NITE Nightstar Therapeutics Plc ADS

Nightstar Therapeutics plc (“Nightstar”) is pleased to announce that, further to the announcement on 5 June 2019 that the High Court of Justice of England and Wales had sanctioned the scheme of arrangement, the Court Order has been delivered to the Registrar of Companies of England and Wales. Accordingly, the Scheme has now become Effective in accordance with its terms and the entire issued and to be issued share capital of Nightstar has been acquired by Tungsten Bidco Limited, a newly-incorporated company and wholly-owned indirect subsidiary of Biogen Inc.

Trading in Nightstar ADSs on the Nasdaq Global Market will be halted with immediate effect from today and the cancellation of listing is expected to become fully effective on 17 June 2019.

Full details of the Scheme are set out in the combined circular and proxy statement dated 9 April 2019 (the “Scheme Document”). Unless otherwise defined herein, capitalised terms and expressions used in this announcement shall have the meanings given to them in the Scheme Document.

Enquiries:

Nightstar

Investor Information                            investors@nightstartx.com

Media Enquiries                                  media@nightstartx.com

Information                                          info@nightstartx.com

Centerview Partners (Financial adviser to Nightstar)

Alan Hartman                                      +1 212 380 2665

Andrew Rymer                                    +1 212 429 2349

James Hartop                                      +44 (0)20 7409 9730

Finsbury (PR adviser to Nightstar)

Kal Goldberg                                       +1 646 805 2005

Chris Ryall                                           +1 646 306 0747

Abigail Farr                                          +1 646 805 2090

Important notices relating to financial advisers

Centerview Partners UK LLP ("Centerview Partners"), which is authorised and regulated by the FCA, is acting exclusively for Nightstar and no one else in connection with the matters referred to in this announcement. Centerview Partners is not and will not be responsible to anyone other than Nightstar for providing the protections afforded to its clients or for providing advice in connection with the contents of this announcement or any matter referred to in this announcement.

The City Code on Takeovers and Mergers

The City Code on Takeovers and Mergers does not apply to the Acquisition.

Overseas shareholders

The release, publication or distribution of this announcement in jurisdictions other than the United Kingdom and the United States may be restricted by law and therefore any persons who are subject to the laws of any jurisdiction other than the United Kingdom or the United States (including Restricted Jurisdictions) should inform themselves about, and observe, any applicable legal or regulatory requirements. Any failure to comply with applicable legal or regulatory requirements of any jurisdiction may constitute a violation of securities laws in that jurisdiction. This announcement has been prepared for the purpose of complying with English law and the information disclosed may not be the same as that which would have been disclosed if this announcement had been prepared in accordance with the laws of jurisdictions outside England.

Copies of this announcement and any formal documentation relating to the Acquisition are not being, and must not be, directly or indirectly, mailed or otherwise forwarded, distributed or sent in or into or from any Restricted Jurisdiction or any jurisdiction where to do so would constitute a violation of the laws of such jurisdiction and persons receiving such documents (including custodians, nominees and trustees) must not mail or otherwise forward, distribute or send them in or into or from any Restricted Jurisdiction. Doing so may render invalid any related purported vote in respect of acceptance of the Acquisition.

Further details in relation to Nightstar Shareholders in overseas jurisdictions are contained in the Scheme Document.

Notice to U.S. investors in Nightstar

The Acquisition relates to the shares of a U.K. company and is being made by means of a scheme of arrangement provided for under Part 26 of the Companies Act 2006 and subject to the proxy solicitation rules under the U.S. Exchange Act. The Acquisition, implemented by way of a scheme of arrangement, is not subject to the tender offer rules under the U.S. Exchange Act.

It may be difficult for U.S. Nightstar Shareholders and Nightstar ADS Holders to enforce their rights and any claim arising out of the U.S. federal securities laws, because Nightstar is located in a non-U.S. country, and some or all of its officers and directors are residents of a non-U.S. country. U.S. Nightstar Shareholders and Nightstar ADS Holders may not be able to sue a non-U.S. company or its officers or directors in a non-U.S. court for violations of the U.S. securities laws. Further, it may be difficult to compel a non-U.S. company and its affiliates to subject themselves to a U.S. court's judgment.

U.S. Nightstar Shareholders and Nightstar ADS Holders are urged to consult with legal, tax and financial advisers in connection with making a decision regarding the Acquisition.

Warning Concerning Forward-Looking Statements

All statements included in this announcement, other than statements or characterisations of historical fact, are forward-looking statements within the meaning of the federal securities laws, including Section 21E of the U.S. Exchange Act, and other securities laws. Whenever Nightstar uses words such as "believe", "expect", "anticipate", "intend", "plan", "estimate", "will", "may", "predict", "could", "seek", "forecast" and negatives or derivatives of these or similar expressions, they are making forward-looking statements. Examples of such forward-looking statements include, but are not limited to, references to the anticipated benefits of the Acquisition and the expected time of effectiveness of the Acquisition. These forward-looking statements are based upon Nightstar's present intent, beliefs or expectations, but forward-looking statements are not guaranteed to occur and may not occur.

Nightstar Shareholders are cautioned that any forward-looking statements are not guarantees of future performance and may involve significant risks and uncertainties, and that actual results may vary materially from those in the forward-looking statements. Important risk factors that may cause Nightstar's actual results to differ materially from their forward-looking statements include, but are not limited to: (1) the risk that the Acquisition disrupts the parties' current operations or affects their ability to retain or recruit key employees; (2) the possible diversion of management time on Acquisition-related issues; (3) litigation relating to the Acquisition; (4) unexpected costs, charges or expenses resulting from the Acquisition; and (5) potential adverse reactions or changes to business relationships resulting from the completion of the Acquisition.

The information contained in Nightstar's filings with SEC, including in Nightstar's Form 10-K, as amended by Form 10-K/A, for the year ended 31 December 2018, identifies other important factors that could cause actual results to differ materially from those stated in or implied by the forward-looking statements in this announcement. Nightstar's filings with the SEC are available on the SEC's website at www.sec.gov. You should not place undue reliance upon forward-looking statements. Except as required by law, Nightstar does not intend to update or change any forward-looking statements as a result of new information, future events or otherwise.