ZymoGenetics, Inc. Presents Results From Two Atacicept Phase 1b Clinical Trials In B-Cell Cancer

SEATTLE, Dec. 12 /PRNewswire-FirstCall/ -- ZymoGenetics, Inc. today presented results from two Phase 1b studies in patients with non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM) at the American Society of Hematology (ASH) annual meeting. Treatment with atacicept was well tolerated and drug activity was demonstrated by consistent biologic marker responses.

"Our Phase 1 clinical trial program has demonstrated that atacicept is well tolerated and has given us a solid understanding of how dosing correlates with biological activity," said Nicole Onetto, M.D., Senior Vice President and Chief Medical Officer of ZymoGenetics. "Based on a foundation of excellent safety data and predictable dose response, we look forward to the results of our additional B-CLL clinical trial and further data from our Phase 2 program in autoimmune disease."

An additional ASH presentation reviewed preclinical data showing that atacicept, which inhibits both BLyS and APRIL, had efficacy in vivo as compared to a BLyS/BAFF-only inhibitor, BAFFR-Ig. The study demonstrated the ability of atacicept to inhibit MM growth in animal models and showed that for several grafts, atacicept was more efficacious in inhibiting MM tumor growth than was BAFFR-Ig. This finding suggests that APRIL has a non-redundant role in the survival of MM cells from certain subjects. The authors further suggested that TACI RNA expression levels in MM cells may be a useful predictive marker for responsiveness to treatment with atacicept.

Study Design and Results

Relapsed and Refractory B-Cell Lymphoma

In the Phase 1b open-label, dose-escalation study of atacicept in 15 patients with relapsed or refractory B-cell lymphoma, atacicept was administered subcutaneously for 5 weeks in single weekly doses of 2, 4, 7 or 10 mg/kg to sequential dose cohorts.

Study results: Atacicept at doses of up to 10 mg/kg was well tolerated. Biological activity was shown by decreasing Ig concentrations in this heavily pretreated cohort of patients with refractory B-cell lymphoma. Tumor responses were not observed.

Refractory or Relapsed Multiple Myeloma or Active Previously Treated Waldenstrom's Macroglobulinemia (WM)

The open-label, dose-escalation Phase 1b study enrolled 16 patients with refractory or relapsed MM or active, progressive WM. Sequential cohorts received one cycle of 5 weekly subcutaneous injections of atacicept at 2, 4, 7 or 10 mg/kg.

Study results: Treatment with atacicept was well tolerated. No dose limiting toxicity was observed. A biological response was observed in this heavily treated refractory population. Disease stabilization was seen in several patients.

About Atacicept

ZymoGenetics and Serono 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.

Posters

The ASH atacicept posters will be available at www.zymogenetics.com in the 'What's New' section on the home page.

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 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, 2005. 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.

Investor Relations John Calhoun, MD, MBA Director, Corporate Communications & Investor Relations 206-442-6744 Media Relations Susan W. Specht, MBA Associate Director, Corporate Communications 206-442-6592

ZymoGenetics, Inc.

CONTACT: investors, John Calhoun, MD, MBA, Director, CorporateCommunications & Investor Relations, +1-206-442-6744, or media, Susan W.Specht, MBA, Associate Director, Corporate Communications, +1-206-442-6592,both of ZymoGenetics, Inc.

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