X0306 4 2017-01-05 0 0001594864 Juno Therapeutics, Inc. JUNO 0001219042 NELSEN ROBERT C/O 8755 WEST HIGGINS ROAD SUITE 1025 CHICAGO IL 60631 1 0 1 0 Common Stock 2017-01-05 4 A 0 659 0.00 A 52594 D Common Stock 10552390 I Held by ARCH Venture Fund VII, L.P. Consists of fully vested restricted stock units. These shares are owned directly by ARCH Venture Fund VII, L.P. ("ARCH Fund VII"). The sole general partner of ARCH Fund VII is ARCH Venture Partners VII, L.P. ("ARCH Partners VII"). The sole general partner of ARCH Partners VII is ARCH Venture Partners VII, LLC ("ARCH VII LLC"). The Reporting Person is a Managing Director of ARCH VII LLC and is deemed to have voting and dispositive power over the shares and may be deemed to beneficially own certain shares held by ARCH Fund VII. The Reporting Person disclaims beneficial ownership of these securities, except to the extent of his pecuniary interest therein, and this report shall not be deemed an admission that the Reporting Person is the beneficial owner of such securities for Section 16 or any other purpose. /s/ Zachary D. Hale, attorney-in-fact 2017-01-09