BLUE bluebird bio Inc

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO/A

TENDER OFFER STATEMENT UNDER SECTION 14(D)(1) OR 13(E)(1)

OF THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 3)

BLUEBIRD BIO, INC.

(Name of Subject Company (Issuer))

BEACON MERGER SUB, INC.

(Names of Filing Persons (Offeror))

a direct wholly owned subsidiary of

BEACON MIDCO, INC.

(Names of Filing Persons (Parent of Offeror))

a direct wholly owned subsidiary of

BEACON PARENT HOLDINGS, L.P.

(Names of Filing Persons (Indirect Parent of Offeror))

whose general partner is

BEACON GENERAL PARTNER, LLC

(Names of Filing Persons (Other Persons))

an affiliate of

CARLYLE PARTNERS GROWTH, L.P.

(Names of Filing Persons (Other Persons))

SK CAPITAL PARTNERS VI-A, L.P.

SK CAPITAL PARTNERS VI-B, L.P.

(Names of Filing Persons (Other Persons))

Common Stock, par value $0.01 per share

(Title of Class of Securities)

09609G 209

(CUSIP Number of Class of Securities (Underlying Common Stock))

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications on Behalf of Filing Persons)

Copies to:

Check the appropriate boxes below to designate any transactions to which the statement relates:

Check the following box if the filing is a final amendment reporting the results of the tender offer: ☐

If applicable, check the appropriate box(es) below to designate the appropriate rule provision(s) relied upon:

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This Amendment No. 3 (this “Amendment”) amends and supplements the Tender Offer Statement on Schedule TO, originally filed with the U.S. Securities and Exchange Commission (the “SEC”) on March 7, 2025, as amended on March 21, 2025 and March 25, 2025 (as amended and together with any subsequent amendments and supplements hereto, the “Schedule TO”), by Beacon Merger Sub, Inc. (“Merger Sub”), a Delaware corporation and wholly owned subsidiary of Beacon Midco, Inc., a Delaware corporation and wholly owned subsidiary of Beacon Parent Holdings, L.P. (“Parent”), a Delaware limited partnership, whose general partner is Beacon General Partner, LLC, a Delaware limited liability company. Parent is controlled by Carlyle Partners Growth, L.P. (“Carlyle”), a Delaware limited partnership, SK Capital Partners VI-A, L.P., a Cayman Islands exempted limited partnership, and SK Capital Partners VI-B, L.P., a Cayman Islands exempted limited partnership (SK Capital Partners VI-A, L.P. and SK Capital Partners VI-B, L.P. together, “SK Capital”). The Schedule TO relates to the tender offer by Merger Sub to purchase all of the outstanding shares of common stock, par value $0.01 per share (the “Shares”), of bluebird bio, Inc., a Delaware corporation (the “Company”), in exchange for (i) $3.00 in cash per Share, subject to any applicable withholding taxes without interest thereon (the “Closing Amount”), plus (ii) one contingent value right (each, a “CVR”) per Share, representing the right to receive one contingent payment of $6.84, in cash (the Closing Amount and one CVR, collectively, or any greater amount per Share that may be paid pursuant to the Offer (as defined below), the “Offer Price”), subject to any applicable withholding taxes and without interest thereon, upon the achievement of the milestone specified in, and on the other terms and subject to the other conditions set forth in the Offer to Purchase, dated March 7, 2025 (the “Offer to Purchase”) and in the related Letter of Transmittal, copies of which are attached to the Schedule TO as Exhibits (a)(1)(A) and (a)(1)(B), respectively (which, together, as they may be amended, supplemented or otherwise modified from time to time, collectively constitute the “Offer”).

Except as otherwise set forth in this Amendment, the information set forth in the Schedule TO remains unchanged. This Amendment is being filed to extend the Expiration Time of the tender offer. Capitalized terms used but not defined herein have the meanings assigned to such terms in the Offer to Purchase or the Schedule TO. You should read this Amendment together with the Schedule TO and the Offer to Purchase.

Items 1 through 9 and Item 11

The Offer to Purchase and Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items 1 through 9 and Item 11 incorporate by reference the information contained in the Offer to Purchase, are hereby amended and supplemented as follows:

1. The Offer to Purchase and Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items 1 through 9 and Item 11 incorporate by reference the information contained in the Offer to Purchase, are hereby amended and supplemented by adding the following paragraphs thereto:

“On April 3, 2025, Carlyle and SK Capital announced an extension of the Expiration Time until one minute after 11:59 p.m., New York City time, on April 18, 2025, unless the Offer is further extended or earlier terminated as permitted by the Merger Agreement. The Offer was previously scheduled to expire one minute after 11:59 p.m., New York City time, on April 4, 2025.

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The Depositary has advised Merger Sub that, as of the close of business on April 2, 2025, approximately 65,120 Shares have been validly tendered and not properly withdrawn pursuant to the Offer.

The press release announcing the extension of the Offer is attached hereto as Exhibit (a)(5)(C) and incorporated herein by reference.”

2. Section 6 (Price Range of Shares; Dividends on the Shares) of the Offer to Purchase is hereby amended and restated in its entirety to read as follows:

6. Price Range of Shares; Dividends on the Shares

The Shares currently trade on Nasdaq under the symbol “BLUE.” The following table sets forth the high and low intraday sale prices per Share for each quarterly period since December 31, 2022, as reported by Nasdaq:

On February 20, 2025, the last full day of trading before we announced the Merger Agreement, the reported closing sales price of the Shares on Nasdaq was $7.04 per Share. On March 6, 2025, the last full day of trading before commencement of the Offer, the reported closing sales price of the Shares on Nasdaq was $4.11 per Share. In comparison to the closing price per Share on March 6, 2025, the price per share being offered by Merger Sub in the Offer is $3.00 in cash per Share, subject to any applicable withholding taxes and without interest thereon, plus one CVR per Share, representing the right to receive one contingent payment of $6.84 in cash, subject to any applicable withholding taxes and without interest thereon, payable upon the achievement of the Milestone. There is no guarantee that the Milestone will be achieved or that stockholders will receive any payment in respect of the CVR. If the Milestone is not achieved, you will not

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receive any payment in respect of the CVR and the Closing Amount of $3.00 in cash per Share that you will receive in the Offer will be below (i) the closing price per Share on February 20, 2025, the last full day of trading before we announced the Merger Agreement, of $7.04, (ii) the closing price per Share on March 6, 2025, the last full day of trading before the commencement of the Offer, of $4.11 and (iii) the closing price per Share on April 2, 2025, the last full day of trading before the date of Amendment No. 3 to the Schedule TO, of $5.03. We encourage you to obtain a recent market price for your Shares before deciding whether to tender your Shares.

Parent and Merger Sub understand that the Company has never declared or paid cash dividends on the Shares and does not intend to declare or pay cash dividends on the Shares in the foreseeable future.

Amendments to the Offer to Purchase and Exhibits to the Schedule TO

All references to “11:59 p.m., New York City time, on April 4, 2025” set forth in the Offer to Purchase (Exhibit (a)(1)(A)), Form of Letter of Transmittal (Exhibit (a)(1)(B)), Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees (Exhibit (a)(1)(C)), and Form of Letter to Clients for use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees (Exhibit (a)(1)(D)) are hereby amended and replaced with “11:59 p.m., New York City time, on April 18, 2025.”

Item 12. Exhibits.

Item 12 of the Schedule TO is hereby amended and supplemented by adding the following exhibit:

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SIGNATURES

After due inquiry and to the best knowledge and belief of the undersigned, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Date: April 3, 2025

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Exhibit (a)(5)(C)

Carlyle and SK Capital Partners Announce Extension of bluebird bio Tender Offer to April 18, 2025

WASHINGTON, DC and NEW YORK, NY—April 3, 2025—Carlyle (NASDAQ: CG) (“Carlyle”), SK Capital Partners, LP (“SK Capital”) and Beacon Parent Holdings, L.P. (“Parent”) today announced that Beacon Merger Sub, Inc. (“Merger Sub”) has extended the expiration date of its offer (the “Offer”) to acquire all of the outstanding common stock of bluebird bio, Inc. (NASDAQ: BLUE) (“bluebird”), to expire at one minute after 11:59 p.m., New York City time, on April 18, 2025. The Offer was previously scheduled to expire one minute after 11:59 p.m., New York City time, on April 4, 2025. The tender offer was extended to allow additional time for the satisfaction of the remaining conditions to the tender offer, including receipt of applicable regulatory approvals.

Equiniti Trust Company, LLC, the depositary for the Offer, has advised Merger Sub that as of the close of business on April 2, 2025, approximately 65,120 shares of bluebird common stock have been validly tendered and not properly withdrawn pursuant to the Offer. Holders that have previously tendered their shares do not need to re-tender their shares or take any other action in response to this extension.

The Offer is being made pursuant to the terms and conditions described in the Offer to Purchase, dated March 7, 2025 (as amended or supplemented from time to time, the “Offer to Purchase”), the related letter of transmittal and certain other offer documents, copies of which are attached to the tender offer statement on Schedule TO filed by Parent and Merger Sub with the U.S. Securities and Exchange Commission (the “SEC”) on March 7, 2025, as amended.

The Offer is conditioned upon the fulfilment of certain conditions described in “Section 15—Conditions to the Offer” of the Offer to Purchase, including, but not limited to, the tender of a majority of the outstanding shares of bluebird, receipt of applicable regulatory approvals, and other customary closing conditions.

About bluebird bio, Inc.

Founded in 2010, bluebird has been setting the standard for gene therapy for more than a decade—first as a scientific pioneer and now as a commercial leader. bluebird has an unrivaled track record in bringing the promise of gene therapy out of clinical studies and into the real-world setting, having secured FDA approvals for three therapies in under two years. Today, we are proving and scaling the commercial model for gene therapy and delivering innovative solutions for access to patients, providers, and payers.

With a dedicated focus on severe genetic diseases, bluebird has the largest and deepest ex-vivo gene therapy data set in the field, with industry-leading programs for sickle cell disease, ß-thalassemia, and cerebral adrenoleukodystrophy. We custom design each of our therapies to address the underlying cause of disease and have developed in-depth and effective analytical methods to understand the safety of our lentiviral vector technologies and drive the field of gene therapy forward.

bluebird continues to forge new paths as a standalone commercial gene therapy company, combining our real-world experience with a deep commitment to patient communities and a people-centric culture that attracts and grows a diverse flock of dedicated birds.

About Carlyle

Carlyle (NASDAQ: CG) is a global investment firm with deep industry expertise that deploys private capital across its business and conducts its operations through three business segments: Global Private Equity, Global Credit and Global Investment Solutions. With $441 billion of assets under management as of December 31, 2024, Carlyle’s purpose is to invest wisely and create value on behalf of its investors, portfolio companies and the communities in which we live and invest. Carlyle employs more than 2,300 people in 29 offices across four continents. Further information is available at www.carlyle.com. Follow Carlyle on X @OneCarlyle and LinkedIn at The Carlyle Group.

About SK Capital

SK Capital is a transformational private investment firm with a disciplined focus on the life sciences, specialty materials, and ingredients sectors. The firm seeks to build resilient, sustainable, and growing businesses that create substantial long-term value. SK Capital aims to utilize its industry, operating, and investment experience to identify opportunities to transform businesses into higher performing organizations with improved strategic positioning, growth, and profitability, as well as lower operating risk. SK Capital’s portfolio of businesses generates revenues of approximately $12 billion annually, employs more than 25,000 people globally, and operates more than 200 plants in over 30 countries. The firm currently has approximately $9 billion in assets under management. For more information, please visit www.skcapitalpartners.com.

Additional Information and Where to Find It

This communication is not an offer to buy nor a solicitation of an offer to sell any securities of bluebird. The solicitation and the offer to buy shares of bluebird’s common stock is only being made pursuant to the Tender Offer Statement on Schedule TO, including an offer to purchase, a letter of transmittal and other related materials, that Parent and Merger Sub filed with the SEC. In addition, bluebird filed with the SEC a Solicitation/Recommendation Statement on Schedule 14D-9 with respect to the tender offer. Investors may obtain a free copy of these materials and other documents filed by Parent, Merger Sub and bluebird with the SEC at the website maintained by the SEC at www.sec.gov. Investors may also obtain, at no charge, any such documents filed with or furnished to the SEC by (i) bluebird under the “Investors & Media” section of bluebird’s website at www.bluebirdbio.com or (ii) by Parent and Merger Sub by calling Innisfree M&A Incorporated, the information agent for the Offer, toll-free at (877) 825-8793 for stockholders or by calling collect at (212) 750-5833 for banks or brokers.

INVESTORS AND SECURITY HOLDERS ARE ADVISED TO READ THESE DOCUMENTS, INCLUDING THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9 OF BLUEBIRD AND ANY AMENDMENTS THERETO, AS WELL AS ANY OTHER DOCUMENTS RELATING TO THE TENDER OFFER AND THE

MERGER THAT ARE FILED WITH THE SEC, CAREFULLY AND IN THEIR ENTIRETY PRIOR TO MAKING ANY DECISIONS WITH RESPECT TO WHETHER TO TENDER THEIR SHARES INTO THE TENDER OFFER BECAUSE THEY CONTAIN IMPORTANT INFORMATION, INCLUDING THE TERMS AND CONDITIONS OF THE TENDER OFFER.

Investors & Media Contacts

Bluebird

Investors:

Courtney O’Leary

978-621-7347

coleary@bluebirdbio.com

Media:

Jess Rowlands

857-299-6103

jess.rowlands@bluebirdbio.com

Carlyle

Media:

Brittany Berliner

+1 (212) 813-4839

brittany.berliner@carlyle.com

SK Capital

Ben Dillon

+1(646)-278-1353

bdillon@skcapitalpartners.com