Press Release

Seattle Genetics Introduces Novel Technology for Empowering Antibodies
BOTHELL, Wash., Sep 22, 2009 (BUSINESS WIRE) -- Seattle Genetics, Inc. (Nasdaq:SGEN) announced today the introduction of its sugar engineered antibody (SEA) technology, a novel approach to increasing the potency of monoclonal antibodies through enhanced effector function. The technology will be presented today by Dennis Benjamin, Ph.D., Senior Director, Chemistry, during the Americas Antibody Congress being held in Washington, DC.

"We are committed to playing a leadership role in the field of empowered antibodies, including both our proprietary antibody-drug conjugate (ADC) and enhanced effector function technologies," said Clay B. Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. "Together, our ADC and SEA technologies provide us with alternative approaches to increase the potency of antibodies, allowing us to determine the most suitable technology based on the antibody, disease and expression profile of the target."

Seattle Genetics' SEA technology comprises modified sugars that inhibit the incorporation of fucose into the carbohydrate chains of monoclonal antibodies, resulting in enhanced antibody-dependent cellular cytotoxicity (ADCC) activity in preclinical models. Significantly, the modified sugars can be readily added to standard cell culture media, without impacting manufacturing processes and while maintaining yields and reproducible product quality. Seattle Genetics believes its SEA technology is simpler and less expensive as compared to existing technologies for enhancing antibody effector function because it can be applied to existing cell lines without cell line re-engineering. In model systems, the technology has been shown to be applicable across a range of antibodies and antibody-producing cell lines. Seattle Genetics has filed a patent application covering its novel SEA technology. The company intends to employ the SEA technology in its internal early-stage pipeline as well as consider collaborations with other companies.

Monoclonal antibodies possessing enhanced effector function are an emerging area of therapeutic research. There are at least 10 ADCC-enhanced antibodies in clinical trials using a variety of technologies. ADCC functions by recruiting the body's immune system to attack and kill target cells and is an important contributor to monoclonal antibody potency.

About Seattle Genetics

Seattle Genetics is a clinical stage biotechnology company focused on the development and commercialization of monoclonal antibody-based therapies for the treatment of cancer and autoimmune disease. The company's lead product candidate, brentuximab vedotin (SGN-35), is in a pivotal trial under a special protocol assessment with the FDA. Brentuximab vedotin is empowered by Seattle Genetics' proprietary ADC technology comprising highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. In addition, Seattle Genetics has two other product candidates in ongoing late-stage clinical trials: lintuzumab (SGN-33) and dacetuzumab (SGN-40) and one in early-stage clinical trials, SGN-70. Dacetuzumab is being developed under a worldwide collaboration with Genentech (a wholly-owned member of the Roche Group). Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen, Progenics, Daiichi Sankyo, MedImmune, a subsidiary of AstraZeneca, and Millennium: The Takeda Oncology Company, as well as an ADC co-development agreement with Agensys, a subsidiary of Astellas Pharma. More information can be found at www.seattlegenetics.com.

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential and future licensing of Seattle Genetics' SEA technology. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include risks inherent in early stage development and failure by Seattle Genetics to secure or maintain relationships with collaborators. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company's 10-Q for the quarter ended June 30, 2009 filed with the Securities and Exchange Commission. Seattle Genetics disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

SOURCE: Seattle Genetics, Inc.

Seattle Genetics, Inc.
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com