Document:

<PAGE>

                                  Exhibit 4.1

                             AMENDED AND RESTATED
                         CERTIFICATE OF INCORPORATION
                                      OF
                          VIMRx PHARMACEUTICALS INC.

          The undersigned, the President of VIMRx PHARMACEUTICALS INC., a
Delaware corporation (the "Corporation"), does hereby execute the following
Amended and Restated Certificate of Incorporation pursuant to Sections 242(b)
and 245 of the Delaware General Corporation Law:

          1.   The name of the Corporation is:

                          VIMRx PHARMACEUTICALS INC.

          2.   The Corporation was originally incorporated under the name of
"Cellular Immunology Corporation" and the original Certificate of Incorporation
of the Corporation was filed in the Office of the Secretary of State of Delaware
on December 30, 1986.

          3.   The Certificate of Incorporation of the Corporation is hereby
amended and restated to read in its entirely as follows:

          "FIRST:  The name of the Corporation is:

                    VIMRx PHARMACEUTICALS INC.

          SECOND:  The address of its registered office in the State of Delaware
is Corporation Trust Center, 1209 Orange Street, Wilmington, Delaware 19801.
The name of its registered agent at such address is The Corporation Trust
Company.

          THIRD:   The nature of the business or purposes to be conducted or
promoted is to engage in any lawful act or activity for which corporations may,
now or hereafter, be organized under the Delaware General Corporation Law
("Delaware Law").

          FOURTH:  The total number of shares of stock which the Corporation
shall have authority to issue is Forty Million (40,000,000), all of which shall
be common stock with a par value of $.001.

          FIFTH:   Except to the extent otherwise specifically provided in the
Bylaws of the Corporation, the Board of Directors may adopt, amend or repeal the
Bylaws of the Corporation.

          SIXTH:   No election of directors of the Corporation need be by
written ballot unless the Bylaws of the Corporation so provide.

          SEVENTH: The Corporation shall, to the fullest extent permitted by
<PAGE>

Section 145 of the General Corporation Law of the State of Delaware, as the same
may be amended and supplemented, or by any successor thereto, indemnify any and
all persons whom it shall have power to indemnify under said Section from and
against any and all of the expenses, liabilities or other matters referred to in
or covered by said Section. The Corporation shall advance expenses to the
fullest extent permitted by said Section. Such right to indemnification and
advancement of expenses shall continue as to a person who has ceased to be a
director, officer, employee or agent and shall inure to the benefit of the
heirs, executors and administrators of such a person. The indemnification and
advancement of expenses provided for herein shall not be deemed exclusive of any
other rights to which those seeking indemnification or advancement of expenses
may be entitled under any Bylaw, agreement, vote of stockholders or
disinterested directors or otherwise.

          EIGHTH:  To the fullest extent that the General Corporation Law of the
State of Delaware, as it exists on the date hereof or as it may hereafter be
amended, permits the limitation or elimination of the liability of directors, no
director shall be personally liable to the Corporation or its stockholders for
any monetary damages for breach of fiduciary duty as a director.
Notwithstanding the foregoing, a director shall be liable to the extent provided
by applicable law (i) for any breach of such director's duty of loyalty to the
Corporation or its stockholders, (ii) for acts or omissions not in good faith or
which involve intentional misconduct or a knowing violation of law, (iii) under
Section 174 of the General Corporation Law of the State of Delaware, or (iv) for
any transaction from which such director derived an improper personal benefit.

          NINTH:   Neither the amendment or repeal of Articles SEVENTH or
EIGHTH, nor the adoption of any provision of this Certificate of Incorporation
inconsistent with such Articles shall adversely affect any right or protection
existing under such Articles at the time of such amendment, repeal or adoption."

          4.   The seven million nine hundred forty seven thousand seven hundred
twenty-four (7,947,724) shares of common stock, $.01 par value, of the
Corporation presently issued and outstanding are hereby converted and changed
into an aggregate of four million seven hundred sixty thousand four hundred
twenty-one (4,760,421) issued and outstanding shares of the new class of common
stock, $.001 par value, of the Corporation at the rate of .59896544 new shares
of $.001 par value for each outstanding share of $.01 par value, rounded up to
the next whole share with respect to the aggregate number of newly converted
shares to be issued to each holder of record of $.01 par value shares, all such
newly converted shares to be restricted from sale, assignment or transfer prior
to August 31, 1991, the certificates for such shares to be legended accordingly,
and any purported sale, assignment or transfer prior to such date to be void and
of no force or effect.

          5.   The foregoing amendment to the Certificate of Incorporation of
the Corporation was adopted by vote of the Board of Directors and the written
consent of the holders of a majority of the outstanding capital stock of the
Corporation in accordance with Sections 228, 242 and 245 of the Delaware Law.
Prompt notice thereof has been

                                      -2-
<PAGE>

given to those stockholders who have not so consented in writing, in accordance
with Section 228 of the Delaware Law.

          IN WITNESS WHEREOF, I have hereunto set my hand this 10th day of July,
1990.

                                                  /s/ Richard F. Maradie
                                                  ------------------------------
                                                  Richard F. Maradie
                                                  President

Attest:    /s/ Barbara Freides
           ---------------------------
           Barbara Freides
           Assistant Secretary

                                      -3-
<PAGE>

                           CERTIFICATE OF AMENDMENT
                                      OF
                             AMENDED AND RESTATED
                         CERTIFICATE OF INCORPORATION
                                      OF
                          VIMRx PHARMACEUTICALS INC.

                    Pursuant to Section 242 of the General
                   Corporation Law of the State of Delaware

          VIMRx Pharmaceuticals Inc., a corporation organized and existing under
the General Corporation Law of the State of Delaware (the "Corporation"), hereby
certifies as follows:

          1.  The name of the Corporation is VIMRx Pharmaceuticals Inc. and the
name under which the Corporation originally was incorporated is Cellular
Immunology Corporation.

          2.  The original Certificate of Incorporation of the Corporation was
filed with the Secretary of State of Delaware on December 30, 1986.

          3.  The Amended and Restated Certificate of Incorporation of the
Corporation as heretofore amended or supplemented, is hereby further amended by
striking out "Article FOURTH" and substituting in lieu thereof a new "Article
FOURTH" changing the authorized capital stock of the Corporation to read as
follows:

          "FOURTH:  The total number of shares of stock which the Corporation
          shall have authority to issue is Sixty Million (60,000,000), all of
          which shall be common stock with a par value of $.001."

          4.  The amendment to the Amended and Restated Certificate of
Incorporation, herein certified has been duly adopted in the manner and by the
vote prescribed by Section 242 of the General Corporation Law of the State of
Delaware.
<PAGE>

          IN WITNESS WHEREOF, the Corporation has caused its corporate seal to
be affixed hereto and this certificate to be signed by its President and
attested by its Secretary this 12th day of June, 1993.

                                             VIMRx PHARMACEUTICALS INC.

                                             By   /s/ Richard I. Podell
                                                ------------------------------
                                                    Richard I. Podell
                                                    President

Attest:

By:   /s/ Lowell S. Lifschultz
    --------------------------------
        Lowell S. Lifschultz
        Secretary

                                      -2-
<PAGE>

                           CERTIFICATE OF AMENDMENT
                                      OF
                         CERTIFICATE OF INCORPORATION
                                      OF
                          VIMRx PHARMACEUTICALS INC.

                    Pursuant to Section 242 of the General
                   Corporation Law of the State of Delaware

          VIMRx Pharmaceuticals Inc., a corporation organized and existing under
the General Corporation Law of the State of Delaware (the "Corporation"), hereby
certifies as follows:

          1.  The name of the Corporation is VIMRx Pharmaceuticals Inc. and the
name under which the Corporation originally was incorporated is "Cellular
Immunology Corporation."

          2.  The original Certificate of Incorporation of the Corporation was
filed with the Secretary of State of Delaware on December 30, 1986.

          3.  The Amended and Restated Certificate of Incorporation of the
Corporation as heretofore amended or supplemented (the "Certificate of
Incorporation"), is hereby further amended by striking out "Article IV" and
substituting in lieu thereof a new "Article IV" changing the authorized capital
stock of the Corporation to read as follows:

          "FOURTH:

          The authorized capitol stock of the Corporation shall consist of one
hundred twenty million (120,000,000) shares, consisting of one hundred twenty
million (120,000,000) shares of Common Stock, each having a par value of  $.001
(the "Common Stock")."

          4.  The amendment to the Certificate of Incorporation herein certified
has been duly adopted in the manner and by the vote prescribed by Section 242 of
the General Corporation Law of the State of Delaware.
<PAGE>

          IN WITNESS WHEREOF, the Corporation has caused its corporate seal to
be affixed hereto and this certificate to be signed by a duly authorized officer
of the Corporation and attested by its Secretary this 20th day of June, 1996.

                                        VIMRx PHARMACEUTICALS INC.

                                        By:  /s/ Richard L. Dunning
                                           -------------------------------------
                                             Richard L. Dunning, President
                                             and Chief Executive Officer

Attest:

By:   /s/ Lowell S. Lifschultz
   ------------------------------
      Lowell S. Lifschultz
      Secretary

                                      -2-
<PAGE>

                   CERTIFICATE OF CHANGE OF REGISTERED AGENT
                                      and
                               REGISTERED OFFICE

          VIMRx PHARMACEUTICALS INC., a corporation organized and existing under
and by virtue of the General Corporation Law of the State of Delaware, DOES
HEREBY CERTIFY:

          The present registered agent of the corporation is The Corporation
Trust Company and the present registered office of the corporation is in the
county of New Castle.

          The Board of Directors of VIMRx PHARMACEUTICALS INC. adopted the
following resolution on the 6th of February, 1997.

          RESOLVED, that the registered office of the Corporation in the State
          of Delaware be and it hereby is changed to 2751 Centerville Road in
          the City of Wilmington, County of New Castle and the authorization of
          the present registered agent of this corporation be and the same is
          hereby withdrawn, and VIMRx PHARMACEUTICAL INC. shall be and is hereby
          constituted and appointed the registered agent of this corporation at
          the above address of its registered office.

IN WITNESS WHEREOF, VIMRx PHARMACEUTICALS INC. has caused this statement to be
signed by Richard L. Dunning, its President this 10th day of March, 1997.

                                             By:  /s/ Richard L. Dunning
                                                ------------------------------
                                                  Richard L. Dunning
                                                  President
<PAGE>

                           CERTIFICATE OF AMENDMENT
                                      OF
                         CERTIFICATE OF INCORPORATION
                                      OF
                          VIMRx PHARMACEUTICALS INC.

                             _____________________

                    Pursuant to Section 242 of the General
                   Corporation Law of the State of Delaware

                             _____________________

     VIMRx Pharmaceuticals Inc., a corporation organized and existing under the
General Corporation Law of the State of Delaware (the "Corporation"), hereby
certifies as follows:

          1.  The name of the Corporation is VIMRx Pharmaceuticals Inc. and the
name under which the Corporation originally was incorporated was "Cellular
Immunology Corporation."

          2.  The original Certificate of Incorporation of the Corporation was
filed with the Secretary of State of Delaware on December 13, 1986.

          3.  The Amended and Restated Certificate of Incorporation of the
Corporation, as heretofore amended or supplemented (the "Certificate of
Incorporation"), is hereby further amended by striking out "Article IV" and
substituting in lieu thereof a new "Article IV" changing the authorized capital
stock of the Corporation to read as follows:

     "FOURTH:

     A.   The authorized capital stock of the Corporation shall consist of one
hundred twenty million one hundred fifty thousand (120,150,000) shares,
consisting of one hundred twenty million (120,000,000) shares of Common Stock,
each having a par value of $.001 (the "Common Stock"), and one hundred fifty
thousand (150,000) shares of Preferred Stock, each having a par value of $.001
(the "Preferred Stock").

     B.   The Board of Directors hereby creates and establishes and authorizes
the issuance of a first series of preferred stock, such series to consist of
150,000 shares of this Corporation's authorized and unissued Preferred Stock,
each share having a par value of $.001, and the Board of Directors hereby fixes
the designation of such series as "Series A Cumulative Convertible Preferred
Stock" (hereinafter referred to as the "Preferred Stock") and fixes the number
of shares constituting such series at 150,000, and hereby determines the powers,
preferences, rights, qualifications, limitations and restrictions of such series
as follows:

                                  Section 1.
                                   Dividends

     (a)  The holders of the Preferred Stock shall be entitled to receive
dividends thereon at the rate of 6% of the Liquidation Preference (as defined in
Section 2) per share per annum, (as adjusted for any combinations,
consolidations, stock distributions or stock dividends with respect to such
shares) as and when declared by the Board of Directors, before any dividend or
<PAGE>

distribution shall be declared, set apart for, or paid upon the Common Stock of
the Corporation, which dividend shall be payable in additional shares of
Preferred Stock, each valued at their Liquidation Preference. The dividends on
the Preferred Stock shall be cumulative, so that if the Corporation fails in any
fiscal year to pay such dividends on all of the issued and outstanding Preferred
Stock, such deficiency in the dividends shall be fully paid before any dividends
or distributions shall be paid on or set apart for the Common Stock. All
dividends and distributions on the Preferred Stock shall be made pro rata per
share to all holders of Preferred Stock; provided, however, that,
notwithstanding the foregoing, until all cumulative dividends on the Preferred
Stock shall have been fully paid, all dividends and distributions on the
Preferred Stock shall be made ratably to the holders thereof in proportion to
the respective amounts that would be payable on such shares if such dividend
arrearages were paid in full. Such dividends shall accrue annually on the
anniversary of the Original Issuance Date (as defined in Section 3(d)).

     (b)  For purposes of this Section 1, unless the context requires otherwise,
"distribution" shall mean the transfer of cash or property without
consideration, whether by way of dividend or otherwise, or the purchase or
redemption of shares of the Corporation (other than repurchases of Common Stock
held by employees or directors of, or consultants to, the Corporation upon
termination of their employment or services pursuant to agreements providing for
such repurchase and other than redemptions in liquidation or dissolution of the
Corporation) for cash or property, including any such transfer, purchase or
redemption by a subsidiary of the Corporation.

                                  Section 2.
                              Liquidation Rights

     (a)  Treatment at Liquidation, Dissolution or Winding Up.

          (i)   Except as otherwise provided in Section 2(b) below, in the event
of any liquidation, dissolution or winding up of the affairs of the Corporation,
whether voluntary or involuntary, the holders of Preferred Stock shall be
entitled to be paid first out of the assets of the Corporation available for
distribution to holders of the Corporation's capital stock of all classes,
before payment or distribution of any of such assets to the holders of any other
class of the corporation's capital stock, an amount equal to $1,000 per share of
Preferred Stock (the "Liquidation Preference,") which amount shall be subject to
equitable adjustment whenever there shall occur a stock dividend, stock split,
combination of shares, reclassification or other similar event affecting such
shares), and shall include any accrued but unpaid dividends.

          (ii)  After payment shall have been made in full to the holders of
Preferred Stock pursuant to Section 2(a)(i) hereof or funds necessary for such
payment shall have been set aside by the Corporation in trust for the account of
the holders of Preferred Stock to be available for such payment, the remaining
assets of the Corporation shall be distributed ratably to the holders of Common
Stock to the exclusion of the Preferred Stock.

          (iii) If the assets of the Corporation shall be insufficient to permit
the payment in full to the holders of Preferred Stock of all amounts
distributable to them under Section 2(a)(i) hereof, then the entire assets of
the Corporation available for such distribution shall be distributed ratably
among the holders of Preferred Stock in proportion to the full preferential
amount each such holder is otherwise entitled to receive.

     (b)  Treatment of Reorganizations, Consolidations, Mergers and Sales of
Assets. A consolidation or merger of the Corporation with or into another
unaffiliated corporation or a sale

                                       2
<PAGE>

of all or substantially all of the assets of the Corporation, shall not be
regarded as a liquidation, dissolution or winding up of the affairs of the
Corporation for purposes of this Section 2, but shall result in conversion of
the Preferred Stock into Common Stock as set forth in Section 3(c).

     (c)  Distributions Other Than Cash. The value of any distribution provided
for in this Section 2, or portion thereof, payable in property other than cash
shall be the fair value (as determined by the Board of Directors in good faith)
of such property at the time of such distribution.

                                  Section 3.
                                  Conversion

     The holders of Preferred Stock shall have conversion rights (the
"Conversion Rights") and the Preferred Stock shall be subject to conversion, as
follows:

     (a)  Right to Convert; Conversion Price. Each share of Preferred Stock
shall be convertible, without the payment of any additional consideration by the
holder thereof and at the option of the holder thereof, at any time after
eighteen (18) months after the Original Issuance Date (as defined in Section
3(d) below), at the office of the Corporation or any transfer agent for the
Preferred Stock, into such whole number of fully paid and nonassessable shares
of Common Stock as is determined by dividing $1,000 by the Conversion Price,
determined as hereinafter provided, in effect at the time of conversion. The
Conversion Price at which shares of Common Stock shall be deliverable upon
conversion without the payment of any additional consideration by the holder of
Preferred Stock (the "Conversion Price") shall initially be the highest average
of closing bid prices per share of Common Stock on the principal market on which
such Common Stock trades for any sixty (60) consecutive trading day period
commencing with the Original Issuance Date and ending on the date which is
eighteen (18) months from such date, but in no event shall such Conversion Price
be less than $5.50 or greater than $7.50. Such initial Conversion Price shall be
subject to adjustment, in order to adjust the number of shares of Common Stock
into which Preferred Stock is convertible, as hereinafter provided. The right of
conversion with respect to any shares of Preferred Stock which the Corporation
redeems pursuant to Section 5(a) hereof shall terminate at the close of business
on the Redemption Date (as defined in Section 5 of this Certificate of
Designations), unless the Corporation shall default in the payment of the
redemption price for such shares of Preferred Stock, in which case such
termination shall occur upon payment of the redemption price of such shares.

     (b)  Mechanics of Conversion; Dividends; Fractional Shares. Before any
holder of Preferred Stock shall be entitled to convert the same into shares of
Common Stock, such holder shall surrender the certificate or certificates
therefor, duly endorsed, at the office of the Corporation or of any transfer
agent for the Preferred Stock, and shall give written notice to the Corporation
at such office that such holder elects to convert the same. At the time of each
conversion of shares of Preferred Stock, the Corporation shall also issue shares
of Common Stock in an amount equal to all dividends declared and unpaid on the
shares of Preferred Stock surrendered for conversion to the date upon which such
conversion is deemed to occur, valued at the Conversion Price. In lieu of any
fractional shares of Common Stock to which the holder would otherwise be
entitled, the Corporation shall pay cash equal to such fraction multiplied by
the then effective Conversion Price. The Corporation shall, as soon as
practicable thereafter, issue and deliver at such office to such holder of
Preferred Stock, a certificate or certificates for the number of shares of
Common Stock to which such holder shall be entitled as aforesaid, together with
cash in lieu of any fraction of a share. Such conversion shall be deemed to have
been made immediately prior to the close of business on the date of such
surrender of the shares

                                       3
<PAGE>

of Preferred Stock to be converted, and the person or persons entitled to
receive the shares of Common Stock issuable upon conversion shall be treated for
all purposes as the record holder or holders of such shares of Common Stock on
such date.

     (c)  Automatic Conversion.

          (i)  Each share of Preferred Stock shall automatically be converted
into shares of Common Stock at the then effective Conversion Price:

               (1)  on the date which is seven (7) years after the Original
Issuance  Date; or

               (2)  immediately prior to the effective time of any merger, sale
of assets, reorganization or like event in which the Corporation is not the
surviving entity (if such event occurs prior to eighteen months from the
Original Issuance Date, then the Conversion Price shall be equal to the fair
value of the consideration to be received by the holder of a share of Common
Stock, as determined in good faith by the Corporation's Board of Directors, but
in no event greater than $7.50), or

               (3)  upon the written election of the holders of not less than a
majority in voting power of the then outstanding shares of Preferred  Stock to
require such mandatory conversion.

          (ii) Upon the occurrence of an event specified in Section 3(c)(i)
hereof, all shares of Preferred Stock shall be converted automatically without
any further action by any holder of such shares and whether or not the
certificate(s) representing such shares are surrendered to the Corporation or
the transfer agent for the Preferred Stock; provided, however, that the
Corporation shall not be obligated to issue a certificate or certificates
evidencing the shares of Common Stock issuable upon such conversion unless the
certificate(s) evidencing such shares of Preferred Stock being converted are
either delivered to the Corporation or the transfer agent for the Preferred
Stock, or the holder notifies the Corporation or such transfer agent that such
certificate or certificates have been lost, stolen, or destroyed and executes an
agreement satisfactory to the Corporation to indemnify the Corporation from any
loss incurred by it in connection therewith ("Indemnity Agreement"), except that
such holder shall not be required to provide any indemnity bond. Upon the
automatic conversion of Preferred Stock, each holder of Preferred Stock shall
surrender the certificate(s) representing such holder's shares of Preferred
Stock or the aforesaid Indemnity Agreement at the office of the Corporation or
of the transfer agent for the Preferred Stock. Thereupon, there shall be issued
and delivered to such holder, promptly at such office and in such holder's name
as shown on such surrendered certificate(s), a certificate or certificates for
the number of shares of Common Stock into which the shares of Preferred Stock
surrendered were convertible on the date on which such automatic conversion
occurred. No fractional shares of Common Stock shall be issued upon the
automatic conversion of Preferred Stock. In lieu of any fractional shares of
Common Stock to which the holder would otherwise be entitled, the Corporation
shall pay cash equal to such fraction multiplied by the then effective
Conversion Price.

     (d)  Adjustment for Stock Splits and Combinations. If the Corporation shall
at any time or from time to time after the date on which shares of the Preferred
Stock are first issued (the "Original Issuance Date") effect a subdivision of
the outstanding Common Stock, the Conversion Price in effect immediately before
that subdivision shall be proportionately

                                       4
<PAGE>

decreased. If the Corporation shall at any time or from time to time after the
Original Issuance Date combine the outstanding shares of Common Stock, the
Conversion Price in effect immediately before the combination shall be
proportionately increased. Any adjustment under this paragraph shall become
effective at the close of business on the date the subdivision or combination
becomes effective.

     (e)  Adjustment for Certain Dividends and Distributions.

          (1)  In the event the Corporation at any time or from time to time
after the Original Issuance Date shall make or issue, or fix a record date for
the determination of holders of Common Stock entitled to receive a dividend or
other distribution payable in additional shares of Common Stock, then and in
each such event the Conversion Price then in effect shall be decreased as of the
time of such issuance or, in the event such a record date shall have been fixed,
as of the close of business on such record date, by multiplying the Conversion
Price then in effect by a fraction:

               (A)  the numerator of which shall be the total number of shares
of Common Stock issued and outstanding immediately prior to the time of such
issuance or the close of business on such record date, and

               (B)  the denominator of which shall be the total number of shares
of Common Stock issued and outstanding immediately prior to the time of such
issuance or the close of business on such record date plus the number of shares
of Common Stock issuable in payment of such dividend or distribution;

provided, however, if such record date shall have been fixed and such dividend
is not fully paid or such distribution is not fully made on the date fixed
therefor, the Conversion Price shall be recomputed accordingly as of the close
of business on such record date and thereafter the Conversion Price shall be
adjusted pursuant to this paragraph as of the time of actual payment of such
dividends or distributions.

          (2)  For the purposes of Section 3(e)(1) hereof, the total number of
shares of Common Stock deemed to be issued and outstanding shall include (i) all
shares of Common Stock issuable on conversion of all shares of Preferred Stock
outstanding and (ii) all shares of Common Stock issued and outstanding and
entitled to receive such dividend.

     (f)  Adjustments for Other Dividends and Distributions. In the event the
Corporation at any time or from time to time after the Original Issuance Date
shall make or issue, or fix a record date for the determination of holders of
Common Stock entitled to receive, a dividend or other distribution payable in
securities of the Corporation other than shares of Common Stock, including a
cash dividend, then and in each such event provision shall be made so that the
holders of Preferred Stock shall receive upon conversion thereof in addition to
the number of shares of Common Stock receivable thereupon, the amount of
securities of the Corporation and/or cash that they would have received had
their Preferred Stock been converted into Common Stock on the date of such event
and had they thereafter, during the period from the date of such event to and
including the conversion date, retained such securities receivable by them as
aforesaid during such period, giving application to all adjustments called for
herein during such period.

                                       5
<PAGE>

     (g)  Adjustment for Reclassification, Exchange or Substitution. If the
Common Stock issuable upon the conversion of the Preferred Stock shall be
changed into the same or a different number of shares of any class or classes of
stock, whether by capital reorganization, reclassification, or otherwise (other
than a subdivision or combination of shares or stock dividend provided for
above, or a reorganization, merger, consolidation, or sale of assets provided
for in Section 3(c), then and in each such event the holder of each such share
of Preferred Stock shall have the right thereafter to convert such share into
the kind and amount of shares of stock and other securities and property
receivable upon such reorganization, reclassification, or other change, by
holders of the number of shares of Common Stock into which such shares of
Preferred Stock might have been converted immediately prior to such
reorganization, reclassification, or change, all subject to further adjustment
as provided herein.

     (h)  [INTENTIONALLY OMITTED]

     (i)  Adjustment of Conversion Price Upon Issuance of Additional Shares of
Common Stock.

          (1)  Subject always to Section 3(i)(5), in the event that at any time
or from time to time after the Original Issuance Date, through and including the
date which ends eighteen (18) months after the Original Issuance Date, but not
thereafter, the corporation shall issue any shares of Common Stock or securities
convertible into or exercisable to purchase shares of Common Stock ("Additional
Shares of Common Stock") excluding shares issued upon a stock split or
combination as provided in Section 3(d) or as a dividend or distribution as
provided in Sections 3(e) or (f)), without consideration or for a consideration
per share less than the Conversion Price in effect on the date of, and
immediately prior to, the issuance or deemed issuance of such Additional Shares
of Common Stock, (which shall include the assumed conversion of all convertible
securities and the assumed exercise of all convertible securities or rights to
purchase shares of Common Stock in accordance with the terms of such convertible
securities or rights to purchase Common Stock), then and in such event, the
applicable Conversion Price then in effect shall be reduced, concurrently with
such issue, to a price (calculated to the nearest cent) determined by
multiplying such Conversion Price by a fraction:

               (A)  the numerator of which shall be (x) the number of shares of
Common Stock outstanding immediately prior to such issue plus (y) the number of
shares of Common Stock which the aggregate consideration received or deemed to
have been received by the corporation for the total number of Additional Shares
of Common Stock so issued would purchase at the Conversion Price in effect on
the date of, and immediately prior to, the issuance or deemed issuance of such
Additional Shares of Common Stock, and

               (B)  the denominator of which shall be the number of shares of
Common Stock outstanding immediately prior to such issue plus the number of such
Additional Shares of Common Stock so issued or deemed to be issued.

          (2)  For the purposes of Section 3(i)(1) hereof, all shares of Common
Stock issuable upon conversion of shares of Preferred Stock outstanding
immediately prior to any issue of Additional Shares of Common Stock, or any
event with respect to which Additional Shares of Common Stock shall be deemed to
be issued, shall be deemed to be outstanding; and immediately after any
Additional Shares of Common Stock are deemed issued pursuant to Section 3(i)(l)
such Additional Shares of Common Stock shall be deemed to be outstanding.

                                       6
<PAGE>

          (3)  Notwithstanding anything to the contrary contained herein, the
applicable Conversion Price in effect at the time Additional Shares of Common
Stock are issued or deemed to be issued shall not be reduced pursuant to Section
3(i)(1) hereof at such time if the amount of such reduction would be an amount
less than $. 01, but any such amount shall be carried forward and reduction with
respect thereto made at the time of and together with any subsequent reduction
which, together with such amount and any other amount or amounts so carried
forward, shall aggregate $.01 or more.

          (4)  Determination of Consideration. For purposes of this Section
3(i), the consideration received by the Corporation for the issue of any
Additional Shares of Common Stock shall be computed as follows:

               (i)  Cash and Property:  Such consideration shall:

                    (A)  insofar as it consists of cash, be computed at the
     aggregate amounts of cash received by the Corporation, excluding amounts
     paid or payable for accrued interest or accrued dividends;

                    (B)  insofar as it consists of property other than cash, be
     computed at the fair value thereof at the time of such issue, as determined
     in good faith by the Board of Directors; and

                    (C)  in the event Additional Shares of Common Stock are
     issued together with other shares or securities or other assets of the
     Corporation for consideration which covers both, be the proportion of such
     consideration so received, computed as provided in clauses (A) and (B)
     above, as determined in good faith by the Board of Directors.

               (ii) Options and Convertible Securities. The consideration per
share received by the Corporation for Additional Shares of Common Stock deemed
to have been issued pursuant to Section 3(i)(1), relating to options, warrants
or rights to purchase Common Stock, and convertible securities, shall be
determined by dividing (W) the total amount, if any, received or receivable by
the Corporation as consideration for the issue of such options or convertible
securities, plus the minimum aggregate amount of additional consideration (as
set forth in the instruments relating thereto, without regard to any provision
contained therein for a subsequent adjustment of such consideration) payable to
the Corporation upon the exercise of such options or the conversion or exchange
of such convertible securities, or in the case of options for convertible
securities, the exercise of such options for convertible securities and the
conversion or exchange of such convertible securities, by (X) the maximum number
of shares of Common Stock (as set forth in the instruments relating thereto,
without regard to any provision contained therein for a subsequent adjustment of
such number) issuable upon the exercise of such options or the conversion or
exchange of such convertible securities. (5)Notwithstanding any other provision
of this Section 3(i), there shall be no deemed issuance of Additional Shares of
Common Stock upon (A) issuance of any shares of Preferred Stock as a dividend on
the Preferred Stock, (B) conversion of any Preferred Stock, (C) exercise of any
options or warrants issued and outstanding on the Original Issuance Date, (D)
grant or exercise of any options to purchase Common Stock pursuant to the
Corporation's Stock Option Plan as in effect on the Original Issuance Date or
any subsequent amendment thereof which is approved by the Corporation's
stockholders pursuant to Securities and Exchange Commission regulations, or (E)
the sale for cash of no more than 3,333,334 shares of Common Stock for aggregate
gross

                                       7
<PAGE>

proceeds of no more than $10,000,000, at a gross per-share price of no less than
$3.00. In the event that the gross per-share sale price of a share of Common
Stock under Section 3(i)(5)(E) shall be less than $3.00, then the difference
between $3.00 and the actual gross per-share sale price shall be subtracted from
the Conversion Price utilized in the calculation set forth in Section
3(i)(1)(A)(y).

     (j)  Certificate as to Adjustments. Upon the occurrence of each adjustment
or readjustment of the Conversion Price pursuant to this Section 3, the
Corporation at its expense shall promptly compute such adjustment or
readjustment in accordance with the terms hereof and furnish to each affected
holder of Preferred Stock a certificate setting forth such adjustment or
readjustment and showing in detail the facts upon which such adjustment or
readjustment is based. The Corporation shall, upon the written request at any
time of any affected holder of Preferred Stock, furnish or cause to be furnished
to such holder a like certificate setting forth (i) such adjustments and
readjustments, (ii) the Conversion Price at the time in effect, and (iii) the
number of shares of Common Stock and the amount, if any, of other property which
at the time would be received upon the conversion of each share of Preferred
Stock.

     (k)  Notices of Record Date.  In the event of any taking by the Corporation
of a record of the holders of any class of securities for the purpose of
determining the holders thereof who are entitled to receive any dividend (other
than a cash dividend which is the same as cash dividends paid in previous
quarters) or other distribution, the Corporation shall mail to each holder of
Preferred Stock at least ten (10) days prior to such record date a notice
specifying the date on which any such record is to be taken for the purpose of
such dividend or distribution.

     (l)  Common Stock Reserved. The Corporation shall reserve and keep
available out of its authorized but unissued Common Stock such number of shares
of Common Stock as shall from time to time be sufficient to effect the
conversion of all Preferred Stock.

     (m)  Certain Taxes. The Corporation shall pay any issue or transfer taxes
payable in connection with the conversion of any shares of Preferred Stock;
provided, however, that the Corporation shall not be required to pay any tax
that may be payable in respect of any transfer to a name other than that of the
holder of such Preferred Stock.

                                  Section 4.
                                 Voting Rights

     Except as otherwise required by law or by Section 7, the holders of
Preferred Stock shall not have the right to vote on any matter submitted to a
vote of the stockholders of the Corporation. With respect to all questions as to
which, under law, stockholders are entitled to vote by classes, the holders of
Preferred Stock shall vote together as a single class separately from the
holders of Common Stock.

                                  Section 5.
                         No Reissuance Preferred Stock

     No share or shares of Preferred Stock acquired by the Corporation by reason
of redemption, purchase, conversion or otherwise shall be reissued, and all such
shares shall be canceled, retired and eliminated from the shares which the
Corporation shall be authorized to issue.

                                       8
<PAGE>

                                  Section 6.
                              Protective Covenant

     The Corporation shall not, without the affirmative vote or written consent
of the holders of a majority of the then issued and outstanding shares of
Preferred Stock, amend its Certificate of Incorporation to provide for the
creation or issuance of any class or series of capital stock which shall rank
pari passu or senior to the Preferred Stock in priority to receive the
liquidation preference on the Preferred Stock."

     4.   The amendment to the Certificate of Incorporation herein certified has
been duly adopted in the manner and by the vote prescribed by Section 242 of the
General Corporation Law of the State of Delaware.

                                       9
<PAGE>

     IN WITNESS WHEREOF, the Corporation has caused this Certificate to be
signed by Richard L. Dunning, its President, and attested by Lowell S.
Lifschultz, its Secretary, as of this 16th day of December, 1997.

                                              VIMRx PHARMACEUTICALS INC.

                                              By:  /s/ Richard L. Dunning
                                                 -------------------------------
                                                   Richard L. Dunning
                                                   President and Chief Executive
                                                   Officer

Attest:

By:  /s/ Lowell S. Lifschultz
   ------------------------------
    Lowell S. Lifschultz
    Secretary

                                      10
<PAGE>

                            CERTIFICATE OF AMENDMENT
                                       OF
                          CERTIFICATE OF INCORPORATION
                                       OF
                           VIMRX PHARMACEUTICALS INC.

                  ============================================

                     Pursuant to Section 242 of the General
                    Corporation Law of the State of Delaware

                  ==============================================

     VIMRX Pharmaceuticals Inc., a corporation organized and existing under the
General Corporation Law of the State of Delaware (the "Corporation"), hereby
certifies as follows:

          1.   The name of the Corporation is VIMRX Pharmaceuticals Inc. and the
name under which the Corporation originally was incorporated was "Cellular
Immunology Corporation."

          2.   The original Certificate of Incorporation of the Corporation was
filed with the Secretary of State of Delaware on December 13, 1986.

          3.   The Amended and Restated Certificate of Incorporation of the
Corporation, as heretofore amended or supplemented (the "Certificate of
Incorporation"), is hereby further amended by striking out "Article I" and
substituting in lieu thereof a new "Article I" changing the name of the
Corporation to read as follows:

          "FIRST:   The name of the Corporation is:
                    Nexell Therapeutics Inc."

          4.   The Amended and Restated Certificate of Incorporation of the
Corporation, as heretofore amended or supplemented (the "Certificate of
Incorporation"), is hereby further amended by striking out "Article IV" and
substituting in lieu thereof a new "Article IV" changing the authorized capital
stock of the Corporation to read as follows:

          "FOURTH

     A.   The authorized capital stock of the Corporation shall consist of one
hundred sixty-one million, one hundred fifty thousand (161,150,000) shares,
consisting of one hundred sixty million (160,000,000) shares of Common Stock,
each having a par value of $.001 (the "Common Stock"), and one million, one
hundred fifty thousand (1,150,000) shares of Preferred Stock, each having a par
value of $.001 (the "Preferred Stock").

     B.   The Preferred Stock may be issued from time to time in one or more
series of any number of shares, provided that the aggregate number of shares
issued and not canceled of any and all such series shall not exceed the total
number of shares of Preferred Stock hereinabove authorized. Each series of
Preferred Stock shall be distinctively designated by letter
<PAGE>

or descriptive words. All series of Preferred Stock shall rank equally and be
identical in all respects except as provided by this Article FOURTH or in a
resolution of the Board of Directors providing for the issuance of any series of
Preferred Stock.

     C.   Authority is hereby expressly vested in the Board of Directors from
time to time to issue the Preferred Stock as Preferred Stock of any series and
in connection with the creation of each such series to fix by the resolution or
resolutions providing for the issue of shares thereof the designations,
preferences, limitations and relative participating, optional or other special
rights, and the qualifications, limitations or restrictions thereof, to the full
extent now or hereafter permitted by this Certificate of Incorporation and the
laws of the State of Delaware, including, without limitation:

          (1)  the distinctive designation of such series and the number of
shares which shall constitute such series, which number may be increased (but
not above the total number of authorized shares of the Preferred Stock) or
decreased (but not below the number of shares thereof then outstanding) from
time to time by a resolution or resolutions of the Board of Directors, all
subject to the conditions or restrictions set forth in the resolution or
resolutions adopted by the Board of Directors providing for the issuance of any
series of Preferred Stock;

          (2)  the dividend rate payable on shares of such series, the
conditions and dates upon which such dividends shall be payable, the preferences
or relation which such dividend shall bear to the dividends payable on any other
class or classes or any other series of capital stock (except as otherwise
expressly provided in this Certificate of Incorporation), and whether such
dividends shall be cumulative or non-cumulative and, if cumulative, the date or
dates from which dividends shall accumulate;

          (3)  whether the shares of such series shall be subject to redemption
by the Corporation and, if made subject to redemption, the price or prices at
which, and the terms and conditions on which, the shares of such series may be
redeemed by the Corporation;

          (4)  the amount or amounts payable upon the shares of such series in
the event of any voluntary or involuntary liquidation, dissolution or winding up
of the Corporation and the preferences or relation which such payments shall
bear to such payments made on any other class or classes or any other series of
capital stock (except as otherwise expressly provided in this Certificate of
Incorporation);

          (5)  whether or not the shares of such series shall be made
convertible into, or exchangeable for, shares of any other class or classes of
capital stock of the Corporation, or any series thereof, or for any other series
of the same class of capital stock of the Corporation or for debt of the
Corporation evidenced by an instrument of indebtedness, and, if so convertible
or exchangeable, the conversion price or prices, or the rate or rates of
exchange, and the adjustments thereof, if any, at which such conversion or
exchange may be made, and any other terms and conditions of such conversion or
exchange;

          (6)  whether the holders of shares of such series shall have any right
or power to vote or to receive notice of any meeting of stockholders, either
generally or as a condition to specified corporate action; and

                                       2
<PAGE>

          (7)  any other preferences and relative, participating, optional or
other special rights and qualifications, limitations or restrictions thereof as
may be permitted by the laws of the State of Delaware and as shall not be
inconsistent with this Article FOURTH.

     D.   Shares of Preferred Stock which have been issued and reacquired in any
manner by the Corporation (excluding, until the Corporation elects to retire
them, shares which are held as treasury shares, but including shares redeemed,
shares purchased and retired and shares which have been converted into shares of
Common Stock) shall have the status of authorized but unissued shares of
Preferred Stock and may be reissued as a part of the series of which they were
originally a part or may be reissued as a part of another series of Preferred
Stock, all subject to the conditions or restrictions on issuance set forth in
the resolution or resolutions adopted by the Board of Directors providing for
the issuance of any series of Preferred Stock.

     E.   Except as otherwise provided by the resolution or resolutions
providing for the issuance of any series of Preferred Stock, or in subsection H
of this Article FOURTH, after payment shall have been made to the holders of
Preferred Stock of the full amount of dividends to which they shall be entitled
pursuant to the resolution or resolutions providing for the issuance of any
series of Preferred Stock, the holders of Common Stock shall be entitled, to the
exclusion of the holders of Preferred Stock of any and all series, to receive
such dividends as from time to time may be declared by the Board of Directors.

     F.   Except as otherwise provided by the resolution or resolutions
providing for the issuance of any series of Preferred Stock, in the event of any
liquidation, dissolution or winding up of the Corporation, whether voluntary or
involuntary, after payment shall have been made to the holders of Preferred
Stock of the full amounts to which they shall be entitled pursuant to the
resolution or resolutions providing for the issuance of any series of Preferred
Stock, the holders of Common Stock shall be entitled, to the exclusion of the
holders of Preferred Stock of any and all series, to share, ratably according to
the number of shares of Common Stock held by them, in all remaining assets of
the Corporation available for distribution to its stockholders.

     G.   The holders of Preferred Stock shall not have any preemptive rights
except to the extent such rights shall be specifically provided for in the
resolution or resolutions providing for the issuance thereof adopted by the
Board of Directors.

     H.   The Board of Directors hereby creates and establishes and authorizes
the issuance of a first series of preferred stock, such series to consist of
150,000 shares of this Corporation's authorized and unissued Preferred Stock,
each share having a par value of $.001, and the Board of Directors hereby fixes
the designation of such series as "Series A Cumulative Convertible Preferred
Stock" (hereinafter referred to as the "Series A Preferred Stock") and fixes the
number of shares constituting such series at 150,000, and hereby determines the
powers, preferences, rights, qualifications, limitations and restrictions of
such series as follows:

                                  SECTION 1.
                                  DIVIDENDS

     (a)  The holders of the Series A Preferred Stock shall be entitled to
receive dividends thereon at the rate of 6% of the Liquidation Preference (as
defined in Section 2) per share per annum, (as adjusted for any combinations,
consolidations, stock distributions or stock dividends with respect to such
shares) as and when declared by the Board of Directors, before any dividend or
distribution shall be declared, set apart for, or paid upon the Common Stock of
the Corporation, which dividend shall be payable in additional shares of Series
A Preferred Stock,

                                       3
<PAGE>

each valued at their Liquidation Preference. The dividends on the Series A
Preferred Stock shall be cumulative, so that if the Corporation fails in any
fiscal year to pay such dividends on all of the issued and outstanding Series A
Preferred Stock, such deficiency in the dividends shall be fully paid before any
dividends or distributions shall be paid on or set apart for the Common Stock.
All dividends and distributions on the Series A Preferred Stock shall be made
pro rata per share to all holders of Series A Preferred Stock; provided,
however, that, notwithstanding the foregoing, until all cumulative dividends on
the Series A Preferred Stock shall have been fully paid, all dividends and
distributions on the Series A Preferred Stock shall be made ratably to the
holders thereof in proportion to the respective amounts that would be payable on
such shares if such dividend arrearages were paid in full. Such dividends shall
accrue annually on the anniversary of the Original Issuance Date (as defined in
Section 3(d)).

     (b)  For purposes of this Section 1, unless the context requires otherwise,
"distribution" shall mean the transfer of cash or property without
consideration, whether by way of dividend or otherwise, or the purchase or
redemption of shares of the Corporation (other than repurchases of Common Stock
held by employees or directors of, or consultants to, the Corporation upon
termination of their employment or services pursuant to agreements providing for
such repurchase and other than redemptions in liquidation or dissolution of the
Corporation) for cash or property, including any such transfer, purchase or
redemption by a subsidiary of the Corporation.

                                   SECTION 2.
                               LIQUIDATION RIGHTS

     (a)  Treatment at Liquidation, Dissolution or Winding Up.

          (i)   Except as otherwise provided in Section 2(b) below, in the event
of any liquidation, dissolution or winding up of the affairs of the Corporation,
whether voluntary or involuntary, the holders of Series A Preferred Stock shall
be entitled to be paid first out of the assets of the Corporation available for
distribution to holders of the Corporation's capital stock of all classes,
before payment or distribution of any of such assets to the holders of any other
class of the corporation's capital stock, an amount equal to $1,000 per share of
Series A Preferred Stock (the "Liquidation Preference"), which amount shall be
subject to equitable adjustment whenever there shall occur a stock dividend,
stock split, combination of shares, reclassification or other similar event
affecting such shares), and shall include any accrued but unpaid dividends.

          (ii)  After payment shall have been made in full to the holders of
Series A Preferred Stock pursuant to Section 2(a)(i) hereof or funds necessary
for such payment shall have been set aside by the Corporation in trust for the
account of the holders of Series A Preferred Stock to be available for such
payment, the remaining assets of the Corporation shall be distributed ratably to
the holders of Common Stock to the exclusion of the Series A Preferred Stock.

          (iii) If the assets of the Corporation shall be insufficient to
permit the payment in full to the holders of Series A Preferred Stock of all
amounts distributable to them under Section 2(a)(i) hereof, then the entire
assets of the Corporation available for such distribution shall be distributed
ratably among the holders of Series A Preferred Stock in proportion to the full
preferential amount each such holder is otherwise entitled to receive.

     (b)  Treatment of Reorganizations, Consolidations, Mergers and Sales of
Assets. A consolidation or merger of the Corporation with or into another
unaffiliated corporation or a sale
<PAGE>

of all or substantially all of the assets of the Corporation, shall not be
regarded as a liquidation, dissolution or winding up of the affairs of the
Corporation for purposes of this Section 2, but shall result in conversion of
the Series A Preferred Stock into Common Stock as set forth in Section 3(c).

     (c)  Distributions Other Than Cash. The value of any distribution provided
for in this Section 2, or portion thereof, payable in property other than cash
shall be the fair value (as determined by the Board of Directors in good faith)
of such property at the time of such distribution.

                                  SECTION 3.
                                  CONVERSION

     The holders of Series A Preferred Stock shall have conversion rights (the
"Conversion Rights") and the Series A Preferred Stock shall be subject to
conversion, as follows:

     (a)  Right to Convert; Conversion Price. Each share of Series A Preferred
Stock shall be convertible, without the payment of any additional consideration
by the holder thereof and at the option of the holder thereof, at any time after
June 17, 1999, at the office of the Corporation or any transfer agent for the
Series A Preferred Stock, into such whole number of fully paid and nonassessable
shares of Common Stock as is determined by dividing $1,000 by the Conversion
Price, determined as hereinafter provided, in effect at the time of conversion.
The Conversion Price at which shares of Common Stock shall be deliverable upon
conversion without the payment of any additional consideration by the holder of
Series A Preferred Stock (the "Conversion Price") shall initially be $2.75. Such
initial Conversion Price shall be subject to adjustment, in order to adjust the
number of shares of Common Stock into which Series A Preferred Stock is
convertible, as hereinafter provided. The right of conversion with respect to
any shares of Series A Preferred Stock which the Corporation redeems pursuant to
Section 5(a) hereof shall terminate at the close of business on the Redemption
Date (as defined in Section 5 of this Certificate of Designations), unless the
Corporation shall default in the payment of the redemption price for such shares
of Series A Preferred Stock, in which case such termination shall occur upon
payment of the redemption price of such shares.

     (b)  Mechanics of Conversion; Dividends; Fractional Shares. Before any
holder of Series A Preferred Stock shall be entitled to convert the same into
shares of Common Stock, such holder shall surrender the certificate or
certificates therefor, duly endorsed, at the office of the Corporation or of any
transfer agent for the Series A Preferred Stock, and shall give written notice
to the Corporation at such office that such holder elects to convert the same.
At the time of each conversion of shares of Series A Preferred Stock, the
Corporation shall also issue shares of Common Stock in an amount equal to all
dividends declared and unpaid on the shares of Series A Preferred Stock
surrendered for conversion to the date upon which such conversion is deemed to
occur, valued at the Conversion Price. In lieu of any fractional shares of
Common Stock to which the holder would otherwise be entitled, the Corporation
shall pay cash equal to such fraction multiplied by the then effective
Conversion Price. The Corporation shall, as soon as practicable thereafter,
issue and deliver at such office to such holder of Series A Preferred Stock, a
certificate or certificates for the number of shares of Common Stock to which
such holder shall be entitled as aforesaid, together with cash in lieu of any
fraction of a share. Such conversion shall be deemed to have been made
immediately prior to the close of business on the date of such surrender of the
shares of Series A Preferred Stock to be converted, and the person or persons
entitled to receive the shares of Common Stock issuable upon conversion shall be
treated for all purposes as the record holder or holders of such shares of
Common Stock on such date.

                                       5
<PAGE>

     (c)  Automatic Conversion.

          (i)  Each share of Series A Preferred Stock shall automatically be
converted into shares of Common Stock at the then effective Conversion Price on
the earliest of:

               (1)  December 17, 2004; or

               (2)  immediately prior to the effective time of any merger, sale
of assets, reorganization or like event in which the Corporation is not the
surviving entity (if such event occurs prior to June 17, 1999, then the
Conversion Price shall be equal to the fair value of the consideration to be
received by the holder of a share of Common Stock, as determined in good faith
by the Corporation's Board of Directors, but in no event greater than $2.75), or

               (3)  upon the written election of the holders of not less than a
majority in voting power of the then outstanding shares of Series A Preferred
Stock to require such mandatory conversion.

          (ii) Upon the occurrence of an event specified in Section 3(c)(i)
hereof, all shares of Series A Preferred Stock shall be converted automatically
without any further action by any holder of such shares and whether or not the
certificate(s) representing such shares are surrendered to the Corporation or
the transfer agent for the Series A Preferred Stock; provided, however, that the
Corporation shall not be obligated to issue a certificate or certificates
evidencing the shares of Common Stock issuable upon such conversion unless the
certificate(s) evidencing such shares of Series A Preferred Stock being
converted are either delivered to the Corporation or the transfer agent for the
Series A Preferred Stock, or the holder notifies the Corporation or such
transfer agent that such certificate or certificates have been lost, stolen, or
destroyed and executes an agreement satisfactory to the Corporation to indemnify
the Corporation from any loss incurred by it in connection therewith ("Indemnity
Agreement"), except that such holder shall not be required to provide any
indemnity bond. Upon the automatic conversion of Series A Preferred Stock, each
holder of Series A Preferred Stock shall surrender the certificate(s)
representing such holder's shares of Series A Preferred Stock or the aforesaid
Indemnity Agreement at the office of the Corporation or of the transfer agent
for the Series A Preferred Stock. Thereupon, there shall be issued and delivered
to such holder, promptly at such office and in such holder's name as shown on
such surrendered certificate(s), a certificate or certificates for the number of
shares of Common Stock into which the shares of Series A Preferred Stock
surrendered were convertible on the date on which such automatic conversion
occurred. No fractional shares of Common Stock shall be issued upon the
automatic conversion of Series A Preferred Stock. In lieu of any fractional
shares of Common Stock to which the holder would otherwise be entitled, the
Corporation shall pay cash equal to such fraction multiplied by the then
effective Conversion Price.

     (d)  Adjustment for Stock Splits and Combinations. If the Corporation shall
at any time or from time to time after December 17, 1997 (the "Original Issuance
Date") effect a subdivision of the outstanding Common Stock, the Conversion
Price in effect immediately before that subdivision shall be proportionately
decreased. If the Corporation shall at any time or from time to time after the
Original Issuance Date combine the outstanding shares of Common Stock, the
Conversion Price in effect immediately before the combination shall be
proportionately increased. Any adjustment under this paragraph shall become
effective at the close of business on the date the subdivision or combination
becomes effective.

                                       6
<PAGE>

     (e)  Adjustment for Certain Dividends and Distributions.

          (1)  In the event the Corporation at any time or from time to time
after the Original Issuance Date shall make or issue, or fix a record date for
the determination of holders of Common Stock entitled to receive a dividend or
other distribution payable in additional shares of Common Stock, then and in
each such event the Conversion Price then in effect shall be decreased as of the
time of such issuance or, in the event such a record date shall have been fixed,
as of the close of business on such record date, by multiplying the Conversion
Price then in effect by a fraction:

               (A)  the numerator of which shall be the total number of shares
     of Common Stock issued and outstanding immediately prior to the time of
     such issuance or the close of business on such record date, and

               (B)  the denominator of which shall be the total number of shares
     of Common Stock issued and outstanding immediately prior to the time of
     such issuance or the close of business on such record date plus the number
     of shares of Common Stock issuable in payment of such dividend or
     distribution;

provided, however, if such record date shall have been fixed and such dividend
is not fully paid or such distribution is not fully made on the date fixed
therefor, the Conversion Price shall be recomputed accordingly as of the close
of business on such record date and thereafter the Conversion Price shall be
adjusted pursuant to this paragraph as of the time of actual payment of such
dividends or distributions.

          (2)  For the purposes of Section 3(e)(1) hereof, the total number of
shares of Common Stock deemed to be issued and outstanding shall include (i) all
shares of Common Stock issuable on conversion of all shares of Series A
Preferred Stock outstanding and (ii) all shares of Common Stock issued and
outstanding and entitled to receive such dividend.

     (f)  Adjustments for Other Dividends and Distributions. In the event the
Corporation at any time or from time to time after the Original Issuance Date
shall make or issue, or fix a record date for the determination of holders of
Common Stock entitled to receive, a dividend or other distribution payable in
securities of the Corporation other than shares of Common Stock, including a
cash dividend, then and in each such event provision shall be made so that the
holders of Series A Preferred Stock shall receive upon conversion thereof in
addition to the number of shares of Common Stock receivable thereupon, the
amount of securities of the Corporation and/or cash that they would have
received had their Series A Preferred Stock been converted into Common Stock on
the date of such event and had they thereafter, during the period from the date
of such event to and including the conversion date, retained such securities
receivable by them as aforesaid during such period, giving application to all
adjustments called for herein during such period.

     (g)  Adjustment for Reclassification, Exchange or Substitution. If the
Common Stock issuable upon the conversion of the Series A Preferred Stock shall
be changed into the same or a different number of shares of any class or classes
of stock, whether by capital reorganization, reclassification, or otherwise
(other than a subdivision or combination of shares or stock dividend provided
for above, or a reorganization, merger, consolidation, or sale of assets
provided for in Section 3(c), then and in each such event the holder of each
such share of Series A Preferred Stock shall have the right thereafter to
convert such share into the kind and amount

                                       7
<PAGE>

of shares of stock and other securities and property receivable upon such
reorganization, reclassification, or other change, by holders of the number of
shares of Common Stock into which such shares of Series A Preferred Stock might
have been converted immediately prior to such reorganization, reclassification,
or change, all subject to further adjustment as provided herein.

     (h)  Certificate as to Adjustments. Upon the occurrence of each adjustment
or readjustment of the Conversion Price pursuant to this Section 3, the
Corporation at its expense shall promptly compute such adjustment or
readjustment in accordance with the terms hereof and furnish to each affected
holder of Series A Preferred Stock a certificate setting forth such adjustment
or readjustment and showing in detail the facts upon which such adjustment or
readjustment is based. The Corporation shall, upon the written request at any
time of any affected holder of Series A Preferred Stock, furnish or cause to be
furnished to such holder a like certificate setting forth (i) such adjustments
and readjustments, (ii) the Conversion Price at the time in effect, and (iii)
the number of shares of Common Stock and the amount, if any, of other property
which at the time would be received upon the conversion of each share of Series
A Preferred Stock.

     (i)  Notices of Record Date. In the event of any taking by the Corporation
of a record of the holders of any class of securities for the purpose of
determining the holders thereof who are entitled to receive any dividend (other
than a cash dividend which is the same as cash dividends paid in previous
quarters) or other distribution, the Corporation shall mail to each holder of
Series A Preferred Stock at least ten (10) days prior to such record date a
notice specifying the date on which any such record is to be taken for the
purpose of such dividend or distribution.

     (j)  Common Stock Reserved. The Corporation shall reserve and keep
available out of its authorized but unissued Common Stock such number of shares
of Common Stock as shall from time to time be sufficient to effect the
conversion of all Series A Preferred Stock.

     (k)  Certain Taxes. The Corporation shall pay any issue or transfer taxes
payable in connection with the conversion of any shares of Series A Preferred
Stock; provided, however, that the Corporation shall not be required to pay any
tax that may be payable in respect of any transfer to a name other than that of
the holder of such Series A Preferred Stock.

                                  SECTION 4.
                                 VOTING RIGHTS

     Except as otherwise required by law or by Section 7, the holders of Series
A Preferred Stock shall not have the right to vote on any matter submitted to a
vote of the stockholders of the Corporation. With respect to all questions as to
which, under law, stockholders are entitled to vote by classes, the holders of
Series A Preferred Stock shall vote together as a single class separately from
the holders of Common Stock.

                                  SECTION 5.
                   NO REISSUANCE OF SERIES A PREFERRED STOCK

     No share or shares of Series A Preferred Stock acquired by the Corporation
by reason of redemption, purchase, conversion or otherwise shall be reissued,
and all such shares shall be canceled, retired and eliminated from the shares
which the Corporation shall be authorized to issue.

                                       8
<PAGE>

                                  SECTION 6.
                              PROTECTIVE COVENANT

     The Corporation shall not, without the affirmative vote or written consent
of the holders of a majority of the then issued and outstanding shares of Series
A Preferred Stock, amend its Certificate of Incorporation or adopt a resolution
of the Board of Directors to provide for the creation or issuance of any class
or series of capital stock which shall rank pari passu or senior to the Series A
Preferred Stock in priority to receive the liquidation preference on the Series
A Preferred Stock."

          5.  The amendment to the Certificate of Incorporation herein certified
has been duly adopted in the manner and by the vote prescribed by Section 242 of
the General Corporation Law of the State of Delaware.

                                       9
<PAGE>

     IN WITNESS WHEREOF, the Corporation has caused its corporate seal to be
affixed hereto and this certificate signed by its President and Chief Executive
Officer and attested by its Secretary this 25th day of May, 1999.

                                   VIMRX PHARMACEUTICALS INC.

                                   By:   /s/ Richard L. Dunning
                                      ------------------------------------------
                                         Richard L. Dunning
                                         President and Chief Executive Officer
Attest:

By:   /s/ Lowell S. Lifschultz
   -------------------------------
     Lowell S. Lifschultz
     Secretary

                                      10
<PAGE>

                          Certificate of Designation

                             _____________________

                     Setting Forth "Resolution Designating
                Series B Cumulative Convertible Preferred Stock
                  and Fixing Preferences and Rights Thereof"
                     Adopted by the Board of Directors of
                           Nexell Therapeutics Inc.

               Pursuant to the Provisions of Section 151 of the
         General Corporation Law of the State of Delaware, as amended

     We, the undersigned, L. William McIntosh and William A. Albright, Jr.,
respectively the President and Secretary of Nexell Therapeutics Inc., a Delaware
corporation (hereinafter sometimes referred to as the "Corporation"), hereby
certify as follows:

          First:  That under the provisions of Article Fourth of the Certificate
     of Incorporation of the Corporation the total number of shares which the
     Corporation may issue is 160,000,000 shares of Common Stock, par value
     $0.001 per share and 1,150,000 shares of Preferred Stock, par value $0.001
     per share, of which 150,000 shares have been previously designated Series A
     Cumulative Convertible Preferred Stock and under said Certificate of
     Incorporation, as amended (the "Certificate of Incorporation"), authority
     is expressly vested in the Board of Directors from time to time to issue
     the Preferred Stock by series and in connection with the creation of each
     such series to fix by the resolution or resolutions providing for the issue
     of shares thereof the designations, preferences, limitations and relative
     participating, optional or other special rights, and the qualifications,
     limitations or restrictions thereof, to the full extent permitted by the
     Certificate of Incorporation and the laws of the State of Delaware.

          Second: That the Board of Directors of the Corporation pursuant to the
     authority so vested in it by Article Fourth of the Certificate of
     Incorporation, and in accordance with the provisions of Section 151 of the
     Delaware General Corporation Law, as amended, adopted on November 9, 1999
     the following resolution creating a series of Preferred Stock of 80,000
     shares designated as "Series B Cumulative Convertible Preferred Stock,"
     which resolution has not been amended, modified, rescinded or revoked and
     is in full force and effect on the date hereof.
<PAGE>

                   "Resolution of the Board of Directors of
                     Nexell Therapeutics Inc. designating
               `Series B Cumulative Convertible Preferred Stock'
                  and Fixing Preferences and Rights Thereof"

     Be It Resolved, that, pursuant to authority expressly granted to and vested
in the Board of Directors of Nexell Therapeutics Inc., hereinafter called the
"Corporation", by the provisions of the Certificate of Incorporation the Board
of Directors of the Corporation hereby fixes the number of shares, the
designation, voting powers, rights on liquidation or dissolution, and other
preferences and rights, and the qualifications, limitations or restrictions
thereof, of the shares of such series (in addition to the designations,
preferences and relative rights, and the qualifications, limitations or
restrictions thereof, set forth in the Certificate of Incorporation which are
applicable to the Series B Preferred Stock) as follows:

     Section 1.  Designation and Number; Classification. The series of Preferred
Stock established hereby shall be designated as the Series B Cumulative
Convertible Preferred Stock (herein called the "Series B Preferred Stock") which
shall have a par value of $0.001 per share and the authorized number of the
shares of such series shall be 80,000, which authorized number shall not be
subject to increase. The Series B Preferred Stock is the second series of
preferred stock of the Corporation and shall rank equally with the Series A
Preferred Stock as to preference in payment of dividends and in distributions of
assets in liquidation, dissolution and winding-up. The Series A Preferred Stock
and the Series B Preferred Stock shall be of the same class.

     Section 2.  Dividends. Except in the case of distributions in liquidation,
dissolution or winding up of the affairs of the Corporation provided for in
Section 3 below, the holders of the Series B Preferred Stock shall be entitled
to receive cumulative cash dividends at the rate of 3% of the Liquidation
Preference provided in Section 3 hereof per annum (computed on the basis of a
360-day year of twelve 30-day months) per share, such dividends to be payable
semi-annually on each November 24 and May 24 in each year commencing May 24,
2000 (each such semi-annual dividend period being hereinafter referred to as a
"Dividend Period" and each such dividend payment date being hereinafter referred
to as a "Dividend Payment Date") and shall accrue on a daily basis whether or
not they have been declared and whether or not there are profits, surplus or
other funds of the Corporation legally available for the payment of dividends.
If the Corporation shall fail to pay in cash the accrued dividends payable on or
within 10 business days after any Dividend Payment Date, to the extent permitted
by applicable law, an additional amount shall thereafter accrue on such accrued
but unpaid dividends which shall be computed at the rate of 6% per annum on the
amount of such accrued but unpaid dividends from the Dividend Payment Date on
which the Corporation shall have failed to pay such accrued but unpaid dividends
to the date on which such accrued but unpaid dividends shall be paid in full in
cash. In addition, the holders of the Series B Preferred Stock shall be entitled
to receive cash dividends in the amount per share determined by multiplying the
amount per share at any time distributed in cash on shares of Common Stock by
the number of shares of Common Stock at the time issuable upon conversion of a
share of Series B Preferred Stock (such distribution being hereinafter referred
to as the "Common Equivalent Dividend"), payable on the date that distributions
shall be paid or set apart for any shares of Common Stock. In no event shall any
dividend be paid or declared, nor shall any distribution be made on the
Corporation's Common Stock, Series A
<PAGE>

Preferred Stock or preferred stock of any other class or series unless (i) all
dividends on the Series B Preferred Stock for all past periods shall have been
paid or declared and a sum sufficient for the payment thereof set apart for
payment, and (ii) Common Equivalent Dividends as set forth above are declared
and paid on the Series B Preferred Stock at or prior to such time. In addition,
upon any conversion of shares of Series B Preferred Stock in accordance with the
provisions of Section 6, all accrued dividends and other amounts, if any,
payable on the Series B Preferred Stock shall be paid in cash, including
dividends for the portion of any Dividend Period in which such conversion shall
have occurred. The Corporation covenants and agrees that dividends on the Series
B Preferred Stock shall be declared at the annual rate of 3% of the Liquidation
Preference per share and shall be paid in cash on each Dividend Payment Date
unless the Corporation is prevented by operation of law from the declaration or
payment of such dividend.

     Section 3.  Preference in Liquidation, Dissolution or Winding-Up. In the
event of any liquidation, dissolution or winding up of the Corporation, either
voluntary or involuntary, the holders of Series B Preferred Stock shall be
entitled to be paid out of the assets of the Corporation available for
distribution to its stockholders ratably with the holders of the Series A
Preferred Stock, before any payment or declaration and setting apart for payment
of any amount shall be made in respect of the Common Stock or stock of any other
class an amount equal to $1,000.00 per share of Series B Preferred Stock (as
adjusted to reflect stock splits, dividends, combinations, reclassifications,
reorganizations and similar events) (the "Liquidation Preference") plus an
amount equal to any accrued but unpaid dividends on such share of Series B
Preferred Stock and other amounts, if any, payable thereon. If, upon such
liquidation, dissolution or winding-up, the assets of the Corporation
distributable as aforesaid among the holders of the Series A Preferred Stock and
the Series B Preferred Stock shall be insufficient to permit the payment to such
holders of said amount, the entire assets shall be distributed ratably among the
holders of Series A Preferred Stock and Series B Preferred Stock in proportion
to their respective interests. Thereafter, the assets shall be distributed
ratably among the holders of Common Stock, Series A Preferred Stock and Series B
Preferred Stock, all in proportion to the number of shares of Common Stock owned
by each such holder and, in the case of the Series A Preferred Stock and the
Series B Preferred Stock, to which such holder would then be entitled upon
conversion of such stock owned by such holder.

     Section 4.  Voting Rights. Except as otherwise required by law and as set
forth in Section 5 below, the holders of the Series B Preferred Stock shall not
have the right to vote on any matter submitted to a vote of the stockholders of
the Corporation. With respect to all matters as to which, under law, the holders
of the Series B Preferred Stock are entitled to vote, the affirmative vote of
the holders of at least 66-2/3% of the shares of Series B Preferred Stock voting
as a separate series shall be required to approve any such matter.

     Section 5.  Restrictions on Corporate Action. (a) In addition to any rights
provided by law, so long as any shares of Series B Preferred Stock remain
outstanding, the consent of the holders of at least 66-2/3% of the shares of the
Series B Preferred Stock outstanding at the time shall be necessary to permit,
effect or validate any one or more of the following:

            (i) the creation, authorization or issuance of any shares of any
     class of Prior Stock or Parity Stock (excluding the Baxter Exchange
     Securities), including the issuance
<PAGE>

     of any indebtedness, stock or other Security convertible into any class or
     series of Prior Stock or Parity Stock, or increase in the number of
     authorized shares of Series A Preferred Stock or Series B Preferred Stock;
     or

            (ii)    the increase of the authorized number of shares of any class
     or series of shares of Prior Stock or Parity Stock of the Corporation,
     including the increase in aggregate principal amount or authorized number
     of shares of any indebtedness, stock or other Security convertible into any
     class or series of Prior Stock or Parity Stock; or

            (iii)   the declaration or payment of any dividend or the making of
     any other distribution on any shares of Prior Stock, Parity Stock or Junior
     Stock (other than (A) dividends payable solely in the same class or series
     of Prior Stock, Parity Stock or Junior Stock, as the case may be, to the
     holders thereof and (B) subject to compliance with Section 2 hereof, the
     payment of regular dividends on the Series A Preferred Stock); or

            (iv)    the purchase, redemption or other acquisition for
     consideration of any shares of Prior Stock, Parity Stock or Junior Stock
     other than the repurchase of shares of Common Stock from employees,
     officers, directors, consultants or other persons performing services for
     the Corporation or pursuant to agreements existing on November 24, 1999
     under which the Corporation has the option to repurchase such shares upon
     the occurrence of certain events, such as the termination of employment, so
     long as the total amount applied to all permitted repurchases of shares of
     Common Stock pursuant to this clause (iv) shall not exceed $2,000,000
     during any twelve-month period; or

            (v)     the execution and delivery of any contract, indenture,
     agreement, instrument, note, debenture, bond or other Security which by its
     terms expressly would restrict or limit the ability of the Corporation to
     make the dividend payments to the holders of the Series B Preferred Stock
     in the amount set forth in Section 2; or

            (vi)    the amendment, alteration or repeal, of any of the
     provisions of this Certificate of Designation, if such amendment,
     alteration or repeal would adversely affect any privilege, preference,
     right or power of the Series B Preferred Stock or the holders thereof; or

            (vii)   the amendment or change of its certificate of incorporation
     or by-laws (each as currently amended and/or restated) if such amendment or
     change would adversely affect any privilege, preference, right or power of
     the Series B Preferred Stock or the holders thereof; or

            (viii)  the merger, consolidation or amalgamation of the Corporation
     with or into any other Person or the sale of all or substantially all of
     the assets of the Corporation, if (A) such transaction constitutes a
     Significant Transaction requiring the consent of such holders of Series B
     Preferred Stock pursuant to Section 4.13 of the Securities Agreement
<PAGE>

     or (B) such transaction would by its terms adversely affect any privilege,
     preference, right or power of the Series B Preferred Stock.

     (b)  In addition to any rights provided by law, so long as any shares of
Series B Preferred Stock remain outstanding, the consent of the holders of at
least 75% of the shares of the Series B Preferred Stock outstanding at the time
shall be necessary to permit, effect or consummate any Approved Significant
Transaction pursuant to Section 4.13 of the Securities Agreement.

     (c)  The Corporation shall not issue any shares of Series B Preferred Stock
other than pursuant to the Securities Agreement and the Side Letter Agreement.

     Section 6. Conversion. (a) (i) Optional Conversion. Each share of the
Series B Preferred Stock shall be convertible, at the option of the holder
thereof, at any time after the date of issuance of such share, at the office of
the Corporation or any transfer agent for the Series B Preferred Stock, into
such number of fully paid and nonassessable shares of Common Stock as is
determined by dividing the Liquidation Preference of such share by the
Conversion Price then in effect. The Conversion Price at which shares of Common
Stock shall be delivered upon conversion of each share of Series B Preferred
Stock without the payment of any additional consideration by the holder thereof
shall initially be $2.75 per share (the "Conversion Price"). Such initial
Conversion Price shall be subject to adjustment as set forth in subparagraph (c)
of this Section 6.

            (ii)  Automatic Conversion. (A) On November 24, 2006 (the "Automatic
     Conversion Date") all (but not less than all) of the shares of Series B
     Preferred Stock shall be converted into shares of Common Stock of the
     Corporation. Each holder of Series B Preferred Stock so converted will be
     entitled to receive such number of fully paid and nonassessable shares of
     Common Stock as is determined by dividing the Liquidation Preference of
     such share by the Conversion Price then in effect.

                  (B) On the Automatic Conversion Date, the outstanding shares
          of the Series B Preferred Stock to be converted shall be converted
          without any further action by the holders of such shares and whether
          or not the certificates representing such shares are surrendered to
          the Corporation or its transfer agent; provided, however, (1) that
          such conversion will not violate any legal requirements (such as
          compliance with the Hart-Scott-Rodino Antitrust Improvement Act of
          1976) and (2) that the Corporation shall not be obligated to issue
          certificates evidencing the shares of Common Stock issuable upon such
          conversion unless certificates evidencing such shares of the Series B
          Preferred Stock being converted are delivered to either the
          Corporation or any transfer agent, as hereinafter provided, or the
          holder notifies the Corporation or any transfer agent, as hereinafter
          provided, that such certificates have been lost, stolen, or destroyed
          and executes an agreement satisfactory to the Corporation to indemnify
          the Corporation from any loss incurred by it in connection therewith.
          Upon the automatic conversion of the Series B Preferred Stock, the
          holders of such Series B Preferred Stock shall surrender the
          certificates representing such shares at the office of the Corporation
          or of any transfer agent for the Common
<PAGE>

          Stock. Thereupon, there shall be issued and delivered to such holder,
          promptly at such office and in such holder's name as shown on such
          surrendered certificate or certificates, a certificate or certificates
          for the number of shares of Common Stock into which the shares of the
          Series B Preferred Stock surrendered were convertible on the Automatic
          Conversion Date.

     (b)  Mechanics of Conversion; Fractional Shares.  (i) The shares of Common
Stock issued to the holders of Series B Preferred Stock pursuant to this Section
6 will be shares of the Corporation's voting Common Stock.  Before any holder of
Series B Preferred Stock shall be entitled to convert the same into shares of
Common Stock pursuant to subparagraph (a)(i) of this Section 6, such holder
shall surrender the certificate or certificates therefor, duly endorsed, at the
office of the Corporation or of any transfer agent for the Series B Preferred
Stock, and shall give written notice by mail, postage prepaid, to the
Corporation at its principal corporate office of the election to convert the
same and shall state therein the name or names in which the certificate or
certificates for shares of Common Stock are to be issued.  The Corporation shall
as soon as practicable thereafter, issue and deliver at such office to such
holder of Series B Preferred Stock, or to the nominee or nominees of such
holder, a certificate or certificates for the number of shares of Common Stock
to which such holder shall be entitled as aforesaid.  Such conversion shall be
deemed to have been made immediately prior to the close of business on the date
of such surrender of the shares of Series B Preferred Stock to be converted, and
the person or persons entitled to receive the shares of Common Stock issuable
upon such conversion shall be treated for all purposes as the record holder or
holders of such shares of Common Stock as of such date.  If the conversion is in
connection with an underwritten offering of securities registered pursuant to
the Securities Act of 1933, the conversion may, at the option of any holder
tendering the Series B Preferred Stock for conversion, be conditioned upon the
closing with the underwriter of the sale of securities pursuant to such
offering, in which event the person(s) entitled to receive the Common Stock
issuable upon such conversion of the Series B Preferred Stock shall not be
deemed to have converted such Series B Preferred Stock until immediately prior
to the closing of such sale of securities.

          (ii)   No fractional shares of Common Stock shall be issued upon
     conversion of Series B Preferred Stock.  All shares of Common Stock
     (including fractions thereof) issuable upon conversion of more than one
     share of Series B Preferred Stock by a holder thereof shall be aggregated
     for purposes of determining whether the conversion would result in the
     issuance of any fractional share.  If, after such aggregation, the
     conversion would result in the issuance of a fraction of a share of Common
     Stock, the Corporation shall, in lieu of issuing any fractional share, pay
     the holder otherwise entitled to such fraction a sum in cash equal to the
     fair market value of such fraction on the date of conversion (as determined
     in good faith by the Board of Directors).  In lieu of any fractional share
     to which the holder would otherwise be entitled, the Corporation shall pay
     cash equal to such fraction multiplied by the then effective Conversion
     Price.

          (iii)  All shares of Series B Preferred Stock which have been
     converted, either optionally or automatically, shall be deemed extinguished
     and no shares of Series B Preferred Stock shall be issued or issuable in
     replacement thereof.
<PAGE>

     (c)  Conversion Price Adjustments of Series B Preferred Stock.  The
Conversion Price shall be subject to adjustment from time to time as follows:

            (i)   Stock Dividends, Subdivisions and Combinations.  In case after
     the original date on which the Series B Preferred Stock is issued the
     Corporation shall:

                  (A) take a record of the holders of its Common Stock for the
          purpose of entitling them to receive a dividend payable in, or other
          distribution of, Common Stock, or

                  (B) subdivide its outstanding shares of Common Stock into a
          larger number of shares of Common Stock, or

                  (C) combine its outstanding shares of Common Stock into a
          smaller number of shares of Common Stock,

          then the Conversion Price shall be adjusted to that rate determined by
          multiplying the Conversion Price in effect immediately prior to such
          event by a fraction (1) the numerator of which shall be the total
          number of outstanding shares of Common Stock of the Corporation
          immediately prior to such event, and (2) the denominator of which
          shall be the total number of outstanding shares of Common Stock of the
          Corporation immediately after such event.  In the event that the
          dividend or distribution referenced in subparagraph (c)(i)(A) above is
          lawfully abandoned, the Conversion Price shall be appropriately
          readjusted.

            (ii)  Issuance of Additional Shares of Common Stock at Less Than
     Conversion Price.  In case after the original date on which the Series B
     Preferred Stock is issued the Corporation shall (except as hereinafter
     provided) issue any Additional Shares of Common Stock for a consideration
     per share which is less than the Conversion Price per share, then the per
     share Conversion Price upon each such issuance shall be adjusted to that
     price determined by multiplying the per share Conversion Price in effect
     immediately prior to such event by a fraction:

                       (x)  the numerator of which shall be the number of shares
                  of Common Stock outstanding immediately prior to the issuance
                  of such Additional Shares of Common Stock plus the number of
                  full shares of Common Stock which the aggregate consideration
                  for the total number of such Additional Shares of Common Stock
                  so issued would purchase at the per share Conversion Price,
                  and

                       (y)  the denominator of which shall be the number of
                  shares of Common Stock outstanding immediately prior to the
                  issuance of such Additional Shares of Common Stock plus the
                  number of such Additional Shares of Common Stock so issued.
<PAGE>

     The provisions of this subparagraph (c)(ii) shall not apply to any
     Additional Shares of Common Stock which are distributed to holders of
     Common Stock as a stock dividend or subdivision, for which an adjustment is
     provided for under subparagraph (c)(i) above.  No adjustment of the per
     share Conversion Price shall be made under this subparagraph (c)(ii) upon
     the issuance of any Additional Shares of Common Stock that are issued
     pursuant to the exercise of any warrants or other subscription or purchase
     rights or pursuant to the exercise of any conversion or exchange rights in
     any Convertible Securities, if any such adjustment shall previously have
     been made upon the issuance of such warrants or other rights or upon the
     issuance of such Convertible Securities (or upon the issuance of any
     warrants or other rights therefor) pursuant to subparagraph (c)(iii) below.

          (iii)  Issuance of Warrants, Other Rights or Convertible Securities.
     In case the Corporation shall issue any options, warrants or other rights
     to subscribe for or purchase any Additional Shares of Common Stock or issue
     Convertible Securities (other than Series A Preferred Stock issued as a
     dividend on the Series A Preferred Stock in accordance with Section 2) and
     the consideration per share for which Additional Shares of Common Stock may
     at any time thereafter be issuable pursuant to such options, warrants or
     other rights or pursuant to the terms of such Convertible Securities shall
     be less than the Conversion Price, then the per share Conversion Price
     shall be adjusted as provided in subparagraph (c)(ii) above.

          For purposes of adjustments in the Conversion Price pursuant to this
     subparagraph (c)(iii), the number of shares of Common Stock outstanding
     shall be deemed to include the maximum number of Additional Shares of
     Common Stock issuable pursuant to all outstanding options, warrants or
     other rights or necessary to effect the conversion or exchange of all such
     outstanding Convertible Securities of the Corporation.  All such options,
     warrants, other rights or Convertible Securities shall be deemed to have
     been issued as of, and the date as of which the Conversion Price per share
     of Common Stock shall be computed shall be, the earlier of (A) the date on
     which the Corporation shall enter a firm contract or commitment for the
     issuance of such options, warrants, other rights or Convertible Securities
     or (B) the date of actual issuance of such options, warrants, other rights
     or Convertible Securities.

          No adjustment of the per share Conversion Price shall be made under
     this subparagraph (c)(iii) upon the issuance of any Convertible Securities
     which are issued pursuant to the exercise of any options, warrants or other
     subscription or purchase rights therefor if any such adjustment shall
     previously have been made upon the issuance of such options, warrants or
     other rights pursuant to said paragraph.

          (iv)   Other Provisions Applicable to Adjustments Under This
     Subparagraph. The following provisions shall be applicable to the making of
     adjustments to the Conversion Price hereinbefore provided in this
     subparagraph (c):

                 (A)  Computation of Consideration.  To the extent that any
          Additional Shares of Common Stock or any Convertible Securities or any
          options, warrants
<PAGE>

          or other rights to subscribe for or purchase any Additional Shares of
          Common Stock or any Convertible Securities shall be issued for a cash
          consideration, the consideration received by the Corporation therefor
          shall be deemed to be the amount of the cash received by the
          Corporation therefor, or, if such Additional Shares of Common Stock or
          Convertible Securities or options, warrants or other rights are
          offered by the Corporation for subscription, the subscription price,
          or, if such Additional Shares of Common Stock or Convertible
          Securities or options, warrants or other rights are sold to
          underwriters or dealers for public offering without a subscription
          offering, the initial public offering price, in any such case
          excluding any amounts paid or receivable for accrued interest or
          accrued dividends and without deduction of any compensation, discounts
          or expenses paid or incurred by the Corporation for and in the
          underwriting thereof, or otherwise in connection with the issue
          thereof. To the extent that such issuance shall be for a consideration
          other than cash, then, except as herein otherwise expressly provided,
          the amount of such consideration shall be deemed to be the fair value
          of such consideration at the time of such issuance as determined in
          good faith by the Board of Directors of the Corporation. The
          consideration for any Additional Shares of Common Stock issuable
          pursuant to any options, warrants or other rights to subscribe for or
          purchase the same shall be the consideration received by the
          Corporation for issuing such options, warrants or other rights, plus
          the additional consideration payable to the Corporation upon the
          exercise of such options, warrants or other rights. The consideration
          for any Additional Shares of Common Stock issuable pursuant to the
          terms of any Convertible Securities shall be the consideration
          received by the Corporation for issuing any options, warrants or other
          rights to subscribe for or purchase such Convertible Securities plus
          the consideration paid or payable to the Corporation in respect of the
          subscription for or purchase of such Convertible Securities, plus the
          additional consideration, if any, payable to the Corporation upon the
          exercise of the right of conversion or exchange in such Convertible
          Securities. In case of the issuance at any time of any Additional
          Shares of Common Stock or Convertible Securities in payment or
          satisfaction of any dividend upon any class of equity securities other
          than Common stock, the Corporation shall be deemed to have received
          for such Additional Shares of Common Stock or Convertible Securities a
          consideration equal to the amount of such dividend so paid or
          satisfied.

                 (B)  Readjustment of Conversion Price.  Upon expiration of the
          right of exercise, conversion or exchange of any Convertible
          Securities, or upon the expiration of any rights, options or warrants,
          or upon the termination of any firm contract or commitment for the
          issuance of such rights, options, warrants or Convertible Securities,
          or upon any increase in the minimum consideration receivable by the
          Corporation for the issuance of Additional Shares of Common Stock
          pursuant to such Convertible Securities, rights, options or warrants,
          if any such Convertible Securities shall not have been converted or
          exchanged, or if any such rights, options or warrants shall not have
          been exercised, the number of shares of Common Stock deemed to be
          issued and outstanding by reason of the fact that they were issuable
          upon conversion or exchange of any such Convertible
<PAGE>

          Securities or upon exercise of any such rights, options or warrants
          shall no longer be computed as set forth above, and the Conversion
          Price shall forthwith be readjusted and thereafter be the rate which
          it would have been (but reflecting any other adjustments in the
          Conversion Price made pursuant to the provisions of this Section 6
          after the issuance of such Convertible Securities, rights, options or
          warrants) had the adjustment of the Conversion Price made upon the
          issuance or sale of such Convertible Securities or the issuance of
          such rights, options or warrants been made on the basis of the
          issuance only of the number of Additional Shares of Common Stock
          actually issued upon conversion or exchange of such Convertible
          Securities or upon the exercise of such rights, options or warrants,
          or upon the basis of such increased minimum consideration, as the case
          may be, and thereupon only the number of Additional Shares of Common
          Stock actually so issued plus the number thereof then issuable upon
          the basis of such increased minimum consideration shall be deemed to
          have been issued and only the consideration actually received plus
          such increased minimum consideration receivable by the Corporation
          (computed as in subparagraph (c)(iv)(A) of this Section 6) shall be
          deemed to have been received by the Corporation.

                 (C)  No Rounding of Conversion Price.  Any determination of the
          Conversion Price hereunder shall be expressed in United States
          Dollars, cents and portions of cents and shall not be subject to
          rounding.

          (v)    Common Equivalent Dividends.  In case the Corporation shall
     declare, to the extent otherwise permitted herein, a dividend upon its
     Common Stock (except a dividend payable in shares of Common Stock referred
     to in subparagraph (c)(i) of this Section 6) or a dividend payable in
     warrants, rights or Convertible Securities referred to in subparagraph
     (c)(iii) of this Section 6 payable otherwise than out of earnings or
     surplus (other than revaluation surplus or paid-in surplus), the
     Corporation shall simultaneously declare a dividend, in cash, upon the
     Series B Preferred Stock equal to, in the case of a cash dividend, the
     amount of the per share dividend declared upon the Common Stock times the
     number of shares of Common Stock to be received by the holders of the
     Series B Preferred Stock upon conversion at the Conversion Price then in
     effect and, in the case of a dividend payable other than in cash, the fair
     value of such dividend declared upon the Common Stock as determined by the
     Board of Directors of the Corporation. For the purposes of the foregoing, a
     dividend payable other than in cash shall be considered payable out of
     earnings or surplus (other than revaluation surplus or paid-in surplus)
     only to the extent that such earnings or surplus are charged an amount
     equal to the fair value of such dividend as determined by the Board of
     Directors of the Corporation.

          (vi)   Additional Adjustments, etc.  If any other transaction or event
     shall occur (excluding any transaction or event explicitly referred to in
     this Section 6, but including, without limitation, any issuance repurchase,
     redemption, or other distribution in respect of any shares or capital stock
     or other securities of the Corporation or of any other person) as to which
     the other provisions of this Section 6 are not strictly applicable but the
     failure to make any adjustment to the Conversion Price of the Series B
     Preferred Stock would not fairly protect the conversion rights and other
     rights of any share of the Series B
<PAGE>

     Preferred Stock, then, and as a condition to the consummation of any such
     transaction or event, and in each such case, the Board of Directors shall
     promptly determine the adjustment, if any, on a basis consistent with the
     essential intent and principles established in this Section 6, which is
     necessary to preserve, without dilution, the conversion rights of each
     share of the Series B Preferred Stock and, promptly following such
     determination, the Corporation shall furnish to each holder of the Series B
     Preferred Stock a certificate setting forth such adjustment and showing in
     detail the facts upon which such adjustment is based. The adjustment set
     forth in such certificate shall be binding upon the Corporation and the
     holders of the Series B Preferred Stock unless, within 30 days following
     receipt of such certificate, the holders of 20% or more of the outstanding
     shares of Series B Preferred Stock shall notify the Corporation of their
     disagreement with such adjustment, in which event such adjustment shall be
     determined at the expense of the Corporation by its independent auditors
     (so long as such auditors' accounting firm ranks among the five largest
     national accounting firms) or by an independent investment banking firm or
     other professional of recognized national standing selected by the
     Corporation and, in all such cases (including the Corporation's selection
     of its auditors), reasonably satisfactory to the holders of 66-2/3% or more
     of the outstanding shares of Series B Preferred Stock, which shall give its
     opinion as to the adjustment, if any, on a basis consistent with the
     essential intent and principles established in this Section 6, which is
     necessary to preserve, without dilution, the conversion rights of each
     share of Series B Preferred Stock. The opinion of any such auditor, banking
     firm or other professional shall be conclusive evidence of the correctness
     of any computation made under this Section 6. The Corporation shall pay all
     fees and expenses in connection with any such opinion. Upon receipt of such
     opinion, the Corporation will promptly deliver a copy thereof to each
     holder of any share of Series B Preferred Stock and the Corporation shall
     (subject to obtaining necessary director and stockholder actions), take all
     actions necessary or appropriate under the laws of the State of Delaware
     and the Certificate of Incorporation consistent with such opinion to effect
     the intent and principles hereof.

          (vii)  Minimum Adjustment.  Except as hereinafter provided, no
     adjustment of the Conversion Price hereunder shall be made if such
     adjustment results in a change of the Conversion Price then in effect of
     less than two cents ($0.02).  Any adjustment of less than two cents ($0.02)
     of any Conversion Price shall be carried forward and shall be made at the
     time of and together with any subsequent adjustment that, together with
     adjustment or adjustments so carried forward, amounts to two cents ($0.02)
     of the Conversion Price then in effect or more.  However, upon the
     conversion of any share of the Series B Preferred Stock, the Corporation
     shall make all necessary adjustments not theretofore made to the Conversion
     Price up to and including the date upon which the conversion is exercised.

          (viii) Notice of Adjustments.  Whenever the Conversion Price shall be
     adjusted pursuant to this subparagraph (c), the Corporation at its expense
     shall promptly prepare a certificate signed by the Chief Financial Officer
     or the Chief Operating Officer and by the Treasurer or an Assistant
     Treasurer setting forth, in reasonable detail, the event requiring the
     adjustment, the amount of the adjustment, the adjusted Conversion Price,
     the method
<PAGE>

     by which such adjustment was calculated (including a description of the
     basis on which the Board of Directors of the Corporation made any
     determination hereunder), and shall promptly cause copies of such
     certificate to be mailed (by first class mail postage prepaid) to each of
     the holders of the Series B Preferred Stock. The adjustments set forth in
     such certificate shall be binding upon the Corporation and the holders of
     the Series B Preferred Stock unless, within 30 days following receipt of
     such Certificate, the holders of 20% or more of the outstanding shares of
     Series B Preferred Stock shall notify the Corporation of their disagreement
     with such adjustments, in which event, such adjustments shall be determined
     at the expense of the Corporation by its independent auditors (so long as
     such auditors' accounting firm ranks among the five largest national
     accounting firms) or by an independent investment banking firm or other
     professional of recognized national standing selected by the Corporation
     and, in all such cases (including the Corporation's selection of its
     auditors), reasonably satisfactory to the holders of 66-2/3% or more of the
     outstanding shares of Series B Preferred Stock, such determination to be
     set forth in a separate report from such auditor, banking firm or other
     professional delivered promptly to the Corporation and the holders of the
     Series B Preferred Stock following the such determination. The Corporation
     shall, upon the written request made at any time by any holder of Series B
     Preferred Stock, furnish to such holder a certificate setting forth (A) all
     adjustments that shall have been made with respect to the Series B
     Preferred Stock pursuant to this Section 6, (B) the Conversion Price at the
     time in effect and (C) the number of shares of Common Stock and the amount,
     if any, of other property which at the time would be received upon the
     conversion of the then outstanding shares of Series B Preferred Stock.

          (ix)   Special Limitation on Adjustments to Conversion Price.  No
     adjustment to the Conversion Price required by this Section 6 shall be made
     to a Conversion Price below the greater of the book value or the market
     value of the Common Stock on the date the Series B Preferred Stock was
     originally issued (the "Issue Date Price") unless stockholder approval is
     obtained in accordance with The Nasdaq Marketplace Rules, provided that
     such stockholder approval shall only be so required if The Nasdaq Market
     Marketplace Rules require such stockholder approval at the time such
     adjustment is required hereunder. If such stockholder approval is required
     by The Nasdaq Market Marketplace Rules, the Corporation shall take all
     actions which are necessary or appropriate to seek to obtain such
     stockholder approval. If such approval is not obtained, an adjustment to
     the Conversion Price shall be made to a Conversion Price which equals the
     Issue Date Price.

     (d)  Mergers, Consolidations, Sales, Reorganization or Reclassification. In
the case of any consolidation or merger of the Corporation with another entity
(regardless of whether the Corporation is the surviving entity), or the sale of
all or substantially all of its assets to another entity, or any reorganization,
recapitalization or reclassification of the Common Stock or other equity
securities of the Corporation (except a split-up or combination, provision for
which is made in subparagraph (c)(i) of this Section 6), then, as a condition of
such consolidation, merger, sale, reorganization, recapitalization or
reclassification, lawful and adequate provision shall be made whereby the
holders of the Series B Preferred Stock shall thereafter have the right to
receive upon the basis and upon the terms and conditions specified herein and in
lieu of the
<PAGE>

shares of Common Stock immediately theretofore receivable hereunder, such shares
of stock, securities or assets as may (by virtue of such consolidation, merger,
sale, reorganization, recapitalization or reclassification) be issued or payable
with respect to or in exchange for a number of outstanding shares of Common
Stock equal to the number of shares of Common Stock immediately theretofore so
receivable hereunder had such consolidation, merger, sale, reorganization,
recapitalization or reclassification not taken place, and in any such case
appropriate provisions shall be made with respect to the rights and interests of
the holders of the Series B Preferred Stock to the end that the provisions
hereof (including, without limitation, provisions for adjustment of the
Conversion Price) shall thereafter be applicable as nearly as may be, in
relation to any shares of stock, securities or assets thereafter deliverable
upon conversion of such Series B Preferred Stock.

     (e)  Dissolution or Liquidation.  In the event of any proposed distribution
of the assets of the Corporation in dissolution or liquidation (except under
circumstances when the foregoing subparagraph (d) of this Section 6 shall be
applicable) the Corporation shall mail notice thereof to the holders of the
Series B Preferred Stock and shall make no distribution to stockholders until
the expiration of 30 days from the date of mailing of the aforesaid notice, and
in any such case, the holders of the Series B Preferred Stock may exercise the
conversion rights with respect to the Series B Preferred Stock within 30 days
from the date of mailing such notice and all rights herein granted not so
exercised within such 30-day period shall thereafter become null and void.

     (f)  No Impairment.  The Corporation will not, by amendment of its
Certificate of Incorporation or through any reorganization, recapitalization,
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 to be observed or performed hereunder by the
Corporation, but will at all times in good faith assist in the carrying out of
all of the provisions of this Section 6 and in the taking of all such action as
may be necessary or appropriate in order to protect the conversion rights of the
holders of the Series B Preferred Stock against impairment.

     (g)  Fully Paid Stock; Taxes.  The shares of stock represented by each and
every certificate for its Common Stock to be delivered on the exercise of the
conversion rights herein provided for shall, at the time of such delivery, be
validly issued and outstanding and be fully paid and nonassessable.  The
Corporation shall pay when due and payable any and all federal and state taxes
(other than taxes in respect of income) which may be payable in respect of the
Series B Preferred Stock or any Common Stock or certificates therefor upon the
exercise of the conversion rights herein provided for pursuant to the provisions
hereof. The Corporation shall not, however, be required to pay any tax which may
be payable in respect of any transfer involved in the transfer and delivery of
stock certificates in the name other than that of the holder of the Series B
Preferred Stock converted, and any such tax shall be paid by such holder at the
time of presentation.

     (h)  Closing of Transfer Books.  The right to convert any of the Series B
Preferred Stock shall not be suspended during any period while the stock
transfer books of the Corporation for its Common Stock may be closed.  The
Corporation shall not be required, however, to deliver certificates of its
Common Stock upon such exercise while such books are duly closed for any
<PAGE>

purpose, but the Corporation may postpone the delivery of the certificate for
such Common Stock until the opening of such books, and they shall, in such case,
be delivered forthwith upon the opening thereof, or as soon as practicable
thereafter.

     (i)  Reservation of Common Stock. The Corporation will at all times reserve
and keep available such number of authorized shares of its Common Stock solely
for the purpose of issue upon the conversion of the Series B Preferred Stock as
herein provided for, as shall then be issuable upon the conversion of all
outstanding shares of Series B Preferred Stock and such shares of Common Stock
shall at no time have a par value which is in excess of the Conversion Price
then in effect.

     Section 7.  Definitions.  In addition to the terms defined elsewhere in
this Designation of Series B Cumulative Convertible Preferred Stock, the
following terms have the following respective meanings:

          The term "Additional Shares of Common Stock" shall mean all shares of
     Common Stock issued by the Corporation on and after the original date on
     which the Series B Preferred Stock was issued, except:

               (A)  Common Stock issued upon conversion of the Series B
          Preferred Stock at the Conversion Price and Common Stock issued upon
          exercise of the Corporation's Class A Warrants or Class B Warrants;

               (B)  Common Stock issued to officers, directors, employees and
          members of the Scientific Advisory Board of the Corporation and Common
          Stock issued pursuant to employee stock option or stock purchase plans
          approved by the Board of Directors, provided that the aggregate number
          of shares of Common Stock issued and/or issuable to such persons and
          pursuant to all such plans and agreements shall not in the aggregate
          at any time exceed 9,000,000 shares (as such number of shares shall be
          appropriately adjusted by the Board of Directors for stock splits,
          dividends, combinations and other similar events), it being understood
          that the shares of Common Stock excluded pursuant to this clause (B)
          are in addition to shares excluded pursuant to clause (D);

               (C)  Common Stock issued in connection with a corporate
          collaboration, development agreement, or commercial relationship which
          is not primarily for the purpose of obtaining financing, approved by
          the Board of Directors and for consideration equal to or greater than
          the fair market value of such shares of Common Stock at the time of
          issue;

               (D)  Up to 16,560,176 shares of Common Stock issued upon
          conversion or exercise of convertible securities, options and warrants
          outstanding on November 24, 1999 (as such number of shares shall be
          appropriately adjusted by the Board of Directors for stock splits,
          dividends, combinations and other similar events);
<PAGE>

               (E)  Common Stock issued upon conversion of the Series A
          Preferred Stock;

               (F)  Common Stock valued at up to $10,000,000 issued as
          consideration in connection with a single acquisition transaction to
          be made by the Corporation on or before December 31, 2000 involving a
          medical therapeutics company consistent with the Corporation's
          business plan;

               (G)  Up to 250,000 shares of Common Stock issued substantially
          concurrently with the initial issuance of the Series B Preferred Stock
          to holders of the Corporation's warrants existing at such time and
          resulting from the operation of dilution protection provisions in such
          warrants arising principally from the issuance of the Class A
          Warrants; and

               (H)  Common Stock issued with the affirmative vote or written
          consent of the holders of at least 66-2/3% of the outstanding shares
          of Series B Preferred Stock.

          The term "Baxter Exchange Securities" shall mean securities of any
     class or classes which are convertible into shares of Common Stock and for
     which the Corporation exchanges any shares of Series B Preferred Stock
     pursuant to the Side Letter Agreement.

          The term "Class A Warrants" shall mean the Class A Warrants to
     purchase Common Stock of the Company issued concurrently with the initial
     issuance of the Series B Preferred Stock.

          The term "Class B Warrants" shall mean the Class B Warrants to
     purchase Common Stock of the Company issued concurrently with the initial
     issuance of the Series B Preferred Stock.

          The term "Common Stock" shall mean (i) the Corporation's Common Stock,
     $0.001 par value, authorized on the date of issuance of the Series B
     Preferred Stock and (ii) any other class of capital stock of the
     Corporation hereafter authorized the right of which to share in
     distributions either of earnings or assets of the Corporation is without
     limit as to any amount or percentage as and to the extent no amounts
     payable on or in respect of such Common Stock and no rights arising in
     connection therewith have preference over any other Common Stock upon
     dissolution, liquidation or winding up of the Corporation; provided that
     the shares to be received by the holders of the Series B Preferred Stock
     upon conversion shall be the Common Stock authorized on the date of
     issuance of the Series B Preferred Stock.

          The term "Conversion Price" shall have the meaning set forth in
     Section 6(a)(i) hereof.
<PAGE>

          The term "Convertible Securities" shall mean evidences of
     indebtedness, shares of stock or other securities which are convertible
     into or exchangeable for Additional Shares of Common Stock, either
     immediately or upon the arrival of a specified date or the happening of a
     specified event, including, without limitation, the Baxter Exchange
     Securities.

          The term "Junior Stock" shall mean all Common Stock and all other
     shares of stock of any other class of the Corporation, whether or not
     presently authorized, ranking as to both payment of dividends and
     distribution of assets upon liquidation, dissolution or winding-up junior
     to the Series B Preferred Stock, and junior to the Series B Preferred
     Stock.

          The term "Parity Stock" shall mean all Series A Preferred Stock and
     all other capital stock of the Corporation, whether or not presently
     authorized, ranking, as to distribution of assets upon liquidation,
     dissolution or winding-up, on a parity with the Series B Preferred Stock;
     provided that in no event shall any such Parity Stock be issued under and
     pursuant to the Certificate of Incorporation, except in compliance with the
     provisions of Section 5.

          The term "Preferred Stock" shall have the meaning set forth in Article
     Fourth of the Certificate of Incorporation of the Corporation.

          The term "Prior Stock" shall mean all stock ranking, either as to
     payment of dividends, liquidation, redemption, sinking fund or distribution
     of assets upon liquidation, dissolution or winding-up, prior to the Series
     B Preferred Stock; provided that in no event shall any such Prior Stock be
     issued under and pursuant to the Certificate of Incorporation, except in
     compliance with the provisions of Section 5.

          The term "Securities Agreement" shall mean the Securities Agreement
     dated as of November 24, 1999 between the Corporation and the original
     institutional investors named therein and pursuant to which the Series B
     Preferred Stock was originally issued and sold.

          The term "Side Letter Agreement" shall mean the Side Letter Agreement
     dated as of November 24, 1999 between the Corporation and Baxter
     International Inc. relating to the Series B Preferred Stock.

     This resolution shall be known and may be referred to as "A Resolution of
the Board of Directors of Nexell Therapeutics Inc. Designating Series B
Cumulative Convertible Preferred Stock and Fixing Preferences and Rights
Thereof."

     Resolved, Further, that following the consent of the holder of the
Corporation's Series A Preferred Stock to the creation and issuance of the
Series B Preferred Stock the appropriate officers of the Corporation are hereby
authorized and directed to execute and acknowledge a certificate setting forth
these resolutions and to cause such certificate to be filed
<PAGE>

and recorded, all in accordance with the requirements of Section 242 of the
General Corporation Law of the State of Delaware, as amended."

          Third:  The number of shares of Series B Preferred Stock that may be
     issued by the Corporation pursuant to said resolution is 80,000.

     In Witness Whereof, this Certificate has been made under the seal of said
Nexell Therapeutics Inc., and has been signed by the undersigned said L. William
McIntosh, President and said William A. Albright, CFO & Treasurer, this 24th day
of November, 1999.

Nexell Therapeutics Inc.

/s/
-------------------------------------------

(Corporate Seal)

_______________________________
     _________________
<PAGE>

                          CERTIFICATE OF AMENDMENT OF
              AMENDED AND RESTATED CERTIFICATE OF INCORPORATION,
                    AS AMENDED, OF NEXELL THERAPEUTICS INC.

          Nexell Therapeutics Inc. (the "Corporation"), a corporation organized
and existing under and by virtue of the General Corporation Law of the State of
Delaware, does hereby certify:

          FIRST:  The name of the Corporation is Nexell Therapeutics Inc. and
the name under which the Corporation originally was incorporated was Cellular
Immunology Corporation.

          SECOND: The original Certificate of Incorporation of the Corporation
was filed with the Secretary of State of the State of Delaware on December 30,
1986 under the name Cellular Immunology Corporation, and the Amended and
Restated Certificate of Incorporation of the Corporation was filed with the
Secretary of State of the State of Delaware on July 11, 1990 under the name
Vimrx Pharmaceuticals Inc.

          THIRD:  The Board of Directors of the Corporation, acting in
accordance with the provisions of Sections 141 and 242 of the General
Corporation Law of the State of Delaware, adopted resolutions at a meeting held
on March 16, 2000 to amend the first paragraph of Article FOURTH of the Amended
and Restated Certificate of Incorporation, as amended, of the Corporation to
read in its entirety as follows:

                  "FOURTH

                       A.   The authorized capital stock of the Corporation
                  shall consist of eighty-one million, one hundred fifty
                  thousand (81,150,000) shares, consisting of eighty million
                  (80,000,000) shares of Common Stock, each having a par value
                  of $.001 (the "Common Stock"), and one million, one hundred
                  fifty thousand (1,150,000) shares of Preferred Stock, each
                  having a par value of $.001 (the "Preferred Stock"). Upon this
                  Certificate of Amendment of Amended and Restated Certificate
                  of Incorporation becoming effective (the "Effective Time"),
                  each four (4) shares of the Corporation's Common Stock issued
                  and outstanding shall, automatically and without any action on
                  the part of the respective holders thereof, be converted into
                  one (1) share of Common Stock of the Corporation. No
                  fractional shares shall be issued and, in lieu thereof, any
                  holder of less than one share of Common Stock shall be
                  entitled to receive cash for such holder's fractional share
                  based upon the closing sales price of the Corporation's Common
                  Stock as reported on the Nasdaq National Market as of the date
                  immediately preceding the Effective Time. The Company may
                  retain a third party to collect and pool fractional share
                  interests, sell the same, and return payment to the holders of
                  the interests."

          FOURTH:  Pursuant to a resolution of the Board of Directors, this
Certificate of Amendment of Amended and Restated Certificate of Incorporation,
as amended, was submitted to the stockholders of the Corporation and was duly
approved by the required vote of stockholders of the Corporation in accordance
with Sections 228 and 242 of the Delaware General Corporation Law. The total
number of outstanding shares entitled to vote or consent to this Amendment was
74,443,657 shares of Common Stock. A majority of the outstanding Common Stock
voted in favor of this Certificate of Amendment of Amended and Restated
Certificate of Incorporation, as amended.

          FIFTH:   This Certificate of Amendment of Amended and Restated
Certificate of Incorporation shall become effective at 9:00 a.m. Eastern
Daylight-Saving Time on June 15, 2000.
<PAGE>

     IN WITNESS WHEREOF, Nexell Therapeutics Inc. has caused this Certificate of
Amendment to be signed by its President this 14th day of June, 2000.

                                        NEXELL THERAPEUTICS INC.

                                        By:  /s/ L. William McIntosh
                                           ---------------------------------
                                             L. William McIntosh, President<PAGE>

                                  Exhibit 4.3

                       1997 INCENTIVE AND NON-INCENTIVE

                               STOCK OPTION PLAN

                                      OF
                            NEXELL THEAPEUTICS INC.
                  (FORMERLY NAMED VIMRx PHARMACEUTICALS INC.)

     1.   Purpose of Plan.

          The purpose of this Incentive and Non-Incentive Stock Option Plan
("Plan") is to further the growth and development of VIMRx Pharmaceuticals Inc.
("Company") and any subsidiaries thereof by encouraging selected employees,
directors and other persons who contribute and are expected to contribute
materially to the Company's success to obtain a proprietary interest in the
Company through the ownership of stock, thereby providing such persons with an
added incentive to promote the best interests of the Company and affording the
Company a means of attracting to its service persons of outstanding ability.

     2.   Stock Subject to the Plan.

          An aggregate of 1,312,500 shares of the Company's Common Stock, $.001
par value ("Common Stock") subject, however, to adjustment or change pursuant to
paragraph 12 hereof, shall be reserved for issuance upon the exercise of options
which may be granted from time to time in accordance with the Plan ("Options").
Such shares may be, in whole or in part, as the committee appointed by the Board
of Directors to administer the Plan (hereinafter, the "Committee") shall from
time to time determine, authorized but unissued shares or issued shares which
have been reacquired by the Company. If, for any reason, an Option shall lapse,
expire or terminate without having been exercised in full, the unpurchased
shares covered thereby shall again be available for purposes of the Plan.

     3.   Administration.

          (a) Except as provided in paragraph (c) below, the Plan shall be
administered by the Committee. The Board of Directors shall appoint the
Committee from among its members. Such Committee shall be composed of two or
more Directors who, to the extent practicable, shall be "outside directors" as
defined in regulations under Section 162(m) of the Internal Revenue Code of
1986, as amended (the "Code"), and "non-employee directors" as defined by
Regulation 240.16b-3 under the Securities Exchange Act of 1934, as amended. Such
Committee shall have and may exercise any and all of the powers relating to the
administration of the Plan and the grant of Options thereunder as are set forth
in subparagraph 3(b) hereof as the Board of Directors shall confer and delegate.
The Board of Directors shall have power at any time to fill vacancies in, to
change the membership of, or to discharge such Committee. The Committee shall
select one of its members as its chairman and shall hold its meetings at such
time and at such places as it shall deem advisable. A majority of such Committee
shall constitute a quorum and such majority shall determine its action. Any
action may be taken without a meeting by written consent of all the members of
the Committee. The Committee shall keep minutes of its proceedings and shall
report the same to the Board of Directors at the meeting next succeeding.

          (b) The Committee shall administer the Plan and, subject to the
provisions of the Plan, shall have sole authority in its discretion to determine
the persons to whom, and the time or times at which, Options shall be granted;
the number of shares to be subject to each such Option; the provisions regarding
exercisability of each Option; the expiration date of each Option; whether the
Option shall contain a "cashless exercise" provision; whether all or any portion
of the Options shall be incentive stock options ("Incentive Options") qualifying
under Section 422A of the Code or stock options which do not so qualify ("Non-
Incentive Options"); whether a Non-Incentive Option shall have limited
transferability as permitted under the Plan; and whether a Non-Incentive Option
granted to a non-employee shall terminate following
<PAGE>

the non-employee's termination of engagement in performing services for the
Company or its subsidiaries pursuant to Section 9 of the Plan. Both Incentive
Options and Non-Incentive Options may be granted to the same person at the same
time provided each type of Option is clearly designated. In making such
determinations, the Committee may take into account the nature of the services
rendered by such persons, their present and potential contribution to the
Company's success and such other factors as the Committee in its sole discretion
may deem relevant. Subject to the express provisions of the Plan, the Committee
shall also have authority to interpret the Plan; to prescribe, amend and rescind
rules and regulations relating thereto; to determine the terms and provisions of
the respective Option Agreements, which shall be substantially in the forms
attached hereto as Exhibit A and Exhibit B; to amend the provisions of
outstanding Options to provide for accelerated exercisability or the extension
of the expiration date of such Options; and to make all other determinations
necessary or advisable for the administration of the Plan, all of which
determinations shall be conclusive and not subject to review.

          (c) The Board of Directors may administer the Plan, in lieu of and
with the same powers as the Committee, with respect to any Options granted or to
be granted under the Plan, provided that such administration is consistent with
the provisions of Section 162(m) of the Code.

     4.   Eligibility for Receipt of Options.

          (a) Incentive Options. Incentive Options may be granted only to
employees (including officers) of the Company and/or any of its subsidiaries. A
director of the Company or any subsidiary who is not an employee of the Company
or of one of its subsidiaries is not eligible to receive Incentive Options under
the Plan. Further, Incentive Options may not be granted to any person who, at
the time the Incentive Option is granted, owns (or is considered as owning
within the meaning of Section 425(d) of the Code) stock possessing more than 10%
of the total combined voting power of all classes of stock of the Company or any
subsidiary (10% Owner), unless at the time the Incentive Option is granted to
the 10% Owner, the option price is at least 110% of the fair market value of the
Common Stock subject thereto and such Incentive Option by its terms is not
exercisable subsequent to five years from the date of grant. The aggregate fair
market value (determined as of the time an Incentive Option is granted) of the
shares of the Company's Common Stock initially purchasable upon exercise of an
Incentive Option during any calendar year may not exceed $100,000.

          (b) Non-Incentive Options. Non-Incentive Options may be granted to any
employees (including employees who have been granted Incentive Options),
directors, consultants, agents, independent contractors and other persons whom
the Board of Directors (or Committee) determines will contribute to the
Company's success.

          (c) The maximum number of shares that may be subject to options under
this Plan granted during any calendar year to any executive officer of the
Company is 200,000 shares.

          (d) In the event an outstanding Incentive Option or a portion thereof
no longer qualifies as an incentive stock option under Section 422A of the Code,
such Option or portion thereof, as applicable, thereafter shall be deemed a Non-
Incentive Option under the Plan.

     5.   Option Price.

          The purchase price of the shares of Common Stock under each Option
shall be determined by the Committee, which determination shall be conclusive
and not subject to review, but in no event shall the purchase price be less than
100% of the fair market value of the Common Stock on the date of grant in the
case of Incentive Options (110% of fair market value in the case of Incentive
Options granted to a 10% Owner) and 50% of the fair market value of the Common
Stock on the date of the grant in the case of Non-Incentive Options.

          For purposes of the Plan, unless the Committee determines otherwise,
the fair market value" of a share of Common Stock as of a certain date shall be
the closing sale price of the Common Stock on The Nasdaq Stock Market or, if the
Common
<PAGE>

Stock is not then traded on The Nasdaq Stock Market, such national securities
exchange on which the Common Stock is then traded, on the trading date
immediately preceding the date the fair market value is being determined. The
Committee may make such other determination of fair market value, based on other
factors, as it shall deem appropriate.

          For purposes of the Plan, the date of grant of an Option shall be the
date on which the Committee shall by resolution duly authorize such Option.

     6.   Term of Options.

          The term of each Option shall be such number of years as the Committee
shall determine, subject to earlier termination as herein provided, but in no
event more than ten years from the date the Option is granted.

     7.   Exercise of Options.

          (l) Each Option shall be exercisable to the extent determined by the
Committee, but in no event shall an Option be exercisable until at least six
months from the date of grant, except as otherwise provided in Paragraph 13
herein.

          (m) An Option may not be exercised for fractional shares of the
Company's Common Stock.

          (n) Except as provided in paragraphs 9, 10 and 11 hereof, and unless
determined otherwise by the Committee with respect to Non-Incentive Options
granted to non-employees, no Option shall be exercisable unless the holder
thereof shall have been an employee, director, consultant, agent, independent
contractor or other person employed by or engaged in performing services for the
Company and/or a subsidiary continuously from the date of grant to the date of
exercise.

          (o) The exercise of an Option shall be contingent upon receipt from
the holder thereof of a written representation that at the time of such exercise
it is the optionee's then present intention to acquire the Option shares for
investment and not with a view to the distribution or resale thereof (unless a
Registration Statement covering the shares purchasable upon exercise of the
Options shall have been declared effective by the Securities and Exchange
Commission) and upon receipt by the Company of cash, or a check to its order,
for the full purchase price of such shares. The Committee may, in its
discretion, include a "cashless exercise" provision in the applicable Option
Agreement, in which event the optionee will be permitted (i) to deliver
previously owned shares of Common Stock with a fair market value equal to the
exercise price in payment of the full purchase price of such shares, or (ii) to
request that the Company withhold shares of Common Stock issuable upon exercise
of such Option with a fair market value equal to the exercise price of the
shares being purchased under the Option (thereby reducing the number of shares
issuable upon exercise of the Option).

          (p) The holder of an Option shall have none of the rights of a
stockholder with respect to the shares purchasable upon exercise of the Option
until a certificate for such shares shall have been issued to the holder upon
due exercise of the Option.

          (q) The proceeds received by the Company upon exercise of an Option
shall be added to the Company's working capital and be available for general
corporate purposes.

     8.   Transferability of Options.

          No Option granted pursuant to the Plan shall be transferable otherwise
than by will or the laws of descent or distribution and an Option may be
exercised during the lifetime of the holder only by such holder, provided,
however, that the Committee may provide for transferability of a Non-Incentive
Option to an optionee's family members or family trusts.

     9.   Termination of Employment or Engagement.

          (a) Except as provided in paragraph (b) below, in the event the
<PAGE>

employment of the holder of an Option shall be terminated by the Company or a
subsidiary for any reason other than by reason of death or disability, or the
engagement of a non-employee holder of a Non-Incentive Option shall be
terminated by the Company or a subsidiary for any reason, such holder may,
within three months from the date of such termination, exercise such Option to
the extent such Option was exercisable by such holder at the date of such
termination. Notwithstanding the foregoing, no Option may be exercised
subsequent to the date of its expiration. Absence on leave approved by the
employer corporation shall not be considered an interruption of employment for
any purpose under the Plan. In addition, at the discretion of the Committee, the
exercisability of an outstanding Non-Incentive Option may be extended to a date
determined by the Committee but not beyond ten years from the date of grant.

          (b) The Committee may, in its discretion, at the time of grant or by
amending the applicable outstanding Non-Incentive Option, delete the foregoing
termination provision with respect to a Non-Incentive Option granted to a non-
employee of the Company or its subsidiaries.

          (c) Nothing in the Plan or in any Option Agreement granted hereunder
shall confer upon any Optionholder any right to continue in the employ of the
Company or any subsidiary or obligate the Company or any subsidiary to continue
the engagement of any Optionholder or interfere in any way with the right of the
Company or any such subsidiary to terminate such Optionholder's employment or
engagement at any time.

     10.  Disability of Holder of Option.

          If the employment of the holder of an Option shall be terminated by
reason of such holder's disability, such holder may, within twelve months from
the date of such termination, exercise such option to the extent such Option was
exercisable by such holder at the date of such termination. Notwithstanding the
foregoing, no Option may be exercised subsequent to the date of its expiration.

     11.  Death of Holder of Option.

          If the holder of any Option shall die while in the employ of, or while
performing services for, the Company or one or more of its subsidiaries (or
within six months following termination of employment due to disability), the
Option theretofore granted to such person may be exercised, but only to the
extent such Option was exercisable by the holder at the date of death (or, with
respect to employees, the date of termination of employment due to disability)
by the legatee or legatees of such person under such person's Last Will, or by
such person's personal representative or distributees, within twelve months from
the date of death but in no event subsequent to the expiration date of the
Option.

     12.  Adjustments Upon Changes in Capitalization.

          If at any time after the date of grant of an Option, the Company shall
by stock dividend, split-up, combination, reclassification or exchange, or
through merger or consolidation or otherwise, change its shares of Common Stock
into a different number or kind or class of shares or other securities or
property, then the number of shares covered by such Option and the price per
share thereof shall be proportionately adjusted for any such change by the
Committee whose determination thereon shall be conclusive.

     13.  Acceleration of Exercisability Upon Change in Control.

          Upon the occurrence of a "change in control" of the Company (as
defined below), all outstanding Options shall become immediately fully
exercisable. For purposes of the Plan, a "change in control" of the Company
shall mean (i) the acquisition at any time by a "person" or "group" (as such
terms are used Sections 13(d) and 14(d)(2) of the Exchange Act of beneficial
ownership (as defined in Rule 13d-3 under the Exchange Act), directly or
indirectly, of securities representing 50% or more of the combined voting power
in the election of directors of the then outstanding securities of the Company
or any successor or the Company; (ii) the termination of service of directors,
for any reason other than death, disability or retirement from the Board of
Directors, during any period of two consecutive years or less, of individuals
who at the beginning of such period constituted a majority of the
<PAGE>

Board of Directors, unless the election of or nomination for election of each
new director during such period was approved by a vote of at least two-thirds of
the directors still in office who were directors at the beginning of the period;
(iii) approval by the stockholders of the Company of any merger, consolidation,
or statutory share exchange as a result of which the Common Stock shall be
changed, converted or exchanged (other than a merger, consolidation or share
exchange with a wholly-owned Subsidiary) or liquidation of the Company or any
sale or disposition of 80% or more of the assets or earning power or the
Company; or (iv) approval by the stockholders of the Company of any merger,
consolidation, or statutory share exchange to which the Company is a party as a
result of which the persons who were stockholders immediately prior to the
effective date of the merger, consolidation or share exchange shall have
beneficial ownership of less than 50% of the combined voting power in the
election of directors of the surviving corporation; provided, however, that no
change in control shall be deemed to have occurred if, prior to such time as a
change in control would otherwise be deemed to have occurred, the Company's
Board of Directors deems otherwise.

     14.  Vesting of Rights Under Options.

          Neither anything contained in the Plan nor in any resolution adopted
or to be adopted by the Committee, the Board of Directors or the stockholders of
the Company shall constitute the vesting of any rights under any Option. The
vesting of such rights shall take place only when a written Option Agreement,
substantially in the form of the Incentive Stock Option Agreement attached
hereto as Exhibit A or the Non-Incentive Stock Option Agreement attached hereto
as Exhibit B, shall be duly executed and delivered by and on behalf of the
Company and the person to whom the Option shall be granted.

     15.  Withholding Taxes.

          Whenever under the Plan shares are to be issued in satisfaction of the
exercise of Options granted thereunder, the Company shall have the right to
require the recipient to remit to the Company an amount sufficient to satisfy
federal, state and local withholding tax requirements prior to the delivery of
any certificate or certificates for such shares.

     16.  Termination and Amendment.

          The Plan, which was adopted by the Board of Directors on February 6,
1997 and is subject to stockholder approval, shall terminate on February 6, 2007
and no Option shall be granted under the Plan after such date. The Board of
Directors may at any time prior to such date terminate the Plan or make such
modifications or amendments thereto as it shall deem advisable, provided,
however, that shareholder approval shall be required:

     (i)    to increase the number of shares reserved for issuance under the
            Plan;

     (ii)   materially increase the benefits accruing to participants under the
            Plan;

     (iii)  materially modify the requirements of eligibility for participation
            in the Plan; or

     (iv)   if otherwise required to comply with the incentive stock option
            provisions of Section 162(m) of the Code or the listed company
            requirements of The Nasdaq Stock Market or of a national securities
            exchange on which the Common Stock is then traded,

and, provided, further, that no modification or amendment shall adversely affect
the rights of a holder of an Option previously granted under the Plan without
such holder's written consent.

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