Biogen Builds on Its 40-Year Legacy in Neuroscience with Presentation of Research from Its Portfolio of Medicines and Investigational Programs for Neurodegenerative Diseases

• New data underscore benefits of SPINRAZA^®
  (nusinersen) across broad spinal muscular atrophy (SMA) populations
  and include longer-term efficacy and safety assessments from the SHINE
  study
• Data from Biogen's multiple sclerosis (MS) research programs
  include results from clinical investigation of a potential biomarker
  for MS and new insights from MS PATHS, its Learning Health System,
  which may inform future care approaches
• Data from movement disorder programs support further clinical
  development of Biogen's investigational compounds for Parkinson's
  disease and progressive supranuclear palsy

Biogen
(NASDAQ:BIIB) announced it will present data from its portfolio of
marketed treatments and clinical development programs for some of the
most complex and difficult-to-treat neurodegenerative diseases at the 70^th
annual meeting of the American Academy of Neurology (AAN) in Los Angeles
(April 21–27).

"Biogen's research efforts are focused on helping to improve the
lives of the approximately one billion people affected by neurological
disorders,¹" said Alfred Sandrock, Jr., M.D., Ph.D.,
executive vice president and chief medical officer at Biogen. "The data
we are presenting at AAN reflect the work we are conducting on multiple
fronts, including research to better understand challenging nervous
system diseases and the clinical development of investigational
treatments for what we believe are some of the most significant unmet
medical needs."

Platform and poster presentations will highlight the benefits SPINRAZA
(nusinersen) provides for individuals with spinal muscular atrophy (SMA)
across the age and disease spectrum; the company's multiple sclerosis
(MS) therapies and non-therapeutic research collaborations designed to
elevate the care of MS; and the company's investigational therapies for
Alzheimer's disease, Parkinson's disease (PD) and progressive
supranuclear palsy (PSP).

Building on Substantial Data, Long-Term Benefits for Broad SMA
Populations

• Biogen will present data demonstrating that with SPINRAZA treatment,
  older patients were able to walk longer distances while experiencing
  stable or less fatigue at the same time, in contrast to SMA natural
  history data. The study participants had Type 2 or 3 SMA and were ages
  2-15 years at study enrollment.
• Several other analyses illustrating SPINRAZA's effectiveness will be
  presented, including part one of the Phase 2 EMBRACE study as well as
  an interim analysis of the SHINE open-label extension study. Featured
  in AAN's Emerging Science program, the SHINE analysis examined the
  longer-term safety and efficacy of SPINRAZA in infantile-onset SMA
  patients.

Elevating the Care of MS

• Data from Biogen's collaborative research initiative to identify a
  quantitative blood biomarker of MS disease severity will be presented.
  These data further support serum neurofilament light (NfL) as a
  promising biomarker for disease severity stratification and treatment
  monitoring in MS. A biomarker like NfL levels may enhance treatment
  decision-making and ultimately lead to better long-term outcomes for
  people with MS.
• Biogen will present updates from MS PATHS (Multiple Sclerosis Partners
  Advancing Technology and Health Solutions), a collaboration with 10
  leading MS centers in the U.S. and Europe that leverages technology
  deployed in routine care to generate standardized, high-quality data.
  Researchers anticipate more than 15,000 people with MS will
  participate in the study. MS PATHS allows researchers to evaluate
  common and disruptive MS symptoms, such as cognitive changes, to help
  drive more evidence-based, personalized treatment decisions.
• Real-world data will be presented that demonstrate people with
  relapsing MS treated with TECFIDERA^® (dimethyl fumarate) or
  TYSABRI^® (natalizumab) early in the course of their
  disease may experience better long-term outcomes.
• MRI and relapse results from the Phase 3 EVOLVE-MS-1 study for BIIB098
  (formerly known as ALKS 8700) in patients with relapsing remitting MS
  will be featured in AAN's Emerging Science program. BIIB098 is an
  oral, monomethyl fumarate (MMF) prodrug in Phase 3 development for the
  treatment of relapsing forms of MS.

Advancing the Company's Neurodegenerative Pipeline

• Data from the Phase 1b study of aducanumab, Biogen's investigational
  treatment for the early stages of Alzheimer's disease, will be
  presented. The aducanumab 36-month data from the Phase 1b PRIME study
  have been identified by AAN as a 2018 Abstract of Distinction, a
  program recognizing top scientific achievements in each abstract topic
  area; 24-month titration data will also be presented.
  
  Both
  slide presentations will be available concurrently with the applicable
  session on the Investor section of the Biogen company website, www.Biogen.com.
  
  Aducanumab
  is currently being evaluated in two global Phase 3 studies, ENGAGE and
  EMERGE, which are designed to evaluate its safety and efficacy in
  slowing cognitive and functional impairment in people with mild
  cognitive impairment (MCI) due to Alzheimer's disease and mild
  Alzheimer's disease dementia. Aducanumab is thought to target
  aggregated forms of beta amyloid, including soluble oligomers and
  insoluble fibrils, which can form into amyloid plaque in the brain of
  Alzheimer's disease patients. As of October 22, 2017, Biogen and Eisai
  Co. Ltd. are collaborating on the development and commercialization of
  aducanumab globally.

• Data from movement disorder programs will be presented at the meeting,
  including Phase 1 study results for BIIB092 (formerly BMS-986168), the
  tau-targeting antibody and investigational compound for PSP, as well
  as details about the design of the ongoing Phase 2 PASSPORT study. PSP
  is a rare neurodegenerative disease, considered to be a primary
  tauopathy, characterized by rapidly progressing physical impairments,
  such as difficulty speaking, swallowing and walking, as well as
  cognitive/behavioral impairments, such as apathy and dementia. Data
  for Biogen's investigation compound for PD, BIIB054, an
  alpha-synuclein targeting antibody, include Phase 1 study results
  demonstrating a favorable pharmacokinetics, as well as a safety and
  tolerability profile which support further clinical development.

Highlights of Biogen's platform and poster presentations:

SPINAL MUSCULAR ATROPHY
Platform Presentation

• Longer-term Assessment of the Safety and Efficacy of Nusinersen for
  the Treatment of Infantile-onset Spinal Muscular Atrophy (SMA): An
  Interim Analysis of the SHINE Study – Platform 003 – Tuesday, April
  24, 5:51-5:54 p.m. PT

Posters

• Evaluating Ambulatory Function and Fatigability in Children Treated
  with Nusinersen – Poster P2.322 – Monday, April 23, 11:30 a.m.-7:00
  p.m. PT
• Safety and Efficacy of Nusinersen in Infants/Children with Spinal
  Muscular Atrophy (SMA): Part 1 of the Phase 2 EMBRACE Study – Poster
  P2.324 – Monday, April 23, 11:30 a.m.-7:00 p.m. PT
• Characterization of Later Childhood/Adult Spinal Muscle Atrophy
  Patients and Their Transitions of Care Within U.S. Hospitals –
  Poster P4.454 – Wednesday, April 25, 11:30 a.m.-7:00 p.m. PT

MULTIPLE SCLEROSIS
Platform Presentations

• Serum Neurofilament Light (NfL): Towards a Blood Test for Prognosis
  and Disease/Treatment Monitoring in Multiple Sclerosis Patients – Platform
  S24.003 – Tuesday, April 24, 3:54-4:06 p.m. PT
• MRI and Relapse Results for ALKS 8700 in Patients with Relapsing
  Remitting Multiple Sclerosis: 1-year Interim Results from the Phase 3
  EVOLVE-MS-1 Study – Platform 006 – Tuesday, April 24, 5:45-7:00
  p.m. PT
• Benchmarks of Cognitive Performance in a Large, Representative Patient
  Population – Platform S44.007 – Thursday, April 26, 4:42-4:54 p.m.
  PT

Posters

• Comparative Effectiveness of Dimethyl Fumarate Versus Fingolimod and
  Teriflunomide on the Risk of Relapse in MS Patients Switching from
  First-generation Platform Therapies in the US – Poster P1.374 –
  Sunday, April 22, 11:30 a.m.-5:30 p.m. PT
• A Comparative Effectiveness Analysis Applying a 3-Way Propensity Score
  Matching to Real-world Data from the MSBase Registry in Preparation
  for a Cost-effectiveness Model: Patients Switching Within First-line
  Agents or to Either Natalizumab or Fingolimod in Active
  Relapsing-remitting Multiple Sclerosis (RRMS) – Poster P1.369 –
  Sunday, April 22, 11:30 a.m.-5:30 p.m. PT
• A Cost-effectiveness Analysis Using Real-world Data from the MSBase
  Registry: Comparing Natalizumab to Fingolimod in Patients with
  Inadequate Response to Disease-modifying Therapies in
  Relapsing-remitting Multiple Sclerosis (RRMS) in Scotland – Poster
  P1.364 – Sunday, April 22, 11:30 a.m.-5:30 p.m. PT
• Comparison of Techniques for Measurement of Brain Volume in Multiple
  Sclerosis Patients – Poster P3.354 – Tuesday, April 24, 11:30
  a.m.-7:00 p.m. PT
• The Functional Brain Network Remains Stable in Natalizumab-treated
  Multiple Sclerosis Patients: A One Year Study – Poster P3.369 –
  Tuesday, April 24, 11:30 a.m.-7:00 p.m. PT
• The Multiple Sclerosis Partners Advancing Technology and Health
  Solutions (MS PATHS) Patient Cohort – Poster P4.381 – Wednesday,
  April 25, 11:30 a.m.-7:00 p.m. PT
• Natalizumab Extended Interval Dosing (EID) is Associated with a
  Significant Reduction in Progressive Multifocal Leukoencephalopathy
  (PML) Risk Compared with Standard Interval Dosing (SID) in the TOUCH^®
  Prescribing Program – Poster P4.475 – Wednesday, April 25, 11:30
  a.m.-7:00 p.m. PT
• Clinical Trial and Post-Marketing Reports Indicate No Increased Risk
  of Herpes Zoster in Patients Treated with Delayed-release Dimethyl
  Fumarate – Poster P5.362 – Thursday, April 26, 11:30 a.m.-7:00 p.m.
  PT
• Real-world Strategies for Management of Gastrointestinal Events in
  Patients Treated with Delayed-release Dimethyl Fumarate: EFFECT
  Gastrointestinal Sub-study Results – Poster P5.345 – Thursday,
  April 26, 11:30 a.m.-7:00 p.m. PT
• Longer Duration of Natalizumab Exposure May Lessen Return of Disease
  Activity Following a Switch from Natalizumab to an Oral Therapy:
  Modelling Real-world Data from Relapsing-remitting Multiple Sclerosis
  (RRMS) Patients in the TYSABRI^® Observational Program (TOP)
  – Poster P6.379 – Friday, April 27, 11:30 a.m.-5:30 p.m. PT
• Real-world Improvement Across Functional Systems (FS) in
  Relapsing-remitting Multiple Sclerosis (RRMS) Patients Treated with
  Natalizumab in the TYSABRI Observational Program (TOP) – Poster
  P6.383 – Friday, April 27, 11:30 a.m.-5:30 p.m. PT

PIPELINE
Platform Presentations

• Aducanumab Titration Dosing Regimen: 24-Month Analysis from PRIME, a
  Randomized, Double-Blind, Placebo-Controlled Phase 1b Study in
  Patients with Prodromal or Mild Alzheimer's Disease – Platform
  S2.003 – Sunday, April 22, 1:24-1:36 p.m. PT
• Aducanumab 36-Month Data from PRIME: A Randomized, Double-blind,
  Placebo-controlled Phase 1b Study in Patients with Prodromal or Mild
  Alzheimer's Disease – Platform S2.004 – Sunday, April 22, 1:36-1:48
  p.m. PT
• Randomized, Double-blind, Placebo-controlled, Single Ascending Dose
  Study of Anti-alpha-synuclein Antibody BIIB054 in Patients with
  Parkinson's Disease – Platform S26.001 – Tuesday, April 24,
  3:30-3:42 p.m. PT
• Multiple Ascending Dose Study of the Tau-directed Monoclonal Antibody
  BMS-986168 in Patients with Progressive Supranuclear Palsy – Platform
  S27.004 – Wednesday, April 25, 8:24-8:32 a.m. PT

Poster

• Efficacy and Safety of BIIB092 in Patients with Progressive
  Supranuclear Palsy: PASSPORT Phase 2 Study Design – Poster P6.073 –
  Friday, April 27, 11:30 a.m.-5:30 p.m. PT

About SPINRAZA^®
SPINRAZA is being
developed globally for the treatment of SMA.

SPINRAZA is an antisense oligonucleotide (ASO), using Ionis
Pharmaceutical Inc.'s proprietary antisense technology, that is designed
to treat SMA caused by mutations or deletions in the SMN1 gene located
in chromosome 5q that leads to SMN protein deficiency. SPINRAZA alters
the splicing of SMN2 pre-mRNA in order to increase production of
full-length SMN protein.² ASOs are short synthetic strings of
nucleotides designed to selectively bind to target RNA and regulate gene
expression. Through use of this technology, SPINRAZA has the potential
to increase the amount of full-length SMN protein in individuals with
SMA.

SPINRAZA must be administered via intrathecal injection, which delivers
therapies directly to the cerebrospinal fluid (CSF) around the spinal
cord,³ where motor neurons degenerate in individuals with SMA
due to insufficient levels of SMN protein.⁴

SPINRAZA demonstrated a favorable benefit-risk profile. The most common
adverse reactions reported for SPINRAZA were upper respiratory
infection, lower respiratory infection, and constipation. Serious
adverse reactions of atelectasis were more frequent in SPINRAZA-treated
patients. Coagulation abnormalities and thrombocytopenia, including
acute severe thrombocytopenia, have been observed after administration
of some ASOs. Individuals may be at increased risk of bleeding
complications. Renal toxicity has been observed after administration of
some ASOs. SPINRAZA is present in and excreted by the kidney.

For additional important safety information, and the United States full
prescribing information, please visit www.spinraza.com or
your respective country's website.

About TECFIDERA^®
TECFIDERA is an oral
therapy for relapsing forms of MS, including relapsing-remitting MS, the
most common form of MS. More than 310,000 patients have been treated
with TECFIDERA worldwide with over 540,000 patient-years of experience.⁵
TECFIDERA has been proven to reduce the rate of MS relapses, slow the
progression of disability, and impact the number of MS brain lesions,
while demonstrating a favorable benefit-risk profile in people with
relapsing forms of MS, notably newly diagnosed and early switch
populations.⁶ In clinical trials, the most common adverse
events associated with TECFIDERA were flushing and gastrointestinal (GI)
events. Other side effects include a decrease in mean lymphocyte counts
during the first year of treatment, which then plateaued, and liver
function abnormalities, which resolved upon treatment discontinuation.
TECFIDERA is contraindicated in patients with a known hypersensitivity
to dimethyl fumarate or any of the excipients of TECFIDERA. Rare cases
of progressive multifocal leukoencephalopathy (PML), a rare
opportunistic viral infection of the brain which has been associated
with death or severe disability, have been seen with TECFIDERA patients
in the setting of prolonged moderate to severe lymphopenia.

The efficacy and safety of TECFIDERA have been studied in a large,
global clinical program, which includes an ongoing long-term extension
study.

For additional important safety information, and the United States full
prescribing information, please visit www.tecfidera.com or
your respective country's website.

About TYSABRI^®
TYSABRI is a disease
modifying therapy (DMT) approved in more than 80 countries including the
United States, the European Union, Canada, Australia and Switzerland. In
the United States, TYSABRI is indicated as monotherapy for the treatment
of patients with relapsing forms of MS. In the European Union, it is
indicated as single disease modifying therapy in adults with highly
active relapsing-remitting MS (RRMS) for patients with highly active
disease activity despite a full and adequate course of treatment with at
least one DMT or patients with rapidly evolving severe RRMS. TYSABRI is
proven effective, with over 10 years of experience in treating RRMS, and
more than 180,000 people treated worldwide and over 635,000
patient-years of experience.⁷

TYSABRI is a monoclonal antibody that selectively binds to α4-integrin
and is thought to interrupt the activity of inflammatory cells in MS
patients by blocking the interaction between α4β1-integrin and vascular
cell adhesion molecule-1. Disruption of these molecular interactions
prevents transmigration of leukocytes across the endothelium into
inflamed parenchymal tissue. The specific mechanism(s) by which TYSABRI
exerts its effects in MS have not been fully defined.

TYSABRI has advanced the treatment of MS patients with its proven
ability to slow the progression of disability, reduce relapse rates, and
impact the number of MRI brain lesions with a well-characterized safety
profile. Data from the Phase 3 AFFIRM trial, which was published in
the New England Journal of Medicine, showed that at two years, TYSABRI
treatment led to a 68 percent relative reduction (p<0.001) in the
annualized relapse rate when compared with placebo and reduced the
relative risk of disability progression by 42 to 54 percent (12-24-week
sustained respectively, both p<0.001). TYSABRI increases the risk of
PML, a rare opportunistic viral infection of the brain which has been
associated with death or severe disability. Risk factors that increase
the risk of PML are the presence of anti-JCV antibodies, prior
immunosuppressant use and longer TYSABRI treatment duration. Patients
who have all three risk factors have the highest risk of developing PML.
TYSABRI increases the risk of developing encephalitis and meningitis
caused by herpes simplex and varicella zoster viruses and clinically
significant liver injury has also been reported in the post-marketing
setting. Serious, life-threatening, and sometimes fatal cases have been
reported in the postmarketing setting in MS patients receiving TYSABRI.
Other serious adverse events that have occurred in TYSABRI-treated
patients include hypersensitivity reactions (e.g., anaphylaxis) and
infections, including opportunistic and other atypical infections.
Clinically significant liver injury has also been reported in the
post-marketing setting.

The overall benefit-risk profile of TYSABRI remains positive. For
additional important safety information and the full United States
prescribing information which includes a full list of adverse events,
please visit www.tysabri.com or
your respective country's website.

About Biogen
At Biogen, our mission is clear: we are
pioneers in neuroscience. Biogen discovers, develops, and delivers
worldwide innovative therapies for people living with serious
neurological and neurodegenerative diseases. One of the world's first
global biotechnology companies, Biogen was founded in 1978 by Charles
Weissmann, Heinz Schaller, Kenneth Murray and Nobel Prize winners Walter
Gilbert and Phillip Sharp, and today has the leading portfolio of
medicines to treat multiple sclerosis; has introduced the first and only
approved treatment for spinal muscular atrophy; and is focused on
advancing neuroscience research programs in Alzheimer's disease and
dementia, multiple sclerosis and neuroimmunology, movement disorders,
neuromuscular disorders, pain, ophthalmology, neuropsychiatry, and acute
neurology. Biogen also manufactures and commercializes biosimilars of
advanced biologics.

We routinely post information that may be important to investors on our
website at www.biogen.com.
To learn more, please visit www.biogen.com
and follow us on social media – Twitter,
LinkedIn,
Facebook,
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Biogen Safe Harbor
This press release contains
forward-looking statements made pursuant to the safe harbor provisions
of the Private Securities Litigation Reform Act of 1995 about additional
results from the Phase 2 EMBRACE study, Phase 2 SHINE study, and
CS2/CS12 study of SPINRAZA, the Phase 3 EVOLVE MS-1 study of BIIB098,
the Phase 1b study of aducanumab, the Phase 1 study of BIIB092, and/or
the Phase 1 study of BIIB054, the potential clinical effects of
SPINRAZA, TECFIDERA, TYSABRI, BIIB098, aducanumab, BIIB092 and/or
BIIB054, the identification and treatment of MS and Alzheimer's disease,
the treatment of SMA, and clinical studies on Parkinson's disease and
PSP. These statements may be identified by words such as "aim,"
"anticipate," "believe," "could," "estimate," "expect," "forecast,"
"intend," "may," "plan," "possible," "potential," "will," and other
words and terms of similar meaning, and are based on our current beliefs
and expectations. You should not place undue reliance on these
statements or the scientific data presented. Drug development and
commercialization involve a high degree of risk, and only a small number
of research and development programs result in commercialization of a
product. Results in early stage clinical trials may not be indicative of
full results or results from later stage or larger scale clinical trials
and do not ensure regulatory approval.

These statements involve risks and uncertainties that could cause actual
results to differ materially from those reflected in such statements,
including without limitation, the risk that we may not fully enroll our
clinical trials or enrollment will take longer than expected, unexpected
concerns may arise from additional data, analysis or results obtained
during our clinical trials, regulatory authorities may require
additional information or further studies, or may fail or refuse to
approve or may delay approval of our drug candidates, the occurrence of
adverse safety events, or we may encounter other unexpected hurdles. The
foregoing sets forth many, but not all, of the factors that could cause
actual results to differ from our expectations in any forward-looking
statement. Investors should consider this cautionary statement, as well
as the risk factors identified in our most recent annual or quarterly
report and in other reports filed with the Securities and Exchange
Commission. These statements are based on our current beliefs and
expectations and speak only as of the date of this press release. We do
not undertake any obligation to publicly update any forward-looking
statements, whether as a result of new information, future developments,
or otherwise.

¹ World Health Organization. Neurological disorders: Public
health challenges. 2007. Available at: http://www.who.int/mental_health/neurology/chapter_4_neuro_disorders_public_h_challenges.pdf?ua=1.
²
Hua Y, Sahashi K, Hung G, Rigo F, Passini MA, Bennett CF, Krainer AR.
Antisense correction of SMN2 splicing in the CNS rescues necrosis in a
type III SMA mouse model. Genes Dev. 2010 Aug 1; 24(15):16344-44.
³
Evers MM, Toonen LJ, van Roon-Mom WM. Antisense oligonucleotides in
therapy for neurodegenerative disorders. Adv Drug Deliv
Rev. 2015;87:90-103.
⁴ Lunn MR, Wang CH. Spinal
muscular atrophy. Lancet. 2008;371(9630):2120-2133.
⁵
Combined post-marketing and clinical trials exposure to TECFIDERA as of
31 January 2018.
⁶ TECFIDERA is approved in the European
Union for relapsing-remitting multiple sclerosis.
⁷
Global Natalizumab (TYSABRI) Postmarketing PML Update, March 2018.

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