Engineering allergy relief? (Molecular Biology).

A new engineered protein known as GE2 may pave the way for future advances in allergy treatment. Since first describing the protein in the May 2002 issue of Nature Medicine, cocreators Andrew Saxon, director of the Asthma, Allergy, and Immunologic Disease Center at the University of California at Los Angeles, and Christopher Kepley, an assistant professor of internal medicine at Virginia Commonwealth University in Richmond, have tested GE2 in several model systems for allergic reactions, with highly promising results.

Saxon, Kepley, and colleagues constructed GE2 by combining Fc[epsilon]RI and Fc[gamma]RIIb, which are receptor binding regions of immunoglobulin E (IgE) and immunoglobulin G, respectively. Both immunoglobulins have receptors on human mast cells and basophils, key players in allergic reactions. Whereas Fc[epsilon]RI triggers cells to release histamine and set off allergic events, Fc[gamma]RIIb blocks the release of histamine. Saxon likens GE2 to connecting the gas pedal and brakes of a car: both are engaged, with the net effect of a slowing or cessation of allergic reactions such as sneezing, swelling, wheezing, itchiness, inflammation, and anaphylactic shock.

In the first proof-of-concept experiments, GE2 prevented the release of histamine in human basophils sensitized to nitrophenylacetyl (NIP), an allergen that Kepley likens to pollen in its effects. One microgram of GE2 per milliliter of growing medium cut histamine release by about hall, and 10 micrograms per milliliter cut it by an average of 84%, compared to untreated cells. GE2 also reduced the severity of allergic skin reactions in NIP-sensitized mice by two- to fourfold.

More recently, the researchers showed that GE2 blocked the secretion of IgE antibodies by human B cells. High blood levels of IgE antibodies are a strong predictor of allergies, says Kepley. GE2 also suppressed histamine release from human lung mast cells, a good model for asthma, and blocked the release of interleukin-16 in Langerhans-like dendritic cells, which contribute to infiammatory allergic processes in the skin. These yet-unpublished findings were presented at the 60th annual meeting of the American Academy of Allergy, Asthma, and Immunology in March 2003.

Moreover, the Fc[gamma]RIIb portion of GE2 can be fused to specific proteins to target specific responses, such as allergic reactions to cats or peanuts. Kepley and Saxon have created transgenic mice that were made allergic to cats through binding of human allergic antibodies as well as mice that were immunized with cat protein and therefore became "naturally" allergic. Then they engineered a chimeric fusion protein called GFD composed of Fc[gamma]RIIb and the cat allergen Fel D1. The GFD protein blocked allergic reactions when either type of mouse was exposed to cat allergens. Similarly, GFD prevented histamine release by basophils taken from cat-allergic humans. Work is also under way to design comparable proteins to prevent peanut allergies. Kepley foresees GE2-based allergy treatments being injected like allergy shots currently in use.

"It's cutting-edge research that could lead to new ways to treat allergic diseases," says Marshall Plaut, chief of the Allergic Mechanisms Section at the National Institute of Allergy and Infectious Diseases. However, Plaut cautions that these molecules may not work equally well in all models. Other unknowns also need to be worked out, such as whether blocking signaling pathways with GE2 could lead to unforeseen adverse effects.