Transkaryotic Therapies, Inc. (TKTX) Achieves GA-GCB Clinical Milestone 
10/19/2005 5:13:13 PM

CAMBRIDGE, Mass., April 20 /PRNewswire-FirstCall/ -- Transkaryotic Therapies, Inc. today announced that the last patient has completed treatment in its open-label Phase I/II clinical trial evaluating its investigational enzyme replacement therapy for Gaucher disease, Gene- Activated(R) glucocerebrosidase, or GA-GCB. The Phase I/II clinical trial evaluated the safety of GA-GCB as well as its clinical activity in 12 patients. The company expects to report top-line results of the study in the second half of 2005. Assuming the results are favorable, the company intends to commence a pivotal trial in 2006, designed to support an approval of GA-GCB in 2008.

In March 2005, TKT completed its pivotal clinical trial evaluating its investigational enzyme replacement therapy Iduronate-2-Sulfatase, I2S, for the treatment of Hunter syndrome in 96 patients. The company is currently gathering and verifying the final data and expects to unblind the study and report top-line results in June 2005. If the results are positive, TKT intends to file for regulatory approval in both the United States and Europe during the second half of 2005. From May 23, 2005 until it reports top-line results TKT will suspend its investor relations activities.

TKT is expecting to receive results of a Phase III study evaluating Dynepo as a treatment for anemia associated with cancer chemotherapy that was previously completed by Sanofi-Aventis. Under a September 2004 agreement, Sanofi-Aventis has agreed to conduct the analysis and provide TKT with the data after the FDA provides final input on the statistical analysis plan. TKT previously expected to report top-line results from this study in the first half of 2005, however the company now expects the results to be available in June or in the third quarter of 2005.

"We are very pleased that the treatment phase of the GA-GCB Phase I/II clinical trial and the I2S pivotal study are now completed. Many of the patients in these trials relocated internationally in order to gain access to our investigational products; and we are very grateful to these patients and their families for their many sacrifices," said Michael J. Astrue, President and Chief Executive Officer of TKT. "We intend to continue executing on our established clinical and regulatory objectives throughout 2005, which we hope will allow us to achieve our goal of generating revenue from three commercial products in 2006."

About TKT

Transkaryotic Therapies, Inc. is a biopharmaceutical company primarily focused on researching, developing and commercializing treatments for rare diseases caused by protein deficiencies. Within this focus, the company markets Replagal(TM), an enzyme replacement therapy for Fabry disease, and is developing treatments for Hunter syndrome and Gaucher disease. In addition to its focus on rare diseases, TKT intends to commercialize Dynepo(TM), its Gene- Activated(R) erythropoietin product for anemia related to kidney disease, in the European Union. TKT was founded in 1988 and is headquartered in Cambridge, Massachusetts, with additional operations in Europe, Canada and South America. Additional information about TKT is available on the company's website at

Forward-Looking Statements

This press release contains forward-looking statements including statements regarding TKT's development of certain products, including I2S, GA- GCB and Dynepo, as well as statements containing the words "believes," "anticipates," "plans," "expects," "estimates," "intends," "should," "could," "will," "may," and similar expressions. There are a number of important factors that could cause the company's actual results to differ materially from those indicated by such forward-looking statements, including: whether any of the company's products will achieve the commercial success anticipated by the company; the timing of submissions to and decisions by regulatory authorities regarding clinical trials and marketing and other applications; whether the FDA, the EMEA and equivalent regulatory authorities will grant marketing approval for the company's products on a timeline consistent with TKT's expectations, or at all; whether TKT will be able to complete clinical trials of its products on a timely basis; whether the results of clinical trials will be consistent with the results of earlier clinical trials of the company's products and warrant further clinical trials or submission of applications for regulatory approval for such products to the FDA and equivalent regulatory authorities; whether TKT and its third party manufacturers will be able to complete the manufacturing development necessary to satisfy regulatory requirements on a timeline consistent with TKT's expectations or at all and to manufacture sufficient quantities of TKT's products to satisfy both clinical trial requirements and commercial demand, or to manufacture material at all, if approved; the availability and extent of coverage from third party payors and the timing and receipt of reimbursement approvals for the company's products; whether competing products will reduce any market opportunity that may exist; whether TKT will be able to enter into a collaboration agreement for Dynepo in Europe and whether such collaboration will be successful; results of ongoing litigation and the risks of future litigation; whether competitors will be able to limit access to markets in which TKT is attempting to sell Dynepo, through legal maneuvering or otherwise; and other factors set forth under the caption "Certain Factors That May Affect Future Results" in the company's annual report on Form 10-K for the year ending December 31, 2004, which is on file with the Securities and Exchange Commission and which factors are incorporated herein by reference. While the company may elect to update forward-looking statements at some point in the future, the company specifically disclaims any obligation to do so, even if its expectations change.

Gene-Activated(R) is a registered trademark and Replagal(TM) is a trademark of Transkaryotic Therapies, Inc. Dynepo(TM) is a trademark of Sanofi-Aventis SA.

For More Information Contact: Justine E. Koenigsberg Senior Director, Corporate Communication (617) 349-0271 Daniella M. Lutz Manager, Corporate Communications (617) 349-0205

Photo: NewsCom: Archive: Photo Desk, photodesk@prnewswire.comTranskaryotic Therapies, Inc.

CONTACT: Justine E. Koenigsberg, Senior Director, CorporateCommunication, +1-617-349-0271, or Daniella M. Lutz, Manager, CorporateCommunications, +1-617-349-0205, both of Transkaryotic Therapies, Inc.