Human proteins manufactured in E. coli cells include, among others, insulin, erythropoietin, blood-clotting factors, somatotropin, os-teogenic protein, and tPA, or tissue plasminogen activator. Insulin is used to assist individuals who cannot make their own insulin, people suffering from type I diabetes. Erythropoietin is a protein factor that plays a key role in the production of red blood cells. It is used to treat anemia, in particular anemia that may follow cancer chemotherapy. It is also a drug abused by some athletes to increase their amount of red blood cells. Blood-clotting factors are administered to patients suffering from hemophilia, a disease that prevents blood from clotting properly. The osteogenic protein can be used to assist in bone healing. Somatotropin, also called growth hormone, is administered to young people of short stature who do not make enough of this hormone. Finally, tissue plasminogen activator is frequently used in the emergency rooms of hospitals to treat patients who have just suffered a se-
Table 5.1 Examples of Recombinant Products on the Market
Blood-clotting factors Factor VII, VIII, IX G-CSF
IL-2 (interleukin-2) Insulin Interferons Interleukin Natriuretic peptide Osteogenic protein Somatotropin tPA
Treating cystic fibrosis
Promotion of red-blood-cell growth, including for patients undergoing chemotherapy
Clotting factors for people with hemophilia
Reduction of infection in cancer patients receiving anticancer drugs
Treating severe hypoglycemia
Long term enzyme-replacement therapy for type I
Treating metastatic cancers
Treating chronic hepatitis C and multiple sclerosis Treating deficiency in blood-clotting cells after chemotherapy Assisting heart function in patients with congestive heart failure Assisting in bone healing
Promotion of growth for those who normally lack this hormone Treating acute myocardial infarctions
vere heart attack. At least a dozen pharmaceutical companies manufacture these and other protein factors, representing a market of several billion dollars (table 5.1).
What is the advantage of making human protein products in E. coli? Let us take the example of insulin. Before the advent of recombinant DNA technology, diabetics had to purchase insulin made from pig pancreases collected from the slaughterhouse. Pig insulin is not very antigenic; that is, this protein does not trigger a quick immunological response in humans. However, after years of daily use, a percentage of patients started developing immune reactions toward pig insulin. They then had to switch to sheep insulin, for example. These inconveniences are now a thing of the past; human insulin made in E. coli does not trigger an immunological response in diabetics because it is genuine human insulin. In addition, human insulin made in bacteria can never be contaminated with animal viruses because these viruses cannot be propagated in bacteria.
A number of blood-clotting factors provide further examples of human products made by using recombinant DNA technology. The clotting process of your blood involves a cascade of events involving different factors. Each factor is encoded by a separate gene. The hemophilia in Queen Victoria's family is due to a dysfunctional gene located on the X chromosome. There is a second gene on the X chromosome that encodes another clotting factor, and there is a third gene, not on the X chromosome, that encodes yet another clotting factor. These factors are now available for hemophiliac patients via recombinant DNA technology as injectable solutions. Before the advent of recombinant technology, hemophilia patients relied upon plasma from donated blood. Factors from donated blood have the potential of containing dangerous viruses such as HIV or hepatitis. In fact until clotting factors were available via the recombinant DNA technology, 90 percent of adult hemophilia patients were infected with either HIV or hepatitis C.
Finally, other types of cells in addition to bacteria can be used to produce recombinant human proteins of medical importance. Yeast cells, normally used to make bread, beer, or wine, do express human proteins when properly engineered with recombinant human genes. Mammalian cells, including human cells, grown in a culture medium are also used to make recombinant human protein.
The scientists who discovered key tools for recombinant DNA technology, such as restriction enzymes and plasmids, did not know that their work would lead to such important practical applications. This is a beautiful example of the power of science: most of the time, basic discoveries are made without any particular practical goal in mind. However, some basic discoveries can be put to practical use in a very short period of time with important results, in particular for the field of human medicine.
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