Cells that have the ability to divide for indefinite periods and, under the right conditions, give rise to many different types of cells. Some scientists believe that stem cells are a promising avenue for curing a number of different diseases, including Type 1 diabetes.
To understand the vast potential of stem cells, it is helpful to remember that a single fertilized egg, or zygote, eventually gives rise to more than 200 different types of cells in the adult mammal, including skin cells, nerve cells, muscle cells, cartilage cells, and bone cells. As cells divide and multiply, successive generations differentiate into increasingly specialized cell types.
In 1998, scientists discovered methods for isolating and growing human embryonic stem cells — stem cells derived from one of the earliest stages of the embryo, the blastocyte. Theoretically, these cells could be cultivated to develop into virtually any cell in the body, including the insulin-producing islet cells of the pancreas, which could then be used to control blood glucose levels in people with Type 1 diabetes. Similar approaches may also be useful to replace tissue damaged by other diseases, such as Parkinson disease, chronic heart disease, and cancer.
Since the early 1970’s, diabetes researchers have sought to “cure” diabetes by transplanting insulin-producing islet cells into people with Type 1 diabetes. This approach has been fraught with two major obstacles: One, the transplanted islets are rejected by the recipient’s immune system unless the recipient takes immunosuppressive drugs, which can make him susceptible to serious infection or disease. Two, not enough human pancreases become available each year to supply enough islets for everyone who could benefit from islet transplants.
Embryonic stem cells may offer a solution to these problems. Since embryonic stem cells replicate relatively easily, cultured stem cells could provide a virtually unlimited supply of donor islet cells. Scientists also believe that stem cells could be genetically manipulated to help them escape detection by the immune system. Alternatively, they could be encased in special membranes that would allow insulin and glucose to pass back and forth freely between the bloodstream and the islet cells, but would not allow the islets to interact with the immune system.
Research using embryonic stem cells remains controversial because it requires embryos to be destroyed. On August 9, 2001, President George W. Bush announced a partial ban on funding for embryonic stem cell research; government financing is now limited to research using already existing stem cell colonies (those created by 9 PM on August 9, when he announced the decision). According to the National Institutes of Health, under this definition, 72 cell lines qualify for government-funded research. Many scientists say that these lines are not fully developed or diverse enough to lead to clinical therapies — and so the controversy continues.