Exhibit 5.1    LOGO

February 3, 2014

Intrexon Corporation

20374 Seneca Meadows Parkway

Germantown, Maryland 20876

Re: Form S-4 Registration Statement

Ladies and Gentlemen:

We have acted as counsel to Intrexon Corporation, a Virginia corporation (the “Company”), in connection with the preparation of the Company’s above-referenced registration statement on Form S-4 (the “Registration Statement”) filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), and relating to the registration of shares of the Company’s common stock, no par value per share (the “Shares”), to be issued to shareholders of Medistem Inc., a Nevada corporation (“Medistem”), in connection with the merger (the “Transaction”) contemplated by the Agreement and Plan of Merger, by and among the Company, XON Cells, Inc., a Nevada corporation, and Medistem, dated as of December 19, 2013, as amended (the “Merger Agreement”).

This opinion is being furnished to you at your request in accordance with the requirements of Item 601(b)(5)(i) of Regulation S-K.

We have examined originals or copies, certified or otherwise identified to our satisfaction, of such corporate records, agreements, and other instruments, certificates, orders, opinions, correspondence with public officials, certificates provided by the Company’s officers and representatives, and other documents as we have deemed necessary or advisable for the purposes of rendering the opinion set forth herein, including (i) the corporate and organizational documents of the Company, including the Amended and Restated Articles of Incorporation, as amended to date, and the Bylaws of the Company, as amended to date, (ii) the resolutions of the board of directors of the Company with respect to the Merger Agreement, Registration Statement and the offering and sale of the Shares, (iii) the Merger Agreement and exhibits thereto and (iv) the Registration Statement and exhibits thereto, including the Proxy Statement/Prospectus comprising a part thereof.

For purposes of the opinions expressed below, we have assumed (i) the authenticity of all documents submitted to us as originals, (ii) the conformity to the originals of all documents submitted as certified, photostatic or electronic copies and the authenticity of the originals thereof, (iii) the legal capacity of natural persons, (iv) the genuineness of signatures not witnessed by us, (v) the due authorization, execution and delivery of all documents by all parties, other than the Company, and the validity, binding effect and enforceability thereof and (vi) the truth, accuracy and completeness of the information, representations and warranties contained in the records, documents, instruments and certificates we have reviewed. We have further assumed that (x) the Registration Statement and any amendment thereto will have become effective (and will remain effective at the time of issuance of the Shares thereunder) and (y) the Prospectus describing the Shares will be filed with the Commission to the extent required by applicable law and relevant rules and regulations of the Commission.

Based on the foregoing and in reliance thereon, and subject to the limitations, qualifications, assumptions, exceptions and other matters set forth herein, we are of the opinion that the Shares have been duly authorized, and, when issued in accordance with the Merger Agreement and the Registration Statement, the Shares will be validly issued, fully paid and non-assessable.

We are members of the bar of the Commonwealth of Virginia and are not purporting to be experts on, or generally familiar with, or qualified to express legal conclusions based upon, laws of any state or jurisdiction other than the federal laws of the United States of America and the Commonwealth of Virginia and we express no opinion as to the effect of the laws of any other jurisdiction or as to the securities or blue sky laws of any state (including, without limitation, Virginia), municipal law or the laws of any local agencies within any state (including, without limitation, Virginia). This opinion is limited to the matters stated herein, and no opinion is implied or may be inferred beyond the matters expressly stated herein.

Our opinion is as of the date hereof and we have no responsibility to update this opinion for events and circumstances occurring after the date hereof or as to facts relating to prior events that are subsequently brought to our attention and we disavow any undertaking to advise you of any changes in law.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the use of our name under the caption “Legal Matters” in the Proxy Statement/Prospectus and Registration Statement. In giving this consent, we do not hereby admit that we come within the category of persons whose consent is required under Section 7 of the Securities Act, or the rules or regulations of the Commission promulgated thereunder.

Very truly yours,

/s/ Troutman Sanders LLP