Document:

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                                                                  Exhibit 10.9.4

          THIS WARRANT AND THE SHARES OF CAPITAL STOCK ISSUED UPON ITS
          EXERCISE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
       1933, AS AMENDED, OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY
             NOT BE SOLD OR TRANSFERRED WITHOUT COMPLIANCE WITH THE
         REGISTRATION OR QUALIFICATION PROVISIONS OF APPLICABLE FEDERAL
          AND STATE SECURITIES LAWS OR APPLICABLE EXEMPTIONS THEREFROM

          THIS WARRANT AND THE SHARES OF CAPITAL STOCK ISSUED UPON ITS
              EXERCISE ARE SUBJECT TO THE RESTRICTIONS ON TRANSFER
                     SET FORTH IN SECTION 6 OF THIS WARRANT

                                                    Number of Shares: 404,366
                                                    (subject to adjustment)

Date of Issuance: August __, 2006

                               BIOVEX GROUP, INC.

                    Series D Preferred Stock Purchase Warrant

     BIOVEX GROUP, INC., a Delaware corporation whose principal office is
located at 34 Commerce Way, Woburn, MA 01801, (the "Company"), for value
received, hereby certifies that EUROPEAN VENTURE PARTNERS II ANNEX LIMITED, a
public company with limited liability incorporated in Jersey under registered
number 93146 whose registered office is at St. Paul's Gate, New Street, St.
Helier, Jersey JE4 8ZB, or its registered assigns (the "Registered Holder"), is
entitled, subject to the terms and conditions set forth below, to purchase from
the Company, at any time or from time to time (i) prior to 5:00 p.m. (Boston
time) on December 31, 2006 (so long as an IPO (as defined below) or the
Termination Date shall not have occurred), and (ii) after 5.01 p.m. (Boston
time) on December 31, 2006 and before 5.00 p.m. (Boston time) on the Termination
Date (as defined below), up to 404,366 shares of Series D Preferred Stock,
$0.0001 par value per share (the "Series D Preferred Stock") of the Company (the
"Warrant Shares"). The purchase price per Warrant Share shall be $0.0001
(subject to adjustment as provided herein). The shares purchasable upon exercise
of this Warrant, and the purchase price per share, are hereinafter referred to
as the "Warrant Shares" and the "Purchase Price," respectively. The Series D
Preferred Stock shall have the rights, restrictions and privileges set forth in
the Restated Certificate of Incorporation of the Company, as amended or restated
from time to time (the "Certificate of Incorporation"). This Warrant is issued
by the Company in connection with the transactions contemplated pursuant to a
Sub-Lease dated August __, 2006 among the Company, BioVex Limited, a
wholly-owned subsidiary of the Company, and Venture Leasing (UK) Annex Limited,
a wholly-owned subsidiary of the Registered Holder. The Company is
simultaneously issuing to the Registered Holder a Common Stock Purchase Warrant
(the "Common Warrant").

     Notwithstanding the foregoing, in the event that an initial firm commitment
underwritten public offering of the Company's Common Stock (the "IPO") closes at
any time prior to 5.00 p.m. on December 31, 2006, this Warrant shall immediately
terminate and shall thereafter be void and of no further force or effect and the
Common Warrant shall be operative.

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     For purposes hereof, "Termination Date" shall be the earliest to occur of
(a) the tenth anniversary hereof, (b) the closing of a Merger/Sale (as defined
below) and (c) the exercise of the Common Warrant; provided however, that the
Company shall provide written notice to the Registered Holder of a pending
Merger/Sale not less than twenty (20) days, nor more than ninety (90) days,
prior to the proposed closing of such Merger/Sale. "Merger/Sale" shall mean the
consummation of (i) the acquisition of the Company by another entity by means of
any transaction or series of related transactions (including, without
limitation, any reorganization, merger or consolidation) that results in the
transfer of 50% or more of the outstanding voting power of the Company;
provided, that the holders of record of the Company's outstanding shares
immediately before such reorganization, merger or consolidation do not,
immediately after such reorganization, merger or consolidation, hold (by virtue
of securities issued as consideration in such transaction or otherwise) a
majority of the voting power of the surviving company of such reorganization,
merger or consolidation; or (ii) the sale, transfer or other disposition of all
or substantially all of the Company's assets. For the avoidance of doubt, the
exercisability of the Common Warrant and this Warrant shall be mutually
exclusive.

     1. Exercise.

          (a) Exercise for Cash. This Warrant may be exercised by the Registered
Holder, in whole or in part, by surrendering this Warrant, with the purchase
form appended hereto as Exhibit I duly executed by such Registered Holder or by
such Registered Holder's duly authorized attorney, at the principal office of
the Company, or at such other office or agency as the Company may designate,
accompanied by payment in full, in lawful money of the United States, of the
Purchase Price payable in respect of the number of Warrant Shares purchased upon
such exercise.

          (b) Cashless Exercise. The Registered Holder may, at its option, pay
the Purchase Price by canceling the portion of this Warrant as is determined by
dividing (i) the total Purchase Price payable in respect of the number of
Warrant Shares being purchased upon such exercise by (ii) the excess of the Fair
Market Value (defined below) per share of Series D Preferred Stock as of the
Exercise Date (as defined in Section 1(d) below) over the Purchase Price per
share. If the Registered Holder wishes to exercise this Warrant pursuant to this
method of payment, with respect to the maximum number of Warrant Shares
purchasable pursuant to this method, then the number of Warrant Shares so
purchasable shall be equal to the total number of exercisable Warrant Shares,
minus the product obtained by multiplying (x) the total number of exercisable
Warrant Shares by (y) a fraction, the numerator of which shall be the Purchase
Price per share and the denominator of which shall be the Fair Market Value per
share of Series D Preferred Stock as of the Exercise Date. The Fair Market Value
per share of Series D Preferred Stock shall be deemed to be the price per share
which the Company could obtain from a willing buyer for shares of Series D
Preferred Stock sold by the Company from authorized but unissued shares, as such
price shall be determined by mutual agreement of the Company and the Registered
Holder. If the Company and the Registered Holder cannot agree on such value, the
fair market value shall be determined by a reputable independent appraiser
selected by the Company with the consent of the Registered Holder (which consent
shall not be unreasonably withheld) (the "Appraiser"), whose fees and expenses
shall be borne equally by the Company and the Registered Holder.

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          (c) Automatic Exercise. Notwithstanding the provisions of Section 1(a)
and (b), this Warrant shall automatically be deemed to undergo a cashless
exercise, without any further action on behalf of the Registered Holder,
immediately prior to the liquidation, dissolution or winding up of the Company.

          (d) Exercise Date. Each exercise of this Warrant shall be deemed to
have been effected immediately prior to the close of business on the day on
which this Warrant shall have been surrendered to the Company as provided in
subsection 1(a), 1(b) or 1(c) above (the "Exercise Date"). At such time, the
person or persons in whose name or names any certificates for Warrant Shares
shall be issuable upon such exercise as provided in subsection 1(e) below shall
be deemed to have become the holder or holders of record of the Warrant Shares
represented by such certificates.

          (e) Issuance of Certificates. As soon as practicable after the
exercise of this Warrant in full or in part, and in any event within 10 days
thereafter, the Company, at its expense, will cause to be issued in the name of,
and delivered to, the Registered Holder, or as such Registered Holder (upon
payment by such Registered Holder of any applicable transfer taxes) may direct:

               (i) a certificate or certificates for the number of full Warrant
     Shares to which such Registered Holder shall be entitled upon such exercise
     plus, in lieu of any fractional share to which such Registered Holder would
     otherwise be entitled, cash in an amount determined pursuant to Section 3
     hereof; and

               (ii) in case such exercise is in part only, a new warrant or
     warrants (dated the date hereof) of like tenor, including but not limited
     to the date of issuance, calling in the aggregate on the face or faces
     thereof for the number of Warrant Shares equal (without giving effect to
     any adjustment therein) to the number of such shares called for on the face
     of this Warrant minus the sum of (a) the number of such shares purchased by
     the Registered Holder upon such exercise plus (b) the number of Warrant
     Shares (if any) covered by the portion of this Warrant canceled in payment
     of the Purchase Price payable upon such exercise pursuant to subsection
     1(b) above.

     2. Adjustments.

          (a) Adjustment for Conversion of Preferred Stock. If all of the
outstanding shares of Series D Preferred Stock are converted into Common Stock
of the Company (in connection with the IPO or otherwise) in accordance with the
terms of the Certificate of Incorporation, then, effective upon such conversion,
(i) this Warrant shall be exercisable for such number of shares of Common Stock
as is equal to the number of shares of Common Stock that each share of Series D
Preferred Stock was converted into, multiplied by the number of shares of Series
D Preferred Stock subject to this Warrant immediately prior to such conversion,
(ii) the Purchase Price shall be the Purchase Price in effect immediately prior
to such conversion divided by the number of shares of Common Stock into which
each share of Series D Preferred Stock was converted, and (iii) all references
in this Warrant to "Series D Preferred Stock" shall thereafter be deemed to
refer to "Common Stock." On the date hereof, every ten (10) shares of Series D
Preferred Stock are convertible into one (1) share of Common Stock.

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          (b) Stock Splits and Combinations of Preferred Stock. If outstanding
shares of the Company's Series D Preferred Stock shall be subdivided into a
greater number of shares or a dividend shall be paid in respect of the Series D
Preferred Stock other than accruing dividends payable pursuant to the
Certificate of Incorporation, the Purchase Price in effect immediately prior to
such subdivision or at the record date of such dividend shall simultaneously
with the effectiveness of such subdivision or immediately after the record date
of such dividend be proportionately reduced. If outstanding shares of Series D
Preferred Stock shall be combined into a smaller number of shares, the Purchase
Price with respect to such shares of Series D Preferred Stock in effect
immediately prior to such combination shall, simultaneously with the
effectiveness of such combination, be proportionately increased. The aggregate
Purchase Price payable for the total number of Warrant Shares purchasable under
this Warrant (as adjusted) shall remain the same. When any adjustment is
required to be made in the Purchase Price in accordance with this Section 2(b),
the number of Warrant Shares purchasable upon the exercise of this Warrant shall
be changed to the number determined by dividing (i) an amount equal to the
number of shares issuable upon the exercise of this Warrant immediately prior to
such adjustment, multiplied by the Purchase Price in effect immediately prior to
such adjustment, by (ii) the Purchase Price in effect immediately after such
adjustment.

          (c) Stock Splits and Combinations of Common Stock. After any mandatory
conversion of shares of Series D Preferred Stock pursuant to the Company's
Certificate of Incorporation, (i) if outstanding shares of the Company's Common
Stock shall be subdivided into a greater number of shares or a dividend in
Common Stock shall be paid in respect of Common Stock, the Purchase Price in
effect immediately prior to such subdivision or at the record date of such
dividend shall simultaneously with the effectiveness of such subdivision or
immediately after the record date of such dividend be proportionately reduced
and (ii) if outstanding shares of Common Stock shall be combined into a smaller
number of shares, the Purchase Price with respect to such shares of Common Stock
in effect immediately prior to such combination shall, simultaneously with the
effectiveness of such combination, be proportionately increased. The aggregate
Purchase Price payable for the total number of Warrant Shares purchasable under
this Warrant (as adjusted) shall remain the same. When any adjustment is
required to be made in the Purchase Price pursuant to this Section 2(c), the
number of Warrant Shares purchasable upon the exercise of this Warrant shall be
changed to the number determined by dividing (i) an amount equal to the number
of shares issuable upon the exercise of this Warrant immediately prior to such
adjustment, multiplied by the Purchase Price in effect immediately prior to such
adjustment, by (ii) the Purchase Price in effect immediately after such
adjustment.

          (d) Adjustment for Reorganization. If there shall occur any capital
reorganization or reclassification of the Company's capital stock of the same
type, class and series as the Warrant Shares then issuable upon exercise of this
Warrant (other than a change in par value or a subdivision or combination as
provided for in subsection 2(b) or 2(c) above), or any consolidation or merger
of the Company with or into another corporation, whether or not the Company is
the surviving corporation, then, as part of any such reorganization,
reclassification, consolidation or merger, as the case may be, lawful provision
shall be made so that the Registered Holder of this Warrant shall have the right
thereafter to receive upon the exercise hereof the kind and amount of shares of
stock or other securities or property which such Registered Holder would have
been entitled to receive if, immediately prior to any such

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reorganization, reclassification, consolidation or merger, as the case may be,
such Registered Holder had held the number of shares of Series D Preferred Stock
which were then purchasable upon the exercise of this Warrant. In any such case,
appropriate adjustment (as reasonably determined in good faith by the Board of
Directors of the Company) shall be made in the application of the provisions set
forth herein with respect to the rights and interests thereafter of the
Registered Holder of this Warrant, such that the provisions set forth in this
Section 2 (including provisions with respect to adjustment of the Purchase
Price) shall thereafter be applicable, as nearly as is reasonably practicable,
in relation to any shares of stock or other securities or property thereafter
deliverable upon the exercise of this Warrant.

          (e) Other Antidilution Protections. Additional antidilution rights
applicable to the Series D Preferred Stock purchasable hereunder are as set
forth in the Certificate of Incorporation. The Company shall promptly provide
the Registered Holder with any restatement, amendment, modification or waiver of
the Certificate of Incorporation.

          (f) Notice of Adjustments. When any adjustment is required to be made
in the Purchase Price, the Company shall promptly mail to the Registered Holder
a certificate setting forth the Purchase Price after such adjustment and setting
forth a brief statement of the facts requiring such adjustment. Such certificate
shall also set forth the kind and amount of stock or other securities or
property into which this Warrant shall be exercisable following the occurrence
of any of the events specified in subsection 2(b), (c), (d) or (e) above.

     3. Fractional Shares. The Company shall not be required upon the exercise
of this Warrant to issue any fractional shares, but shall pay the value thereof
to the Registered Holder in cash on the basis of the Fair Market Value per share
of Series D Preferred Stock (or Common Stock if there has been a mandatory
conversion of the Series D Preferred Stock pursuant to Section 2(a) above), as
determined pursuant to subsection 1(b) above.

     4. Reservation of Stock. The Company will at all times reserve and keep
available, solely for issuance and delivery upon the exercise of this Warrant,
such number of Warrant Shares and other stock, securities and property, as from
time to time shall be issuable upon the exercise of this Warrant and such number
of shares of Common Stock, as from time to time shall be issuable upon
conversion of the Warrant Shares.

     5. Representations, Warranties and Covenants of the Company.

          (a) Reservation of Series D Preferred Stock. The Series D Preferred
Stock issuable upon exercise of this Warrant has been duly and validly reserved
and, when issued in accordance with the provisions of this Warrant, will be
validly issued, fully paid and non-assessable, and will be free of any taxes,
liens, charges or encumbrances of any nature whatsoever; provided, however, that
the Series D Preferred Stock issuable pursuant to this Warrant may be subject to
restrictions on transfer under state and/or Federal securities laws. The Company
has made available to the Registered Holder true, correct and complete copies of
its Certificate of Incorporation and Bylaws, as amended as of the date of this
Warrant. The issuance of certificates for shares of Series D Preferred Stock
upon exercise of the Warrant shall be made without charge to the Registered
Holder for any issuance tax in respect thereof, or other cost incurred by the
Company in connection with such exercise and the related issuance of shares of

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Series D Preferred Stock, provided that the Company shall not be required to pay
any tax which may be payable in respect of any transfer involved and the
issuance and delivery of any certificate in a name other than that of the
Registered Holder.

          (b) Due Authority. The execution and delivery by the Company of this
Warrant and the performance of all obligations of the Company hereunder, have
been duly authorized by all necessary corporate action on the part of the
Company, and this Warrant does not contravene any provision of, or constitute a
default under, any indenture, mortgage, contract or other instrument to which it
is a party or by which it is bound, and this Warrant constitutes a legal, valid
and binding agreement of the Company, enforceable in accordance with its terms.
The Company received all consents and/or approvals of any third party required
in respect of the issuance of the Warrant Shares pursuant to any applicable laws
and/or regulation and/or agreement and/or other instrument to which the Company
is party and/or by which it is bound.

     6. Requirements for Transfer.

          (a) This Warrant and the Warrant Shares shall not be sold or
transferred unless either (i) they first shall have been registered under the
Securities Act of 1933, as amended (the "Act"), or (ii) the Company first shall
have been furnished with an opinion of legal counsel of the Registered Holder
(such opinion may be from the Registered Holder's inside counsel), reasonably
satisfactory to the Company, to the effect that such sale or transfer is exempt
from the registration requirements of the Act.

          (b) Notwithstanding the foregoing, no registration or opinion of
counsel shall be required for (i) a transfer by a Registered Holder which is a
corporation to a wholly owned subsidiary of such corporation or to a parent of
such corporation, a transfer by a Registered Holder which is a partnership to a
partner of such partnership or a retired partner of such partnership who retires
after the date hereof, or to the estate of any such partner or retired partner,
or to its nominee or from such nominee to its beneficial owner, if the
transferee agrees in writing to be subject to the terms of this Section 6,
provided that, in no event shall such transferee be a competitor of the Company
or (ii) a transfer made in accordance with Rule 144 under the Act. Without
limiting the generality of the foregoing, the rights of the Holder under this
Warrant may be assigned in whole or in part to Deutsche Trustee Company Limited,
Deutsche Bank AG London and to any third party who controls, is controlled by or
is under common control with the Holder and to European Venture Partners II
Leveraged Venture Leasing Company Limited.

          (c) Each certificate representing Warrant Shares shall bear a legend
substantially in the following form:

          "The securities represented by this certificate have not been
          registered under the Securities Act of 1933, as amended, and may not
          be offered, sold or otherwise transferred, pledged or hypothecated
          unless and until such securities are registered under such Act or an
          opinion of counsel satisfactory to the Company is obtained to the
          effect that such registration is not required."

                                      -6-

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The foregoing legend shall be removed from the certificates representing any
Warrant Shares, at the request of the holder thereof, at such time as they
become eligible for resale pursuant to Rule 144(k) under the Act.

     7. Representations of the Registered Holder. The Registered Holder
represents and warrants to the Company as follows:

          (a) Investment. It is acquiring the Warrant, and (if and when it
exercises this Warrant) it will acquire the Warrant Shares, and the shares of
Common Stock into which the Warrant Shares may be converted, for its own account
for investment and not with a view to, or for sale in connection with, any
distribution thereof, nor with any present intention of distributing or selling
the same; and the Registered Holder has no present or contemplated agreement,
undertaking, arrangement, obligation, indebtedness or commitment providing for
the disposition thereof.

          (b) Accredited Investor. The Registered Holder is an "accredited
investor" as defined in Rule 501(a) under the Securities Act of 1933, as amended
(the "Act").

          (c) Experience. The Registered Holder has made such inquiry concerning
the Company and its business and personnel as it has deemed appropriate; and the
Registered Holder has sufficient knowledge and experience in finance and
business that it is capable of evaluating the risks and merits of its investment
in the Company.

     8. No Impairment. The Company will not, by amendment of its charter or
by-laws or through reorganization, transfer of assets, consolidation, merger,
dissolution, issue or sale of securities or any other voluntary action, avoid or
seek to avoid the observance or performance of any of the terms of this Warrant,
but will at all times in good faith assist in the carrying out of all such terms
and in the taking of all such action as may be necessary or appropriate in order
to protect the rights of the holder of this Warrant against impairment.

     9. Notices of Record Date, etc. In case:

          (a) the Company shall take a record of the holders of its Series D
Preferred Stock (or other stock or securities at the time deliverable upon the
exercise of this Warrant) for the purpose of entitling or enabling them to
receive any dividend or other distribution, or to receive any right to subscribe
for or purchase any shares of stock of any class or any other securities, or to
receive any other right; or

          (b) of any capital reorganization of the Company, any reclassification
of the capital stock of the Company, any consolidation or merger of the Company
with or into another corporation (other than a consolidation or merger in which
the Company is the surviving entity), or any transfer of all or substantially
all of the assets of the Company; or

          (c) of the voluntary or involuntary dissolution, liquidation or
winding-up of the Company;

then, and in each such case, the Company will mail or cause to be mailed to the
Registered Holder of this Warrant a notice specifying, as the case may be, (i)
the date on which a record is

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to be taken for the purpose of such dividend, distribution or right, and stating
the amount and character of such dividend, distribution or right, or (ii) the
effective date on which such reorganization, reclassification, consolidation,
merger, transfer, dissolution, liquidation or winding-up is to take place, and
the time, if any is to be fixed, as of which the holders of record of Series D
Preferred Stock (or such other stock or securities at the time deliverable upon
the exercise of this Warrant) shall be entitled to exchange their shares of
Series D Preferred Stock (or such other stock or securities) for securities or
other property deliverable upon such reorganization, reclassification,
consolidation, merger, transfer, dissolution, liquidation or winding-up. Such
notice shall be mailed at least fifteen (15) days prior to the record date or
effective date for the event specified in such notice.

     10. Exchange of Warrants. Upon the surrender by the Registered Holder of
any Warrant or Warrants, properly endorsed, to the Company at the principal
office of the Company, the Company will, subject to the provisions of Section 6
hereof, issue and deliver to or upon the order of such Registered Holder, at the
Company's expense, a new Warrant or Warrants of like tenor, in the name of such
Registered Holder or as such Registered Holder (upon payment by such Registered
Holder of any applicable transfer taxes) may direct, calling in the aggregate on
the face or faces thereof for the number of shares of Series D Preferred Stock
called for on the face or faces of the Warrant or Warrants so surrendered.

     11. Replacement of Warrants. Upon receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and (in the case of loss, theft or destruction) upon delivery of an
indemnity agreement (with surety if reasonably required) in an amount reasonably
satisfactory to the Company, or (in the case of mutilation) upon surrender and
cancellation of this Warrant, the Company will issue, in lieu thereof, a new
Warrant of like tenor.

     12. Transfers, etc.

          (a) The Company will maintain a register containing the names and
addresses of the Registered Holders of this Warrant. Any Registered Holder may
change its or his address as shown on the warrant register by written notice to
the Company requesting such change.

          (b) Subject to the provisions of Section 6 hereof, this Warrant and
all rights hereunder are transferable, in whole or in part, upon surrender of
this Warrant with a properly executed assignment (in the form of Exhibit II
hereto) at the principal office of the Company.

          (c) Until any transfer of this Warrant is made in the warrant
register, the Company may treat the Registered Holder of this Warrant as the
absolute owner hereof for all purposes; provided, however, that if and when this
Warrant is properly assigned in blank, the Company may (but shall not be
obligated to) treat the bearer hereof as the absolute owner hereof for all
purposes, notwithstanding any notice to the contrary.

     13. Lock-up Agreement; Stockholders' Agreement.

          (a) As a condition to the issuance of this Warrant, the Registered
Holder agrees that it shall enter into any form of lock up agreement with any
other underwriter engaged by the Company in connection with the IPO, providing
that the Registered Holder shall not sell

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any shares of capital stock of the Company without the consent of such
underwriters for a period of not more than 180 days following the effective date
of the registration statement relating to such offering, provided that all
officers and directors of the Company and all two percent (2%) stockholders
enter into substantially the same agreement.

          (b) As a condition to the exercise of this Warrant (in whole or in
part), the Registered Holder agrees that it shall become a party to the
Stockholders' Agreement of the Company dated as of August 30, 2005, as the same
may be amended from time to time, as a "Preferred Holder" thereunder.

     14. Notices. All notices and other communications from the Company to the
Registered Holder in connection herewith shall be mailed by certified or
registered mail, postage prepaid, or sent via a reputable nationwide overnight
courier service guaranteeing next business day delivery, to (i) its registered
office set forth in the first paragraph of this Warrant and (ii) Cardinal House,
39-40 Albermarle Street, London, England W1S 4TE, Attn: Maurizio Petitbon, with
a copy, which shall not constitute notice, to Sonnenschein Nath and Rosenthal
LLP, 1221 Avenue of the Americas, New York, New York, 10020, Attn: Denise
Tormey, Esq. or to such other address furnished to the Company in writing by the
Registered Holder. All notices and other communications from the Registered
Holder to the Company in connection herewith shall be mailed by certified or
registered mail, postage prepaid, or sent via a reputable nationwide overnight
courier service guaranteeing next business day delivery, to the Company at its
principal office set forth below. If the Company should at any time change the
location of its principal office to a place other than as set forth below, it
shall give prompt written notice to the Registered Holder and thereafter all
references in this Warrant to the location of its principal office at the
particular time shall be as so specified in such notice. All such notices and
communications shall be deemed delivered (i) two business days after being sent
by certified or registered mail, return receipt requested, postage prepaid, or
(ii) one business day after being sent via a reputable nationwide overnight
courier service guaranteeing next business day delivery.

     15. No Rights as Stockholder. Until the exercise of this Warrant, the
Registered Holder of this Warrant shall not have or exercise any rights by
virtue hereof as a stockholder of the Company, except as set forth herein.

     16. Information. The Company shall deliver to the registered Holder hereof
such information as may be delivered from time to time by the Company to the
holders of the Series D Preferred Stock pursuant to Section 6.1 of the
Stockholders' Agreement of the Company dated as of August 31, 2005, as and when
so delivered. The foregoing covenant shall terminate upon the closing of the
IPO.

     17. Change or Waiver. Any term of this Warrant may be changed or waived
only by an instrument in writing signed by the party against which enforcement
of the change or waiver is sought. No waivers of any term, condition or
provision of this Warrant, in any one or more instances, shall be deemed to be,
or construed as, a further or continuing waiver of any such term, condition or
provision.

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     18. Section Headings. The section headings in this Warrant are for the
convenience of the parties and in no way alter, modify, amend, limit or restrict
the contractual obligations of the parties.

     19. Governing Law. This Warrant will be governed by and construed in
accordance with the internal laws of the State of Delaware (without reference to
the conflict of law provisions thereof).

     20. Waiver of Jury Trial. EACH PARTY HEREBY IRREVOCABLY WAIVES, TO THE
FULLEST EXTENT PERMITTED BY LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL
PROCEEDING ARISING OUT OF OR RELATING TO THIS WARRANT OR THE TRANSACTIONS
CONTEMPLATED BY THIS WARRANT.

     21. Counterparts. This Warrant may be executed in two or more counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.

     22. Facsimile Signatures. This Warrant may be executed by facsimile
signature.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

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     IN WITNESS WHEREOF, the undersigned parties have executed this Warrant as
of August ___, 2006.

                                       BIOVEX GROUP, INC.

                                       By:
                                           -------------------------------------
                                           Philip Astley-Sparke
                                           President and Chief Financial Officer

                                       EUROPEAN VENTURE PARTNERS II
                                       ANNEX LIMITED

                                       By:
                                           -------------------------------------
                                       Name:
                                             -----------------------------------
                                       Title:
                                              ----------------------------------

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<PAGE>

                                                                       EXHIBIT I

                                  PURCHASE FORM

To: BioVex Group, Inc., Company Secretary

                                        Dated: ______________

     The undersigned, pursuant to the provisions set forth in the attached
Warrant, hereby irrevocably elects to purchase _____ shares of the [Series D
Preferred Stock] [Common Stock] covered by such Warrant. The undersigned
herewith makes payment of $____________, representing the full purchase price
for such shares at the price per share provided for in such Warrant. Such
payment takes the form of (check applicable box or boxes):

               [ ]  $_________ in lawful money of the United States, and/or

               [ ]  the cancellation of such portion of the attached Warrant as
                    is exercisable for a total of ______ Warrant Shares (using a
                    Fair Market Value of $_______ per share for purposes of this
                    calculation).

     Please issue a certificate or certificates representing said shares in the
name of the undersigned as specified below:

     -------------------------------

                                        Signature:
                                                   -----------------------------
                                        Address:
                                                 -------------------------------

                                        ----------------------------------------

LONDON 181973v4

                                      -12-

<PAGE>

                                                                      EXHIBIT II

                                 ASSIGNMENT FORM

     FOR VALUE RECEIVED, _______________________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant with respect to the number of Warrant Shares covered thereby set forth
below, unto:

<TABLE>
<CAPTION>
Name of Assignee   Address   No. of Shares
----------------   -------   -------------
<S>                <C>       <C>

</TABLE>

Dated:                                  Signature:
       --------------                              -----------------------------

Dated:                                  Witness:
       --------------                            -------------------------------

LONDON 181973v4

                                      -13-

<PAGE>

                                                                     EXHIBIT III

                                LOCK UP AGREEMENT

                                    Attached

LONDON 181973v4

                                      -14-<PAGE>

                                                                  Exhibit 10.9.5

                               GUARANTY AGREEMENT

     This GUARANTY AGREEMENT (this "GUARANTY"), dated as of August 25, 2006, is
made by BIOVEX GROUP, INC. (the "GUARANTOR") in favor of VENTURE LEASING (UK)
ANNEX LIMITED (the "LESSOR").

     BIOVEX LIMITED (the "LESSEE") is a Subsidiary of Guarantor. Substantially
concurrently herewith the Lessee is entering into that certain English Master
Sub-lease dated August 25, 2006 with the Lessor (the "SUB-LEASE"). The Sub-Lease
will be beneficial to the Guarantor and to its business and financial
activities.

     To induce the Lessor to enter into the Sub-Lease and the other Sub-Lease
Documents, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Guarantor has agreed to
guarantee the Guaranteed Obligations upon the terms and conditions of this
Guaranty. Accordingly, the Guarantor agrees with the Lessor as follows:

     SECTION 1. DEFINITIONS.

     1.01. Definitions. Unless otherwise defined herein, all capitalized terms
used in this Guaranty that are defined in the Sub-Lease (including those terms
incorporated by reference) shall have the respective meanings assigned to them
in the Sub-Lease. In addition, the following terms shall have the following
meanings under this Guaranty:

     "AFFILIATE" shall mean, with respect to any Person, (a) each Person that,
directly or indirectly, owns or controls, whether beneficially, or as a trustee,
guardian or other fiduciary, 10% or more of the capital stock having ordinary
voting power in the election of directors of such Person, (b) each Person that
controls, is controlled by or is under common control with such Person or any
Affiliate of such Person, (c) each of such Person's officers, directors,
managers, joint venturers, members and partners, (d) any trust or beneficiary of
a trust of which such Person is the sole trustee or (e) any lineal descendants,
ancestors or spouse of such Person (or any trust for the benefit of such Person)
living in such Person's household. For the purpose of this definition, "CONTROL"
of a Person shall mean the possession, directly or indirectly, of the power to
direct or cause the direction of its management or policies, whether through the
ownership of voting securities, by contract or otherwise.

     "APPLICABLE LAW" shall mean, in respect of any Person, all provisions of
constitutions, statutes, rules, regulations and orders of Governmental
Authorities applicable to such Person, including, without limiting the
foregoing, zoning ordinances and all environmental laws, communications laws and
all orders, decisions, judgments and decrees of all courts and arbitrators in
proceedings or actions to which the Person in question is a party or by which it
is bound.

     "BANKRUPTCY CODE" shall mean Title 11 of the United States Code, as
amended.

     "GAAP" shall mean generally accepted accounting principles in the United
States of America as in effect from time to time.

<PAGE>

     "GOVERNMENTAL AUTHORITY" shall mean any nation or government, any state or
other political subdivision thereof, and any agency, department or other entity
exercising executive, legislative, judicial, regulatory or administrative
functions of or pertaining to government.

     "GUARANTEED OBLIGATIONS" shall mean (a) any and all Obligations and any and
all obligations of the Lessee for the performance of its agreements, covenants
and undertakings under or in respect of the Sub-Lease Documents, and (b) any and
all other obligations of the Lessee for the payment of all amounts, liabilities
and indebtedness (whether for principal, interest, reimbursement, fees, charge,
indemnification or otherwise) now or in the future owed to the Lessor, and for
the performance by the Lessee of its agreements, covenants and undertakings, in
each case under or in respect of any and all of the Sub-Lease Documents, it
being acknowledged by the Guarantor that such other obligations may arise or be
created, incurred or assumed at any time and from time to time and in such
manner and such circumstances and with such terms and provisions as the Lessee
and the Lessor may agree without notice or demand of any kind or nature
whatsoever to the Guarantor.

     "LIEN" shall mean any mortgage or deed of trust, pledge, hypothecation,
assignment, deposit arrangement, lien, charge, claim, security interest,
easement or encumbrance, or preference, priority or other security agreement or
preferential arrangement of any kind or nature whatsoever (including, without
limitation, any title retention agreement, any financing lease having
substantially the same economic effect as any of the foregoing, and the filing
of, or agreement to give, any financing statement perfecting a security interest
as to assets owned by the relevant Person under the Uniform Commercial Code or
comparable law of any jurisdiction).

     "OBLIGATIONS" shall mean all amounts owing by the Lessee to the Lessor (and
any of its respective assignees) pursuant to any of the Sub-Lease Documents,
including all Rental Payments, charges, fees, expenses, reasonable attorneys'
fees and any other sum payable by the Lessee under any of the Sub-Lease
Documents.

     "PERSON" shall mean an individual, a partnership, a joint venture, a trust,
an unincorporated organization, an association, a limited liability company and
a government or any department or agency thereof.

     "SUB-LEASE DOCUMENTS" shall mean the Sub-Lease and all other documents
evidencing the terms of the leasing arrangements between the Lessor and the
Lessee and shall also mean any other agreement (oral or written), instrument,
document or book entry evidencing, creating, securing or otherwise relating to
all or any part of the Guaranteed Obligations referred to in clause (b) of the
definition of "Guaranteed Obligations" that is intended by the Lessee, the
Lessor or any such Person (as the case may be) to be guaranteed by this
Guaranty.

     "SUBSIDIARY" shall mean, with respect to any Person, (a) any corporation of
which an aggregate of more than 50% of the outstanding capital stock having
ordinary voting power to elect a majority of the board of directors of such
corporation (irrespective of whether, at the time, capital stock of any other
class or classes of such corporation shall have or might have voting power by
reason of the happening of any contingency) is at the time, directly or
indirectly, owned legally or beneficially by such Person and/or one or more
Subsidiaries of such Person and (b) any partnership or other entity in which
such Person and/or one or more Subsidiaries of such

                                        2

<PAGE>

Person shall have an interest (whether in the form of voting or participation in
profits or capital contribution) of more than 50%.

Interpretation. In this Guaranty, unless otherwise indicated, the singular
includes the plural and plural the singular; words importing any gender include
the other gender; references to statutes or regulations are to be construed as
including all statutory or regulatory provisions consolidating, amending or
replacing the statute or regulation referred to; references to "WRITING" include
printing, typing, lithography and other means of reproducing words in a tangible
visible form; the words "INCLUDING," "INCLUDES" and "INCLUDE" shall be deemed to
be followed by the words "without limitation"; references to articles, sections
(or subdivisions of sections), exhibits, annexes or schedules are to this
Guaranty; references to agreements and other contractual instruments shall be
deemed to include all subsequent amendments, extensions and other modifications
to such instruments (without, however, limiting any prohibition on any such
amendments, extensions or modifications by the terms of this Guaranty); and
references to Persons include their respective successors and permitted assigns
and, in the case of Governmental Authorities, Persons succeeding to their
respective functions and capacities.

     SECTION 2. THE GUARANTEE

     2.01. Guarantee. Subject to the limitation set forth in Section 2.09, the
Guarantor hereby guarantees to the Lessor the timely payment in full when due
and performance of the Guaranteed Obligations in each case strictly in
accordance with their terms. Without limitation upon the generality of the
foregoing, the Guarantor hereby further agrees that if the Lessee shall fail to
pay in full when due all or any part of the Guaranteed Obligations, the
Guarantor will immediately pay the same, without any demand or notice
whatsoever, and that in the case of any extension of time of payment or renewal
of all or any part of the Guaranteed Obligations, the same will be timely paid
in full when due (whether at extended maturity, by acceleration or otherwise) in
accordance with the terms of such extension or renewal. This Guaranty is
absolute, irrevocable and unconditional in nature and is made with respect to
any and all Guaranteed Obligations now existing or in the future arising. The
Guarantor's liability under this Guaranty shall continue until full satisfaction
of all Guaranteed Obligations. This Guaranty is a guarantee of due and punctual
payment and performance and not of collectibility.

     2.02. Acknowledgments, Waivers and Consents. The Guarantor acknowledges
that the obligations undertaken by it under this Guaranty involve the guarantee
of obligations of Persons other than the Guarantor and that such obligations of
the Guarantor are absolute, irrevocable and unconditional under any and all
circumstances. In full recognition and in furtherance of the foregoing, the
Guarantor agrees that:

     (a) Without affecting the enforceability or effectiveness of this Guaranty
in accordance with its terms and without affecting, limiting, reducing,
discharging or terminating the liability of the Guarantor, or the rights,
remedies, powers and privileges of the Lessor under this Guaranty, the Lessor
may, at any time and from time to time and without notice or demand of any kind
or nature whatsoever, in each case to the extent and in the manner provided in
the Sub-Lease Documents:

                                        3

<PAGE>

          (i) amend, supplement, modify, extend, renew, waive, accelerate or
otherwise change the time for payment or performance of, or the terms of, all or
any part of the Guaranteed Obligations;

          (ii) amend, supplement, modify, extend, renew, waive or otherwise
change, or enter into or give, any Sub-Lease Document or any agreement, security
document, guarantee, approval, consent or other instrument with respect to all
or any part of the Guaranteed Obligations, any Sub-Lease Document or any such
other instrument or any term or provision of the foregoing;

          (iii) accept or enter into new or additional agreements, security
documents, guarantees (including letters of credit) or other instruments in
addition to, in exchange for or relative to any Sub-Lease Document, all or any
part of the Guaranteed Obligations or any collateral now or in the future
serving as security for the Guaranteed Obligations;

          (iv) accept or receive (including from any other guarantor) partial
payments or performance on the Guaranteed Obligations (whether as a result of
the exercise of any right, remedy, power or privilege or otherwise);

          (v) accept, receive and hold any additional collateral for all or any
part of the Guaranteed Obligations (including from any other guarantor);

          (vi) release, reconvey, terminate, waive, abandon, allow to lapse or
expire, fail to perfect, subordinate, exchange, substitute, transfer, foreclose
upon or enforce any collateral, security documents or guarantees (including
letters of credit or the obligations of any other guarantor) for or relative to
all or any part of the Guaranteed Obligations;

          (vii) apply any collateral or the proceeds of any collateral or
guarantee (including any letter of credit or the obligations of any other
guarantor) to all or any part of the Guaranteed Obligations in such manner and
extent as the Lessor may in its discretion determine;

          (viii) release any Person (including any other guarantor) from any
personal liability with respect to all or any part of the Guaranteed
Obligations;

          (ix) settle, compromise, release, liquidate or enforce upon such terms
and in such manner as the Lessor may determine or as applicable law may dictate
all or any part of the Guaranteed Obligations or any collateral on or guarantee
of (including any letter of credit issued with respect to) all or any part of
the Guaranteed Obligations (including with any other guarantor);

          (x) consent to the merger or consolidation of, the sale of substantial
assets by, or other restructuring or termination of the existence of the Lessee
or any other Person (including any other guarantor);

          (xi) proceed against the Lessee, the Guarantor or any other guarantor
of (including any issuer of any letter of credit issued with respect to) all or
any part of the Guaranteed Obligations or any collateral provided by any Person
and exercise the rights, remedies, powers and privileges of the Lessor under the
Sub-Lease Documents or otherwise in

                                        4

<PAGE>

such order and such manner as the Lessor may, in its discretion, determine,
without any necessity to proceed upon or against or exhaust any collateral,
right, remedy, power or privilege before proceeding to call upon or otherwise
enforce this Guaranty as to the Guarantor;

          (xii) foreclose upon any deed of trust, mortgage or other instrument
creating or granting liens on any interest in real property by judicial or
nonjudicial sale or by deed in lieu of foreclosure, bid any amount or make no
bid in any foreclosure sale or make any other election of remedies with respect
to such liens or exercise any right of set-off;

          (xiii) obtain the appointment of a receiver with respect to any
collateral for all or any part of the Guaranteed Obligations and apply the
proceeds of such receivership as the Lessor may in its discretion determine (it
being agreed that nothing in this clause (xiii) shall be deemed to make the
Lessor a party in possession in contemplation of law, except at its option);

          (xiv) enter into such other transactions or business dealings with the
Lessee, any Subsidiary or Affiliate of the Lessee or any other guarantor of all
or any part of the Guaranteed Obligations as the Lessor may desire; and

          (xv) do all or any combination of the actions set forth in this
Section 2.02(a).

     (b) The enforceability and effectiveness of this Guaranty and the liability
of the Guarantor, and the rights, remedies, powers and privileges of the Lessor,
under this Guaranty shall not be affected, limited, reduced, discharged or
terminated, and the Guarantor hereby expressly waives to the fullest extent
permitted by law any defense now or in the future arising, by reason of:

          (i) the illegality, invalidity or unenforceability of all or any part
of the Guaranteed Obligations, any Sub-Lease Document or any agreement, security
document, guarantee or other instrument relative to all or any part of the
Guaranteed Obligations;

          (ii) any disability or other defense with respect to all or any part
of the Guaranteed Obligations of the Lessee or any other guarantor of all or any
part of the Guaranteed Obligations (including any issuer of any letters of
credit), including the effect of any statute of limitations that may bar the
enforcement of all or any part of the Guaranteed Obligations or the obligations
of any such other guarantor;

          (iii) the illegality, invalidity or unenforceability of any security
or guarantee (including any letter of credit) for all or any part of the
Guaranteed Obligations or the lack of perfection or continuing perfection or
failure of the priority of any lien on any collateral for all or any part of the
Guaranteed Obligations;

          (iv) the cessation, for any cause whatsoever, of the liability of the
Lessee or any other guarantor of all or any part of the Guaranteed Obligations
(other than, subject to Section 2.05, by reason of the full payment and
performance of all Guaranteed Obligations);

          (v) any failure of the Lessor to marshal assets in favor of the Lessee
or any other Person (including any other guarantor), to exhaust any collateral
for all or any part of the Guaranteed Obligations, to pursue or exhaust any
right, remedy, power or privilege it may have

                                        5

<PAGE>

against the Lessee, any other guarantor of all or any part of the Guaranteed
Obligations (including any issuer of any letter of credit) or any other Person
or to take any action whatsoever to mitigate or reduce the Guarantor's or any
other guarantor's liability under this Guaranty, the Lessor being under no
obligation to take any such action notwithstanding the fact that all or any part
of the Guaranteed Obligations may be due and payable and that the Lessee may be
in default of its obligations under any Sub-Lease Document;

          (vi) any failure of the Lessor to give notice of sale or other
disposition of any collateral (including any notice of any judicial or
nonjudicial foreclosure or sale of any interest in real property serving as
collateral for all or any part of the Guaranteed Obligations) for all or any
part of the Guaranteed Obligations to Lessee, the Guarantor or any other Person
or any defect in, or any failure by the Guarantor or any other Person to
receive, any notice that may be given in connection with any sale or disposition
of any collateral;

          (vii) any judicial or nonjudicial foreclosure or sale of, or other
election of remedies with respect to, any interest in real property or other
collateral serving as security for all or any part of the Guaranteed
Obligations, even though such foreclosure, sale or election of remedies may
impair the subrogation rights of the Guarantor or may preclude the Guarantor
from obtaining reimbursement, contribution, indemnification or other recovery
from the Lessee, any other guarantor or any other Person and even though the
Lessee may not, as a result of such foreclosure, sale or election of remedies,
be liable for any deficiency;

          (viii) any law which provides that the obligation of a surety or
guarantor must neither be larger in amount nor in other respects more burdensome
than that of the principal or which reduces a surety's or guarantor's obligation
in proportion to the principal obligation;

          (ix) the possibility that the obligations of the Lessee to the Lessor
may at any time and from time to time exceed the aggregate liability of the
Guarantor under this Guaranty;

          (x) any counterclaim, set-off or other claim which the Lessee or any
other guarantor has or alleges to have with respect to all or any part of the
Guaranteed Obligations;

          (xi) any failure of the Lessor to file or enforce a claim in any
bankruptcy or other proceeding with respect to any Person;

          (xii) the election by the Lessor in any bankruptcy proceeding of any
Person, of the application or nonapplication of Section 1111(b)(2) of the
Bankruptcy Code or comparable law of any jurisdiction;

          (xiii) any extension of credit or the grant of any Lien under Section
364 of the Bankruptcy Code or comparable law of any jurisdiction;

          (xiv) any use of cash collateral under Section 363 of the Bankruptcy
Code or comparable law of any jurisdiction;

          (xv) any agreement or stipulation with respect to the provision of
adequate protection in any bankruptcy proceeding of any Person;

          (xvi) the avoidance of any Lien in favor of the Lessor for any reason;

                                        6

<PAGE>

          (xvii) any bankruptcy, insolvency, reorganization, arrangement,
readjustment of debt, liquidation or dissolution proceeding commenced by or
against any Person, including any discharge of, or bar or stay against
collecting, all or any part of the Guaranteed Obligations (or any interest on
all or any part of the Guaranteed Obligations) in or as a result of any such
proceeding;

          (xviii) any action taken by the Lessor, whether similar or dissimilar
to any of the foregoing, that is authorized by this Section 2.02 or otherwise in
this Guaranty or by any other provision of any Sub-Lease Document or any
omission to take any such action; or

          (xix) any other circumstance whatsoever, whether similar or dissimilar
to any of the foregoing, that might otherwise constitute a legal or equitable
discharge or defense of a surety or guarantor.

     (c) The Guarantor expressly waives, for the benefit of the Lessor, all
set-offs and counterclaims and all presentments, demands for payment or
performance, notices of nonpayment or nonperformance, protests, notices of
protest, notices of dishonor and all other notices or demands of any kind or
nature whatsoever with respect to the Guaranteed Obligations, and all notices of
acceptance of this Guaranty or of the existence, creation, incurring or
assumption of new or additional Guaranteed Obligations. The Guarantor further
expressly waives the benefit of any and all statutes of limitation and any and
all laws providing for the exemption of property from execution or for valuation
and appraisal upon foreclosure, to the maximum extent permitted by applicable
law.

     (d) The Guarantor represents and warrants to the Lessor that the Guarantor
has established adequate means of obtaining financial and other information
pertaining to the business, operations and condition (financial and otherwise)
of the Lessee and its properties on a continuing basis and that the Guarantor is
now and will in the future remain fully familiar with the business, operations
and condition (financial and otherwise) of the Lessee and its properties. The
Guarantor further represents and warrants that it has reviewed and approved each
of the Sub-Lease Documents and is fully familiar with the transaction
contemplated by the Sub-Lease Documents and that it will in the future remain
fully familiar with such transaction and with any new Sub-Lease Documents and
the transactions contemplated by such Sub-Lease Documents. The Guarantor hereby
expressly waives and relinquishes any duty on the part of the Lessor (should any
such duty exist) to disclose to the Guarantor or any other guarantor any matter
of fact or other information known to the Lessee or otherwise related to the
business, operations or condition (financial or otherwise) of the Lessee or its
properties or to any Sub-Lease Document or the transactions undertaken pursuant
to, or contemplated by, any such Sub-Lease Document, whether now or in the
future known by the Lessor.

     (e) The Guarantor intends that its rights and obligations shall be those
expressly set forth in this Guaranty and that its obligations shall not be
affected, limited, reduced, discharged or terminated by reason of any principles
or provisions of law which conflict with the terms of this Guaranty.

     (f) Any provision hereof to the contrary notwithstanding, any defense
available to the Lessee with respect to payment and performance of the
Guaranteed Obligations shall also be available to the Guarantor with respect to
the Guaranteed Obligations.

                                        7

<PAGE>

     2.03. Understanding With Respect to Waivers and Consents. The Guarantor
warrants and agrees that each of the waivers and consents set forth in this
Guaranty is made voluntarily and unconditionally after consultation with outside
legal counsel and with full knowledge of its significance and consequences, with
the understanding that events giving rise to any defense or right waived may
diminish, destroy or otherwise adversely affect rights which the Guarantor or
any other guarantor otherwise may have against the Lessee, the Lessor or any
other Person or against any collateral. If, notwithstanding the intent of the
parties that the terms of this Guaranty shall control in any and all
circumstances, any such waivers or consents are determined to be unenforceable
under applicable law, such waivers and consents shall be effective to the
maximum extent permitted by law.

     2.04. Subrogation. The Guarantor hereby agrees that, until the payment and
satisfaction in full of all of the Guaranteed Obligations under the Sub-Lease
Documents, it shall not exercise any right, remedy, power or privilege, such as
any right of subrogation, contribution or indemnity or related remedy, power or
privilege, arising (whether by contract or operation of law, including under the
Bankruptcy Code or comparable law of any jurisdiction) against the Lessee or any
other guarantor of all or any part of the Guaranteed Obligations or any
collateral for all or any part of the Guaranteed Obligations by reason of any
payment or other performance pursuant to the provisions of this Guaranty and, if
any amount shall be paid to the Guarantor on account of such rights, remedies,
powers or privileges, it shall hold such amount in trust for the benefit of, and
pay the same over to, the Lessor on account of the Guaranteed Obligations. The
Guarantor understands that the exercise by the Lessor of any right, remedy,
power or privilege that it may have under the Sub-Lease Documents, any
agreement, security document, guarantee or other instrument relative to all or
any part of the Guaranteed Obligations or otherwise may affect or eliminate the
Guarantor's or any other guarantor's right of subrogation or similar recovery
against the Lessee, any other guarantors or any collateral and that the
Guarantor and the other guarantors may therefore incur partially or totally
nonreimbursable liability under this Guaranty. Notwithstanding the foregoing,
all of the Lessor's rights and remedies shall be cumulative and may be exercised
by Lessor in its sole discretion.

     2.05. Reinstatement. The obligations of the Guarantor under this Guaranty
shall be automatically reinstated if and to the extent that for any reason any
payment by or on behalf of the Lessee, any other guarantor or any other Person
or any other application of funds (including the proceeds of any collateral for
all or any part of the Guaranteed Obligations) in respect of all or any part of
the Guaranteed Obligations is rescinded or must be otherwise restored by any
holder of such Guaranteed Obligations, whether as a result of any proceedings in
bankruptcy, reorganization or otherwise and the Guarantor agrees that it will
indemnify the Lessor on demand for all reasonable costs and expenses (including
fees and expenses of counsel) incurred by the Lessor in connection with such
rescission or restoration.

     2.06. Remedies. The Guarantor hereby agrees that, between it and the
Lessor, the obligations of the Lessee under the Sub-Lease and the other
Sub-Lease Documents may be declared to be forthwith (or may become
automatically) due and payable as provided in clause 12 of the Sub-Lease for
purposes of Section 2.01 notwithstanding any stay, injunction or other
prohibition preventing such declaration (or such obligations becoming due and
payable as against the Lessee) and that, in the event of such declaration (or
such obligation being deemed

                                        8

<PAGE>

due and payable), such obligations (whether or not due and payable by the
Lessee) shall forthwith become due and payable for purposes of Section 2.01.

     2.07. Separate Action. The Lessor may bring and prosecute a separate action
or actions against the Guarantor whether or not the Lessee, any other guarantor
or any other Person is joined in any such action or a separate action or actions
are brought against the Lessee, any other guarantor, any other Person, or any
collateral for all or any part of the Guaranteed Obligations. The obligations of
the Guarantor under, and the effectiveness of, this Guaranty are not conditioned
upon the existence or continuation of any other guarantee (including any letter
of credit) of all or any part of the Guaranteed Obligations.

     2.08. Subordination of Indebtedness of the Lessee. The Guarantor agrees
that any indebtedness of the Lessee now or in the future owed to the Guarantor
is hereby subordinated to the Guaranteed Obligations; provided, however, that
unless an event of default under the Sub-Lease has occurred and is continuing,
such indebtedness may be paid in the ordinary course of business. If the Lessor
so requests, any such indebtedness shall be collected, enforced and received by
the Guarantor as trustee for the Lessor and shall be paid over to the Lessor in
kind on account of the Guaranteed Obligations. If, after the Lessor's request,
the Guarantor fails to collect or enforce any such indebtedness or to pay the
proceeds of such indebtedness to the Lessor, the Lessor as the Guarantor's
attorney-in-fact may do such acts and sign such documents in the Guarantor's
name and on the Guarantor's behalf as the Lessor reasonably considers necessary
or desirable to effect such collection, enforcement or payment, the Lessor being
hereby appointed the Guarantor's attorney-in-fact for such purpose.

     2.09. Limitation on Guarantee. If under any applicable law (including
without limitation state and Federal fraudulent transfer laws) the obligations
of the Guarantor under Section 2.01 would otherwise be held or determined to be
void, invalid or unenforceable or if the claims of the Lessor in respect of such
obligations would be subordinated to the claims of any other creditors on
account of the Guarantor's liability under Section 2.01, then, notwithstanding
any other provision of this Guaranty to the contrary, the amount of such
liability shall, without any further action by the Guarantor, the Lessor or any
other Person, be automatically limited and reduced to the highest amount which
is valid and enforceable and not subordinated to the claims of other creditors
as determined in such action or proceeding.

     2.10. Revocation. To the fullest extent permitted by law, the Guarantor
hereby waives all right of revocation with respect to the Guaranteed
Obligations.

     SECTION 3. REPRESENTATIONS OF THE GUARANTOR.

     As of the date hereof, the Guarantor represents to the Lessor that:

     3.01. Existence. Each of the Guarantor and its Subsidiaries: (i) is a
corporation, partnership or other entity duly organized, validly existing and in
good standing under the laws of the jurisdiction of its incorporation; (ii) has
all requisite corporate or other power, and has all material Governmental
Approvals, necessary to own its assets and carry on its business as now being or
as proposed to be conducted; and (iii) is qualified to do business in all
jurisdictions in which the nature of the business conducted by it makes such
qualification necessary and where the failure so to qualify would have a
material adverse effect.

                                        9

<PAGE>

     3.02. Litigation. Except as disclosed under the caption "Business--Legal
Proceedings" in Amendment No. 1 to the Registration Statement on Form S-1 of the
Guarantor (Registration No. 333-135148) filed with the U.S. Securities and
Exchange Commission on August 11, 1006, there are no legal or arbitral
proceedings, or any proceeding by or before any Governmental Authority now
pending or, to the knowledge of the Guarantor, threatened against the Guarantor
(i) as to which there is a reasonable possibility of an adverse determination
and that if adversely determined could reasonably be expected to have a material
adverse effect or (ii) which purports to affect the legality, validity or
enforceability of this Guaranty.

     3.03. No Breach. None of the execution and delivery of this Guaranty, the
consummation of the transactions contemplated by this Guaranty or compliance
with the terms and provisions of this Guaranty will conflict with or result in a
breach of, or require any consent under, the certificate of incorporation of the
Guarantor, or any applicable Governmental Rule, or any agreement or instrument
to which the Guarantor or any of its Subsidiaries is a party or by which any of
them is bound or to which any of them is subject, or constitute a default under,
or result in the acceleration or mandatory prepayment of, any indebtedness
evidenced by, or termination of, any such agreement or instrument, or result in
the creation or imposition of any Lien upon any property of the Guarantor or any
of its Subsidiaries pursuant to the terms of any such agreement or instrument
(except for Liens created pursuant to any security documents).

     3.04. Necessary Action. The Guarantor has all necessary corporate power and
authority to execute, deliver and perform its obligations under this Guaranty;
the execution, delivery and performance by the Guarantor of this Guaranty have
been duly authorized by all necessary corporate action on its part (including
any required stockholder approvals); and this Guaranty has been duly and validly
executed and delivered by the Guarantor and constitutes its legal, valid and
binding obligation, enforceable in accordance with its terms.

     3.05. Approvals. No Governmental Approvals are necessary for the execution,
delivery or performance by the Guarantor of this Guaranty or for the legality,
validity or enforceability of this Guaranty.

     3.06. Taxes. The Guarantor and each of its Subsidiaries have filed all
Federal income tax returns and all other material tax returns that are required
to be filed by the Guarantor or such Subsidiary and paid all taxes due pursuant
to such returns and all other related penalties and charges, except for any such
tax, assessment, penalty or charge the payment of which is being contested in
good faith and the failure to pay of which does not result in a Lien being
placed on any Property of the Guarantor or such Subsidiary (other than Liens
imposed by a Governmental Authority for taxes, assessments or charges not yet
due or which are being contested in good faith and by appropriate proceedings if
adequate reserves with respect to such Liens are maintained on the books of such
Guarantor, in accordance with GAAP).

     3.07. Certain Regulations. The Guarantor is not (a) an "investment
company," or a company "controlled" by an "investment company," within the
meaning of the Investment Company Act of 1940, (b) a "holding company," or an
"affiliate" of a "holding company" or a "subsidiary company" of a "holding
company," within the meaning of the Public Utility Holding Company Act of 1935
or (c) subject to any other Governmental Rule restricting its ability to incur
Indebtedness or to issue guarantees.

                                       10

<PAGE>

     SECTION 4. COVENANTS OF THE GUARANTOR.

     So long as this Guaranty is in effect and until all of the Guaranteed
Obligations have been paid in full, the Guarantor agrees as follows:

     4.01. Reporting Requirements. The Guarantor shall deliver to the Lessor:

     (a) promptly after the sending or filing thereof, copies of all regular,
periodic and special reports, and all registration statements, which the
Guarantor or any Subsidiary of the Guarantor files with the Securities and
Exchange Commission or any governmental authority which may be substituted
therefor or with any national securities exchange (provided, however, that any
such documents that are publicly available on the Securities and Exchange
Commission's EDGAR website shall be deemed so delivered and no physical delivery
thereof shall be required); and

     (b) with reasonable promptness, such other information and data (financial
or other) as may from time to time be reasonably requested by the Lessor.

     4.02. Litigation. The Guarantor will, or will cause the Lessee to, promptly
give notice to the Lessor of all material actions, suits and proceedings of the
type described in Section 3.02 before any Governmental Authority.

     4.03. Existence, Etc. The Guarantor will, and will cause its Subsidiary to:
preserve and maintain its legal existence, and all of its material rights,
privileges and franchises; comply with the requirements of all Applicable Laws
if the failure to comply with such requirements has a material adverse effect;
pay and discharge all taxes, assessments and governmental charges or levies
imposed on it or on its income or profits or on any of its other Property prior
to the date on which penalties would attach, except for any such tax,
assessment, charge or levy, the payment of which is being contested in good
faith and by proper proceedings and against which adequate reserves are being
maintained; maintain all of its properties used or useful in its business in
good working order and condition, ordinary wear and tear excepted; permit
representatives of the Lessor, upon reasonable advance notice and during normal
business hours, to examine, copy and make extracts from its books and records,
to inspect its properties, and to discuss its business and affairs with its
officers, all to the extent reasonably requested by the Lessor; keep adequate
records and books of account, in which complete entries will be made in
accordance with GAAP; and keep insured by financially sound and reputable
insurers all property of a character usually insured by companies engaged in the
same or similar business similarly situated against loss or damage of the kinds
and in the amounts customarily insured against by such companies and carry such
other insurance as is usually carried by such companies.

     SECTION 5. MISCELLANEOUS PROVISIONS.

     5.01. Waiver. No failure or delay by the Lessor in exercising any remedy,
right, power or privilege under this Guaranty or any other Sub-Lease Document
shall operate as a waiver of such remedy, right, power or privilege, nor shall
any single or partial exercise of such remedy, right, power or privilege
preclude any other or further exercise of such remedy, right, power or privilege
or the exercise of any other remedy, right, power or privilege. The remedies,
rights, powers and privileges provided by this Guaranty are, to the extent
permitted by law, cumulative

                                       11

<PAGE>

and not exclusive of any remedies, rights, powers or privileges provided by the
other Sub-Lease Documents or by law.

     5.02. Notices. All notices, requests, demands, and other communications to
be delivered hereunder shall be in writing and shall be delivered by hand or
mailed, by facsimile (receipt confirmed), by internationally recognized courier
service, or by express, registered or certified mail, postage and fees prepaid,
return receipt requested, at or to the following address:

                    BioVex Group, Inc.
                    34 Commerce Way
                    Woburn, Massachusetts 01801
                    Attn: Chief Executive Officer
                    Fax: (781) 933-6025

                    with a copy to:

                    Timothy Corbett, Esq.
                    WilmerHale
                    10 Noble Street
                    London, England EC2V 7QJ
                    Fax: 011-44-20-7645-2424

     5.03. Expenses, Etc. The prevailing party in any litigation brought in
respect of this Guaranty shall be entitled to recover from the other party, and
such other party agrees to pay to the prevailing party, concurrently with the
conclusion of such litigation, all reasonable costs and expenses (including
reasonable fees and expenses of counsel) incurred by the prevailing party in
connection with such litigation. All amounts due under this Guaranty (including
under Section 2.01) not paid when due shall bear interest at the prime rate per
annum published from time to time in The Wall Street Journal plus four (4%)
percent.

     5.04. Amendments, Etc. Any provision of this Guaranty may be waived,
altered or amended only by an instrument in writing signed by the Guarantor and
the Lessor. Any waiver, alteration or amendment shall be for such period and
subject to such conditions as shall be specified in the written instrument
effecting the same and shall be binding upon the Lessor, each holder of
Guaranteed Obligations and the Guarantor, and any such waiver shall be effective
only in the specific instance and for the purpose for which given.

     5.05. Successors and Assigns. This Guaranty shall be binding upon and inure
to the benefit of its parties and their respective successors and assigns. The
Guarantor may not assign or transfer its rights or obligations under this
Guaranty without the prior written consent of the Lessor. Any attempted
assignment or transfer in violation of this Section 5.05 shall be null and void.

     5.06. Survival. All representations and warranties made in this Guaranty or
in any certificate or other document delivered pursuant to or in connection with
this Guaranty shall survive the execution and delivery of this Guaranty or such
certificate or other document (as the case may be) or any deemed repetition of
any such representation or warranty.

                                       12

<PAGE>

     5.07. Agreements Superseded. This Guaranty supersedes all prior agreements
and understandings, written or oral, among the parties with respect to the
subject matter of this Guaranty.

     5.08. Severability. Any provision of this Guaranty that is prohibited or
unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective
to the extent of such prohibition or unenforceability without invalidating the
remaining provisions of this Guaranty, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

     5.09. Captions. The table of contents, captions and section headings
appearing in this Guaranty are included solely for convenience of reference and
are not intended to affect the interpretation of any provision of this Guaranty.

     5.10. Counterparts. This Guaranty may be executed in any number of
counterparts, all of which taken together shall constitute one and the same
instrument and any of the parties to this Guaranty may execute this Guaranty by
signing any such counterpart. Transmission by telecopier of an executed
counterpart of this Agreement shall be deemed to constitute due and sufficient
delivery of such counterpart. The signature page from any such counterpart may
be attached to another counterpart to form one complete Agreement.

     5.11. GOVERNING LAW; SUBMISSION TO JURISDICTION. THIS GUARANTY SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAW OF THE STATE OF DELAWARE.
THE GUARANTOR HEREBY SUBMITS TO THE NONEXCLUSIVE JURISDICTION OF THE UNITED
STATES DISTRICT COURT FOR THE DISTRICT OF DELAWARE AND OF ANY DELAWARE STATE
COURT SITTING IN WILMINGTON, DELAWARE FOR THE PURPOSES OF ALL LEGAL PROCEEDINGS
ARISING OUT OF OR RELATING TO THIS GUARANTY OR THE TRANSACTIONS CONTEMPLATED BY
THIS GUARANTY. THE GUARANTOR IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED
BY APPLICABLE LAW, ANY OBJECTION WHICH IT MAY NOW OR HEREAFTER HAVE TO THE
LAYING OF THE VENUE OF ANY SUCH PROCEEDING BROUGHT IN SUCH A COURT AND ANY CLAIM
THAT ANY SUCH PROCEEDING BROUGHT IN SUCH A COURT HAS BEEN BROUGHT IN AN
INCONVENIENT FORUM.

     5.12. Waiver of Jury Trial. THE GUARANTOR HEREBY IRREVOCABLY WAIVES, TO THE
FULLEST EXTENT PERMITTED BY LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL
PROCEEDING ARISING OUT OF OR RELATING TO THIS GUARANTY OR THE TRANSACTIONS
CONTEMPLATED BY THIS GUARANTY.

                                       13

<PAGE>

     IN WITNESS WHEREOF, the undersigned has executed this Guaranty as of the
date first above written.

                                        GUARANTOR:

                                        BIOVEX GROUP, INC.

                                        By: /s/ Philip Astley-Sparke
                                            ------------------------------------
                                        Name: Philip Astley-Sparke
                                        Title: President

                                       14

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