The human body is a remarkable self-service center, open 24 hours a day, including weekends. It provides routine maintenance and repair free of charge, with no wait and no hassle. Most of us have no idea what makes us run, yet our own bodies are our best mechanics.

Our cells are microscopic specialists that tend to our daily upkeep, leaving us free to pursue other important — or frivolous — matters. They are dispatchers, sentries, soldiers, builders, destroyers, and mechanics. They also manufacture products to help with their chores. Among these products are cytokines.

"Cytokines are hormone-like proteins that act as communicators between cells," says Theresa Gerrard, Ph.D., acting director of FDA's division of cytokine biology. "They're made by one cell and act on another, relaying a message telling that cell to grow, stop growing, move to a trouble spot, or otherwise somehow modify its function."

An explosion in cytokine research has occurred in the last decade. Using genetic engineering techniques, researchers are producing large quantities of these human proteins and testing them for possible medical applications.

Developing biological products — naturally occurring substances — for medicine is not a new concept. Doctors have long used whole blood and blood products to replace blood lost due to injury or during surgery, for example, and to treat anemia and hemophilia.

Gerrard describes cytokines as "new era" biologics, explaining that even though they originally derived from human cells, they're mostly manufactured using recombinant DNA technology. They may even be chemically altered to achieve a desired characteristic, such as greater activity, thus becoming more like drugs than the "old-time biologicals," she says.

Developing cytokines for medical treatment can be a tricky business. Some are very specific, and their effects are predictable. Others, however, can produce a variety of effects depending on the type of cell they're acting on. Because of this, cytokine research often takes somewhat of a "shotgun" approach.

"Even though you may not know exactly how the cytokine will act in the body, information from laboratory experiments or animal studies may provide a good indication," Gerrard says. "If a particular cytokine modulates immune function, for example, it can affect countless things, and you might try it in cancer, infectious diseases, or various other things."

Interferons

That was the case with interferons, for example. Interferon alfa (Intron-A, Roferon-A) was the first cytokine FDA licensed. In June 1986, it was approved to treat hairy cell leukemia — a rare cancer primarily affecting adults. Since then, it has been licensed for Kaposi's sarcoma (a type of cancer mostly affecting people with AIDS), genital warts, hepatitis C, and hepatitis B.

Interferon gamma (Actimmune) was licensed in 1990 to treat chronic granulomatous disease, a hereditary disease that strikes primarily young boys. These children have a defect in a certain type of white blood cell, so that the cells can ingest bacteria, but can't kill them. The patients suffer repeated bouts of life- threatening infections from common organisms that normally wouldn't present serious problems. Children treated with Actimmune have fewer serious infections.

The most recent cytokine to be licensed is another interferon. In 1993, FDA approved interferon beta (Betaseron) for multiple sclerosis, after studies showed it helped prevent flare-ups of the disease.

Scientists don't know exactly how interferons work to produce the desired effects in any of these diseases. All interferons have anti-viral activity, Gerrard says, but that's about all they have in common. In some cases, the substance may act directly on tumor cells; in others, it may enhance an immune response, or perhaps subdue it.

Most patients have not had serious side effects from the interferons licensed so far. The most common adverse effects are flu-like symptoms, including fatigue, fever, chills, and headache. Less frequent side effects include abnormal liver function and severe depression.

Other classes of cytokines commanding considerable interest among researchers are wound-healing factors, neurotrophic factors, inflammatory and anti-inflammatory factors, and hematopoietic growth factors. Scientists working with cytokines expect to eventually develop products in all these categories. So far, however, only interferons and hematopoietic growth factors have been shown safe and effective for certain conditions.

Tags: Health

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.