Positive Topline Results from Phase II Trial (EDEMA2) with DX-88 for the Treatment of Hereditary Angioedema Presented at AAAAI Meeting.

CAMBRIDGE, Mass. -- Dyax Corp. (Nasdaq:DYAX) today announced the presentation of positive topline data from the Company's completed open-label Phase II clinical trial, referred to as EDEMA2, with DX-88 for the treatment of hereditary angioedema (HAE). In this study DX-88 was well tolerated and successful in treating all types of attacks, including peripheral, abdominal and life-threatening laryngeal attacks, whether administered through the intravenous (IV) or subcutaneous (SQ) route of administration. DX-88 is being developed in a joint venture with Genzyme Corporation for the treatment of HAE, a debilitating and life-threatening inflammatory condition characterized by unpredictable attacks of severe pain and swelling.

Dr. William Lumry, M.D., medical director and principal investigator of AARA Research Center of Dallas, TX, presented topline data from Dyax's open-label, EDEMA2 (Evaluation of DX-88's Effects on Mitigating Angioedema) trial in an oral presentation titled, "A Multicenter, Open-Label, Study of DX-88 for Multiple Attacks of Hereditary Angioedema; EDEMA2 Interim Results" at the American Academy of Asthma, Allergy & Immunology Conference (AAAAI) in Miami Beach, FL on Sunday, March 5, 2006.

The topline results indicate that, in this study, DX-88 provided substantial therapeutic benefit in HAE patients who experienced acute attacks, including life-threatening laryngeal attacks. Dr. Lumry presented results on a subset of the 240 attacks that were treated in the trial. He presented data on 215 attacks observed in 72 patients who had variable or fixed doses of DX-88, either 5 mg/m2, 10 mg/m2 or 20 mg/m2 intravenously or 30 mg subcutaneously. Of the 215 attacks analyzed in the presentation, 176 attacks were treated in 62 patients through IV infusion and 39 attacks were treated in 22 patients through SQ administration, with 42 patients receiving multiple doses. Of the patients treated for multiple attacks, one was dosed 10 times, another 12 and a third 18 times.

In this study, all types of attacks were treated by either IV or SQ administration of DX-88: laryngeal (n=31, 14.4%), abdominal (n=101, 47.0%), and peripheral (n=83, 38.6%). Clinical response, defined as beginning of improvement of HAE symptoms within four hours of dosing with DX-88, was observed at all dose levels. For the IV dosing (5 mg/m2, 10 mg/m2, 20 mg/m2), the response rates ranged from 86% to 100%, while the SQ outcome (30 mg fixed dose) showed a 100% response rate. The overall median time to onset of improvement for the 215 attacks was 28 minutes. The time to onset of response was slightly better (20 minutes) with SQ compared to IV administration. In a preliminary analysis, data to date indicate that time to significant improvement as well as maintenance of response at 24 hours appear to be dose and route dependent with the 30 mg SQ dose being superior to the IV administration at any dose.

With regard to the overall safety profile of DX-88 in EDEMA2, the drug has been well tolerated. There have been no local injection site reactions. In the overall DX-88 experience to date, eight patients (4%) have experienced an acute dosing reaction: six patients on first administration (two patients in EDEMA2) of the IV infusion (probably related to infusion rate) and two patients (both in EDEMA2) after multiple administration (one IV and one SQ). These symptoms included rhinitis, flushing and nausea, but with no evidence of anaphylaxis, such as tryptase elevation. All patients responded rapidly to the treatment and had complete resolution of the HAE symptoms, showing no decrease in efficacy of the drug upon repeat dosing.

DX-88 antibodies have been detected in three patients treated in this study. One patient had DX-88 antibodies with no apparent impact. Two patients with antibodies did manifest single, separate acute dosing reactions. Both patients have since been rechallenged, with one patient being retreated three times subsequent to rechallenge. There has been no recurrence of these side effects in either patient or decrease in efficacy in the patient retreated for HAE symptoms.

Commenting on the program, Dr. Lumry stated, "I'm very impressed with the DX-88 results to date. Since there is no current treatment in the U.S. for acute HAE attacks, I believe that, if approved, DX-88 has great potential in the U.S. market." He added, "HAE patients live in constant fear of having an attack, and Dyax and Genzyme are tackling this issue head on in their trials. I continue to be encouraged by the high response rates to date and believe that DX-88 represents a real possible breakthrough in the treatment of hereditary angioedema."

Dr. Thomas R. Beck, President and Chief Operating Officer of Dyax Corp., stated, "We are extremely pleased with the topline results from our EDEMA2 trial. In this open-label trial, we were able to move to a fixed dose of 30 mg, the same dose currently being administered subcutaneously in our ongoing pivotal Phase III trial. By January 2006, we had administered 327 doses of DX-88 to 113 angioedema patients. With the breadth and depth of data from our program to date, we think that it is clear that we are on the right track to be first to market with a treatment for the U.S. HAE population."

About Dyax

Dyax Corp. is focused on advancing novel biotherapeutics for unmet medical needs, with an emphasis on cancer and inflammatory indications. Dyax utilizes its proprietary drug discovery technology to identify antibody, small protein and peptide compounds for clinical development.

Dyax's lead product candidate is DX-88, a recombinant small protein that is currently in clinical trials for its therapeutic potential in two separate indications. In its joint venture with Genzyme Corporation, Dyax has successfully completed three Phase II trials of DX-88 for the treatment of hereditary angioedema (HAE). A pivotal Phase III trial is ongoing. Independently, Dyax has successfully completed a Phase I/II trial of DX-88 for the prevention of blood loss during heart surgery (CABG procedures) and is in partnering discussions for further development of DX-88 in this indication as well as planning a Phase IIb trial. DX-88 has orphan drug designation in the U.S. and E.U., as well as Fast Track designation in the U.S., for the treatment of HAE.

Dyax identified DX-88 and other compounds in its pipeline using Dyax's patented phage display technology, which rapidly selects compounds that bind with high affinity and specificity to therapeutic targets. Dyax leverages its technology broadly with over 75 revenue generating licenses and collaborations for therapeutic discovery, as well as in non-core areas such as affinity separations, diagnostic imaging, and research reagents.

Dyax Disclaimer

This press release contains forward-looking statements, including statements regarding the potential administration, dosing, safety and therapeutic benefit of DX-88 for HAE, its position versus other products in development for HAE and plans for development of DX-88 for CABG. Statements that are not historical facts are based on Dyax's current expectations, beliefs, assumptions, estimates, forecasts and projections about the industry and markets in which Dyax competes. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors which may affect the potential administration, dosing and therapeutic benefit of DX-88 for HAE, and its position versus other products in development for HAE include the risks that: DX-88 may not show sufficient therapeutic effect or an acceptable safety profile in clinical trials or could take a significantly longer time to gain regulatory approval than Dyax expects or may never gain approval; others may develop technologies or products superior to DX-88 or that are on the market before DX-88; DX-88 may not gain market acceptance; Dyax is dependent on the expertise, effort, priorities and contractual obligations of third parties in the clinical trials, manufacture, marketing, sales and distribution of DX-88; and other risk factors described or referred to in Dyax's most recent Annual Report on Form 10-K and other periodic reports filed with the Securities and Exchange Commission. Dyax cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Dyax undertakes no obligations to update or revise these statements, except as may be required by law. Dyax and the Dyax logo are the registered trademarks of Dyax Corp. EDEMA2 is a service mark of Dyax Corp.

Dyax is headquartered in Cambridge, Massachusetts, and has antibody discovery facilities in Liege, Belgium. For online information about Dyax Corp., please visit www.dyax.com.