X0306 4 2015-12-10 0 0001594864 Juno Therapeutics, Inc. JUNO 0001627387 Harr Steve 307 WESTLAKE AVENUE NORTH, SUITE 300 SEATTLE WA 98109 0 1 0 0 See Remarks Common Stock 2015-12-10 4 S 0 31400 46.3774 D 768600 D Common Stock 2015-12-10 4 S 0 3600 46.8955 D 765000 D This transaction was executed in multiple trades at prices ranging from $45.82 to $46.81. 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 $46.82 to $47.08. 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, as amended March 24, 2015. Chief Financial Officer and Head of Corporate Development /s/ Zachary Hale, attorney-in-fact 2015-12-11