Preclinical Study Published in Nature Medicine Shows Anti-LINGO-1 Antibody Promotes Remyelination

Biogen Idec (NASDAQ: BIIB) announced today the publication of
findings from a preclinical study reporting that the anti-LINGO-1
antibody can promote spinal cord remyelination and axonal integrity,
suggesting a potential role as a treatment for multiple sclerosis (MS)
and other demyelinating diseases of the central nervous system (CNS).
The results are published in the October issue of Nature Medicine, and
confirm previously published data that suggested a role for the
anti-LINGO-1 antibody in CNS myelin repair.

LINGO-1 appears to act as a molecular switch that controls the
ability of cells in the CNS to produce myelin, the protective cellular
sheath surrounding nerve fibers that assists nerves in conducting
electrical impulses. When myelin is damaged by autoimmune diseases
such as MS, nerve cells lose their ability to send signals to the
body. As this damage progresses, these cells may eventually die,
contributing to disability. Although MS therapies can slow the
progression of this damage, none are able to repair the lost myelin.
Biogen Idec scientists had previously discovered that LINGO-1 may act
to prevent myelin repair after injury. In the study published today,
by blocking LINGO-1, scientists were able to promote myelin repair and
improve recovery in an animal model of MS.

"While preliminary, these findings are encouraging and suggest
that the anti-LINGO-1 antibody has the potential to repair some of the
damage caused to the CNS. This may be an entirely new approach to
treating MS," said Alfred Sandrock, MD, PhD, Senior Vice President,
Neurology Research and Development, Biogen Idec. "The anti-LINGO-1
program is a key part of our research and development efforts in MS.
We have a diverse pipeline of therapeutic candidates targeting
multiple pathways and patient needs with the goal of offering a
portfolio of options for people living with this devastating disease."

In the study, functional recovery from demyelination was modeled
by tracking the disease progression of experimental autoimmune
encephalomyelitis (EAE), a widely accepted animal model for studying
the clinical and pathological features of MS. The anti-LINGO-1
antibody was administered before disease onset and was found to
decrease the severity of EAE across all stages of disease progression,
when compared to the control treatment group. In a related study,
anti-LINGO-1 antibody treatment resulted in significantly reduced EAE
symptoms even when it was administered after disease onset.

The study found that functional recovery, as measured by EAE
scores, correlated with improved axonal integrity and axonal
remyelination. Physiological improvements in axonal integrity were
revealed by magnetic resonance DTI imaging. At the cellular level, the
production of new myelin sheaths was revealed by histological staining
and electron microscopy.

"This is a very exciting early indication that therapies targeted
at myelin repair within the CNS can have a dramatic effect on
behavioral functional outcome in models of multiple sclerosis, and
opens the door for the identification of additional regulators of
myelin repair that might be used to enhance functional recovery in
patients with MS," said Robert H. Miller, PhD, Principal Investigator,
Myelin Repair Foundation and Director of the Center for Translational
Neuroscience, Case Western Reserve University.

Anti-LINGO-1 was discovered by Biogen Idec and is one of several
programs in the company's industry-leading research and development
efforts in MS. In addition to its two marketed products, the company
has four programs in clinical development for the treatment of MS.

About Biogen Idec

Biogen Idec creates new standards of care in therapeutic areas
with high unmet medical needs. Founded in 1978, Biogen Idec is a
global leader in the discovery, development, manufacturing, and
commercialization of innovative therapies. Patients in more than 90
countries benefit from Biogen Idec's significant products that address
diseases such as lymphoma, multiple sclerosis, and rheumatoid
arthritis. For product labeling, press releases and additional
information about the company, please visit www.biogenidec.com.

Safe Harbor/Forward-Looking Statements

This press release contains forward-looking statements regarding
anti-LINGO-1 antibody, which is currently in the preclinical stage of
drug development. Drug development involves a high degree of risk.
Only a small number of research and development programs result in
commercialization of a product. Factors which could cause actual
results to differ materially from Biogen Idec's current expectations
include the risk that the company may not be able to demonstrate the
safety and efficacy of anti-LINGO-1 antibody at each stage of the
clinical trial process; technical hurdles relating to the manufacture
of anti-LINGO-1 antibody may be encountered; the company may not be
able to meet applicable regulatory standards or regulatory authorities
may fail to approve anti-LINGO-1 antibody; and the company may
encounter other unexpected hurdles. For more detailed information on
the risks and uncertainties associated with Biogen Idec's drug
development and other activities, see the periodic and current reports
that the company has filed with the Securities and Exchange
Commission. Biogen Idec assumes no obligation to update any
forward-looking statements, whether as a result of new information,
future events or otherwise.