This Amendment No. 3 (this “Amendment”) amends and supplements the Tender Offer
Statement on Schedule TO filed with the Securities and Exchange Commission on October 12, 2021 (together with any subsequent amendments and supplements thereto, the “Schedule TO”), by Astros Merger Sub, Inc., a Delaware
corporation (“Purchaser”) and a wholly owned subsidiary of Merck Sharp & Dohme Corp., a New Jersey corporation (“Parent”), and Parent. The Schedule TO relates to the offer by Purchaser to purchase all of
the outstanding shares of common stock, par value $0.001 per share (the “Shares”), of Acceleron Pharma Inc., a Delaware corporation (“Acceleron”), at a purchase price of $180.00 per Share (the “Offer
Price”), net to the seller in cash, without interest and less any applicable tax withholding, on the terms and subject to the conditions set forth in 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.
Except as otherwise set forth in this Amendment, the information set forth
in the Schedule TO remains unchanged and is incorporated herein by reference to the extent relevant to the items in this Amendment. Capitalized terms used but not defined herein have the meanings ascribed to them in the Schedule TO.
Items 1 through 9; and Item 11
The disclosure in
the Offer to Purchase and Item 11 of the Schedule TO is hereby amended and supplemented by deleting the second sentence of the first paragraph under Section 16—“Certain Legal Matters; Regulatory Approvals – Antitrust
Compliance” of the Offer to Purchase and replacing it with the following sentence:
“Parent and Acceleron filed their respective Premerger
Notification and Report Forms with the FTC and the Antitrust Division on October 14, 2021.”
The disclosure in the Offer to Purchase and Item 11
of the Schedule TO is hereby further amended and supplemented by adding the following new paragraph after the second paragraph in Section 16—“Certain Legal Matters; Regulatory Approvals – Antitrust Compliance” of the
Offer to Purchase:
“The waiting period under the HSR Act expired, effective November 16, 2021 at 11:59 p.m. Eastern Time. Accordingly, the
condition to the Offer requiring that the waiting period (or any extension thereof) applicable to the Offer under the HSR Act shall have expired or been terminated has been satisfied.”
The disclosure in the Offer to Purchase and Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items incorporate by reference the
information contained in the Offer to Purchase, is hereby amended and supplemented as follows:
“On November 17, 2021, as agreed with Acceleron,
Purchaser extended the expiration of the Offer. The Offer was previously scheduled to expire at 5:00 p.m., Eastern Time, on November 18, 2021. The expiration date of the Offer is extended to 5:00 p.m., Eastern Time, on November 19, 2021,
unless further extended. The Depositary has advised Parent that, as of 5:00 p.m., Eastern time, on November 16, 2021, approximately 11,980,722 Shares had been validly tendered and received, and not validly withdrawn, pursuant to the Offer,
representing approximately 19.6% of the outstanding Shares.
On November 17, 2021, Parent issued a press release relating to the expiration of the
waiting period under the HSR Act and announcing Purchaser’s extension of the Offer. The full text of the press release is attached as Exhibit (a)(5)(H) to the Schedule TO and is incorporated herein by reference.”
Amendments to the Offer to Purchase and Exhibits to the Schedule TO
All references to (i) “5:00 p.m., Eastern Time, on November 18, 2021” set forth in the Offer to Purchase (Exhibit (a)(1)(A)), Form of Letter of
Transmittal (including Guidelines for Certification of Taxpayer Identification Number on IRS Form W-9 or IRS Form W-8) (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 “5:00 p.m., Eastern Time, on November 19, 2021.”
