BLUEBIRD BIO, INC. 2,941,176 Shares of Common Stock, par value $0.01 per share Underwriting AgreementBluebird Bio, Inc. • June 24th, 2015 • Biological products, (no disgnostic substances) • New York
bluebird bio, Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the several Underwriters listed in Schedule 1 hereto (the “Underwriters”), for whom you are acting as representatives (the “Representatives”), an aggregate of 2,941,176 shares of common stock, par value $0.01 per share (“Common Stock”), of the Company (the “Underwritten Shares”) and, at the option of the Underwriters, up to an additional 441,176 shares of Common Stock of the Company (the “Option Shares”). The Underwritten Shares and the Option Shares are herein referred to as the “Shares”. The shares of Common Stock, par value $0.01 per share, of the Company to be outstanding after giving effect to the sale of the Shares are referred to herein as the “Stock”.
