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Genetic Engineering
Understanding the Immune System

Adapted by Mary Shomon

Genetic engineering, more formally known as recombinant DNA technology, allows scientists to pluck genes (segments of DNA) from one type of organism and combine them with genes of a second organism. In this way, relatively simple organisms such as bacteria or yeast, or even mammalian cells in culture and mammals such as goats and sheep, can be induced to make quantities of human proteins, including hormones such as insulin as well as lymphokines and monokines. Microorganisms can also be made to manufacture proteins from infectious agents such as the hepatitis virus or the AIDS virus, for use in vaccines.

Another facet of recombinant DNA technology involves gene therapy: replacing defective or missing genes with normal genes. The first approved gene therapy trials involved children with severe combined immunodeficiency disease, or SCID (Immunodeficiency Diseases), which is caused by lack of an enzyme due to a single abnormal gene. The missing gene is introduced into a harmless virus, then mixed with progenitor cells from the patient's bone marrow. When the virus splices its genes into those of the bone marrow cells, it simultaneously inserts the gene for the missing enzyme. Injected back into the patient, the treated marrow cells produce the missing enzyme and revitalize the immune defenses. Researchers are also investigating the use of gene therapy for such diverse conditions as hemophilia, Parkinson's disease, diabetes, a hereditary form of dangerously high cholesterol, and AIDS.

genetic engineering

An increasingly important target for gene therapy is cancer. In pioneering experiments, scientists are removing the immune cell known as the tumor-infiltrating lymphocyte or TIL(Immunity and Cancer), or tumor cells themselves, inserting a gene that boosts the cells' ability to make quantities of a natural anticancer product such as tumor necrosis factor (TNF) or interleukin-2, and then growing the restructured cells in quantity in the laboratory. When the altered cells are returned to the patient, they seek out the tumor and deliver large doses of the anticancer chemical. They also appear to mobilize, in some unknown way, additional antitumor defenses.

On the horizon are anticancer vaccines made by manipulating genes. Intended to protect cancer patients against a recurrence, these vaccines can incorporate genes for immunogenic tumor antigens or genes for histocompatibility antigens able to galvanize killer T cells, as well as genes for substances such as TNF or interleukin-2. Other anticancer strategies call for introducing genes that can shut down cancer-promoting oncogenes or replace faulty cancer-restraining suppressor genes.

Genes can be packaged, for delivery, in a variety of ways: inserted into the genetic material of such carriers as the familiar vaccinia virus (Vaccines Through Biotechnology) or inactivated retroviruses, grafted onto a protein carrier that magnifies the immune response (an adjuvant), or tucked into fat globules known as liposomes.

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