Corixa Provides Clinical Research and Product Development Update at its First Annual Analyst Conference on August 16, 2000.

Business Editors & Health/Medical Writers

SEATTLE--(BW HealthWire)--Aug. 16, 2000

PVAC, Double-Blind, Controlled Phase II, U.S. Clinical Trial Doubled

in Size and Fully Accrued -- Data Expected by Year-End

Melacine Pre-BLA Meeting Scheduled with FDA for September -- Data

Reported from Phase III Trial of Intron A + Melacine vs. Intron A

At its first annual analyst conference in Bellevue, Wash., Corixa Corporation (Nasdaq:CRXA), a research- and development-based biotechnology company, provided analysts in attendance with an update on key company product developments.

Cindy Jacobs, Vice President of Clinical Research, detailed the current clinical research status of the company's PVAC(TM) treatment for psoriasis. Steven Gillis, Chairman and Chief Executive Officer reviewed clinical results from a number of Phase III Melacine(R) clinical trials and provided a brief status report on additional programs in the company's preclinical and clinical pipeline.

Important new information regarding some of the company's more advanced product developments was provided, including the following:

Melacine

Corixa reported completion of a 253 patient Phase III clinical trial comparing Melacine + Intron A (alpha interferon) therapy in Stage IV metastatic melanoma patients to therapy with Intron A alone. Stage IV melanoma is an aggressive malignancy associated with an extremely high rate of mortality. While there was no survival advantage noted in the overall trial between the treatment groups, women treated with Melacine + Intron A survived significantly longer than did women treated with Intron A alone (p equals 0.018). Median duration of survival in the Intron A group was 187 days, whereas median survival in women treated with Intron A and Melacine was 353 days. Response rates (complete and partial responders) in both treatment arms were similar, ranging from 8 to 10 percent. Moreover, in women who responded, the median duration of response was much longer in women treated with Intron A and Melacine (668 days) as compared to women treated with Intron A only (157 days). In part, this may be due to a more potent immune response against self-antigens in women, given that the rate of development of autoimmune disease in women is far higher than that observed in men.

The company also provided additional data from the trial evaluating Melacine in Stage II melanoma. Stage II melanoma is defined as patients who present with a primary malignancy of between 1.5 mm and 4.0 mm in thickness, with no evidence of metastases. Data from this study were originally reported in March 2000. In this Phase III trial, 689 patients had their primary malignancy removed surgically and were then randomized to either observation or Melacine therapy.

After five years of observation, it was observed that patients randomized to the Melacine arm exhibited a statistically significant (p equals 0.04) increase in their median duration of disease-free survival. In subsequent analyses conducted by Corixa it was further confirmed that improvement in median duration of disease free survival was associated with Melacine treatment in patients whose tumors at entry into the study were less than or equal to 3mm thick (p equals 0.018). Based on information obtained from the results of Intron A and Melacine therapy, additional statistical analyses were conducted on women in the Stage II melanoma study. These analyses also confirmed a statistically significant benefit associated with Melacine therapy in women as compared to observation in women with Stage II disease.

Melacine was approved for sale in Canada in November 1999 based on data from a U.S. study comparing Melacine to moderate dose chemotherapy, once again in Stage IV melanoma patients. In this study response rates in both arms of the trial were not statistically different, however, Melacine had a superior safety profile as compared to that manifested by chemotherapy. Corixa has completed a third party review of responder patients in the Melacine arm of the trial and confirmed the previously reported response rate. Of particular note at the time the study was analyzed were the presence of long term survivors treated with Melacine. Presently, four Stage IV melanoma patients (from Phase II and Phase III studies) treated with Melacine remain as disease free, stable survivors. These patients have all survived between 7 and 10 years from initial date of treatment.

Corixa is currently scheduled to discuss the results and statistical analyses of its Phase III clinical trials of Melacine with representatives of the FDA at a pre-Biological License Application (BLA) meeting in September 2000. Based on the outcome of the meeting, the company may proceed with compilation and filing of a Biological License Application for Melacine for treatment of certain stages of melanoma.

PVAC Treatment

In response to further discussions with the FDA regarding the design of its PVAC(TM) treatment Phase II, randomized, controlled trial in the United States, Corixa has doubled the size of the study from 132 to 240 patients. The patients have been randomized to treatment with either the control, or one of three different dosages of PVAC treatment. The study size was increased in order to allow the trial to potentially qualify as one of the efficacy trials for subsequent consideration for approval, should positive results be obtained in the high dose group. Even though the trial size was increased, Corixa reported that as of August 16, all 240 patients had been accrued to the study. The major efficacy endpoint, a 75 percent improvement in disease severity as assessed by decrease in PASI (psoriasis area and severity index) score, is measured at twelve weeks following the first administration of PVAC. The product is given via intradermal injection on Day 0 and Day 21 of the study. Given the status of enrollment, Corixa believes that it will be in position to analyze data from the trial's database by the end of the year.

On August 15, 2000, Corixa announced it had entered into a multi-year development, commercialization and license agreement with Medicis Pharmaceutical Corporation for the commercialization of PVAC in the United States and Canada. Under the terms of the agreement, Medicis will pay Corixa license fees, research funding and milestone payments of up to $107 million. Upon effectiveness, Corixa will receive a non-refundable payment of $17 million with additional potential development milestone payments of $35 million, and commercialization and cumulative net sales threshold milestone payments of $55 million. Additionally, upon commercial sale of the product, Medicis will purchase inventory from Corixa and pay a royalty on net sales of the product. The effectiveness of the collaboration agreement between Corixa and Medicis is subject to certain customary conditions, including any required approval of the transaction by applicable government agencies.

PVAC treatment is a derivative of Mycobacterium vaccae (M.vaccae) developed by Corixa, in collaboration with New Zealand-based Genesis Research and Development Corporation Limited. Revenue received by Corixa will be shared on a pro-rata basis consistent with each of Corixa's and Genesis' share of project development efforts. Prior to paying Genesis, Corixa will pay a percentage of revenue received related to the potential product to SR Pharma, Corixa's licensor for certain intellectual property related to PVAC treatment.

Additional Clinical Stage Programs

Corixa reviewed the status of it's Her-2/neu vaccine studies and the Anergix.RA(TM) clinical development program. With respect to Her-2/neu vaccines, a number of Phase I clinical studies are ongoing in testing various formulations and methods of delivery including the use of mixed peptides together with GM-CSF as an adjuvant, optimized peptides, as well as both dendritic cells and microspheres as delivery methods. The studies have shown that a number of Her-2/neu vaccine formulations are antigenic and have enabled refinement of methods for analyzing anti-cancer vaccine immunity in vitro using patient reagents. The company is in the process of starting Her-2/neu protein domain vaccine clinical studies.

A phase I/II clinical trial of an Anergix(R)-based product in rheumatoid arthritis was completed earlier in the year. The final study report from this randomized, placebo controlled dose-escalation study was submitted to Corixa's corporate development partner on AnergiX.RA -- Organon -- in the spring, resulting in a $1 million milestone payment to Corixa. Final data from the trial has been accepted for presentation at the American College of Rheumatology meeting in Philadelphia in November 2000.

Preclinical Activity

During the analyst meeting, Dr. Gillis also provided select highlights from the company's pipeline of novel vaccines and immunotherapies. When Corixa purchased Anergen in February of 1999, it realized that existing methods of manufacture of Anergix-based vaccines, as natural products, were not cost effective. Since then, Corixa has invested considerable time and effort in producing a recombinant version of the complex. The company has made considerable progress on recombinant expression of these vaccines and plans to introduce recombinant AnergiX-based products into clinical trials in the near future.

Earlier this year, Corixa announced two major collaborations with human monoclonal antibody producers Abgenix and Medarex. In both transactions, Corixa has agreed to provide proprietary antigen targets for production of human monoclonal antibodies. When it is determined that an antibody is worthy of clinical investigation, Corixa and the antibody-producing company enter into a closed auction to determine which party will retain the development rights. The party that loses the bid process will receive the up-front bid in cash as well as downstream development milestones and royalties. Gillis introduced two targets, both of which are currently being examined for production of monoclonal antibodies. The first target is an antigen from Candida, with the goal of the program being development of therapeutic antibodies for the treatment of systemic candidiasis, an often fatal infection in transplant and elderly patients. The second target was a peptide sequence from the human CXCR3 receptor. The CXCR3 receptor is a cell surface binding protein that interacts with several immune system hormones responsible for trafficking of autoimmune T-cells. Corixa has already shown that murine monoclonal antibodies directed against the CXCR3 receptor can provide effective therapy in multiple models of autoimmune disease.

About Melacine

Melacine melanoma vaccine consists of lysed (broken) cells from two human melanoma cell lines combined with Corixa's proprietary Detox(R) adjuvant. Detox adjuvant includes MPL(R) adjuvant (monophosphoryl lipid A) and mycobacterial cell wall skeleton, both of which activate the human immune system in the context of vaccination. Melacine, MPL and Detox were acquired by Corixa as part of its purchase of Ribi ImmunoChem Research, Inc., in October 1999.

About PVAC Treatment

According to the National Psoriasis Foundation, there are approximately seven million people in the U.S. with psoriasis. Published studies also indicate approximately 30 percent of U.S. psoriasis patients have a moderate to severe form of the disease. The disease is characterized by chronic inflammatory lesions with red, scaling plaques and is believed to be an autoimmune phenomenon mediated by T cells.

PVAC treatment is currently in Phase II clinical trials in the United States, the Philippines and Brazil. It is currently not approved for use by FDA. Moderate to severe psoriatic patients will receive two injections of PVAC treatment administered three weeks apart and will be monitored for a twelve week period following the second injection. Corixa hopes to complete the Phase II randomized, controlled trial by the end of calendar year 2000. Data from a Phase I/II open-label, trial performed in the Philippines demonstrated encouraging preliminary results. Approximately 20 moderate to severe psoriatic patients were treated in this investigational study. More than half of the patients treated demonstrated greater than a 75 percent decrease in disease severity in the 52-week trial. The main side effect was redness and erythema at the injection site. Median duration of improvement for the patients who responded was 51 weeks.

About Corixa

Corixa is a research- and development-based biotechnology company committed to treating and preventing autoimmune diseases, cancer and infectious diseases by understanding and directing the immune system. 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 vaccine components on a standalone basis. The company partners with numerous developers and marketers of pharmaceuticals and diagnostics, targeting products that are Powered by Corixa(TM) 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, Wash., with additional operations in Hamilton, Mont. and Redwood City, Calif. For more information, please visit Corixa's website at www.corixa.com or call the company's investor relations information line at 877/4CORIXA or 877/426-7492.

Forward Looking Statements

Except for the historical information presented, certain matters discussed in this press release are forward-looking statements. 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. Such risks and uncertainties include risks associated with product discovery and development as well as risks detailed from time to time in the company's public disclosure filings with the U.S. Securities and Exchange Commission (SEC), including its Quarterly Report on Form 10-Q filed on August 14, 2000, copies of which are available from the company's 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.