighed in on the controversy by restricting federal

funding to research on hES cell lines already in existence by August 9, 2001. This way,

there would be no federal support for destroying any additional embryos (Embryonic,

2003). At the time, it was believed that there were over 60 existing stem cell lines, but in

fact only around 11 have proven to be usable (Embryonic, 2003). The effect of the

president’s ruling has been to drastically restrict hES cell research in America and

possibly to drive researchers into other countries that do support the research (Drazen,

2004).
   In the absence of significant federal funding, stem cell research advocates have turned

to private organizations, such as the Juvenile Diabetes Research Foundation, and state

governments to finance this research. Thus far, only two states, New Jersey and

California, have actually passed legislation authorizing embryonic stem cell research

(Chase and Gorner, 2004). In California, $3 billion in tax-exempt state funds were

approved by Proposition 71, which passed on November 2, 2004 by a 59-41 percent

margin (Broder, 2004). In Illinois, a bill to endorse but not fund stem cell research was

passed by the state House, but defeated in the state Senate by two votes (Wills, 2004).

Pro-stem-cell research Illinois State Senator Dan Hynes has countered with a proposed

statewide referendum to authorize as well as fund the research by a tax on cosmetic

surgery. He believes the measure would pass since the majority of Americans favor

embryonic stem cell research (Chase & Gorner, 2004).

   The IDDM community has been active in promoting hES cell research, both through

fundraising and involvement with the legislative process on the federal and state levels.

Representatives of the Juvenile Diabetes Research Foundation have testified before

Congress in support of the research, and their Position Paper opposes current federal

funding restrictions (Embryonic, 2003). The activism of the JDRF and similar disease-

related groups has borne fruit in pending federal legislation, “The Stem Cell Research

Enhancement Act of 2004,” H.B. 4682, which now has 191 co-sponsors in the U.S.

House of Representatives (Stem Cell Legislative Update, 2004; U.S. House, 2004). The

proposed Act would increase federal funding beyond the limits imposed by President

Bush. At the state level, diabetes patients, family members, and their doctors worked

with other disease-related groups to pass California’s Proposition 71 (Broder, 2004). In
Illinois, House Republican Leader Tom Cross supports hES cell research in the hope of a

cure for his daughter’s diabetes (Chase & Gorner, 2004).

   Opponents of embryonic stem cell research claim that adult stem cells can cure

diseases without destroying embryos (Kessler, 2004). New research tends to refute that

possibility in the case of IDDM. According to the results of a study published in Nature

by Dor et al. (2004), “embryonic stem cells are currently the only type of stem cell that is

unquestionably capable of differentiation into β-cells.” These findings have redoubled

the commitment of the JDRF to supporting embryonic stem cell research (Stem Cell

Research, 2004).

   How might embryonic stem cells actually aid in the treatment and cure of IDDM?

The most obvious method is by using them to create healthy β-cells for transplantation

into the patient, but transplantation is not the only use for hES cells in medical research.

Embryonic stem cells containing certain genetic defects, including a predisposition to

develop IDDM, could be studied to better understand the biological basis of the disease

and even test medications. These cells might come from embryos produced in fertility

clinics or derived from patients through therapeutic cloning. In IDDM, “as embryonic

stem cells develop into immune cells, researchers could look for differences between

these immune cells and those of someone without Type 1 diabetes. These differences

could provide insights into the mechanism of type 1 diabetes and offer new ways to test

drugs or therapies in their earliest stages, thereby speeding the process toward human

clinical trials” (Global Conference, 2004).

   Of course, researchers are striving toward the “holy grail” of replacing the destroyed

β-cells and thereby curing the patient. Harvard researcher Douglas Melton, father of two
diabetic children, explains one method: beta-cells obtained from directed differentiation

of stem cells from an embryo would be injected into the patient in a variant of the

Edmonton protocol. To prevent rejection, researchers hope to create a device that would

“encapsulate it [β-cell tissue] in a Gore-Tex-like membrane that would allow glucose and

insulin, but not immune cells, to pass through” (Shaw, 2004).

   To a different solution to the problem of rejection, researchers also hope to create β-

cells “custom-made” for the patient through SCNT or “therapeutic cloning” (Shaw, 2004;

Lanza & Rosenthal, 2004). First performed by Hwang et al. (2004), this procedure would

generate stem cells by injecting an egg with a nucleus containing the patient’s own DNA.

Many technical obstacles still exist toward actually carrying out this procedure to treat

patients with an illness such as IDDM. Potential hazards include the creation of

teratomas through uncontrolled differentiation of stem cells (Lanza & Rosenthal, 2004).

Lanza and Rosenthal (2004) also discuss the potential for even more innovative stem cell

therapies that would avoid the problem of tissue rejection, such as directing the patient’s

already existing cells to revert from “terminal differentiation” to “stemness” and

transformation into the type of cells needed by the patient.

   Meanwhile, scientists continue the basic research that will hopefully turn stem cell

therapy into reality. One promising avenue is studies conducted on animal models. At

the University of Wisconsin, Brenda W. Kahan et al. (2003) manipulated mouse ES cells

to differentiate into “cells resembling all islet cell types.” Their goal was to better

understand how “beta-cells develop from embryonic endoderm and pancreatic

progenitors.” At the University of Oregon, Linda B. Lester et al. (2004) recently

differentiated rhesus monkey embryonic stem cells (rES cells) into “insulin-producing,
beta-like cells with the beta-cell growth factor.” The goal is to treat diabetes in a non-

human primate model with the ultimate aim of duplicating this therapy in humans. Both

research groups were careful to demonstrate that their cultured β-cells were actually

producing insulin. Their caution on this point was based on a mistake made in an earlier

study where insulin was believed to be produced by the manipulated stem cells, but was

actually absorbed from the cell culture (Rajagopal, 2003). Additional experience

underscores the need to verify that insulin is being produced by differentiated β-cells and

not by “uptake of exogenous insulin” (Hansson, 2004.)

       Further basic research has been performed in mouse ES cells in vitro to determine

which genes code for pancreatic β-cells that secrete insulin. Thus far, several groups

have identified pdx-1 as the main transcriptional factor in expression of several genes

linked to coding for insulin-secreting β-cells (Miyazaki et al. 2004; Moritoh et al., 2003;

Wilding & Gannon, 2004). These genes include insulin 2, somatostatin, Kir6.2,

glucokinase, neurogenin3, p48, Pax6, PC2, and HNF6 (Miyazaki et al. 2004). However,

one group has found that expression of the Pax4 gene is a pdx-1 inhibitor (Wang et al.,

2004). In my opinion, Pax4 could be one of the genes causing IDDM, yet the research to

show this has not been supported, or at least published, to date. If this hypothesis turns

out to be justified, it will greatly increase our understanding of the biological basis of

IDDM and possibly lead to improved therapy. This progress in determining which genes

code for β-cells could possibly allow for a treatment using a patient’s own DNA with the

correct genes turned on or off respectively to derive insulin secreting tissue. Even though

steps are being made toward diabetic treatment, there is yet to be a successful protocol to
culture insulin-producing cells from mouse ES cells and cure a mouse with “mouse-

model” IDDM.

   While still in its infancy, embryonic stem cell research shows great promise for the

treatment of Type 1 (insulin dependent) diabetes mellitus. This research may be

especially vital for IDDM because the disease would be cured by the creation and

successful transplantation of a single cell type. Also, adult stem cells may not be usable

at all in the differentiation of β-cells. At this time, there is almost no federal funding for

ES cell research because of political opposition to destruction of embryos and therapeutic

cloning of humans. Patients, family members, and researchers in the IDDM community

have performed an active role in private fundraising for ES cell research and lobbying

their legislators for more supportive policies, both at the state and federal levels.
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