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EXHIBIT *(10.47)

                            PATENT SECURITY AGREEMENT
                             (United States Patents)

This Patent Security Agreement ("Agreement") is made this 29th day of October,
1999, by IGEN, INC., a Delaware corporation having a mailing address at Wheat
Road and Lincoln Avenue, Buena, NJ 08310 ("Grantor") and delivered to AMERICAN
CAPITAL STRATEGIES, LTD., a Delaware corporation having a mailing address at 2
Bethesda Metro Center, 14th Floor, Bethesda, Maryland 20814 ("Lender").

                                   BACKGROUND

A. Grantor has entered into that certain Note and Equity Purchase Agreement
dated as of even date herewith among Grantor, IGI, Inc., ImmunoGenetics, Inc.,
and Blood Cells, Inc. (collectively, "Borrowers") and Lender (as it may
hereafter be supplemented, restated, amended, superseded or replaced from time
to time, the "Purchase Agreement"). Capitalized terms not defined herein shall
have the meanings given to such terms in the Purchase Agreement.

B. This Agreement is being executed contemporaneously with that certain Security
Agreement of even date herewith among Borrowers and Lender (as it may hereafter
be supplemented, restated, amended, superseded or replaced from time to time,
the "Security Agreement"), under which, inter alia, Grantor is granting Lender a
lien on and security interest in certain assets of Grantor associated with or
relating to products leased or sold or services provided under Grantor's patents
and the goodwill associated therewith as security for the payment and
performance of all the Obligations (as defined in the Security Agreement) of all
the Borrowers, and under which Lender is entitled to foreclose or otherwise deal
with such assets and patents under the terms and conditions set forth therein.

C. Pursuant to the Security Agreement, Lender is acquiring a lien on, and
security interest in, and license to use (which license is conditioned upon the
occurrence and continuance of an Event of Default), among other things, (i) the
United States Letters Patent and the inventions described and claimed therein
set forth on Schedule A hereto and (ii) the applications for Letters Patent and
the inventions described and claimed therein set forth on Schedule A hereto and
any United States Letters Patent which may be issued upon any of said
applications, together with all the goodwill of Grantor associated therewith and
represented thereby, as security for all of the Obligations, and desires to have
its security interest in such letters patent and applications confirmed by a
document identifying same and in such form that it may be recorded in the United
States Patent and Trademark Office.

NOW THEREFORE, with the foregoing Background hereinafter deemed incorporated by
reference and made a part hereof, and in consideration of the premises and
mutual promises herein contained, the parties hereto, intending to be legally
bound hereby, covenant and agree as follows:
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1.    In consideration of and pursuant to the terms of the Purchase
      Agreement, and for other good, valuable and sufficient consideration,
      the receipt of which is hereby acknowledged, and to secure the payment
      and performance of all the Obligations of all Borrowers under the
      Purchase Documents, Grantor grants to Lender a lien on and security
      interest in all patents and patent applications, including, without
      limitation, the inventions and improvements described and claimed
      therein, and those patents and patent applications listed on Schedule
      "A" attached hereto and made a part hereof, and the reissues,
      divisions, continuations, renewals, extensions and
      continuations-in-part thereof (collectively, the "Schedule A Patents"),
      all of Grantor's rights and obligations pursuant to any license
      agreements between Grantor and any other Person or Persons, whether
      Grantor is a licensor or licensee under any such license agreements,
      including, without limitation, the licenses listed on Schedule "C"
      attached hereto and made a part hereof with respect to the patents and
      patent applications listed on Schedule "B" attached hereto and made a
      part hereof (collectively the "Schedule B Patents" and, together with
      the Schedule A Patents, the "Patents"), and, subject to the terms of
      such licenses, the right to prepare for sale, sell and advertise for
      sale, all Inventory now or hereafter owned by such Assignor and now or
      hereafter covered by such licenses (collectively, the "Licenses", and
      together with the Patents, the "Patent Rights") and all proceeds
      thereof and all Grantor's right, title, interest, claims and demands
      that Grantor has or may have in profits and damages for past and future
      infringements of the Patent Rights (such rights, interest, claims and
      demand being herein called the "Claims") (the Patent Rights and Claims
      are collectively referred to as the "Patent Collateral").

2.    Grantor hereby covenants and agrees to maintain the Patent Collateral in
      full force and effect until all of the Obligations are satisfied in full.

3. Grantor represents, warrants and covenants to Lender that:

      (a)   The Patent Collateral is subsisting and has not been adjudged
invalid or unenforceable;

      (b) All of the Patent Rights subsisting, and, to the best of Grantor's
knowledge, valid and enforceable;

      (c) Grantor is the sole and exclusive owner of the entire and unencumbered
right, title and interest in and to the Patent Collateral (excepting the
Schedule B Patents, but including the Grantor's rights under the Licenses).
Except for Liens permitted under Section 7.2(b) of the Purchase Agreement, all
of the Patent Collateral (other than the Schedule B Patents, but including
Grantor's right under the Licenses) is free and clear of any liens, charges and
encumbrances including, without limitation, pledges, assignments, options and
covenants by Grantor not to sue third persons;

      (d) Except for Liens permitted under Section 7.2(b) of the Purchase
Agreement, the Grantor's rights under the Licenses are free and clear of any
liens, claims,


                                       2
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charges and encumbrances, including, without limitation, pledges,
assignments, options, and covenants by Grantor not to sue third persons;

      (e) Grantor has no notice of any suits or actions commenced or threatened
against it, or notice of claims asserted or threatened against it, with
reference to the Patent Collateral;

      (f) Grantor has the unqualified right, power and authority to enter into
this Agreement and perform its terms; and

      (g) Grantor has complied with, and will continue for the duration of this
Agreement to comply with the requirements set forth in 15 U.S.C.
Section 1051-1127 and any other applicable statutes, rules and regulations in
connection with its use of the Patent Collateral except where failure to comply
would not have a material adverse effect on Grantor or its Property.

4. Grantor further covenants that:

      (a) Until all of the Obligations have been satisfied in full, Grantor will
not enter into any agreement which is inconsistent with Grantor's obligations
under this Agreement, Grantor's obligations under the Purchase Agreement or
which may restrict or impair Lender's rights or priorities hereunder.

      (b) If Grantor acquires rights to any new owned Patent Collateral, the
provisions of this Agreement shall automatically apply thereto and such Patent
Collateral shall be deemed part of the Patent Collateral. Grantor shall give
Lender prompt written notice thereof along with an amended Schedule "A."
Furthermore, if Grantor acquires rights as a licensee to any new patents, the
provisions of this Agreement shall automatically apply thereto and such patent
shall be deemed part of the Schedule B Patents, and any license agreement
pursuant to which Grantor acquires such rights shall be deemed to be included in
the definition of "Licenses." Grantor shall give Lender written notice promptly
upon its first use thereof along with an amended Schedule "B."

5.    So long as this Agreement is in effect and so long as Grantor has not
      received notice from Lender that an Event of Default has occurred and
      is continuing under the Notes and the Purchase Agreement and that
      Lender has elected to exercise its rights hereunder (i) Grantor shall
      continue to have the exclusive right to use the Patent Collateral; and
      (ii) Lender shall have no right to use the Patent Collateral or issue
      any exclusive or non-exclusive license with respect thereto, or assign,
      pledge or otherwise transfer title in the Patent Collateral to anyone
      else.

6.    Grantor agrees not to sell, license, grant any option, assign or
      further encumber its rights and interest in the Patent Collateral to
      any entity or person other than Grantor without the prior written
      consent of Lender or as may be expressly permitted under the Purchase
      Agreement.  Notwithstanding the foregoing, and providing that no
      Default or Event of Default has occurred and is outstanding, Grantor
      shall be entitled to license any Patents in exchange for fair market
      consideration in the exercise of its reasonable business judgment.


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7.    Anything herein contained to the contrary notwithstanding, if and while
      Grantor shall be in default hereunder or an Event of Default exists
      under the Notes or the Purchase Agreement, Grantor hereby covenants and
      agrees that Lender as the holder of a security interest under the
      Uniform Commercial Code, as now or hereafter in effect in the State
      whose law governs the interpretation of the Purchase Documents, may
      take such action permitted under the Purchase Documents, hereunder or
      under any law, in its exclusive discretion, to foreclose upon the
      Patent Collateral covered hereby. For such purposes, Grantor hereby
      authorizes and empowers Lender, its successors and assigns to make,
      constitute and appoint any officer or agent of Lender as Lender may
      select, in its exclusive discretion, as Grantor's true and lawful
      attorney-in-fact, with the power to endorse Grantor's name on all
      applications, documents, papers and instruments necessary for Lender to
      use the Patent Collateral or to grant or issue any exclusive or
      non-exclusive license under the Patent Collateral to anyone else, or
      necessary for Lender to assign, pledge, convey or otherwise transfer
      title in or dispose of the Patent Collateral to anyone else including,
      without limitation, the power to execute a Patent Collateral assignment
      in the form attached hereto as Exhibit 1.  Grantor hereby ratifies all
      that such attorney shall lawfully do or cause to be done by virtue
      hereof, except for the gross negligence or willful misconduct of such
      attorney. This power of attorney shall be irrevocable for the life of
      this Agreement, the Purchase Documents, and until all of the
      Obligations of all of the Borrowers are indefeasibly paid and satisfied
      in full.

8.    This Agreement shall be subject to the terms, provisions, and conditions
      set forth in the Purchase Agreement and may not be modified without the
      written consent of the party against whom enforcement is being sought.

9.    All rights and remedies herein granted to Lender shall be in addition to
      any rights and remedies granted to Lender under the Purchase Documents. In
      the event of an inconsistency between this Agreement and Purchase
      Agreement, the language of this Agreement shall control.

10.   Upon Borrowers' performance of all of the Obligations under the Purchase
      Documents and full and unconditional satisfaction of all of the Borrowers'
      Obligations, Lender shall execute and deliver to Grantor all documents
      reasonably necessary to terminate Lender's security interest in the Patent
      Collateral.

11.   Any and all reasonable fees, costs and expenses, of whatever kind or
      nature, including the reasonable attorneys' fees and legal expenses
      incurred by Lender in connection with the preparation of this Agreement
      and all other documents relating hereto and the consummation of this
      transaction, the filing or recording of any documents (including all
      taxes in connection therewith) in public offices, the payment or
      discharge of any taxes, reasonable counsel fees, maintenance fees,
      encumbrances or costs otherwise incurred in protecting, maintaining,
      preserving the Patent Collateral, or in defending or prosecuting any
      actions or proceedings arising out of or related to the Patent
      Collateral, in each case in accordance with the terms of this
      Agreement, shall be borne and paid by Grantor on demand by


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<PAGE>   5
      Lender and until so paid shall be added to the principal amount of the
      Obligations to Lender and shall bear interest at the rate of interest
      determined in accordance with Section 8.2(c) of the Purchase Agreement.

12.   Subject to the terms of the Purchase Agreement and the Notes, Grantor
      shall have the duty to prosecute diligently any application with
      respect to the Patent Collateral (other than the Schedule B Patents or
      any applications or inventions relating thereto) pending as of the date
      of this Agreement or thereafter, until Borrowers' Obligations shall
      have been satisfied in full, to preserve and maintain all rights in the
      Patent Collateral (other than the Schedule B Patents or any application
      or inventions relating thereto), and upon reasonable request of Lender,
      Grantor shall make federal application on registrable but unregistered
      Patent Collateral (other than the Schedule B Patents or any
      applications, or inventions relating thereto) belonging to Grantor and
      licensed to Grantor.  To the extent that Grantor has the duty or right
      to make any patent applications under any License, Grantor shall have
      the same duties with respect to the Schedule B Patents as stated in the
      previous sentence.  Grantor shall not abandon any Patent Collateral
      without the prior written consent of the Lender, which consent shall
      not be unreasonably withheld.

13.   Grantor shall have the right to bring suit in its own name to enforce
      the Patent Collateral, in which event Lender may, if Grantor reasonably
      deems it necessary, be joined as a nominal party to such suit if Lender
      shall have been satisfied, in its sole discretion, that it is not
      thereby incurring any risk of liability because of such joinder.
      Grantor shall promptly, upon demand, reimburse and indemnify Lender for
      all damages, costs and expenses, including attorneys' fees and costs,
      incurred by Lender in the fulfillment of the provisions of this
      paragraph.

14.   Upon the occurrence of an Event of Default under the Purchase Agreement or
      hereunder, Lender may, without any obligation to do so, complete any
      obligation of Grantor hereunder, in Grantor's name or in Lender's name,
      but at the expense of Grantor, and Grantor hereby agrees to reimburse
      Lender in full for all expenses, including, without limitation, all
      attorneys' fees incurred by Lender in protecting, defending and
      maintaining the Patent Collateral.

15.   No course of dealing between Grantor and Lender, nor any failure to
      exercise, nor any delay in exercising, on the part of Agent, any right,
      power or privilege hereunder, shall operate as a waiver thereof, and all
      of Lender's rights and remedies with respect to the Patent Collateral,
      whether established hereby or by the Purchase Documents, or by any other
      future agreements between Grantor and Lender or by law, shall be
      cumulative and may be exercised singularly or concurrently.

16.   The provisions of this Agreement are severable and the invalidity or
      unenforceability of any provision herein shall not affect the remaining
      provisions which shall continue unimpaired and in full force and effect.


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<PAGE>   6
17.   This Agreement shall inure to the benefit of and be binding upon the
      respective successors and permitted assigns of the parties.

18.   This Agreement shall be governed by and construed in conformity with the
      laws of the State of Maryland, without regard to its otherwise applicable
      principles of conflicts of laws.

19.   GRANTOR AND LENDER EACH WAIVES ANY AND ALL RIGHTS EITHER MAY HAVE TO A
      JURY TRIAL ARISING IN CONNECTION WITH ANY PROCEEDING OR CONTROVERSY
      RELATING TO THIS AGREEMENT OR ANY OTHER AGREEMENT BETWEEN GRANTOR AND
      LENDER.


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20. GRANTOR AND LENDER EACH WAIVES ANY AND ALL RIGHTS EITHER MAY HAVE TO A JURY
TRIAL ARISING IN CONNECTION WITH ANY PROCEEDING OR CONTROVERSY RELATING TO THIS
AGREEMENT OR ANY OTHER AGREEMENT BETWEEN GRANTOR AND LENDER.

21. THE OBLIGATIONS SECURED HEREBY AND THE SECURITY INTERESTS GRANTED HEREUNDER
ARE SUBORDINATE IN THE MANNER AND TO THE EXTENT SET FORTH IN THAT CERTAIN
SUBORDINATION AGREEMENT (THE "SUBORDINATION AGREEMENT") DATED AS OF OCTOBER 29,
1999, AMONG FLEET CAPITAL CORPORATION, AS AGENT FOR THE SENIOR LENDERS, AMERICAN
CAPITAL STRATEGIES, LTD., AND ASSIGNORS TO THE INDEBTEDNESS AND OTHER
LIABILITIES OWED BY ASSIGNORS UNDER AND PURSUANT TO THE LOAN AND SECURITY
AGREEMENT DATED AS OF OCTOBER 29, 1999, AND EACH RELATED "LOAN DOCUMENT" (AS
DEFINED THEREIN), AND EACH ASSIGNEE HEREUNDER, BY ITS ACCEPTANCE HEREOF,
ACKNOWLEDGES AND AGREES TO BE BOUND BY THE PROVISIONS OF THE SUBORDINATION
AGREEMENT.


IN WITNESS WHEREOF, the parties hereto have executed this Patent Security
Agreement, under seal, the day and year first above written.

                                   IGEN, INC.



                                   By:    /s/ MANFRED HANUSCHEK
                                       -------------------------------

                                   Name:  MANFRED HANUSCHEK
                                         -----------------------------

                                   Title: CFO
                                         -----------------------------


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<PAGE>   8
                            CORPORATE ACKNOWLEDGMENT

UNITED STATES OF AMERICA            :
STATE OF                            :SS
COUNTY OF                           :




      On this 29th of October, 1999, before me personally appeared to me known
and being duly sworn, deposes and says that s/he is
 of IGEN, INC.; that s/he signed the Agreement thereto as such officer pursuant
to the authority vested in him by law; that the within Agreement is the
voluntary act of such corporation; and s/he desires the same to be recorded as
such.






                                    _________________________________
                                    Notary Public

                                    My Commission Expires:


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<PAGE>   9
                                   SCHEDULE A

<TABLE>
<CAPTION>
Patent                        Registration No.        Country     Filing Date
------                        ----------------        -------     -----------
<S>                           <C>                     <C>         <C>


</TABLE>


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<PAGE>   10
                                    EXHIBIT I

                                PATENT ASSIGNMENT

WHEREAS, IGEN, INC., a Delaware corporation ("Grantor") is the registered owner
of: (i) the United States Letters Patent and the inventions described and
claimed therein set forth on Schedule A hereto (hereinafter referred to
collectively as the "Patents"); (ii) the applications for Letters Parent and the
inventions described and claimed therein set forth on Schedule A hereto and any
United States Letters Patent which may be issued upon any of said applications
(hereinafter referred to collectively as the "Applications"), which are
registered with the United States Patent and Trademark Office.

WHEREAS, in conjunction with the Patents and Applications, Grantor may use or
adopt any reissues, extensions, divisions or continuations of the Patents or
Applications (such reissues, extension, divisions and continuations being herein
referred to collectively as the "Reissued Patents"); may be entitled to all
future royalties or other fees paid or payments made to Grantor in respect of
the Patents (hereinafter referred to collectively as the "Royalties"), (the
Patents, Applications and the Reissued Patents and the Royalties being herein
referred to collectively as the "Patent Rights") and may be entitled to profits
and damages for past and future infringements of the Patent Rights (such rights,
interest, claims and demand being herein called the "Claims') (the Patent Rights
and Claims are collectively referred to as the "Patent Collateral").

WHEREAS,                         , ("Grantee") having a place of business at
                        is desirous of acquiring said Patent Collateral;

NOW THEREFORE, for good and valuable consideration, receipt of which is hereby
acknowledged, and intending to be legally bound hereby, Grantor, its successors
and assigns, does hereby transfer, assign and set over unto Grantee, its
successors, transferees and assigns, all of its present and future right, title
and interest in and to the Patent Collateral and all proceeds thereof and all
goodwill associated therewith. No rights or duties of any kind are intended to
be granted or conferred upon Grantee unless and until this Patent Assignment is
recorded with the United States Patent and Trademark Office.

IN WITNESS WHEREOF, the undersigned has caused this Patent Assignment to be
executed as of the 29th day of October, 1999.


                                   IGEN, INC.



                                    By:  _________________________________
                                           As Attorney-in-fact


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<PAGE>   11
STATE OF                :
                        : S.S.
COUNTY OF               :

On this 29th day of October, 1999, ____________________ before me, a Notary
Public for the said County and State, personally appeared known to me or
satisfactorily proven to me to be attorney-in-fact on behalf of IGEN, INC.
("Grantor") and s/he acknowledged to me that s/he executed the foregoing Patent
Assignment on behalf of Grantor, and as the act and deed of Grantor for the
purposes therein contained.

IN WITNESS WHEREOF, I hereunto set my hand and official seal.




                                     _________________________________
                                          Notary Public





My Commission Expires:

_________________________________


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<PAGE>   12
                                POWER OF ATTORNEY

IGEN., INC., a Delaware corporation, ("Grantor"), hereby authorizes AMERICAN
CAPITAL STRATEGIES, LTD., its successors and assigns, and any officer or agent
thereof (collectively, "Lender") as Grantor's true and lawful attorney-in-fact,
with the power to endorse Grantor's name on all applications, assignments,
documents, papers and instruments necessary for Lender to enforce and effectuate
its rights under a certain Patent Security Agreement (United States Patents)
between Grantor and Lender dated the date hereof (as it may hereafter be
supplemented, restated, superseded, amended or replaced, the "Patent
Agreement"), including, without limitation, the power to use the Patent
Collateral (as defined in the Patent Agreement), to grant or issue any exclusive
or nonexclusive license under the Patent Collateral to anyone else, or to
assign, pledge, convey or otherwise transfer title in or dispose of the Patent
Collateral.

This Power of Attorney is given and any action taken pursuant hereto is intended
to be so given or taken pursuant to a certain Loan and Security agreement
bearing even date herewith between Grantor and Lender as it may be hereinafter
supplemented, restated, superseded, amended or replaced.

Grantor hereby unconditionally ratifies all that such attorney shall law fully
do or cause to be done by virtue hereof.

This Power of Attorney shall be irrevocable for the life of the Patent
Agreement.

IN WITNESS WHEREOF, the Grantor has executed this Power of Attorney, under seal,
this 29th day of October, 1999.

                                   IGEN, INC.



                                   By:    /s/ MANFRED HANUSCHEK
                                       -------------------------------

                                   Name:  MANFRED HANUSCHEK

                                   Title: CFO


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<PAGE>   13
                            CORPORATE ACKNOWLEDGMENT

UNITED STATES OF AMERICA            :
STATE OF                            :SS
COUNTY OF                           :


On this 29th of October, 1999 personally appeared, to me known and being duly
sworn, deposes and says that s/he is ____________ of IGEN, INC., the Grantor
corporation described in the foregoing Power of Attorney; that s/he signed the
Power of Attorney as such officer pursuant to the authority vested in her/him by
law; that the within Power of Attorney is the voluntary act of such corporation;
and s/he desires the same to be recorded as such.





                                    _________________________________
                                    Notary Public

                                    My Commission Expires:


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