ZymoGenetics, Inc. today announced that interim findings were presented from a Phase 1b clinical trial with atacicept in B-cell chronic lymphocytic leukemia (B-CLL) at the American Society of Clinical Oncology (ASCO) 2007 annual meeting.



SEATTLE, WA, USA | June 4, 2007 |
ZymoGenetics, Inc. (Nasdaq: ZGEN) today announced that interim findings were presented from a Phase 1b clinical trial with atacicept in B-cell chronic lymphocytic leukemia (B-CLL) at the American Society of Clinical Oncology (ASCO) 2007 annual meeting. The study included intravenous administration of higher doses than had been tested in previous studies.

"We found that atacicept was well-tolerated and biologically active at all dose levels in this study, consistent with the results of our other clinical trials," said Douglas E. Williams, Ph.D., Executive Vice President and Chief Scientific Officer of ZymoGenetics. "Together with our partner Merck Serono, we will assess the results of this and our other B-cell malignancy studies, once the studies are complete, to see whether the data support moving forward in these indications."

Atacicept in B-CLL Study Design and Results
In a Phase 1b open-label, dose escalation study, 15 patients with refractory or relapsed disease were given weekly intravenous doses of atacicept ranging from 1 mg/kg to 20 mg/kg, for five weeks. Treatment with atacicept was well tolerated at all dose levels in the study. No dose limiting toxicities or serious adverse events related to study drug have been reported to date. Among the six patients given 10 mg/kg and 15 mg/kg, three (50%) showed signs of disease stabilization, using National Cancer Institute-sponsored Working Group criteria, during the treatment period. Prior to atacicept treatment, all of these patients had rapidly increasing leukocyte counts. One patient, who received 10 mg/kg, exhibited stable disease for over six months.

Biological activity of atacicept was demonstrated in these patients by reduced immunoglobulin (Ig) concentrations after treatment at all dose levels. Mean IgA, IgG and IgM concentrations decreased by 20%, 22% and 15% from baseline, respectively, after the first cycle of atacicept. Accrual and treatment of one additional cohort of B-CLL patients at a higher dose level is ongoing.

Abstract
The abstract is available at http://www.zymogenetics.com in the "What’s New" section on the home page.

About Atacicept
ZymoGenetics and Merck Serono, an affiliate of Merck KGaA, Darmstadt, Germany, are developing atacicept (formerly referred to as TACI-Ig) for the treatment of autoimmune diseases and B-cell malignancies. Atacicept contains the soluble TACI receptor that binds to the cytokines BLyS and APRIL. These cytokines are members of the tumor necrosis factor family that promote B-cell survival and autoantibody production associated with certain autoimmune diseases such as systemic lupus erythematosus (SLE). Current data indicates that levels of BLyS and APRIL are elevated in patients with rheumatoid arthritis, SLE and B-cell malignancies. Atacicept has been shown to affect several stages of B-cell development and may inhibit the survival of cells responsible for making antibodies.

About ZymoGenetics
ZymoGenetics creates novel protein drugs with the potential to significantly help patients fight their diseases. The Company is developing a diverse pipeline of potential proprietary product candidates that are moving into and through clinical development. These candidates span a wide array of clinical opportunities that include bleeding, autoimmune diseases and cancer. ZymoGenetics intends to commercialize these product candidates through internal development, collaborations with partners, and out-licensing of patents from its extensive patent portfolio. For further information, visit http://www.zymogenetics.com.

This press release contains "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements are based on the current intent and expectations of the management of ZymoGenetics. These statements are not guarantees of future performance and involve risks and uncertainties that are difficult to predict. ZymoGenetics’ actual results and the timing and outcome of events may differ materially from those expressed in or implied by the forward-looking statements because of risks associated with our unproven discovery strategy, preclinical and clinical development, regulatory oversight, intellectual property claims and litigation and other risks detailed in the company’s public filings with the Securities and Exchange Commission, including the company’s Annual Report on Form 10-K for the year ended December 31, 2006. Except as required by law, ZymoGenetics undertakes no obligation to update any forward-looking or other statements in this press release, whether as a result of new information, future events or otherwise.

SOURCE: ZymoGenetics, Inc.