Exhibit 2.1

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

SHARE PURCHASE AGREEMENT

related to

PROJECT SPYDER

1

TABLE OF CONTENTS

2

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

3

4

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

5

6

THIS AGREEMENT is made

BETWEEN

- the “ Seller 1 ”-

- the “ Seller 2 ”-

- the “ Seller 3 ”-

and

- the “ Purchaser ”-,

(Seller 1, Seller 2 and Seller 3 collectively also referred to as the “ Sellers ”, and each of them as a “ Seller ”; the Sellers and the Purchaser collectively also referred to as the “ Parties ”, and each of them as a “ Party ”).

7

RECITALS

NOW, THEREFORE, the Parties agree as follows:

In this Agreement, the following terms and abbreviations shall have the following meanings:

“ Affiliate(s) ” means any affiliated company ( verbundenes Unternehmen ), irrespective whether German or foreign, within the meaning of Section 15 of the German Stock Corporation Act ( Aktiengesetz );

“ Agreement ” means this share purchase agreement;

“ Amendment, Assumption and Release Agreement(s) ” has the meaning given in Section 4.3.1;

“Balance Sheet Date ” has the meaning given in Section 7.5.1;

“ BGB ” means the German Civil Code ( Bürgerliches Gesetzbuch );

“ Breach ” has the meaning given in Section 9.1.1;

“ Breach Notice ” has the meaning given in Section 9.2.1;

“ Business ” means the Company’s business, taken as a whole, as presently conducted;

“ Business Day ” means any day (other than a Saturday or Sunday) on which banks are open for business in Munich;

“ Cash Purchase Price Portion ” has the meaning given in Section 4.1.1(a);

“ Cash Wage Taxes ” shall mean with regard to any cash payment to the Phantom Stockholders such amount which has to be withheld and paid by or on behalf of the Company to the competent Taxing Authority as Wage Tax on such payment, including Wage Tax on third party wage payments ( von einem Dritten gewährter Arbeitslohn ) and including Wage Tax on previous payments, transactions and/or transfers to any Phantom Stockholder to the extent the amount of Wage Tax withheld by the Purchaser on such previous payments, transactions

8

and/or transfers falls short of the amount of Wage Tax actually due and payable for such previous payments, transactions and/or transfers. For purposes of payment of the Purchase Price, the Cash Wage Taxes shall be determined by the Purchaser based on the calculation and information provided to the Purchaser by the Company.

“ Clinical Trials ” has the meaning given in Section 7.13.1;

“ Closing ” has the meaning given in Section 6.1;

“ Closing Action(s) ” has the meaning given in Section 6.2.1;

“ Closing Confirmation ” has the meaning given in Section 6.2.3;

“ Collective Agreements ” has the meaning given in Section 7.14.2;

“ Company ” has the meaning given in Recital (A);

“ Company Data ” means all data and information to the extent relating to the Business and the Company, or the customers, financial statements, conditions or operations of the Company (including such data and information in the control or possession of Sellers or any such data and information obtained after the consummation of the Closing from or on behalf of the Purchaser, the Company, or any of their respective Affiliates or Representatives under this Agreement);

“ Company Registered Intellectual Property Rights ” has the meaning given in Section 7.10.2;

“ Confidentiality Agreement ” means the confidential disclosure agreement between the Parties dated 21 January 2015;

“ Corporate Documents ” has the meaning given in Section 7.4.2;

“ Default Interest Rate ” has the meaning given in Section 5.4;

“ Exempted Claims ” has the meaning given in Section 9.3.1;

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

9

“ [***] ” means [***]

“ Financial Statements ” has the meaning given in Section 7.5.1;

“ Governmental Authority ” means (i) any government, governmental or quasi-governmental authority, entity, ministry, department, commission, board, agency or instrumentality; (ii) any court, tribunal, or judicial or arbitral body, whether federal, state, provincial, local or foreign; and (iii) any body exercising or entitled to exercise any administrative, executive, judicial, legislative, regulatory or taxing authority or power of any nature;

“ IBA ” has the meaning given in Section 6.2.1(c);

“ IBA Loan ” has the meaning given in Section 6.2.1(c);

“ Incentive Schemes ” has the meaning given in Section 7.14.5;

“ Indemnifiable Taxes ” has the meaning given in Section 11.1.1;

“ Intellectual Property Rights ” has the meaning given in Section 7.10.2;

“ Interim Period ” has the meaning given in Section 8.1.1;

“ Investor Documentation ” has the meaning given in Section 6.2.1(e);

“ Joint Representative ” shall mean Dr. Lothar Germeroth.

“ Key Employee Agreements ” has the meaning given in Section 6.2.1(a);

“ Key Employees ” has the meaning given in Section 6.2.1(a);

“ Leakage ” has the meaning given in Section 7.6.1;

“ Losses ” has the meaning given in Section 9.1.2;

“ Material Adverse Change ” means a situation where events have occurred or been revealed which have had, or may reasonably be expected to have, individually or in the aggregate, a material adverse effect on the assets and liabilities, financial condition, results of operations, cash flows or business prospects of the Company or its ability to carry on its Business in the same manner as currently conducted;

“ Material Agreements ” has the meaning given in Section 7.12.1;

“ Material Intellectual Property Rights ” has the meaning given in Section 7.10.2;

“ Milestone Notice ” has the meaning given in Section 4.3.6(a);

“ Milestone Notice Recipient ” has the meaning given in Section 4.3.6(c);

“ Milestone Notice Sender ” has the meaning given in Section 4.3.6(a);

“ Milestone Purchase Price(s) ” has the meaning given in Section 4.1.1(b);

“ Part(y/ies) ” has the meaning given in the Parties’ Section;

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

10

“ Pension Schemes ” has the meaning given in Section 7.14.4;

“ Permits ” has the meaning given in Section 7.17.1;

“ Permitted Pre-Signing Leakage ” has the meaning given in Section 7.6.2;

“ Phantom Stock Agreement(s) ” has the meaning given in Section 4.3.1;

“ Phantom Stockholder(s) ” has the meaning given in Section 4.3.1;

“ Phantom Stockholder Documentation ” has the meaning given in Section 6.2.1(f);

“ Phantom Stockholders’ Common Stock ” has the meaning given in Section 4.3.2;

“ [***] Efforts ” has the meaning given in Section 13.1.2(a);

“ Platform Milestones ” has the meaning given in Section 13.1.2;

“ Platform Milestone Products ” has the meaning given in Section 13.1.2(b);

“ Purchase Price ” has the meaning given in Section 4.1.1;

“ Purchase Price Allocation ” has the meaning given in Section 4.1.2;

“ Purchaser ” has the meaning given in the Parties’ Section;

“ Purchaser’s Account ” has the meaning given in Section 5.2.2;

“ Purchaser’s Common Stock ” has the meaning given in Section 4.1.1(a);

“ Purchaser’s Representation(s) ” has the meaning given in Section 12;

“ Purchaser’s Representatives ” means the Purchaser’s directors, officers, employees, representatives, advisors and counsel;

“ Purchaser’s Tax Relief ” means a relief, allowance, credit, deduction, exemption or set-off in respect of any Tax or a right to repayment of or saving of Tax arising to the Company as a consequence of an event occurring after the Seller Period;

“ Registered Intellectual Property Rights ” has the meaning given in Section 7.10.1;

“ Related Part(y/ies) ” shall mean each Seller and persons related to any Seller ( einem Verkäufer nahestehende Personen ) within the meaning of Section 138 German Insolvency Code ( Insolvenzordnung );

“ Related Party Agreements ” has the meaning given in Section 7.8.1;

“ Relevant Tax Proceedings ” has the meaning given in Section 11.4.1;

“ [omitted] Cash Purchase Price Portion ” has the meaning given in Section 4.3.5(c);

“ [omitted] Portion ” has the meaning given in Section 4.3.1(b);

“ [***] Efforts ” has the meaning given in Section 13.1.3(a);

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

11

“ Seller Period ” means (i) the taxable periods ( Veranlagungs- bzw. Erhebungszeiträume ) ending on or before the Targeted Closing Date, 24:00 hours German time and (ii) with respect to a taxable period beginning before and ending after the Targeted Closing Date, 24:00 hours German time (the “ Straddle Period ”), that portion of such taxable period ending on the Targeted Closing Date, 24:00 hours German time;

“ Sellers’ Account ” has the meaning given in Section 5.2.1;

“ Sellers’ Cash Purchase Price Portion ” has the meaning given in Section 4.3.5(a);

“ Sellers’ Covenants ” means the Sellers’ obligations under the covenants set forth under Section 8.1 through 8.2;

“ Sellers’ Indemnities ” means the Sellers’ obligations under the indemnities set forth under Section 8.4;

“ Sellers’ Knowledge ” has the meaning given in Section 7.1.2;

“ Sellers’ Portion ” has the meaning given in Section 4.3.6(d)(i);

“ Sellers’ Representation(s) ” has the meaning given in Section 7.1.1;

“ Sellers’ Representatives ” means the Sellers’ employees, representatives, advisors and counsel;

“ Shareholder Receivables ” has the meaning given in Section 6.2.1(b);

“ Signing Date ” has the meaning given in Section 3.3;

“ Sold Seller 1 Share ” has the meaning given in Section 2.2(a);

“ Sold Seller 2 Share ” has the meaning given in Section 2.2(b);

“ Sold Seller 3 Share ” has the meaning given in Section 2.2(c);

“ Sold Shares ” has the meaning given in Section 2.2(c);

“ Sponsor ” has the meaning given in Section 7.13.1;

“ Sponsored Clinical Trials ” has the meaning given in Section 7.13.1(a);

“ Stage Clinical Milestones ” has the meaning given in Section 13.1.3;

“ [omitted] Cash Purchase Price Portion ” has the meaning given in Section 4.3.5(b);

“ [omitted] Portion ” has the meaning given in Section 4.3.1;

“ Stock Purchase Price Portion ” has the meaning given in Section 4.1.1(a);

12

“ Stock Wage Taxes ” shall mean with regard to any transfer of the Phantom Stockholders’ Common Stock to the Phantom Stockholders such amount, which has to be withheld and paid by or on behalf of the Company to the competent Taxing Authority as Wage Tax on such transfer, including Wage Tax on third party wage payments ( von einem Dritten gewährter Arbeitslohn ). For purposes of payment of the Purchase Price, the Stock Wage Taxes shall be determined by the Purchaser based on the calculation and information provided to the Purchaser by the Company in line with the rules for the valuation of payments in kind ( Sachbezüge ) for wage tax purposes applying reasonable estimates where necessary;

“ Targeted Closing Date ” has the meaning given in Section 6.1;

“ Tax ” and “ Taxes ” shall mean (i) any tax ( Steuer ) within the meaning of Section 3 of the German Tax Code ( Abgabenordnung ), including corporate income, income, value-added, sales, stamp, salary withholding tax/wage tax, withholding tax, transfer tax and customs, and comparable payments ( Geldleistungen ) under the laws of any other jurisdiction and all secondary liabilities ( Haftungsschulden ) for such Taxes as well as (ii) the employer’s share ( Arbeitgeberanteil ) of social security contributions ( Sozialversicherungsbeiträge ) or similar public social security contributions under the laws of any jurisdiction, in each case imposed by any Taxing Authority or payable under any contractual arrangement and together with any accessory charges ( steuerliche Nebenleistungen ) (including penalties, fines, interest, late payment fees, surcharges or similar additions to tax) and (iii) any penalties or administrative fines for non-adequate and/or non-proper documentation of intra-group transactions and transfer prices, or due to late or inadequate filing of a Tax Return;

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

13

“ Tax Refund ” has the meaning given in Section 11.2.1;

“ Tax Return ” shall mean any return, declaration, report, notice, form or information relating to any Tax to be filed, including any schedule or attachment thereto;

“ Taxing Authority ” shall mean any competent domestic or foreign authority in charge of imposing any Tax or any Wage Tax;

“ Termination Agreements ” has the meaning given in Section 6.2.1(h);

“ Third Party Claim ” has the meaning given in Section 9.2.2;

“ Threshold Amount ” has the meaning given in Section 9.3.2;

“ Title Claims ” has the meaning given in Section 9.3.1(a);

“ Transaction ” means the transactions contemplated by this Agreement;

“ Transfer ” has the meaning given in Section 4.3.4;

“ Wage Tax ” shall mean (i) any Tax and (ii) any employee’s share ( Arbeitnehmeranteil ) of social security contributions ( Sozialversicherungsbeiträge ) or similar public security contributions under the laws of any jurisdiction, in each case on wages or other employment income or otherwise in connection with any employment.

The Company is a limited liability company ( Gesellschaft mit beschränkter Haftung ) organized under the laws of Germany, registered with the commercial register ( Handelsregister ) of the local court ( Amtsgericht ) in Göttingen under registration number HRB 3573 and having its registered office at Rudolf-Wissell-Straße 28, 37079 Göttingen, Germany.

The registered share capital ( Stammkapital ) of the Company amounts to EUR 29,167 (in words: Euro twenty nine thousand one hundred sixty seven). It is divided into four (4) shares which are held as follows:

14

Subject to ( aufschiebend bedingt auf ) the satisfaction, or due waiver, of the Closing Actions,

The Sold Shares are sold to the Purchaser with all rights and obligations pertaining thereto, including the right to receive all profits for the Company’s current fiscal year as well as all profits for previous fiscal years of the Company not yet distributed prior to the date of this Agreement (the “ Signing Date ”).

For the period between Closing and the time at which the Purchaser is regarded as the owner of the Sold Shares vis-à-vis the Company in accordance with Section 16 para 1 sent. 1 German limited liability companies act ( GmbHG ), the Sellers herewith grant to the Purchaser irrevocable powers of attorney to exercise all shareholder rights, including to pass shareholders’ resolutions of all kind, but expressly excluding the right to sign a declaration of subscription ( Übernahmeerklärung ) on their behalf for the Company.

15

The Purchase Price is, subject to Section 4.1.1(b) only, a fixed price and is not subject to any adjustments, e.g. because of a change in the economic condition of the Company or the Business or otherwise; provided, however, that any payments by the Sellers under this Agreement for damages, indemnification, in particular under Sections 9 or 11, or otherwise shall be deemed to be, and treated as, a subsequent reduction of the Purchase Price.

16

The Phantom Stock Agreements will be amended by the Amendment, Assumption and Release Agreements, inter alia , in a way, that

In each case of Section 4.3.1(a) and 4.3.1(b) the Phantom Stockholders are, for the avoidance of doubt, also entitled to claim from the Sellers the relevant portion of the Stock Purchase Price Portion in accordance with Section 4.3.2 and the relevant portions of Milestone Purchase Prices in accordance with Section 4.3.6 below.

(the Purchaser’s Common Stock to be paid directly to the Phantom Stockholders in accordance with Sections 4.3.2(b) and 4.3.2(c) the “ Phantom Stockholders’ Common Stock ”).

17

For the avoidance of doubt, any payment of Phantom Stockholder’s Common Stock to the Phantom Stockholders on behalf of the Sellers shall be deemed to be paid to, and received by, the Sellers (with respect to each Seller, in the proportion set forth in Section 4.1.2 hereof) for the purposes of this Agreement.

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF A REGISTRATION STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES UNDER SUCH ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE ISSUER THAT SUCH REGISTRATION IS NOT REQUIRED OR UNLESS SOLD PURSUANT TO RULE 144 OF SUCH ACT.

18

For the avoidance of doubt, any payment of portions of the Cash Purchase Price Portion to the Phantom Stockholders on behalf of the Sellers in accordance with this Section 4.3.5 shall be deemed to be paid to, and received by, the Sellers (with respect to each Seller, in the proportion set forth in Section 4.1.2 hereof) for the purposes of this Agreement.

19

20

For the avoidance of doubt, any payment of portions of any Milestone Purchase Price to the Phantom Stockholders on behalf of the Sellers in accordance with this Section 4.3.6 shall be deemed to be paid to, and received by, the Sellers (with respect to each Seller, in the proportion set forth in Section 4.1.2 hereof) for the purposes of this Agreement.

With the exception of the Stock Purchase Price Portion, any payments under or in connection with this Agreement shall be made in Euros by irrevocable wire transfer of immediately available funds, free of bank and other charges. Any such payment shall be deemed made only upon the irrevocable and unconditional crediting of the amount payable (without deduction of any costs or charges) to the relevant bank account.

Bank Name: Hypo Vereinsbank

IBAN: DE32700202700015376393

Swift Code / BIC: HYVEDEMMXXX

Location: 35005 – Filiale Promedadeplatz Kasse KF 14 – München

Credit to the Account of: m law group Partnerschaft von Rechtsanwälten Besner Kremer

Account Number: [omitted]

Bank Code: [omitted]

Any payment made to the Sellers’ Account shall have a releasing effect ( befreiende Wirkung ) for the Purchaser vis-à-vis the Sellers, and shall be deemed to have been paid to, and received by, by the Sellers (with respect to each Seller, in the proportion set forth in Section 4.1.2 hereof).

21

Bank Name: JPMorgan Chase Bank, N.A.

ABA/Routing Number: 021000021

Swift Code: CHASUS33

Location: New York, NY

Credit to the Account of: Juno Therapeutics, Inc.

Account Number: [omitted]

For the avoidance of doubt, if the Purchaser has complied with the process outlined above, the Purchaser shall be entitled retention rights retroactively from the moment in time when the respective Milestone Purchase Price has become due. Any retention rights pursuant to this Section 5.3.2 shall, for the avoidance of doubt, also apply to any payments to be made to Phantom Stockholders on behalf and at the request of the Sellers.

22

Any failure by a Party to make any payment under this Agreement on the date when it comes due in accordance with this Agreement shall result in such Party’s immediate default ( Verzug ), without any reminder ( Mahnung ) being required. Any cash payments due under this Agreement shall bear default interest ( Verzugszins ) from but excluding the date it becomes due until and excluding the date of actual receipt an interest rate of five (5) percentage points per annum above base interest rate ( Basiszinssatz ) (the “ Default Interest Rate ”). Section 288 para 5 BGB shall apply.

Interest for any amounts due under or in connection with this Agreement shall be calculated on the basis of actual days elapsed and a calendar year with 360 days.

The consummation of the transactions contemplated under this Agreement (the “ Closing ”) shall occur at the offices of the notary (Notariat am Alstertor 14), Alstertor 14, 20095 Hamburg, Germany

(the “ Targeted Closing Date ”).

23

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

24

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

25

provided that any right of a Party to terminate this Agreement pursuant to this Section 6.3.1 shall cease ( verfallen ) upon the earlier of (i) the respective Closing Actions, the non-satisfaction of which entitles the Party to such termination, being satisfied or duly waived, and (ii) the occurrence of the Closing. For the avoidance of doubt, the right of either Party to seek, instead of exercising the termination right provided for hereunder, specific performance with respect to the Closing Actions to be satisfied by the other Party on the Targeted Closing Date shall remain unaffected.

26

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

27

28

29

The Company has no Financial Indebtedness towards any third party (including any Related Party). “ Financial Indebtedness ” means any long term or short term financial indebtedness and obligations (and incurrence of any obligation to that effect) of any sort, including (i) under loans, facilities, overdrafts or used lines of credit, shareholders loans and any other item having the commercial effect of a borrowing, (ii) under bonds of any nature, including convertible bonds or bonds with attached warrants, (iii) under financings based on receivables such as factoring, securitization of assets and discounted trade receivables, (iv) under financing leases, sale and lease back transactions and hire purchase contracts, (v) under deferred or conditional payments for the acquisition of fixed assets, (vi) under reimbursable subsidies and aids from any Governmental Authority, (vii) under guarantees and other similar off-balance sheet commitments for third party debt, (viii) under financial products (in particular derivatives) such as options, swaps, hedges and futures, and (ix) any expenses borne or to be borne by the Company in connection with the preparation of and entering into this Agreement and the performance of the Transaction; and (x) all interest on the items set forth under (i) through (ix).

30

Except as disclosed in Exhibit 7.9 , since the Balance Sheet Date through the Signing Date (i) the Business has been conducted in the ordinary course of business in a manner consistent with past practice and with the care of a prudent business man, (ii) the Company has used reasonable best efforts to preserve intact the business organizations and relationships with third parties and to keep available the services of its present directors, officers and employees, (iii) the Company’s capital expenditure and working capital have been maintained on a normal level, consistent with the requirements of the Business and (iv) no events have occurred or been revealed which have constituted, or may reasonably be expected to have constituted, individually or in the aggregate, a Material Adverse Change. Without limiting the generality of the foregoing, in the period between the Balance Sheet Date and the Signing Date, there has not been (and neither the Company nor the Sellers have incurred any obligation with respect to):

31

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

32

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

33

34

35

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

36

37

38

39

The Company does not have any obligation or liability to pay any fees or commissions to any broker, finder or agent with respect to this Agreement and the consummation of the Transaction.

The Company is not a party to any pending civil, criminal or administrative action, suit, investigation or other legal proceedings (including disputes with or administrative proceedings initiated by Governmental Authorities). No such proceedings have been threatened against the Company and, to Sellers’ Knowledge, there are no facts which are likely to result in such proceedings.

40

41

42

The Sellers acknowledge and agree that, from and after the consummation of the Closing, all Company Data shall be deemed the exclusive property of the Company. The Sellers agree from and after the consummation of the Closing, to treat all Company Data as confidential, to preserve the confidentiality thereof, not to duplicate or use or disclose to any person or entity such Company Data and to cause Sellers’ Representatives who have had access to Company Data to keep confidential and not to use any such Company Data ( provided that Seller shall have the right to disclose Company Data to Sellers’ Representatives solely for the purposes set

43

forth in Sections 4.3.6, 9.2, 11 and 13.1), (i) unless such Company Data is now or is hereafter disclosed, through no prohibited act or omission of a Seller or Sellers’ Representatives, including any act or omission in violation of this Agreement, in a manner making it available to the general public, (ii) unless such Company Data is received from a third party that is not subject to any contractual, legal, fiduciary or other obligation of confidentiality with respect to such information, (iii) unless such Company Data is required by law or legal process to be disclosed (in which event Seller shall (unless prohibited by Law or legal process) inform Purchaser in advance of any such required disclosure and cooperate with Purchaser in all reasonable ways in obtaining a protective order or other protection in respect of such required disclosure, and shall in any event limit such disclosure to the extent reasonably possible while still complying with such requirements), (iv) except as reasonably necessary to prepare Sellers’ tax returns and statements, forms and schedules in connection therewith, or (v) if a Seller continues to be an employee of the Company, except in the course of performing such Seller’s duties as a Company employee and subject to confidentiality obligations applicable to Seller as an employee. The Sellers agree, after the consummation of the Closing, to safeguard the Company Data and to protect it against disclosure (except as provided above), misuse, espionage, loss and theft using at least the same efforts as the Sellers use to safeguard their own information or data of a similar nature, and with no less than a reasonable degree of care. Purchaser shall be entitled to injunctive relief to enforce this Section 8.2 .

The Sellers shall fulfill and settle any and all claims the Phantom Stockholders have under the Phantom Stock Agreements and the Amendment, Assumption and Release Agreements and shall deliver evidence thereof reasonably acceptable to the Purchaser, including providing evidence to the Purchaser of the prompt payment to the Phantom Stockholders of the portion of the Cash Purchase Price Portion and any Milestone Purchase Prices to which they have a claim against Sellers pursuant to the Phantom Stock Agreements and Release Agreements.

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

44

procure that their respective Related Parties and commercial agents refrain, other than on behalf of the Company, the Purchaser or any of their respective subsidiaries or affiliates, from competing, directly or indirectly, with the Business, including through [***] . For avoidance of doubt, the foregoing shall not restrict the ability of the Sellers (i) to develop, manufacture or sell products or reagents for research use to academic institutions, to the extent permitted by [***] , or (ii) to engage in any academic and non-commercial research, development or teaching activities.

It is assumed that interests in competitors of the Business are not held for purely financial investment purposes if they exceed 5% of the total interests of the company, or if Sellers are among the ten (10) largest interest holders in the competitor of the Business; or

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

45

46

47

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

48

For the avoidance of doubt, any Purchase Price payment (including Cash Purchase Price Portion payments, payments of Purchaser’s Common Stock and Milestone Purchase Price Payments) made to any Phantom Stockholder in accordance with this Agreement shall be deemed to have been paid to, and received by, the Sellers (with respect to each Seller, in the proportion set forth in Section 4.1.2 hereof) and any Cash Wage Taxes and/or Stock Wage Taxes withheld in accordance with this Agreement shall also be deemed to be paid to, and received by, the Sellers (with respect to each Seller, in the proportion set forth in Section 4.1.2 hereof) for the purposes of this Section 9.3.3.

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

49

Section 203 BGB shall not apply. The fact that a Title Claim has become time-barred according to this Section 9.3.4 shall in no event limit the Purchaser’s right to set-off or retention rights and claims in accordance with Section 5.3. For the avoidance of doubt, the Purchaser shall be entitled (i) to set-off Title Claims against any claims of the Sellers for payment of any Milestone Purchase Price (or any portion thereof) and (ii) to refuse to perform the payment of any Milestone Purchase Price (or any portion thereof) on the grounds of a right of retention ( Zurückbehaltungsrecht ) in accordance with Section 5.3, even at a time when the Title Claim has already become time-barred according to this Section 9.3.4.

Except as expressly stated otherwise in this Agreement, the Sellers shall be [***] liable [***] , subject to the caps on each Seller’s aggregate liability as set forth in Section 9.3.3, towards the Purchaser for any claims that the Purchaser may have against any Seller pursuant to or in connection with this Agreement.

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

50

51

52

Each Seller is jointly and severally liable ( gesamtschuldnerische Haftung ) under this Section 11.

Claims of the Purchaser or the Sellers pursuant to this Section 11 and to Section 8.4.1 (to the extent relating to Taxes) shall be time-barred ( verjährt ) for each claim six (6) months after the Tax assessment of the relevant Tax has become non-appealable ( unanfechtbar ) and is no longer subject to change.

The Purchaser hereby represents to the Sellers in the form of an independent promise of guarantee ( selbständiges Garantieversprechen ) within the meaning of Section 311 BGB that the statements in Section 12.1 through Section 12.3 (collectively the “ Purchaser’s Representations ” and each a “ Purchaser’s Representation ”) are correct as of the Signing Date, unless it is specifically provided that a Purchaser’s Representation is made as of a different or additional date or dates, in which case such Purchaser’s Representation shall be correct as of such different or additional date or dates.

The Purchaser has sufficient immediately available funds or valid, enforceable, binding, unconditional and irrevocable ( unwiderrufliche ) equity and financing commitments to pay the Purchase Price and to make any other payments under or in connection with this Agreement when due.

53

The Purchaser is purchasing the Sold Shares on its own account for investment purposes only, and not with a view to or for public sale or distribution in whole or in part directly or indirectly (including by way of equity syndication).

The Purchaser’s Common Stock has been duly and validly authorized and, when issued pursuant to this Agreement, will be validly issued, fully paid and non-assessable, and shall be free and clear of all restrictions, except for restrictions on transfer imposed by applicable securities law or by this Agreement. The issuance of the Purchaser’s Common Stock to be issued to the Sellers pursuant to this Agreement does not contravene the rules and regulations of The NASDAQ Global Select Market. Based on representations from the Sellers, the Purchaser’s Common Stock to be issued to the Sellers pursuant to this Agreement will be exempt from registration pursuant to Section 4(a)(2) of the Securities Act of 1933, as amended, and other applicable state securities laws.

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

54

The Purchaser shall support and assist the Sellers in removing the transfer restrictions for the Purchaser’s Common Stock under applicable Securities Laws as soon as reasonably practicable.

[***] Certain information in this document has been omitted and filed separately with the Securities and Exchange Commission. Confidential treatment has been requested with respect to the omitted portions.

55

The Parties agree to execute, or cause ( steht dafür ein ) to be executed all agreements and documents and to give and take, or cause to be given and taken, respectively, all other declarations and actions necessary under applicable laws and regulations to consummate the Transaction, unless the execution of such agreements and documents or the giving of such declarations or the taking of such actions would cause an unreasonable hardship ( Unzumutbarkeit ) to the respective Party.

If and to the extent any of the Purchaser’s Representations or the Purchaser’s covenants under Section 13, are breached, the liability of the Purchaser shall be determined in accordance with statutory law, with any specific claims or remedies provided for under this Agreement remaining unaffected.

All notices, requests and other communications under or in connection with this Agreement shall be made in writing in the English language and delivered by hand, courier, mail, or e-mail to the person at the addresses set forth below, or such other person or address as may be designated by the respective Party in writing from time to time, provided that (1) receipt of a copy of a notice, request or other communication by a Party’s advisors shall not constitute or substitute receipt thereof by the respective Party itself and (2) any notice, request or other communication shall be deemed received by a Party regardless of whether a copy thereof was sent to or received by an advisor of such Party, regardless of whether the delivery of such copy was mandated by this Agreement:

Dr. Lothar Germeroth

[omitted]

56

Germany

E-mail: [omitted]

with a copy to:

m law group

Attn.: Dr. Hubert Besner

Schackstr. 1, 80539 Munich

Germany

E-mail: hubert.besner@mlawgroup.de

Juno Therapeutics, Inc.

Attn.: General Counsel

307 Westlake Avenue N., Ste 300

Seattle, WA 98109

United States

E-mail: [omitted]

with a copy to (which shall not constitute notice):

Latham & Watkins LLP

Attn.: Christoph Engeler

Warburgstrasse 50

20354 Hamburg

Germany

E-mail: Christoph.Engeler@lw.com

Any notice, request or other communication given to the Joint Representative under or in connection with this Agreement shall be considered a notice, request or other communication given to all Sellers. With respect to the Sellers, any notice, request or other communication given or any right or claim asserted, shall be given or asserted only jointly on behalf of all Sellers ( einheitliche Rechtsausübung ) and exclusively by the Joint Representative.

57

Except for the Purchaser’s press release in a form substantially similar to that set forth in Exhibit 15.3 , no Party shall make any press release or similar announcement with respect to this Agreement or the Transaction, and each Party shall keep confidential the contents of this Agreement and any confidential information regarding the other Parties disclosed to it in connection with this Agreement or its implementation, except as expressly agreed with the respective other Party or Parties and except as may be required in order to comply with the requirements of applicable laws or stock exchange regulations (including any Form 8-K, Form 10-Q, Form 10-K, or other filing by the Purchaser with the U.S. Securities and Exchange Commission that the Purchaser determines in its sole discretion it is required to make with respect to this Agreement or the transactions contemplated hereby).

This Agreement (together with all Exhibits hereto) contains the entire agreement between the Parties concerning its subject matter and supersedes all prior agreements, oral and written declarations of intent and other legal arrangements (whether binding or non-binding) made by the Parties in respect to all or any part of the subject matter of this Agreement.

Any amendments to this Agreement (together with all Exhibits hereto) (including amendments to this Section) or a waiver of terms and conditions shall be valid and binding upon the Parties only if approved in writing by an authorized representative of each Party, unless applicable mandatory law requires otherwise.

The Parties may not assign, delegate or otherwise transfer any right or claim they may have under or in connection with this Agreement without the other Parties’ written consent. However, the Purchaser may assign or pledge for security purposes rights and claims under this Agreement to the banks and financing institutions financing the Transaction (including the refinancing of existing indebtedness of the Company).

This Agreement shall not grant any rights to, and is not intended to operate for, the benefit of any third parties ( kein echter Vertrag zugunsten Dritter ).

15.8.1 Exhibits . All Exhibits to this Agreement constitute an integral part of this Agreement.

58

If any court of competent jurisdiction holds any provision of this Agreement invalid or unenforceable, the other provisions of this Agreement shall remain in full force and effect. The invalid or unenforceable provision shall be deemed to have been replaced by a valid, enforceable and fair provision which comes as close as possible to the intentions of the Parties hereto at

59

the time of the conclusion of this Agreement. It is the express intent of the Parties that the validity and enforceability of all other provisions of this Agreement shall be maintained and that this Section 15.10 shall not result in a reversal of the burden of proof but that Section 139 BGB is hereby excluded in its entirety.

* * * *

60

NOTARIAT AM ALSTERTOR

DR. ROLF-HERMANN HENNIGES    DR. WOLFGANG ENGELHARDT    JOHANN JONETZKI

DR. ROBERT DIEKGRÄF    DR. ARNE HELMS, LL.M.    DR. MICHAEL VON HINDEN

NOTARE

Register of Deeds No. 1539/2015 HL

Done

in the

Free and Hanseatic City of Hamburg

on

11 May 2015

Before me, the Hamburg Notary

Dr. Arne Helms

with official residence in Hamburg,

appeared today at my office at the address Alstertor 14, 20095 Hamburg:

born on [omitted],

address: [omitted], Germany,

identity proven by a German identity card,

acting according to his declaration

– hereinafter also referred to as the “ Seller 1 ” –

Prof. Dr. Dirk Busch,

born on [omitted],

address: [omitted] Germany,

– hereinafter also referred to as the “ Seller 3 ” –

born on [omitted],

address: [omitted], Germany,

identity proven by a German identity card,

– hereinafter also referred to as the “ Seller 2 ” –

ALSTERTOR 14 - 20095 HAMBURG - ECKE FERDINANDSTRASSE

TELEFON: + 49 (0)40 30 05 02-0 - TELEFAX: + 49 (0)40 30 05 02-92

POSTANSCHRIFT: POSTFACH 10 54 09 - 20037 HAMBURG

WWW.ALSTERTOR.DE - NOTARIAT@ALSTERTOR.DE

NOTARIAT AM ALSTERTOR

born on [omitted],

business address: LATHAM & WATKINS LLP, Warburgstraße 50, 20354 Hamburg, Germany,

identity proven by a German passport,

acting according to his declaration under exclusion of any personal liability, including any liability for the notary public’s fees, in his capacity as an agent exempted from the restrictions of Section 181 of the German Civil Code (BGB) - presenting a notarially certified and apostilled power of attorney as well as an up-to-date Certificate of Good Standing regarding Juno Therapeutics, Inc., each in the original - it herewith being certified that the photocopies attached to this record as Annex R 2 are true and complete copies of the originals presented at the recording-on behalf of

Juno Therapeutics, Inc.,

a corporation organized under the laws of Delaware, USA,

registered with the Corporate Division of the Secretary of State of the State of Delaware under

file number 5378373,

having its principal executive offices at 307 Westlake Avenue North, Suite 300, Seattle, WA

98109, USA,

– hereinafter also referred to as the “Purchaser ” –.

Seller 1, Seller 2 and Seller 3 collectively also referred to as the “ Sellers ”, and each of them as a “ Seller ”; the Sellers and the Purchaser collectively also referred to as the “ Parties ”, and each of them as a “ Party ”.

First, it was declared that there had been sufficient opportunity to examine the subject matter of the recording.

I, the Notary, have sufficient command of the English language, and was requested to notarize this Deed mainly in the English language. From a conversation with the present persons, I, the Notary, took evidence that the present persons have sufficient command of the English and of the German language to follow and to understand the document here notarized and its Exhibits.

Then the following was declared to my record:

Share Purchase Agreement

related to

PROJECT SPYDER

I

Reference Deed

To simplify the recording procedure a Reference Deed was drawn up on 8 May 2015 and on 11 May

2015 under Register of Deeds No. 1178/2015 DI of the Notary Dr. Robert Diekgräf in Hamburg

(hereinafter “ Reference Deed ”).

Except for Exhibit 4.1.1(b) to this Deed, any and all Exhibits to the Share Purchase Agreement related to Project Spyder ( Annex I to the present Deed) are contained in the Reference Deed. References to such Exhibits in the Share Purchase Agreement related to Project Spyder ( Annex I to the present Deed) therefore constitute references to the Reference Deed.

- 2 -

NOTARIAT AM ALSTERTOR

The persons appearing declared on behalf of the Parties that they are aware of the contents of the abovementioned Reference Deed. As a precaution, the Parties hereby confirm that Ms. Ina Kursawe was authorized to draw up the Reference Deed on their behalf. The Parties hereby confirm the statements included in the Reference Deed and approve same as a precaution. They dispensed with having the Reference Deed read out once more and with having it attached to the present deed. The original of the Reference Deed was present during the recording of this deed. The Notary has pointed out the consequences of the reference according to Section 13a BeurkG (German Recording Act).

The following Exhibit is attached to this Deed directly:

II

Share Purchase Agreement

related to Project Spyder

The parties designated therein herewith conclude the Share Purchase Agreement related to Project Spyder attached as

Annex I

that was read aloud and herewith make the statements contained therein including the Exhibits thereto.

III

Execution

Each Party receives a counterpart of this deed. The Company receives no counterpart of this deed.

The Notary has pointed out, that he can only draw up and file the list of shareholders when he has received a copy of the Closing Confirmation pursuant to Section 6.2.3 of the Share Purchase Agreement (fax transmission or PDF is sufficient). The Notary is not obliged to examine the authenticity of signatures or the powers of representation.

- 3 -

NOTARIAT AM ALSTERTOR

IV

Notes

The Notary pointed out that

Finally, the Notary pointed out that

- 4 -

NOTARIAT AM ALSTERTOR

V

Concluding Statement

Read out, approved and signed:

/s/ H. Stadler

/s/ Lothar Germeroth

/s/ Christoph Engeler

/s/ Arne Helms, Notary

- 5 -