Corixa Announces Initiation of Phase I Clinical Trial of CRX-675 in Patients with Seasonal Allergic Rhinitis.

Business Editors/Health/Medical Writers

SEATTLE--(BUSINESS WIRE)--April 26, 2004

TLR4 Agonist Product Candidate First to Enter Clinic

From Corixa's Innate Immunity Program

Corixa Corporation (Nasdaq:CRXA), a developer of immunotherapeutics, today announced the initiation of a Phase I clinical trial to test the safety and immune response activity of CRX-675 for seasonal allergic rhinitis (SAR). The trial is being conducted in the United States under a U.S. Food and Drug Administration (FDA) Investigational New Drug Application (IND). CRX-675 is a member of Corixa's family of proprietary compounds that interact with toll-like receptor 4 (TLR4).

As a TLR4 agonist, CRX-675 may influence innate immunity, the body's first line of defense against a variety of infectious pathogens. TLR4 agonists can also affect the immune system's response to allergens, antigens that trigger allergic reactions. Research and development activities focused on toll-like receptors have gained considerable attention in the past several years, as government and venture funding for TLR-related programs has increased, including a recent National Institutes of Health (NIH) grant to Corixa for $11.6 million.

The company's TLR4 agonists have been shown in preclinical studies to markedly reduce allergic reactions and to protect against infections, especially those that affect the respiratory tract. Moreover, preclinical testing of CRX-675 has shown that allergic animals become non-responsive to allergen challenge of the airways after one or two doses of CRX-675 administered in a nasal spray. CRX-675 is one of several TLR4 agonists in development by Corixa, all of which may be administered via non-injectable routes such as intranasal and potentially via oral administration.

"Our development of TLR4 agonists and antagonists represents a wealth of new and exciting product opportunities for Corixa," said Steven Gillis, Ph.D., chairman and chief executive officer at Corixa. "Initiation of this clinical trial represents an important step in our program development, and we are excited about the prospects of CRX-675 for the management of seasonal allergic rhinitis."

About the Trial

The Phase I study is designed to evaluate the safety of CRX-675 given as a single intranasal dose in adults allergic to ragweed pollen. Corixa expects to enroll 64 volunteers in the randomized, blinded, placebo-controlled, dose-escalation trial evaluating four different dose levels. The trial will be conducted at Creighton University in Omaha, Nebraska.

About Corixa's TLR Program

There are 10 kinds of TLRs, and each recognizes a different type of antigen. Corixa's proprietary compounds bind to TLR4, which can be found on a range of antigen-presenting cell types, including hematopoietic (blood-forming) cells, many epithelial cells, and cells associated with vascular stability. Corixa is exploring the use of these compounds as stand alone immunotherapies based on their ability to influence innate immune responses.

Corixa has discovered that some of its compounds act as agonists, or stimulants, of TLR4-mediated immune responses and some act as antagonists of TLR4 signaling. While all of the compounds are glycolipid in nature, their precise structure varies from compound to compound. Corixa has screened TLR4 agonist and antagonist compounds for their ability to protect animals from infection by a variety of pathogens and to promote anti-inflammatory immune reactivity.

About Seasonal Allergic Rhinitis

Allergic Rhinitis is an inflammation of the mucous membranes that occurs when allergens touch the lining of the nose. It is characterized by sneezing, congestion, itching and dripping of the nose, and itchy, watery eyes. Allergic Rhinitis may be seasonal or perennial. When symptoms are worse during warmer months, they are likely triggered by pollens and/or molds and indicate seasonal allergic rhinitis, sometimes referred to as hay fever. Seasonal allergic rhinitis affects more than 35.9 million Americans according to the American Academy of Allergy, Asthma and Immunology. Allergic rhinitis can develop at any age, and heredity plays a key role in who will develop an allergy.

About Corixa

Corixa is a developer of immunotherapeutics with a commitment to treating and preventing cancer and infectious diseases by understanding and directing the immune system. On June 30, 2003, Corixa announced that the FDA approved BEXXAR(R) for the treatment of patients with CD20-positive, follicular, non-Hodgkin's lymphoma (NHL) with and without transformation, whose disease is refractory to Rituximab and has relapsed following chemotherapy.

Corixa is focused on immunotherapeutic products and has a broad technology platform enabling both fully integrated vaccine design and the use of its separate, proprietary product components on a standalone basis. In addition to BEXXAR, Corixa currently has multiple programs in clinical development, including several product candidates that have advanced to and through late stage clinical trials. The company partners with numerous developers and marketers of pharmaceuticals, targeting products that are Powered by Corixa(R) technology with the goal of making its potential products available to patients around the world. Corixa was founded in 1994 and is headquartered in Seattle, with additional operations in Hamilton, Mont., and South San Francisco. For more information, please visit Corixa's Web site at http://www.corixa.com.

Corixa Forward-Looking Statements

This press release contains forward-looking statements, including statements about the expected completion of the Phase I clinical trial, statements about the expected business opportunities presented by Corixa's TLR-4 program, statements about the prospects of CRX-675 in the treatment of seasonal allergic rhinitis and other statements about our plans, objectives, intentions and expectations. Forward-looking statements are based on the opinions and estimates of management at the time the statements are made. They are subject to certain risks and uncertainties that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by such statements. Factors that could affect Corixa's actual results include, but are not limited to, possible delays in the completion of the Phase I clinical trial, failure by Corixa to develop and/or commercialize a a product from CRX-675 or its TLR-4 program, failure of Corixa to demonstrate safety or efficacy of CRX-675 in the Phase I clinical trial or future clinical trials and the "Factors Affecting Our Operating Results, Our Business and Our Stock Price," described in our Annual Report on Form 10-K for the year ended Dec. 31, 2003, copies of which are available from our investor relations department. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date of this release.

Background on Corixa TLR4 Agonists and Antagonists -- Modulators of Innate Immunity

OVERVIEW

Corixa has developed a class of compounds that interact with a type of cell receptor which, when stimulated, initiates the body's innate immune response. Innate immunity provides the body with an immediate response mechanism to fight a variety of pathogens. A key component of innate immunity is a family of cell-surface receptors that recognize "molecular signatures" found on invading microorganisms. Known as toll-like receptors, or TLRs, these receptors recognize specific antigens and are responsible for turning on and off critical aspects of the innate immune response.

Corixa's TLR4 Expertise

There are 10 kinds of TLRs, and each recognizes a different type of antigen. Corixa's synthetic compounds are recognized by toll-like receptor 4, or TLR4, which can be found on a range of antigen-presenting cell types, including hematopoietic, or blood-forming, cells, many epithelial cells, and cells associated with vascular stability. Corixa is exploring the use of these synthetic compounds as stand alone immunotherapies based on their recognition by TLR4s, and their possible lack of toxicity associated with natural TLR4 immunostimulants such as lipopolysaccharide.

Corixa has discovered that some of its compounds act as agonists, or stimulants, of the TLR4-based innate immune response and some act as antagonists, or deactivators, of this innate immune response. The structure of each of the Company's synthetic compounds differs slightly. Therefore, Corixa has screened each TLR4 agonist and antagonist for its ability to protect the body from viral, bacterial, fungal and parasitic infection. The variety of these compounds may yield multiple applications for immunotherapy.

Corixa's TLR4 Library

Corixa intends to pursue several indications using its TLR4 agonists and antagonists as stand alone immunotherapeutic agents. Potential applications for the agonists include chronic obstructive pulmonary disease, which is often triggered by respiratory viral infections such that treatment with antibiotics is often ineffective, upper airway resistance to biological warfare agents, seasonal or constitutive rhinitis, allergies and asthma. Potential applications for the antagonists include inflammatory bowel disease (IBD) and cystic fibrosis.

TLR-4 Agonists

Corixa's TLR4 agonists have been successfully evaluated in viral, parasite and bacterial resistance models. Based on their proven ability to induce cytokines in a variety of animal models, to facilitate resistance to bacterial and viral challenges, and to down-regulate existing allergic responses, TLR4 agonists offer several potential clinical applications.

CRX-675. Seasonal allergic rhinitis (SAR) is characterized by an overproduction of the cytokines in the nasal mucosa and associated with atopic or allergic sensitization. Administration of our TLR4 agonist, CRX-675, has been shown in animal models to significantly decrease allergic rhinitis. This product is currently in Phase I clinical evaluation.

In addition, the Company is evaluating another TLR4 agonist candidate for use in the treatment of atopic diseases, or genetically determined hypersensitivity diseases such as hay fever and asthma. Corixa's preclinical studies indicate that its TLR4 agonist candidate is absorbed into the body and is biologically active at mucosal, or mucous membrane, surfaces. The tolerability and effectiveness demonstrated by preclinical mucosal delivery models indicate that aqueous formulations of the agonist may have particular utility in treating or preventing atopic diseases of the respiratory tract.

TLR-4 Antagonists

Preclinical studies are under way to evaluate the effectiveness of Corixa's TLR4 antagonists as novel, specific, synthetic, anti-inflammatory agents capable of inhibiting innate immune responses.

The Company's TLR4 antagonist lead candidate has shown the ability to quantitatively block signaling through TLR4 and therefore has potential use as an anti-inflammatory compound in IBD and other indications.

Several formulations of the antagonist, including an aqueous formula and stable emulsion formula may provide unique benefits. Corixa is also exploring whether the antagonist may be formulated and delivered orally.

RECENT NEWS

On April 26, 2004, Corixa announced the initiation of a Phase I clinical trial to test safety and immune response activity of CRX-675 for SAR.

On Jan. 5, 2004, Corixa announced it had been awarded an $11.6 million, five-year contract from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), to develop the company's proprietary synthetic molecules that act on TLR4. The contract is being funded by the Biodefense Partnership program at the NIH.