Asthma and allergic rhinitis omalizumab
Asthma and allergic rhinitis are both mediated by immunoglobulin E (IgE). Allergies occur when an otherwise harmless substance causes an abnormal response in a sensitised person, and allergic rhinitis is the inflammation of the mucus membranes caused by airborne allergens such as pollen, dust mites or cat fur.
Asthma is a chronic inflammatory condition of the airway, and asthma attacks may be set off by exercise or infections, but also by exposure to the same allergens that cause allergic rhinitis.
The allergen binds to the IgE, which then binds to receptors on the surface of mast cells and basophils, causing the release of histamine, leukotrienes and other substances that cause inflammation.
So a potential treatment of these allergic responses would be to target this interaction of IgE with the cell surface receptors.
Genentech discovered a monoclonal antibody that has just this effect, which it has now licensed to Novartis and Tanox. Omalizumab, previously referred to as rhuMAb E25 and given the trade name Xolair, is a humanised mouse-derived anti-IgE antibody.1 Around 95% of its sequence is derived from human IgG1, and it binds to circulating IgEs, preventing it binding with surface cells and so stopping the release of the mediators involved in the allergic reaction.2
Weekly doses of 0.15mg/kg subcutaneously, or 0.50mg/kg intravenously, reduced free serum levels of IgE by 60 and 20% respectively after 21 days.3 A randomised clinical trial was carried out on 251 adult patients suffering from hayfever. The subjects were given 300mg omalizumab or placebo subcutaneously two or three times during the season. Those given the monoclonal antibody had significantly improved nasal symptoms and had to take fewer antiallergy medications.4
Omalizumab has also been assessed as a treatment for asthma. Few adverse effects were seen in either adults or children. No immune complex disease has been observed, and antibodies against omalizumab do not develop with treatment, indicating that the antibody is both safe and well tolerated, even in high risk patients.5 Omalizumab has been approved for treating moderate allergic asthma in Australia, and other submissions have been filed around the world.