X0306 4 2018-08-10 0 0001293971 bluebird bio, Inc. BLUE 0001578251 Walsh Jeffrey T. C/O BLUEBIRD BIO, INC. 60 BINNEY STREET CAMBRIDGE MA 02142 0 1 0 1 Chief Financial and Strategy Officer Common Stock 2018-08-10 4 M 0 1500 5.5004 A 36995 D Common Stock 2018-08-10 4 S 0 425 155.4059 D 36570 D Common Stock 2018-08-10 4 S 0 350 156.6293 D 36220 D Common Stock 2018-08-10 4 S 0 620 157.8581 D 35600 D Common Stock 2018-08-10 4 S 0 105 158.5667 D 35495 D Stock Option (right to buy) 5.5004 2018-08-10 4 M 0 1500 0.00 D 2023-01-16 Common Stock 1500 4007 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on July 2, 2018. The range of prices for the transaction reported on this line was $155.15 to $156.05. The average weighted price was $155.4059. The reporting person will provide, upon request by the SEC, the issuer or a security holder of the issuer, full information regarding the number of shares sold at each separate price. The range of prices for the transaction reported on this line was $156.20 to $156.95. The average weighted price was $156.6293. The reporting person will provide, upon request by the SEC, the issuer or a security holder of the issuer, full information regarding the number of shares sold at each separate price. The range of prices for the transaction reported on this line was $157.30 to $158.20. The average weighted price was $157.8581. The reporting person will provide, upon request by the SEC, the issuer or a security holder of the issuer, full information regarding the number of shares sold at each separate price. The range of prices for the transaction reported on this line was $158.55 to $158.90. The average weighted price was $158.5667. The reporting person will provide, upon request by the SEC, the issuer or a security holder of the issuer, full information regarding the number of shares sold at each separate price. This option to purchase shares of our common stock was granted on January 16, 2013 with performance-based vesting criteria that were met as of January 1, 2013. The shares underlying these options vested as follows: 25% vested on January 1, 2014, with the remainder of the shares vesting in equal monthly installments over the following three years. /s/ Jason F. Cole, Attorney-in-Fact 2018-08-14