AMEVIVE(TM) Phase II Clinical Trial on Retreatment of Patients With Moderate to Severe Chronic Plaque Psoriasis Presented at American Academy of Dermatology

Biogen, Inc. (Nasdaq: BGEN) today announced that retreatment with AMEVIVE(TM) (alefacept) in patients with moderate to severe chronic plaque psoriasis demonstrated positive results similar to that of the initial course of treatment. The results from this
Phase II multicenter retreatment trial were presented at the annual meeting of
the American Academy of Dermatology in Washington, DC.

Results from an earlier Phase II randomized, placebo controlled, double-
blind, multiple-dose study in patients with moderate to severe chronic plaque
psoriasis were previously reported. Because AMEVIVE is intended to be used as intermittent therapy, following the completion of the Phase II trial, patients from the study could elect to enroll into a retreatment protocol. The retreatment study, which is an on-going trial, is designed to determine the tolerability and efficacy of repeated courses of treatment with AMEVIVE. A large percentage of patients opted for retreatment. In total, 174 people have enrolled into the retreatment study.

The clinical response to AMEVIVE(TM) (alefacept) was consistent over
repeated courses of treatment, suggesting that subsequent courses have a similar profile as the initial course of treatment. Patients received two
courses of study therapy, and clinical response was evaluated at two weeks
post dosing using the Psoriasis Area and Severity Index (PASI). Responses were observed within the first four weeks and tended to be more rapid with the second course of treatment.

There were no reports of disease rebound, a condition where a patient’s
psoriasis becomes substantially more severe than at baseline once treatment is withdrawn.

Burt A. Adelman, M.D., Biogen’s Vice President of Medical Research, said, “The potential of AMEVIVE to provide the needed long-term and sustained solution for patients with moderate to severe chronic psoriasis is an exciting discovery for us. These data move us closer to our final goal of improving both the duration of response and safety for patients with moderate to severe chronic plaque psoriasis. We are looking forward to the results of the Phase III clinical trials which will be available mid-year.”

AMEVIVE is a disease-modifying agent with a highly selective mode of
action targeting a subset of T-cells – the memory effector T-cells – that play
a critical role in the pathogenesis of psoriasis. Earlier Phase II trials
yielded promising results including remission in some patients without
rebound. To date more than 1,500 people have been treated with AMEVIVE.

Psoriasis is a T-cell mediated inflammatory disorder of the skin that can cause considerable discomfort. It is a disease for which there is no cure and affects people of all ages. Psoriasis affects approximately two percent of the populations of European and North America. The rash of psoriasis consists of red, scaly areas that commonly occur on the scalp, elbows and knees. In moderate and severe cases, the involved areas can be extensive and cover a substantial percentage of a patient’s body.

In addition, limited disease can be considered severe if occurring on critical areas such as the palms or soles. Although individuals with mild psoriasis can often control their disease with topical agents, more than one million patients worldwide require
ultraviolet or systemic imunosuppressive therapy. Unfortunately, the inconvenience and risks of ultraviolet radiation and the toxicities of many therapies limit their long-term use. Moreover, patients usually have recurrence of psoriasis, and in some cases rebound, shortly after stopping immunosuppressive therapy. According to the National Psoriasis Foundation(NPF), the disease impacts a person’s psychological well being and social functioning as well as their physical functioning.

In addition to historical information, this press release contains
forward-looking statements within the meaning of the “safe harbor” provisions
of the Private Securities Litigation Reform Act of 1995. Reference is made in particular to statements regarding the therapeutic and commercial potential of AMEVIVE(TM) (alefacept). These statements are based on the Company’s current beliefs and expectations as to such future outcomes. Drug development
involves a high degree of risk. Success in early-stage clinical trials does not ensure that later-stage or larger scale clinical trials will be
successful. Factors which could cause actual results to differ materially
from the Company’s current expectations include the risk that the product may
not show the same therapeutic effect or safety profile in Phase III trials or
that problems or delays may arise during the development and testing of the commercial manufacturing process and product or in connection with the
regulatory approval process if the Company is successful in its clinical trial efforts, as well as the other risks and uncertainties described from time to time in the Company’s periodic reports filed with the Securities and Exchange Commission.

Biogen, Inc., winner of the U.S. National Medal of Technology, is a
biopharmaceutical company principally engaged in discovering and developing
drugs for human healthcare through genetic engineering. Headquartered in
Cambridge, MA, the Company’s revenues are generated from international sales
of AVONEX(R) (Interferon beta-1a) for treatment of relapsing forms of multiple
sclerosis, and from the worldwide sales by licensees of a number of products,
including alpha interferon and hepatitis B vaccines and diagnostic products ( Prescribing Information ).
Biogen’s research and development activities are focused on novel products to
treat inflammatory and autoimmune diseases, neurological diseases, cancer,
fibrosis and congestive heart failure. The Company maintains active clinical
research programs in protein therapeutics, small molecules, genomics and gene
therapy. For copies of press releases and additional information about the
Company, please consult Biogen’s Homepage on the World Wide Web at