CAMBRIDGE, Mass.
March 17, 2008

Archemix Corp., a biotechnology company focused on discovering, developing and commercializing aptamer therapeutics for rare hematological diseases, today announced that it started a Phase 2 clinical trial of ARC1779, which is designed to evaluate the safety and efficacy of ARC1779 as a first-in-class anti-platelet agent in patients suffering from a rare, life-threatening blood disorder known as thrombotic thrombocytopenic purpura, or TTP. There is no drug approved for the treatment of TTP and acute episodes of TTP are associated with a significant mortality rate, estimated to be as high as 20 percent.

"The initiation of this Phase 2 trial represents an important strategic milestone for Archemix because it demonstrates the continued advancement of our product portfolio of novel aptamer therapeutics for rare hematological diseases," said Errol DeSouza, Ph.D, President and Chief Executive Officer, Archemix. "Our emerging pipeline of aptamers for rare hematological conditions includes preclinical programs in sickle cell disease and hemophilia, as well as our clinical programs in TTP and other related platelet-mediated disorders. Focusing on rare diseases represent a strategic opportunity because there are often few or no approved therapies, a high unmet medical need, and a rapid regulatory path to commercialization, all in addition to requiring less commercialization infrastructure."

TTP is caused by failure of regulation of the activity of the protein known as von Willebrand Factor (vWF), which under normal conditions plays a key role in protecting the body from bleeding. However, if vWF is not properly regulated, it can lead to the formation of blood clots. These blood clots consume platelets causing a severe drop in a patient's normal platelet level. Patients suffering an acute episode of TTP experience widespread clotting and the resulting restriction of blood flow to critical organs such as the brain, kidneys and heart, which may cause strokes, seizures, kidney failure or heart attack. ARC1779 is an novel aptamer therapeutic designed to bind to and inhibit vWF, thus potentially increasing or restoring platelet counts to normal levels and reducing or eliminating the formation of blood clots that cause the morbidity and mortality associated with acute episodes of TTP.

This Phase 2 trial of ARC1779 in TTP is being conducted at the Medical University of Vienna, Austria and will assess the safety, pharmacokinetics and pharmacodynamic effects of ARC1779 in approximately 28 patients with vWF-mediated platelet function disorders, including acute TTP.

"This Phase 2 trial is a unique opportunity to characterize the pharmacodynamic effects of ARC1779 with respect to its fundamental mechanism of action in patients with a spectrum of vWF-related platelet function disorders," commented Dr. Bernd Jilma of the University of Vienna. "This trial will also assess the safety of ARC1779 in critically ill patients with acute TTP, and it will teach us how to optimize the regimen for administration of ARC1779 in such patients who are undergoing plasma exchange therapy, the current mainstay of treatment for TTP."

About TTP
Thrombotic thrombocytopenic purpura, or TTP, is a rare blood disorder that arises from uncontrolled activation of von Willebrand Factor (vWF), a protein which under normal conditions plays a key role in maintaining the normal balance between bleeding and clotting. In patients suffering from TTP, vWF binds excessively to platelets, causing excessive blood clots. These clots form throughout the circulation and can lead to serious medical consequences such as strokes, seizures, kidney failure and heart attack. Each year in the United States, between four and 11 new cases of TTP per million of the total population are diagnosed. There is no approved drug treatment for patients with TTP.

About ARC1779
ARC1779, a pegylated aptamer consisting of 40 nucleotides, is Archemix' lead product candidate for the treatment of TTP. ARC1779 is designed to inhibit the function of a protein called von Willebrand Factor, or vWF, which is, when activated, responsible for the adhesion, activation and aggregation of platelets.

In a Phase 1 trial conducted in 47 healthy volunteers, intravenous administration of ARC1779 demonstrated dose- and concentration-dependent inhibition of plasma vWF activity and platelet function. Furthermore, no serious adverse events were reported in the trial and no subject was withdrawn from the trial due to an adverse event. The key results of this trial were presented at the 2007 annual meeting of the American Heart Association, and were published in full in the journal Circulation in December, 2007.

About Aptamers
Aptamers are synthetically-derived oligonucleotides, or short nucleic acid sequences, that bind to protein targets with high affinity and specificity and can be designed to have a specified duration of action. Aptamers represent an emerging class of potential therapeutic agents that Archemix believes may have broad application to treat a variety of human diseases.

About Archemix
Archemix is a biotechnology company focused on discovering, developing and commercializing aptamer therapeutics. Using Archemix's proprietary processes for discovering aptamers, which are protected by its broad patent portfolio, Archemix is developing aptamer product candidates for rare hematological diseases. In addition, Archemix has licensed its intellectual property to third parties to develop their own aptamer product candidates. Currently, Archemix and its licensees are evaluating five different aptamer product candidates in human clinical trials; three in Phase 2 and two in Phase 1. To date, Archemix has licensed its intellectual property to discover and develop aptamer product candidates to nine biotechnology and pharmaceutical companies, including Pfizer, Merck Serono, Takeda Pharmaceuticals and Elan Pharma.