Interferons And Interleukins: From Bench To Bedside

Interferons (IFs) and interleukins (ILs) are immune system biochemicals at the intersection of basic research and medical technology. Part of the class of secreted cellular regulators known as cytokines, IFs and ILs have experienced dizzying public relations ups and downs, hailed one season as tomorrow's wonder drugs, derided the next as toxic side effects emerge during therapy. With many questions about the basic biology of these enigmatic immunochemicals still to be answered, suppliers--some of whom are listed below--are likely to have a ready research market. CALBIOCHEM Corp. 10933 N. Torrey Pines Rd. La Jolla, Calif. 92037 (800) 854-3417 Fax: (800) 776-0999 Cellular Products Inc. 872 Main St. Buffalo, N.Y. 14202 (800) CPI-KITS Fax: (716) 882-0959 Cetus Oncology Corp. 4560 Horton St. Emeryville, Calif. 94608 (800) 238-8779 Genzyme Corp. One Kendall Square Cambridge, Mass. 02139 (800) 332-1042 Fax: (617) 252-7700 R&D Systems Inc. 614 McKinley Place, N.E. Minneapolis, Minn. 55413 (612) 379-2956 Fax: (612) 379-6580 RDI Research Diagnostics Inc. Pleasant Hill Rd. Flanders, N.J. 07836 (201) 584-7093 Fax: (201) 584-0210 Despite the cytokines' slower-than-expected entry into the clinic, applications are accumulating, and basic research in this area remains vigorous. This means a continuing market for vendors who provide these intriguing immunochemicals. Many researchers elect to purchase a cytokine rather than extract or synthesize it themselves. If they go this route, they benefit from the advantages that come with obtaining any biochemical from a vendor--consistency of product, purity of product, and time saved. Cytokines offered for sale, for example, are routinely screened for contamination by bacteria, fungi, and mycoplasma. And companies cite the biological activity of their products, or sell assays--such as Madison, Wis.-based Promega Corp.'s Cell Titer 96 Non-Radioactive Cell Proliferation/Cytotoxicity Assay-- for users to determine this themselves. Most company literature indicates that these cytokines and related products are for research uses only. Cytokine manufacturers offer a variety of both human and murine IFs and ILs, from natural sources or recombinant DNA technology and in tissue culture or ultrapure grades. R&D Systems Inc. of Minneapolis sells a "cytokine sampler kit" that includes eight types of cytokines. Some companies offer glycosylated or nonglycosylated forms of certain cytokines. CALBIOCHEM Corp. of San Diego improves on nature, offering a variant IL-2 that has two amino acid substitutions that render it more soluble. The problem researchers have had in taking an IF or IL to the clinic is that there are so many of these cytokines, and they interact in so many ways, that limiting their actions to just one effect is nearly impossible. And even if a benefit predicted by in vitro studies--such as shrinking of a tumor--occurs, effects here in the body can be diverse and dangerous. "There's a difference between what a cytokine does in molecular terms and what it does in a physiological sense--that is, in the big picture of what it does in the body," says Corrado Baglioni, a professor of biology at the State University of New York, Albany. At the basic research level, to decipher cytokine activity, a researcher attempts to selectively block the function of one type of molecule, and then observes the effects on the organism, typically a mouse. This is done by any of several techniques, including gene targeting (in which a nonfunctional version of a gene is swapped for the working one in the organism); using neutralizing antibodies to take a cytokine out of circulation; and designing molecules to block cell surface cytokine receptors with precise specificity. These in vitro and animal studies are complemented by correlations of cytokine levels to specific diseases in humans-- such as increased IL-1 in rheumatoid arthritis. The need to measure precise and minute amounts of specific cytokines in plasma, sera, and cell culture supernatants opens a market for assay kits. Genzyme Corp. and Advanced Magnetics Inc., both of Cambridge, Mass., for example, offer cytokine immunoassay kits that include all reagents (antibodies, buffers, standards, and diluents). Other firms, such as Oncogene Sciences Inc., Uniondale, N.Y., and R&D Systems offer antibodies against specific cytokines. Once cytokine levels have been linked to certain disease states, the next step is to manipulate them to achieve a therapeutic goal. But harnessing cytokine action is complicated by a staggering interplay of biochemicals. Consider septic shock, an often-fatal immune response to gram-negative bacterial infection. Septic shock is triggered when white blood cells encounter a lipid called endotoxin in the microbes' cell walls. As a result, the body becomes flooded with at least three types of ILs, as well as a cyto-kine called tumor necrosis factor (TNF). Not only is a particular medical condition often associated with a multiple cytokine response, but also the cytokines themselves have diverse effects. IFs, for example, broadly affect physiology by activating certain genes and immune system cells and by inhibiting cell division and blood vessel growth--often simultaneously. Even when the effects of one cytokine can be tracked, the picture is still quite complicated. IL-1, for example, induces fever, sleep, anorexia, hypotension, and production of blood cells. It is also linked to a veritable medical dictionary of conditions, including leukemia, arthritis, colitis, atherosclerosis, and many others (C.A. Dinarello and S. M. Wolff, New England Journal of Medicine, 328:106-12, 1993). Using IL-1, or any cytokine, means finding a dose that optimizes the beneficial effects while dampening the destructive ones. Interferons, as a group, were discovered in the late 1950s. They were described as a family of species-specific proteins that interfere with a range of viral infections in vertebrates. Because IFs also inhibit cell division, they quickly attained a reputation as potential wonder drugs, possibly able to fight viruses and cancer. Initially, however, the proc-ess of developing IF into a drug was stymied by the need to extract and purify it from donated blood, with a dauntingly high estimated price tag of $178 million per ounce. When recombinant DNA technology made possible the economical, safe scale-up of biological proteins, IF was one of the first in line. In 1982, backed by the American Cancer Society, IF alpha started clinical trials. Three years later, it became the first pure human protein approved by the Food and Drug Administration as a treatment for the rare hairy cell leukemia. "There are so many different types of interferons in our bodies," says Charles Pfau, a professor of biology at Rensselaer Polytechnic Institute in Troy, N.Y., "and only a few have been produced by genetic engineering. These have some limited effects on certain diseases, but we still don't know how to utilize them. We don't know the checks and balances of the body." For example, Pfau and coworkers developed a mouse model showing that "in some viral diseases, IF actually exacerbates instead of ameliorating the condition," he says. If IF could worsen a viral infection in mice, they hypothesized that it might in humans, too. As potential examples of the mechanism, they cited a viral disease in South America, called junin, and the deadly Lassa fever of Africa. People with these disorders make "horrendously high titers of IF," according to Pfau. Although Pfau says that they never actually proved the link between high IF and viral disease in humans, their work made headlines when people in clinical trials of IF in France died. But today IF research is alive and well. Several clinical trials are under way, including IF alpha to treat certain life- threatening bulges of blood vessels, IF beta for multiple sclerosis and hyperlipidemias, and IF gamma for lowering the frequency of bacterial infection in chronic granulomatous disease. In cancer therapy, IFs may be promising adjuvants to standard therapies, greatly expanding the market for each type of treatment. IFs have been found to prolong the effectiveness of traditional cancer treatment protocols in some patients with non- Hodgkin's lymphoma, myeloma, or colorectal or bronchial cancer. Interleukins were originally thought to oversee interactions between white blood cells, the emissaries of the immune system, but now are known to affect a wider variety of cell types. Most clinical interest is currently focused on IL-1 and IL-2, with researchers beginning to glimpse the roles of others of the 14 known interleukins. IL-1 was discovered in 1972, and its structure and function were delineated over the next seven years. Human IL-1 was first manufactured by recombinant DNA technology in 1984. A key immune system regulator, IL-1 sets into motion a chain reaction that intensifies the immune response. It is IL-1 that responds to the initial presence of a foreign antigen, activating T cells to mature, proliferate, and produce other cytokines. IL-1 also hikes production of collagenase, prostaglandins, and antibodies. Because collagenase breaks down connective tissue, and prostaglandins are associated with inflammation, excess IL-1 may lie behind many inflammatory disorders. The cytokine is also responsible for the fever, headache, ache, fatigue, and weakness of influenza. Efforts to control IL-1 activity in the treatment of inflammatory illness have taken advantage of a naturally occurring molecule in the human body. This molecule, the IL-1 receptor antagonist, blocks cell surface receptors for IL-1. "The IL-1 receptor antagonist is now being produced by recombinant DNA technology in large amounts. We expect to see it neutralize the cytokine's effects," says Baglioni. Evidence for that is already strong. The IL-1 receptor antagonist (IL-1ra, or Antril) is in phase III clinical trials by Synergen Inc. of Boulder, Colo. In a large study, Synergen scientists found that 16 percent of septic shock patients given Antril died, compared with 44 percent of those given placebo. The company anticipates FDA approval this year. IL-2 has followed the pattern of other cytokines--initially greeted with unreasonably high expectations, it has since found a niche or two, and a few new applications are in the offing. It was discovered in 1976 (D.A. Morgan, et al., Science, 193:1007-9, 1976), becoming available via recombinant DNA technology in 1984. IL-2 maintained a high profile through the 1980s, as Steven Rosenberg at the National Cancer Institute and others found that when IL-2 is applied to white blood cells removed from patients, and then reinfused as "lymphokine activated killer cells" along with a booster of IL-2, some patients experienced spectacular remissions. Even such devastating conditions as advanced malignant melanoma showed improvement. Enthusiasm for IL-2 plummeted, though, when the cytokine was found to have highly toxic side effects. But recent progress with IL-2 to treat metastatic kidney cancer, for which there is no other treatment, suggests that a combination of lower doses and physicians learning how to manage the side effects will make IL-2 safer to use. FDA approved IL-2 to treat metastatic kidney cancer in February 1992. Known as Proleukin, IL-2 for this use is produced by Cetus Oncology Corp. of Emeryville, Calif. On another front, IL-2 is in phase I clinical trials to treat CD8 cells removed from people with AIDS. The IL-2 matures the cells, which are then returned to the donor along with IL-2, better able to mount an immune defense. Development of this use for IL-2 is a joint venture between Applied Immune Sciences Inc. of Menlo Park, Calif., and Care- mark Inc. of Lincolnshire, Ill. Other interleukins are in the pipeline. Genetics Institute Inc., based in Cambridge, Mass., is looking at IL-11 in vitro and in mice to stimulate platelet production, which could help counter the platelet-depleting effects of chemotherapy. IL-6, also known as beta-2 interferon, may have a bright future as a platelet growth stimulator, and as an antiproliferative treatment for breast, colon, and skin cancer. IL-6 is in preclinical testing by Ajinomoto Co. Ltd. in Tokyo, Ares-Serono NV in Geneva, and Genetics Institute. As biotechnology and pharmaceutical companies pursue direct application of IFs and ILs to human health care, basic researchers are still trying to more precisely define the roles of these complex biochemicals. They may get some help from examining how viruses evade a cytokine attack. For example, says Baglioni, "Some viruses, such as cowpox, have genes that are used to neutralize cytokines. This gives the virus a better chance to replicate, or inflammation does not occur until the virus has had a head start at replicating. Cytokines must be very important, if viruses bother to acquire an evolutionary way to neutralize them." Ricki Lewis is a freelance science writer based in Scotia, N.Y. She is the author of a biology textbook and has just completed a human genetics text.

Interferons And Interleukins: From Bench To Bedside

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