Americans accustomed to the seasonal misery of sneezing, runny noses and itchy, watery eyes caused by ragweed pollen might one day benefit from an experimental allergy treatment that not only requires fewer injections than standard immunotherapy, but leads to a marked reduction in symptoms that persists for at least a year after therapy has stopped, according to a new study in the October 5 issue of The New England Journal of Medicine.
The research was sponsored by the Immune Tolerance Network, which is funded by the National Institute of Allergy and Infectious Diseases (NIAID) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), both components of the National Institutes of Health (NIH), and the Juvenile Diabetes Research Foundation International.
Finding New Therapies
"As many as 40 million Americans suffer from seasonal allergies caused by airborne pollens produced by grasses, trees and weeds," says NIH Director Elias A. Zerhouni, M.D. "Finding new therapies for allergy sufferers is certainly an important research goal."
"This innovative research holds great promise for helping people with allergies," says NIAID Director Anthony S. Fauci, M.D. "A short course of immunotherapy that reduces allergic symptoms over an extended period of time will significantly improve the quality of life for many people."
Ragweed is one of the most common pollens in the United States and is prevalent in the Northeast, Midwest and the South. In Baltimore, where the NEJM study was conducted, the ragweed pollen season lasts from mid-August to October.
Not Completing Treatment
Physicians treat people suffering from mild and moderate ragweed allergies with antihistamines or nasal corticosteroids. However, when people with allergies do not respond to these treatments or experience severe symptoms, the next therapeutic option is a course of subcutaneous injections of the allergen, which is called allergen immunotherapy. Although this standard immunotherapy is often effective, it has two major drawbacks. First, it can cause systemic allergic reactions, such as anaphylaxis, a hypersensitivity reaction that can lead to severe and sometimes life-threatening physical symptoms. Second, to provide long-lasting relief, standard immunotherapy may require frequent injections over a 3- to 5-year period. The large number of injections over such an extended period of time often results in many people not completing the treatment.
In the study detailed in NEJM, lead investigator Peter Creticos, M.D., medical director of the Johns Hopkins Asthma and Allergy Center in Baltimore, and his research team found that an investigational therapy based on the major ragweed allergen, Amb a 1, coupled to a unique short, synthetic sequence of DNA that stimulates the immune system, reduced allergy symptoms in adults for at least one year when given just once a week over a 6-week period. The therapeutic agent was provided by Dynavax Technologies Corp., based in Berkeley, CA.
"For almost 100 years, we've been using the tedious process of giving allergy sufferers one to two shots a week for up to 4 to 5 years to ensure its success," Dr. Creticos says. "This study is an important immunotherapy advance in that we've shown you can induce long-lasting relief from allergic rhinitis with just a few weeks of injections."
The study initially involved 25 adult volunteers, ages 23 to 60, with a history of seasonal allergic rhinitis, positive skin test reactions to ragweed pollen, and an immediate reaction when nasally challenged with ragweed. Prior to the start of the 2001 fall ragweed season, the study participants received six injections, each a week apart, of either the investigational therapy in increasingly higher doses or a placebo. They received no other injections throughout the course of the study. Fourteen volunteers received the study drug; 11 were given the placebo. The therapy was well-tolerated and caused only limited local reactions, which required neither medication nor change in treatment dose. No clinically significant, therapy-related adverse events occurred.
Only Six Injections
Throughout the 2001 and 2002 ragweed seasons, the volunteers were monitored for allergy-related symptoms, including the number of sneezes and the degree of post-nasal drip, allergy medication use and quality-of-life scores. Compared with the placebo recipients, the group that received the therapy experienced dramatically better outcomes that continued throughout the 2002 ragweed season even though therapy ended one year earlier.
Clearly, the regimen of only six injections showed therapeutic promise when compared with the current therapy, the study authors note. However, because the results are based on a small number of volunteers and the long-term safety of the therapy is unknown, they say additional clinical trials with longer-term follow-up to adequately assess the therapy's safety and effectiveness are necessary.
Understanding the Immune Response
How the experimental therapy relieves ragweed allergy symptoms is not fully understood at this time. When exposed to ragweed pollen, people who are allergic to ragweed experience an increase in IgE (immunoglobulin) antibodies; immunotherapy blocks this increase in IgE. Researchers believe the experimental therapy tempers the release of immune regulatory proteins called cytokines, which blocks increases in the level of IgE antibodies.
"Using ragweed as a model allergen system with a predictable seasonal pattern of symptoms and pollen counts, it is possible to correlate pollen levels with symptoms and measure treatment effects on symptoms. This enables us to better understand immune response to allergens and serves as an approach to similar therapies to manage other allergic reactions for which there are currently no treatments, such as food allergies," says Marshall Plaut, M.D., chief of the Allergic Mechanisms Section of NIAID's Division of Allergy, Immunology and Transplantation.