X0306 4 2017-09-14 0 0001594864 Juno Therapeutics, Inc. JUNO 0001398322 Cassidy Bernard J C/O 400 DEXTER AVENUE NORTH SUITE 1200 SEATTLE WA 98109 0 1 0 0 General Counsel & Secretary Common Stock 2017-09-14 4 S 0 23054 44.6656 D 55970 D Common Stock 2017-09-14 4 S 0 3441 45.9002 D 52529 D Common Stock 2017-09-14 4 S 0 1505 46.5797 D 51024 D Common Stock 26869 I By Morgan Stanley Smith Barney LLC as Custodian for Bernard Cassidy IRA The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on March 23, 2017. This transaction was executed in multiple trades at prices ranging from $44.27 to $45.25. 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 $45.34 to $46.32. 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 $46.38 to $46.93. 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. /s/ Zachary D. Hale, attorney-in-fact 2017-09-14