X0306 4 2016-01-19 0 0001594864 Juno Therapeutics, Inc. JUNO 0001398322 Cassidy Bernard J C/O 307 WESTLAKE AVENUE NORTH, SUITE 300 SEATTLE WA 98109 0 1 0 0 General Counsel and Secretary Common Stock 2016-01-19 4 S 0 2400 33.3654 D 67683 D Common Stock 2016-01-19 4 S 0 800 34.12 D 66883 D Common Stock 26869 I By Morgan Stanley Smith Barney LLC as Custodian for Bernard Cassidy IRA This transaction was executed in multiple trades at prices ranging from $32.89 to $33.76. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. This transaction was executed in multiple trades at prices ranging from $33.89 to $34.68. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 23, 2014, in which the shares were sold through a trust for the sole benefit of the reporting person and his spouse. /s/ Zachary Hale, attorney-in-fact 2016-01-20