Seattle Genetics Reports Preclinical Data on its SGN-40 and SGN-70 Programs at the American Society of Hematology Annual Meeting.

BOTHELL, Wash. -- SGN-40 clinical data reported in prior meeting sessions

Seattle Genetics, Inc. (Nasdaq:SGEN) reported preclinical data from its SGN-40 and SGN-70 programs at the American Society of Hematology (ASH) 2005 Annual Meeting being held in Atlanta December 10-13. Preclinical studies of SGN-40 demonstrated broad application in B-cell malignancies, including Hodgkin's disease and chronic lymphocytic leukemia, and in combination with lenalidomide (Revlimid(R)). Preclinical studies of SGN-70 have shown that it has therapeutic potential in hematologic malignancies.

"At this year's ASH conference, Seattle Genetics reported data on multiple clinical and preclinical programs, which we believe demonstrates our significant progress and the depth of our science and product pipeline," said Clay B. Siegall, Ph.D., President and Chief Executive Officer at Seattle Genetics. "Our preclinical studies supplement the objective responses reported at ASH in our SGN-40 clinical trials and underscore the potential of SGN-40 as a single agent, as well as in combination with other treatments. SGN-70 represents an exciting future product opportunity that we are advancing toward a planned clinical trial in 2007."

SGN-40 Preclinical Studies

SGN-40 is a humanized monoclonal antibody that targets the CD40 antigen, which is expressed on most B-cell lineage hematologic malignancies. Seattle Genetics is conducting clinical trials of SGN-40 in multiple myeloma, non-Hodgkin's lymphoma and chronic lymphocytic leukemia. In addition, a number of preclinical studies are ongoing.

Humanized Anti-CD40 Antibody SGN-40 Effectively Induces Cytotoxicity Against Chronic Lymphocytic Leukemia (CLL) Cells through Antibody Mediated Cytotoxicity and Demonstrates Modest Biologic Evidence of CD40 Activation (Abstract #2966)

In preclinical studies, SGN-40 was found to have antitumor activity in models of chronic lymphocytic leukemia (CLL) through antibody-dependent cellular cytotoxicity (ADCC). Seattle Genetics recently initiated a phase I/II clinical trial of SGN-40 in CLL.

The Humanized Anti-CD40 Monoclonal Antibody SGN-40 Targets Hodgkin's Disease Cells Through Multiple Mechanisms (Abstract #1476)

CD40 was found to be highly expressed on approximately 80 percent of Hodgkin's disease primary patient samples. SGN-40 was shown to have potent effector function against CD40-positive Hodgkin's disease cells, suggesting that Hodgkin's disease may be a suitable therapeutic target for SGN-40.

Immunomodulatory Drug Lenalidomide (CC-5013, IMiD3) Augments Anti-CD40 SGN-40-Induced Cytotoxicity in Human Multiple Myeloma: Clinical Implications (Abstract #5150)

SGN-40 was evaluated in preclinical studies in combination with the immunomodulatory drug lenalidomide (Revlimid(R)), an investigational compound for the treatment of multiple myeloma. Results indicate that the combination enhanced cell-killing against multiple myeloma cells, suggesting that a clinical regimen combining SGN-40 and lenalidomide may result in increased efficacy.

SGN-70 Preclinical Studies

A Humanized Anti-CD70 Monoclonal Antibody Targets CD70-Expressing Multiple Myeloma (Abstract #1591)

SGN-70 is a humanized monoclonal antibody that targets the CD70 antigen, which is highly expressed on a variety of hematologic malignancies. SGN-70 demonstrates potent effector functions, including antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC) and antibody-dependent cellular phagocytosis (ADCP). SGN-70 also significantly prolongs survival in preclinical models of lymphoma and multiple myeloma. These data indicate that SGN-70 possesses potent antitumor activity and has therapeutic potential in the treatment of hematologic malignancies.

About Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development of monoclonal antibody-based therapies for the treatment of cancer and immunologic diseases. The company is conducting multiple clinical trials of its three lead product candidates, SGN-30, SGN-40 and SGN-33, and preclinical development of several late-stage programs. In addition, Seattle Genetics has developed proprietary antibody-drug conjugate (ADC) technology comprised of highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. The company currently has license agreements for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen and MedImmune. More information about Seattle Genetics' pipeline and technologies 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 future advancement and therapeutic potential of Seattle Genetics' SGN-40 and SGN-70 programs. 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 negative or adverse results in clinical trials as SGN-40 progresses or delays in, or the inability to initiate, clinical trials for SGN-70. More information about the risks and uncertainties faced by Seattle Genetics is contained in the Company's filings 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.