<PAGE>
 
                                                                     Exhibit 2.5


                             ACQUISITION AGREEMENT
                             ---------------------

        ACQUISITION AGREEMENT ("Agreement"), made this 18th day of February,
     1999, by and among BAXTER HEALTHCARE CORPORATION, a Delaware corporation
     with offices at 1627 Lake Cook Road, Deerfield, Illinois 60015 ("Baxter"),
     VIMRx PHARMACEUTICALS INC., a Delaware corporation with offices at 2751
     Centerville Road, Suite 210, Wilmington, Delaware 19808 ("VIMRx") and
     NEXELL THERAPEUTICS INC. (f/k/a BIT ACQUISITION CORP.), a Delaware
     corporation with offices at 9 Parker, Irvine, California 92518 ("Nexell").

        WHEREAS, pursuant to an Asset Purchase Agreement, dated as of October
     10, 1997, by and among Baxter, VIMRx and Nexell (the "Asset Purchase
     Agreement"), Baxter, VIMRx and Nexell agreed to enter certain transactions
     whereby, among other things, certain assets from the Immunotherapy Division
     of Baxter's Biotech Business Group were acquired by Nexell, a then wholly-
     owned subsidiary of VIMRx, in exchange for Baxter's acquisition of certain
     securities of VIMRx and Nexell (the "Original Transactions"); and

        WHEREAS, the Original Transactions were consummated as of December 17,
     1997; and

        WHEREAS, Baxter now desires to have VIMRx acquire, and VIMRx now desires
     to acquire, Baxter's entire interest in Nexell, in exchange for Baxter's
     acquisition of additional VIMRx Common Stock (as hereinafter defined) and
     certain other securities of VIMRx; and

        WHEREAS, upon VIMRx's acquisition of Baxter's interest in Nexell in
     accordance with the terms and conditions hereof, Nexell would become a
     wholly-owned subsidiary of VIMRx; and

        WHEREAS, the parties hereto wish to set forth their agreement with
     respect to the purchase and the sale of such securities; and

        NOW, THEREFORE, in consideration of the mutual covenants and promises
     herein contained, the parties hereto agree as follows:

        1. Definitions and Interpretation
           ------------------------------

        1.1 Definitions. Capitalized terms used herein shall have the following
            -----------
    meanings:

        "Acquired VIMRx Securities" shall mean the VIMRx Common Stock, VIMRx
     Preferred Stock (if any),  VIMRx Warrant and VIMRx Convertible Debentures
     to be acquired by Baxter pursuant to Section 2.2 hereof.
<PAGE>
 
        "Affiliate" shall mean, with respect to any party hereto, any entity (i)
     which directly, or indirectly through one or more intermediaries, Controls,
     is Controlled by, or is under common Control with, the party hereto or (ii)
     fifty percent (50%) or more of the voting capital stock (or in the case of
     an entity which is not a corporation, fifty percent (50%) or more of the
     equity interest) of which is beneficially owned or held by a party hereto
     or any of such party's Subsidiaries.

        "Agreement" shall have the meaning assigned thereto in the Preamble to
     this Agreement.

        "Asset Purchase Agreement" shall have the meaning assigned thereto in
     the Preamble to this Agreement.

        "Authority" shall mean any federal, state, municipal, foreign or other
     government or governmental department, commission, board, bureau, agency or
     instrumentality.

        "Baxter" shall have the meaning assigned thereto in the Preamble to this
     Agreement.

        "Baxter Shares" shall have the meaning assigned thereto in Section
     2.2(B) hereof.

        "Closing Date" shall have the meaning assigned thereto in Section 2.5
     hereof.

        "Closing" shall have the meaning assigned thereto in Section 2.5 hereof.

        "Control" shall mean the possession, directly or indirectly, of the
     power to direct or cause the direction of the management and policies of an
     entity (other than a natural person), whether through the ownership of
     voting capital stock, by contract or otherwise.

        "Conversion VIMRx Securities" shall mean any VIMRx Common Stock issuable
     upon conversion or exercise of the Acquired VIMRx Securities other than the
     VIMRx Common Stock to be acquired by Baxter pursuant to Section 2.2(A)
     hereof.

        "Encumbrance" shall mean collectively all liens, charges, security
     interests, encumbrances or claims of every kind or nature whatsoever,
     whether legal or equitable.

        "Exchange Act" shall mean the Securities Exchange Act of 1934, as
     amended, and the rules and regulations promulgated thereunder.

        "Nasdaq" shall mean the Nasdaq Stock Market.

        "Nexell" shall have the meaning assigned thereto in the Preamble to this
     Agreement.

                                       2
<PAGE>
 
        "Nexell Common Stock" shall mean the common stock of Nexell, $.001 par
     value per share.

        "Nexell Convertible Debentures" shall collectively mean (i) the Series 1
     6.5% Convertible Subordinated Debenture due November 30, 2004 in the
     principal amount of $10,000,000.00 and (ii) the Series 3 6.5% Convertible
     Subordinated Debenture due November 30, 2004 in the principal amount of
     $20,000,000.00, issued by Nexell to Baxter pursuant to the Asset Purchase
     Agreement.

        "Nexell Securities" shall mean the Nexell Common Stock, the Nexell
     Warrant and the Nexell Convertible Debentures acquired by Baxter pursuant
     to the Asset Purchase Agreement.

        "Nexell Warrant" shall mean the Common Stock Purchase Warrant for 6.383
     shares of Nexell Common Stock at a per share price of $939,996.86, issued
     by Nexell to Baxter pursuant to the Asset Purchase Agreement.

        "Original Transactions" shall have the meaning assigned thereto in the
     Preamble to this Agreement.

        "Original Transaction Agreements" shall mean the following documents
     executed by Baxter, VIMRx and Nexell, as the case may be, in connection
     with the Original Transactions pursuant to the Asset Purchase Agreement
     (except for the Registration Rights Agreement and the Stockholders'
     Agreement, each such document shall have the meaning ascribed thereto in
     the Asset Purchase Agreement):


        (i)    the Distribution Agreement,
        (ii)   the Non-Competition and Confidentiality Agreement,
        (iii)  the Assignment of Parker Lease,
        (iv)   the Registration Rights Agreement,
        (v)    the First BD Sublicense,
        (vi)   the Second BD Sublicense,
        (vii)  the Dorken Sublicense,
        (viii) the Chiron Sublicense,
        (ix)   the Stockholders' Agreement,
        (x)    the Services Agreement,
        (xi)   the Antibody Manufacturing and Storage Agreement,
        (xii)  the Royalty Assignment and Agreement,
        (xiii) the Hardware and Disposables Manufacturing Agreement,
        (xiv)  the Hardware and Disposables Supply Agreement,
        (xv)   the Voting Agreement, and
        (xvi)  and each other agreement, document, certificate and instrument
     executed in connection with the Original Transactions.

        "Person" shall mean any individual, corporation, partnership, limited
     partnership, limited liability partnership, joint venture, limited
     liability company, 

                                       3
<PAGE>
 
     association, joint-stock company, trust, unincorporated organization,
     Authority or other entity.

        "Proxy Statement" shall mean a proxy statement on Schedule 14A prepared
     by VIMRx in connection with a meeting of VIMRx stockholders and which,
     among other items of business, requests VIMRx stockholder consideration and
     approval of this Agreement and all transactions and actions contemplated
     herein requiring VIMRx stockholder approval (including (i) VIMRx's purchase
     from Baxter of the Nexell Securities and VIMRx's sale to Baxter of the
     Acquired VIMRx Securities, (ii) the change in the conversion price of the
     VIMRx Preferred Stock to $2.75 per share and (iii) the change of VIMRx's
     name to "Nexell Therapeutics Inc."). The Proxy Statement may address other
     matters not relating to this Agreement as VIMRx may determine.

        "Registration Rights Agreement" shall mean that certain Registration
     Rights Agreement, dated as of December 17, 1997, by and between VIMRx and
     Baxter.

        "SEC" shall mean the United States Securities and Exchange Commission.

        "SEC Reports" shall mean all forms, reports and documents required to be
     filed with the SEC by VIMRx pursuant to the Securities Act or the Exchange
     Act since January 1, 1997.

        "Securities Act" shall mean the Securities Act of 1933, as amended, and
     the rules and regulations promulgated thereunder.

        "Stockholders' Agreement" shall mean that certain Stockholders'
     Agreement, dated as of December 17, 1997, between Baxter, VIMRx and Nexell.

        "Transaction Documents" shall mean all documents, agreements,
     certificates and instruments other than this Agreement to be executed
     and/or delivered by Baxter, VIMRx and Nexell, as the case may be, in
     connection with the transactions contemplated hereunder.

        "Transactional Taxes" shall mean all transfer, conveyance or other such
     taxes, duties, excises or governmental charges imposed by any taxing
     jurisdiction.

        "VIMRx" shall have the meaning assigned thereto in the Preamble to this
     Agreement.

        "VIMRx Convertible Debentures" shall mean collectively the 6.5%
     convertible subordinated debentures to be issued by VIMRx to Baxter,
     substantially in the forms annexed hereto as Exhibits A and B, in an
                                                  ----------------       
     aggregate principal amount equal to (i) $30,000,000.00 plus (ii) all
                                                            ----         
     accrued but unpaid interest (if any) on the Nexell Convertible Debentures
     as of the Closing Date, which debentures shall be convertible into
     additional shares of VIMRx Common Stock commencing November 30, 2002, at a
     conversion price equal to ninety-five percent (95%) of the average closing
     sale 

                                       4
<PAGE>
 
     prices of VIMRx Common Stock on the thirty (30) trading days preceding, but
     not including, the date of such conversion, as reported by Nasdaq.

        "VIMRx Common Stock" shall mean the common stock of VIMRx, $.001 par
     value per share.

        "VIMRx Preferred Stock" shall mean Series A Convertible Preferred Stock
     of VIMRx, par value $.001 per share.

        "VIMRx Warrant" shall mean a common stock purchase warrant,
     substantially in the form annexed hereto as Exhibit C, for the purchase by
                                                 ---------                     
     Baxter of up to and including 5,200,000 additional shares of VIMRx Common
     Stock at a per share price of $1.15.

        1.2  Interpretation.
             -------------- 
             (A) Whenever in this Agreement the phrase "in the ordinary course
     of business" is used, it shall be construed as meaning "in the ordinary
     course of business and substantially consistent with prior practice."

             (B) Whenever in this Agreement the term "including" is used, it
     shall be construed as meaning "including but not limited to."

             (C) Whenever in this Agreement the term "all" is used, it shall be
     construed as meaning "any and all."

             (D) Whenever in this Agreement the term "every" is used, it shall
     be construed as meaning "every and all."

             (E) Whenever in this Agreement the term "agreement" is used, it
     shall be deemed to refer to commitments, leases, licenses, contracts and
     other agreements.

        2.   Purchase and Sale of the Securities; Closing
             --------------------------------------------

        2.1 Purchase and Sale. In reliance on the representations and warranties
            -----------------    
     contained herein and subject to all of the terms and conditions hereof,
     Baxter hereby agrees to sell, assign, transfer and deliver (or cause to be
     sold, assigned, transferred and delivered) to VIMRx and VIMRx agrees to
     purchase from Baxter, on the Closing Date, all of Baxter's right, title and
     interest in and to the Nexell Securities.

        2.2 Purchase Consideration. In reliance on the representations and
            ----------------------    
     warranties contained herein and subject to all of the terms and conditions
     hereof, and in consideration of the sale, assignment, transfer and delivery
     of the Nexell Securities, VIMRx hereby agrees to issue to Baxter the
     following consideration:

             (A)  three million (3,000,000) shares of VIMRx Common Stock;

                                       5
<PAGE>
 
             (B) in the event that the total amount of shares of VIMRx Common
     Stock held by Baxter immediately prior to the Closing (the total amount of
     such shares shall be collectively hereinafter referred to as the "Baxter
     Shares") plus the three million shares of VIMRx Common Stock to be issued
     to Baxter pursuant to Section 2.2(A) hereof will be equivalent to twenty
     percent (20%) or more of the aggregate number of shares of VIMRx Common
     Stock issued and outstanding immediately following the Closing, then:

                    (i) the number of shares of VIMRx Common Stock to be issued
     to Baxter pursuant to Section 2.2(A) above will be reduced so that the
     total amount of shares of VIMRx Common Stock issued to Baxter pursuant to
     Section 2.2(A) above, combined with the Baxter Shares, will be equivalent
     to less than twenty percent (20%) (but equal to the highest percentage
     possible under twenty percent (20%)) of the aggregate number of shares of
     VIMRx Common Stock issued and outstanding by VIMRx immediately following
     the Closing; and

                    (ii) VIMRx shall issue to Baxter such number of shares of
     VIMRx Preferred Stock so that the number of shares of VIMRx Common Stock
     issuable upon conversion thereof shall be equal to the number of shares of
     VIMRx Common Stock required to be reduced at the Closing pursuant to this
     Section 2.2(B);


             (C)  the VIMRx Warrant; and

             (D)  the VIMRx Convertible Debentures.

        2.3 Nexell Securities. At the Closing provided for in Section 2.5
            -----------------    
     hereof, Baxter shall deliver to VIMRx, as provided for in Section 2.1
     hereof, the certificates representing the Nexell Common Stock together with
     the Nexell Warrant and the Nexell Convertible Debentures, all duly endorsed
     to VIMRx or with transfer powers attached thereto, against delivery of the
     items designated to be delivered by VIMRx and/or Nexell at Closing pursuant
     to Section 8.2 hereof.

        2.4 Acquired VIMRx Securities. At the Closing provided for in Section
            -------------------------    
     2.5 hereof, VIMRx shall deliver to Baxter certificates representing VIMRx
     Common Stock and VIMRx Preferred Stock (if any) as provided for in Section
     2.2 hereof, together with the VIMRx Warrant and the VIMRx Convertible
     Debentures, against delivery of the items designated to be delivered by
     Baxter at Closing pursuant to Section 8.1 hereof.

        2.5 Closing. The closing of the purchase and sale of the securities as
            -------
     set forth in this Section 2 (the "Closing") shall be held at the offices of
     counsel to Baxter, Seyfarth, Shaw, Fairweather & Geraldson, 55 East Monroe
     Street, Chicago, Illinois, within thirty (30) days after the last of the
     conditions set forth in Section 7 hereof has been satisfied or waived in
     accordance with the terms of this Agreement, or on such other date, and at
     such other time and place, as Baxter and VIMRx shall mutually agree in
     writing (the day of occurrence of the Closing being referred to hereinafter
     as the "Closing Date").

                                       6
<PAGE>
 
        3. Representations and Warranties of Baxter
           ----------------------------------------

        Baxter represents and warrants to VIMRx and Nexell, as of the Closing
     Date, as follows:

        3.1 Good Standing. Baxter is a corporation organized, validly existing
            -------------    
     and in good standing under the laws of the State of Delaware, with all
     necessary corporate power and authority to own, lease and operate its
     properties and to carry on its business as the same is now being conducted.

        3.2  Authority.  Baxter possesses full right, corporate power and legal
             ---------   
     authority to execute and deliver this Agreement and the Transaction
     Documents to which Baxter is a party and to perform each of the agreements
     and make each of the representations and warranties on its part to be
     performed and made hereunder and thereunder. The execution and delivery of
     this Agreement and the Transaction Documents to which Baxter is a party and
     the consummation by it of the transactions contemplated hereby and thereby
     have been duly and validly authorized by all necessary corporate action on
     the part of Baxter. This Agreement has been duly and validly executed by
     Baxter and constitutes, and the Transaction Documents (upon and subject to
     their execution and delivery by all parties thereto) shall constitute, the
     legal, valid and binding obligation of Baxter enforceable against it in
     accordance with their respective terms subject to the qualification that
     the enforceability thereof may be limited by bankruptcy, insolvency,
     fraudulent conveyance, reorganization, moratorium and similar laws, now or
     hereafter in effect, affecting creditors' rights and except that the
     availability of equitable remedies, including specific performance, is
     subject to the discretion of the court before which any proceeding for the
     enforcement thereof may be brought.

        3.3 Consents and Approvals. No other action or consent, whether
            ----------------------    
     corporate or otherwise, including action or consent by any Authority, is
     necessary in connection with the execution, delivery, validity or
     enforceability of this Agreement or the Transaction Documents with respect
     to Baxter or the consummation by it of the transactions contemplated hereby
     and thereby.

        3.4 Ownership of Nexell Securities. Baxter is the sole and exclusive
            ------------------------------    
     beneficial and legal owner of all of the Nexell Securities, and Baxter has
     good title to, and the absolute right to sell and transfer, all Nexell
     Securities to VIMRx, free and clear of all Encumbrances.

        3.5 Investment. Baxter is acquiring the Acquired VIMRx Securities and
            ----------    
     will acquire any Conversion VIMRx Securities for investment for Baxter's
     own account and not with the view to, or for resale in connection with, the
     distribution thereof. Subject to Baxter's rights under the Registration
     Rights Agreement, Baxter understands that the Acquired VIMRx Securities
     (and any Conversion VIMRx Securities) have not been and will not be
     registered under the Securities Act by reason of a specific exemption from
     the registration provisions of the Securities Act which depends upon, among
     other things, the bona fide nature of the investment 
                       --------- 

                                       7
<PAGE>
 
     intent as expressed herein. Baxter further represents that it does not have
     any contract, undertaking, agreement or arrangement with any person to
     sell, transfer or grant participation to any third person with respect to
     any of the Acquired VIMRx Securities (or any Conversion VIMRx Securities).
     Subject to Baxter's rights under the Registration Rights Agreement, Baxter
     understands and acknowledges that the offering and issuance of the Acquired
     VIMRx Securities pursuant to this Agreement, and any issuance of Conversion
     VIMRx Securities, will not be registered under the Securities Act on the
     ground that the sale provided for in this Agreement and the issuance of
     securities hereunder is exempt from the registration requirements of the
     Securities Act based on, among other things, the bona fide nature of the
                                                      ---------          
     investment intent as expressed herein.

        3.6 Rule 144. Subject to the terms of the Registration Rights Agreement,
            --------    
     Baxter acknowledges that the Acquired VIMRx Securities (and any Conversion
     VIMRx Securities) must be held indefinitely unless subsequently registered
     under the Securities Act or an exemption from such registration is
     available. Baxter is aware of the provisions of Rule 144 promulgated under
     the Securities Act which permit limited resale of certain securities
     purchased in a private placement subject to the satisfaction of certain
     conditions. In connection therewith, Baxter acknowledges that VIMRx will
     make a notation on their stock books regarding the restrictions on
     transfers set forth in this Section 3.6. Baxter acknowledges that all
     shares representing Acquired VIMRx Securities (and any Conversion VIMRx
     Securities) will bear appropriate restrictive legends reflecting the
     transfer restrictions reflected in this Section 3.6.

        3.7 No Public Market. Baxter understands that no public market now
            ----------------    
     exists or is expected to ever exist for the VIMRx Preferred Stock, the
     VIMRx Warrant or the VIMRx Convertible Debentures.

        3.8 Access to Data. For purposes of satisfying the applicable
            --------------    
     requirements for the exemptions from registration relating to the issuance
     of the Acquired VIMRx Securities, Baxter acknowledges that it has received
     and reviewed such information about VIMRx as it deems necessary and has had
     an opportunity to discuss VIMRx's business, management and financial
     affairs with its management and to review its facilities.

        4. Representations and Warranties of VIMRx
           ---------------------------------------

        VIMRx represents and warrants to Baxter and Nexell, as of the Closing
     Date, as follows:

        4.1 Good Standing. VIMRx is a corporation organized, validly existing
            -------------    
     and in good standing under the laws of the State of Delaware, with all
     necessary corporate power and authority to own, lease and operate its
     properties and to carry on its business as the same is now being conducted.
     True, accurate and complete copies of the Certificate of Incorporation and
     By-Laws of VIMRx have been provided to Baxter.

                                       8
<PAGE>
 
        4.2 Authority. VIMRx possesses full right, corporate power and legal
            ---------    
     authority to execute and deliver this Agreement and the Transaction
     Documents to which VIMRx is a party and to perform each of the agreements
     and make each of the representations and warranties on its part to be
     performed and made hereunder and thereunder. The execution and delivery of
     this Agreement and the Transaction Documents to which VIMRx is a party and
     the consummation by it of the transactions contemplated hereby and thereby
     have been duly and validly authorized by all necessary corporate action on
     the part of VIMRx. This Agreement has been duly and validly executed by
     VIMRx and constitutes, and the Transaction Documents (upon and subject to
     their execution and delivery by all parties thereto) shall constitute, the
     legal, valid and binding obligation of VIMRx enforceable against it in
     accordance with their respective terms subject to the qualification that
     the enforceability thereof may be limited by bankruptcy, insolvency,
     fraudulent conveyance, reorganization, moratorium and similar laws, now or
     hereafter in effect, affecting creditors' rights and except that the
     availability of equitable remedies, including specific performance, is
     subject to the discretion of the court before which any proceeding for the
     enforcement thereof may be brought.

        4.3 Consents and Approvals. No other action or consent, whether
            ----------------------    
     corporate or otherwise, including action or consent by any Authority, is
     necessary in connection with the execution, delivery, validity or
     enforceability of this Agreement or the Transaction Documents with respect
     to VIMRx or the consummation by it of the transactions contemplated hereby
     and thereby.

        4.4 Valid Issuance of VIMRx Warrant and VIMRx Common Stock. The VIMRx
            ------------------------------------------------------    
     Warrant, when issued and delivered in accordance with the terms of this
     Agreement for the consideration expressed herein, will be duly and validly
     authorized and issued, fully paid and nonassessable, and will be free of
     restrictions on transfer other than restrictions on transfer under this
     Agreement and the Registration Rights Agreement, and under applicable state
     and federal securities laws. The shares of VIMRx Common Stock that are
     being acquired by Baxter hereunder, when issued and delivered in accordance
     with the terms of this Agreement for the consideration expressed herein,
     will be duly and validly authorized and issued, fully paid and
     nonassessable, and will be free of restrictions on transfer other than
     restrictions on transfer under this Agreement and the Registration Rights
     Agreement, and under applicable state and federal securities laws. The
     VIMRx Common Stock issuable upon exercise of the VIMRx Warrant has been
     duly authorized and validly reserved for issuance and, upon issuance upon
     such exercise in accordance with the terms of the VIMRx Warrant, will be
     duly and validly authorized and issued, fully paid, and nonassessable, and
     will be free of restrictions on transfer other than restrictions on
     transfer under this Agreement and the Registration Rights Agreement, and
     under applicable state and federal securities laws.

        4.5 Valid Issuance of VIMRx Preferred Stock. The shares of VIMRx
            ---------------------------------------    
     Preferred Stock that may be acquired by Baxter hereunder, when issued and
     delivered in accordance with the terms of this Agreement for the
     consideration 

                                       9
<PAGE>
 
     expressed herein, will be duly and validly authorized and issued, fully
     paid and nonassessable. The VIMRx Common Stock issuable upon conversion of
     the VIMRx Preferred Stock has been duly authorized and validly reserved for
     issuance and, upon issuance upon such conversion in accordance with the
     terms of the Certificate of Incorporation of VIMRx, will be duly and
     validly authorized and issued, fully paid, and nonassessable, and will be
     free of restrictions on transfer other than restrictions on transfer under
     this Agreement and the Registration Rights Agreement, and under applicable
     state and federal securities laws.

        4.6 Valid Issuance of VIMRx Convertible Debentures. The VIMRx
            ----------------------------------------------    
     Convertible Debentures, when issued and delivered in accordance with the
     terms of this Agreement for the consideration expressed herein, shall be
     legal, valid and binding obligations of VIMRx enforceable against it in
     accordance with their respective terms, subject to the qualification that
     the enforceability thereof may be limited by bankruptcy, insolvency,
     fraudulent conveyance, reorganization, moratorium and similar laws, now or
     hereafter in effect, affecting creditors' rights and except that the
     availability of equitable remedies, including specific performance, is
     subject to the discretion of the court before which any proceeding for the
     enforcement thereof may be brought. The VIMRx Common Stock issuable upon
     conversion of the VIMRx Convertible Debentures has been duly authorized and
     validly reserved for issuance and, upon issuance upon such conversion in
     accordance with the terms of each such VIMRx Convertible Debenture, will be
     duly and validly authorized and issued, fully paid, and nonassessable, and
     will be free of restrictions on transfer other than restrictions on
     transfer under this Agreement and the Registration Rights Agreement, and
     under applicable state and federal securities laws. Notwithstanding the
     foregoing, as there is no "floor" or minimum conversion price of the VIMRx
     Convertible Debentures, it is mathematically possible that the VIMRx
     Convertible Debentures could convert into a number of shares of VIMRx
     Common Stock that is in excess of VIMRx's authorized capitalization
     thereof.

        4.7 SEC Reports. VIMRx has delivered or made available to Baxter true
            -----------    
     and complete copies of the SEC Reports. As of their respective dates, the
     SEC Reports complied in all material respects with the requirements of the
     Exchange Act or the Securities Act, as applicable, and the rules and
     regulations of the SEC promulgated thereunder, and the SEC Reports did not
     contain any untrue statement of a material fact or omit to state a material
     fact required to be stated therein or necessary in order to make the
     statements therein, in light of the circumstances under which they were
     made, not misleading. Since the date of the last of the SEC Reports filed
     with the SEC, VIMRx has not become aware of any fact which has not been
     disclosed herein which (i) would make the statements contained herein or in
     the SEC Reports filed with the SEC materially misleading; (ii) has had, or
     would reasonably be expected to have, a Material Adverse Effect (as that
     capitalized term is defined in the Asset Purchase Agreement) on VIMRx; or
     (iii) would reasonably be expected to materially and adversely affect the
     ability of VIMRx to perform its obligations under this Agreement.

                                       10
<PAGE>
 
        5. Representations and Warranties of Nexell
           ----------------------------------------

        Nexell represents and warrants to Baxter and VIMRx, as of the Closing
     Date, as follows:

        5.1 Good Standing. Nexell is a corporation organized, validly existing
            -------------    
     and in good standing under the laws of the State of Delaware, with all
     necessary corporate power and authority to own, lease and operate its
     properties and to carry on its business as the same is now being conducted.

        5.2 Authority. Nexell possesses full right, corporate power and legal
            ---------    
     authority to execute and deliver this Agreement and the Transaction
     Documents to which Nexell is a party and to perform each of the agreements
     and make each of the representations and warranties on its part to be
     performed and made hereunder and thereunder. The execution and delivery of
     this Agreement and the Transaction Documents to which Nexell is a party and
     the consummation by it of the transactions contemplated hereby and thereby
     have been duly and validly authorized by all necessary corporate action on
     the part of Nexell. This Agreement has been duly and validly executed by
     Nexell and constitutes, and the Transaction Documents (upon and subject to
     their execution and delivery by all parties thereto) shall constitute, the
     legal, valid and binding obligation of Nexell enforceable against it in
     accordance with their respective terms subject to the qualification that
     the enforceability thereof may be limited by bankruptcy, insolvency,
     fraudulent conveyance, reorganization, moratorium and similar laws, now or
     hereafter in effect, affecting creditors' rights and except that the
     availability of equitable remedies, including specific performance, is
     subject to the discretion of the court before which any proceeding for the
     enforcement thereof may be brought.

        5.3 Consents and Approvals. No other action or consent, whether
            ----------------------    
     corporate or otherwise, including action or consent by any Authority, is
     necessary in connection with the execution, delivery, validity or
     enforceability of this Agreement or the Transaction Documents with respect
     to Nexell or the consummation by it of the transactions contemplated hereby
     and thereby.

        6. Certain Covenants and Agreements
           --------------------------------

        6.1  Pre-Closing Covenants.
             --------------------- 

             (A) Covenants of Baxter. From the date hereof until the Closing
                 ------------------- 
    Date, Baxter covenants that it shall do the following:

                 (i) not sell, transfer or otherwise dispose of any of the
    Nexell Securities;

                 (ii) not mortgage, pledge or otherwise subject any of the
    Nexell Securities to any Encumbrance, except for Encumbrances arising by
    operation of law and not due to any action or inaction on the part of
    Baxter;

                                       11
<PAGE>
 
                 (iii) not take any action inconsistent with the consummation of
    this Agreement and the transactions contemplated hereunder;

                 (iv) cooperate with VIMRx in VIMRx's preparation of the Proxy
    Statement, including providing to VIMRx, at its request, all information,
    with respect to Baxter and its business, properties, personnel and
    operations, as may be required for inclusion in the Proxy Statement and, to
    the extent that any information previously provided to VIMRx pursuant to
    this paragraph is discovered to be false or misleading, provide to VIMRx,
    in writing, such additional or different information as may be required to
    correct such deficiency; and

                 (v) in the event and to the extent, that events or
    circumstances occur or arise, or Baxter becomes aware of events or
    circumstances, which render any of the representations and warranties set
    forth in Section 3 hereof inaccurate, and without limiting in any way
    VIMRx's or Nexell's rights under Section 7.2 hereof, promptly notify VIMRx
    and Nexell thereof.

        (B) Covenants of VIMRx. From the date hereof until the Closing Date,
    VIMRx covenants that it shall, and shall (except with respect to items (v)
    and (vi) below) cause Nexell to :

                 (i) preserve and maintain its corporate existence and good
     standing in the jurisdiction of its incorporation;

                 (ii) continue to operate, in all material respects, in the
     ordinary course of business;

                 (iii) not take any action inconsistent with the consummation of
     this Agreement and the transactions contemplated hereunder;

                 (iv) use its best efforts to maintain and preserve satisfactory
     relationships with suppliers, contractors, customers, creditors and others
     with which it has a business relationship;

                 (v) promptly prepare and file with the SEC the Proxy Statement,
     and prior to filing the Proxy Statement with the SEC, submit such material
     to Baxter and its counsel and provide Baxter and its counsel a reasonable
     opportunity to review and comment upon such materials;

                 (vi) duly and promptly call, give notice of, convene and hold a
     meeting of the VIMRx stockholders for the purpose of considering and taking
     action upon this Agreement and all transactions and actions contemplated
     herein requiring VIMRx stockholder approval, and, subject to the fiduciary
     duties of the VIMRx Board of Directors under applicable law, include in the
     Proxy Statement the recommendation of the VIMRx Board of Directors that the
     VIMRx stockholders vote in favor of this Agreement and all such
     transactions and actions;

                                       12
<PAGE>
 
                 (vii) in the event and to the extent, that events or
     circumstances occur or arise, or it becomes aware of events or
     circumstances, which render any of the representations and warranties set
     forth in Sections 4 or 5 hereof inaccurate, and without limiting in any way
     Baxter's rights under Section 7.1 hereof, promptly notify Baxter thereof;

                 (viii) assume all of Nexell's obligations under Nexell's 1998
     Non-Incentive Stock Option Plan;

                 (ix) cause Nexell to file with the Secretary of State for the
     State of Delaware a Certificate of Amendment of Certificate of
     Incorporation of Nexell whereby the corporate name of Nexell is changed to
     "Nexell of California, Inc."; and

                 (x) subject to the approval of VIMRx's stockholders, file with
     the Secretary of State for the State of Delaware a Certificate of Amendment
     of Certificate of Incorporation of VIMRx in substantially the form annexed
     hereto as Exhibit D, whereby, among other things, (x) the name of VIMRx is
               --------- 
     changed to "Nexell Therapeutics Inc." and (y) the Conversion Price
     of the VIMRx Preferred Stock is changed to $2.75 per share.


        6.2  Post-Closing Covenants by VIMRx and Nexell.
             ------------------------------------------   

             (A) Qualification to do Business in California. As soon as is
                 ------------------------------------------
     reasonably practicable following the Closing Date, (a) Nexell shall file an
     Amended Statement and Designation by Foreign Corporation (or similar
     document) with the Secretary of State of the State of California changing
     its corporate name to "Nexell of California, Inc." and (b) if required by
     California law, VIMRx (under the name "Nexell Therapeutics Inc.") shall
     file a Statement and Designation by Foreign Corporation (or similar
     document) with the Secretary of State of the State of California,
     evidencing its qualification to do business in California.

             (B) No Change of Control of Nexell. On and after the Closing Date,
                 ------------------------------
     VIMRx covenants and agrees that it shall not, and it shall cause Nexell not
     to, either directly or indirectly, without the prior written consent of
     Baxter so long as Baxter owns three percent (3%) or more of the issued and
     outstanding capital stock of VIMRx, (i) sell, transfer or otherwise dispose
     of all or substantially all of the operating assets of Nexell, (ii) issue,
     sell, transfer or otherwise dispose of any securities of Nexell, or (iii)
     permit a merger or consolidation involving Nexell where immediately
     following such merger or consolidation Nexell shall not be the surviving
     entity, VIMRx shall cease to own 100% of any securities of Nexell, and
     VIMRx shall cease to possess 100% of the voting interest in Nexell.

             (C) Notification to Nexell Employees. As soon as is reasonably
                 --------------------------------
     practicable following the Closing Date, VIMRx shall notify all holders of
     options to purchase shares of Nexell Common Stock under Nexell's 1998 Non-
     Incentive 

                                       13
<PAGE>
 
     Stock Option Plan of VIMRx's acquisition of all of the capital stock of
     Nexell and VIMRx's assumption of such Plan.

             (D) Authorized Shares of VIMRx Common Stock. On and after the
                 ---------------------------------------       
     Closing Date, VIMRx covenants and agrees that, in the event that any VIMRx
     Convertible Debenture would be convertible into a number of shares of VIMRx
     Common Stock which is in excess of the authorized amount of VIMRx Common
     Stock as then stated in VIMRx's certificate of incorporation, VIMRx shall
     use its best efforts, without demand by Baxter, to obtain VIMRx stockholder
     approval of any amendments to its certificate of incorporation required to
     increase its authorized shares of Common Stock to such amount as is
     necessary to issue Baxter authorized shares of VIMRx Common Stock upon such
     conversion.

             (E) No Redemption of Shares of VIMRx. On and after the Closing
                 --------------------------------       
     Date, VIMRx covenants and agrees that it shall not, either directly or
     indirectly, without the prior written consent of Baxter, purchase, redeem
     or otherwise acquire any outstanding shares of VIMRx Common Stock where,
     immediately following such purchase, redemption or acquisition, Baxter
     would own 20% or more of the issued and outstanding VIMRx Common Stock,
     unless immediately prior to such purchase, redemption or other acquisition,
     ------   
     Baxter already owned 20% or more of the issued and outstanding VIMRx Common
     Stock.

        7. Conditions to Obligations of Baxter, VIMRx and Nexell
           -----------------------------------------------------

        7.1  Baxter's Conditions. The obligations of Baxter to consummate the
             -------------------   
     transactions contemplated hereunder are conditioned upon the following, any
     or all of which may be waived by Baxter in its sole and absolute
     discretion:

             (A) All warranties and representations of VIMRx and Nexell
     contained in this Agreement that are qualified as to materiality shall be
     true and correct on and as of the Closing Date with the same force and
     effect as though such representations and warranties had been made on and
     as of the Closing Date, and all representations and warranties of VIMRx and
     Nexell which are not so qualified shall, in all material respects, be true
     and correct on and as of the Closing Date with the same force and effect as
     though such representations and warranties had been made on and as of the
     Closing Date.

             (B) VIMRx and Nexell shall, in all material respects, have
     performed and complied with all of the covenants and agreements (including
     the agreements to make the deliveries set forth in Section 8.2 hereof)
     required by or pursuant to this Agreement or any Transaction Document
     delivered pursuant to this Agreement, to be performed or complied with by
     them on or prior to the Closing Date.

             (C) There has not been, and no facts or circumstances exist as of
     the Closing Date that would be reasonably likely to cause, any material
     adverse 

                                       14
<PAGE>
 
     change in either VIMRx's or Nexell's financial condition, operating
     results or business prospects.

             (D) VIMRx shall have assumed all of Nexell's obligations under
     Nexell's 1998 Non-Incentive Stock Option Plan.

             (E) Nexell shall have filed with the Secretary of State for the
     State of Delaware a Certificate of Amendment of Certificate of
     Incorporation of Nexell whereby the corporate name of Nexell is changed to
     "Nexell of California, Inc."

             (F) VIMRx shall have filed with the Secretary of State for the
     State of Delaware, a Certificate of Amendment of Certificate of
     Incorporation of VIMRx in substantially the form annexed hereto as 
     Exhibit D, whereby, among other things, (x) the name of VIMRx is changed to
     ---------   
     "Nexell Therapeutics Inc." and (y) the Conversion Price of the VIMRx
     Preferred Stock is changed to $2.75 per share.

        7.2 VIMRx's and Nexell's Conditions. The obligations of VIMRx and Nexell
            -------------------------------    
     to consummate the transactions contemplated hereunder are conditioned upon
     the following, any or all of which may be waived by VIMRx in its sole and
     absolute discretion:

            (A) All representations and warranties of Baxter contained in this
     Agreement shall, in all material respects, be true and correct on and as of
     the Closing Date with the same force and effect as though such
     representations and warranties had been made on and as of the Closing Date.

            (B) Baxter shall, in all material respects, have performed and
     complied with all of the covenants and agreements (including the agreement
     to make the deliveries set forth in Section 8.1 hereof) required by or
     pursuant to this Agreement, or any Transaction Document delivered pursuant
     to this Agreement, to be performed or complied with by it on or prior to
     the Closing Date.

            (C) The Board of Directors of VIMRx shall have received a fairness
     opinion by Piper Jaffray Inc., in form and substance satisfactory to such
     Board, as to the fairness to VIMRx of the transactions contemplated herein.

        7.3 Mutual Conditions. The respective obligations of each party hereto
            -----------------    
     to consummate the transactions contemplated hereunder are conditioned upon
     the following:

            (A) This Agreement and the transactions and actions contemplated
     herein shall have been approved and adopted by the requisite vote of
     VIMRx's stockholders in accordance with applicable Delaware General
     Corporation Laws and the rules and regulations of Nasdaq.

            (B) No order of any court or Authority shall be in effect which
     restrains or prohibits the transactions contemplated hereby, and no suit,
     action or 

                                       15
<PAGE>
 
     proceeding by any Authority or other person shall be pending or threatened
     which seeks to restrain the consummation, or challenges the validity or
     legality, of the transactions contemplated by this Agreement.

            (C) All other consents, approvals or orders of any Authority, the
     granting of which is required for the lawful consummation of the
     transactions contemplated hereby, shall have been obtained; and all other
     waiting and notification periods specified under applicable law, the
     termination or expiration of which is necessary for such consummation,
     shall have been terminated or shall have expired.

                                       16
<PAGE>
 
        8. Deliveries of the Parties
           -------------------------

        8.1 Deliveries of Baxter. At the Closing, Baxter shall deliver to VIMRx
            --------------------
     the following:

            (A) the original Stock Certificate No. 3, representing the 19.5
     shares of Nexell Common Stock in the name of Baxter, duly endorsed to VIMRx
     or with stock powers attached thereto;

            (B) the Nexell Warrant duly endorsed to VIMRx or with transfer
     powers attached thereto;

            (C) the Nexell Convertible Debentures duly endorsed to VIMRx or with
     transfer powers attached thereto;

            (D) an executed copy of each of the Transaction Documents to which
     Baxter is a party;

            (E) all governmental or other approvals, consents, grants, and
     licenses, if any, required to be procured by Baxter in connection with the
     transactions contemplated hereby; and

            (F) a certificate of the Secretary or an Assistant Secretary of
     Baxter, certifying the incumbency, signature and authorization of Victor W.
     Schmitt, President, Venture Management, to execute, deliver and perform
     this Agreement and all Transaction Documents on behalf of Baxter.

        8.2 Deliveries of VIMRx. At the Closing, VIMRx shall deliver (or, as
            -------------------    
     applicable, cause Nexell to deliver) to Baxter the following:

            (A) stock certificate(s) evidencing the issuance to Baxter of the
     number of shares of VIMRx Common Stock in accordance with Sections 2.2 (A)
     and (B) hereof;

            (B) stock certificate(s) evidencing the issuance to Baxter of the
     number of shares of VIMRx Preferred Stock in accordance with Section 2.2
     (B) hereof, if any;

            (C)  the VIMRx Warrant;

            (D)  the VIMRx Convertible Debentures;

            (E) an executed copy of each of the other Transaction Documents to
     which VIMRx and/or Nexell is a party;

            (F) all governmental or other approvals, consents, grants, and
     licenses, if any, required to be procured by VIMRx and/or Nexell in
     connection with the transactions contemplated hereby;

                                       17
<PAGE>
 
            (G) copy of the certificate of incorporation of VIMRx, certified as
     of the date as close as practicable to the Closing Date, by the Secretary
     of State of the State of Delaware;

            (H) copy of the certificate of incorporation of Nexell, certified as
     of the date as close as practicable to the Closing Date, by the Secretary
     of State of the State of Delaware;

            (I) a certificate of the Secretary or an Assistant Secretary of
     VIMRx, certifying and including the resolutions of the VIMRx Board of
     Directors authorizing the execution, delivery and performance of this
     Agreement and all Transaction Documents, and attesting to the incumbency
     and signatures of all officers executing this Agreement and any Transaction
     Document;

            (J) a certificate of the Secretary or an Assistant Secretary of
     Nexell, certifying and including the resolutions of the Nexell Board of
     Directors authorizing the execution, delivery and performance of this
     Agreement and all Transaction Documents, and attesting to the incumbency
     and signatures of all officers executing this Agreement and any Transaction
     Document; and

            (K) a certificate of the President or Chief Executive Officer of
     VIMRx, certifying as to the voting results with respect to VIMRx
     stockholder consideration of this Agreement and all transactions and
     actions contemplated herein requiring VIMRx stockholder approval.

        9. Amendment to Registration Rights Agreement
           ------------------------------------------

          Baxter and VIMRx hereby agree that, conditioned upon Closing and
     effective as of the Closing Date, the Registration Rights Agreement is
     amended so that the definition of "Registrable Securities" contained in
     Section 1(e) thereof shall be deemed to include, in addition to all VIMRx
     Common Stock set forth therein, all VIMRx Common Stock and all Conversion
     VIMRx Securities to be acquired by Baxter pursuant to Section 2.2 hereof.

        10. Termination of Stockholders' Agreement
            --------------------------------------

          Baxter, VIMRx and Nexell hereby agree that, conditioned upon Closing
     and effective as of the Closing Date, the Stockholders' Agreement is
     terminated and of no further force and effect.

        11. Amendments to Certain Original Transaction Agreements
            -----------------------------------------------------

          In addition to Sections 9 and 10 hereof, and conditioned upon Closing
     and effective as of the Closing Date, Baxter, VIMRx, and Nexell, as the
     case may be, hereby amend the provisions of certain Original Transaction
     Agreements as follows:

        11.1 Certain Original Transaction Documents. The first sentence of each
             --------------------------------------   
     of Section 23 of the Distribution Agreement, Section 13 of the Services
     Agreement, 

                                       18
<PAGE>
 
     Section 38 of the Antibody Manufacturing and Storage Agreement,
     Section 38 of the Hardware and Disposables Manufacturing Agreement and
     Section 36 of the Hardware and Disposables Supply Agreement is amended and
     restated to read as follows:

               Newco may assign its rights and obligations under this Agreement
               to any Affiliate of Newco without the prior written consent of
               Baxter, provided that such Affiliate is a wholly-owned subsidiary
                       --------                                                 
               of VIMRx.

        11.2 Hardware and Disposables Supply Agreement  Section 2.3 of the
             -----------------------------------------                    
     Hardware and Disposables Supply Agreement is amended and restated in its
     entirety to read as follows:

               2.3 Licenses:  Licenses granted by Baxter to Newco pursuant to
               this Section 2 shall not be assignable and sublicenses may not be
               granted thereunder, except (i) any such license may be assigned
               in the event of an acquisition or transfer of substantially all
               of the Ex Vivo Cell Processing business of Newco to a third
               party;  (ii) Newco may grant a sublicense under any such license
               to an Affiliate of Newco that is a wholly-owned subsidiary of
               VIMRx; and (iii) Newco may grant a sublicense under any such
               license to a third party manufacturer in connection with the
               manufacturing for Newco of any Supplied Product, provided that
                                                                --------     
               such assignee, licensee or third party manufacturer has agreed to
               be bound by the terms of that certain Non-Competition and
               Confidentiality Agreement of even date herewith, by and among
               Baxter, VIMRx and Newco, in the same manner as Newco is bound.


        11.3 Non-Competition and Confidentiality Agreement
             ---------------------------------------------

            (A) Section 2.2 of the Non-Competition and Confidentiality Agreement
     is amended and restated in its entirety to read as follows:
                
                2.2. Baxter's obligations under the foregoing covenant and
            agreement shall begin on the date hereof and shall expire on the
            date that is the later of (i) the date that is five (5) years after
            the date hereof or (ii) one year after the first date on which
            Baxter neither owns at least ten percent (10%) of the Common Stock
            of VIMRx, on a fully diluted basis, nor retains a seat on VIMRx's
            board of directors, or (iii) the date on which the Marketing, Sales
            and Distribution Agreement expires, as its term may be extended,
            provided that all of Baxter's obligations under the foregoing
            --------    
            covenant and agreement shall expire not later than the date that is
            fifteen (15) years after the date hereof, except that following the
            date that is fifteen (15) years after the date hereof, Baxter's
            obligations shall continue (a) to the extent and for the period of
            time that Baxter continues to act as Newco's exclusive worldwide
            distributor for an Isolex(R) or Maxsep(R) Product or Reagent 

                                       19
<PAGE>
 
            Kit under the terms of the Marketing, Sales and Distribution
            Agreement, but only with respect to such Isolex(R) or Maxsep(R)
            Product or Reagent Kit, and (b) to the extent and for the period of
            time that Baxter continues to supply any Supplied Product under the
            terms of the Hardware and Disposables Supply Agreement, but only
            with respect to such Supplied Product.

        (B) Section 3.1 of the Non-Competition and Confidentiality Agreement is
     amended and restated in its entirety to read as follows:

                3.1 Except as otherwise agreed by Baxter in writing, including
             in any Acquisition and Operation Document, VIMRx covenants and
             agrees that neither VIMRx nor any of its Affiliates (other than
             Newco or any entity wholly-owned by VIMRx) shall, directly or
             indirectly, anywhere in the world, (i) engage in, or (ii) render
             consulting or advisory services to any entity that engages in, or
             (iii) be a joint venturer, partner, licensor, member, shareholder
             (other than, in the case of an entity with securities that are
             publicly traded, a holder of 2% or less of the voting securities of
             such an entity) or trustee of any entity for the purpose of
             engaging in, the production, manufacture, marketing, sale or
             distribution of any product which directly competes with any
             Supplied Product or any product of the Business. VIMRx's
             obligations under the foregoing covenant and agreement shall begin
             on the date hereof and shall expire on the date that is the later
             of (i) the date that is five (5) years after the date hereof or
             (ii) one year after the first date on which VIMRx neither owns
             voting control of Newco nor retains a seat on Newco's board of
             directors; provided that all of obligations under the foregoing
                        --------
             covenant and agreement shall expire not later than the date that is
             fifteen (15) years after the date hereof, except that following the
             date that is fifteen (15) years after the date hereof, VIMRx's
             obligations shall continue to the extent and for the period of time
             that Baxter continues to supply any Supplied Product under the
             terms of the Hardware and Disposables Supply Agreement, but only
             with respect to such Supplied Product.

        (C) Section 3.2 of the Non-Competition and Confidentiality Agreement is
     amended and restated in its entirety to read as follows:
                
                3.2. Except as otherwise agreed by Baxter in writing, including
             in any Acquisition and Operating Document, VIMRx covenants and
             agrees that neither VIMRx nor any of its Affiliates shall, directly
             or indirectly, anywhere in the world, (i) engage in, or (ii) render
             consulting of advisory services to any entity that engages in, or
             (iii) be a joint venturer, partner, licensor, member, shareholder
             (other than in the case of any entity with securities that are
             publicly traded, a holder of 2% or less of the voting securities of
             such an 

                                       20
<PAGE>
 
             entity) or trustee of any entity for the purpose of engaging in the
             marketing, sale or distribution of any product which directly
             competes with any product of Baxter for use in the separation of
             human blood into its constituents, such as platelets, plasma, red
             blood cells, leukocytes, and mononuclear cells, while a live donor
             or patient is connected to the separation device (hereinafter
             referred to as "On-Line Separation"). VIMRx's obligations under the
             foregoing covenant and agreement shall begin on the date hereof and
             shall expire on the date that is the later of (i) the date that is
             five (5) years after the date hereof, or (ii) one year after the
             first date on which Baxter neither owns at least ten percent (10%)
             of the Common Stock of VIMRx, on a fully diluted basis, nor retains
             a seat on VIMRx's board of directors, or (iii) the date on which
             the Marketing, Sales and Distribution Agreement expires, as its
             term may be extended; provided that all of VIMRx's obligations
                                   --------
             under the foregoing covenant and agreement shall expire not later
             than the date that is fifteen (15) years after the date hereof.

        (D) Section 4.1 of the Non-Competition and Confidentiality Agreement is
     amended and restated in its entirety to read as follows:
                
                 4.1. Except as otherwise agreed by Baxter in writing, including
             in any Acquisition and Operating document, Newco covenants and
             agrees that neither Newco nor any of its Affiliates shall, anywhere
             in the world, (i) engage in, or (ii) render consulting or advisory
             services to any entity that engages in, or (iii) be a joint
             venturer, partner, licensor, member, shareholder (other than in the
             case of any entity with securities that are publicly traded, a
             holder of 2% or less of the voting securities of such entity) or
             trustee of any entity for the purpose of engaging in, the
             production, manufacture, marketing, sale or distribution of any
             product which directly competes with any Supplied Product, except
             as such production, manufacture, marketing, sale or distribution is
             conducted by Newco or an entity wholly-owned by VIMRx, for use in
             Ex Vivo Cell Processing. Newco's obligations under the foregoing
             covenant and agreement shall begin on the date hereof and shall
             expire on the date that is the later of (i) eleven (11) years after
             the date hereof or (ii) the date on which Baxter's obligation to
             supply such Supplied Product expires or is terminated under the
             terms of the Hardware and Disposables Supply Agreement for a reason
             other than Newco's breach; provided that of Newco's obligations
                                        --------        
             under the foregoing covenant and agreement shall expire not later
             than the date that is fifteen (15) years after the date hereof,
             except that following the date that is fifteen (15) years after the
             date hereof, Newco's obligations shall continue to the extent and
             for the period of time that Baxter continues to supply any Supplied
             Product under the terms of the Hardware and Disposables Supply
             Agreement, but only with respect to such Supplied Product.

                                       21
<PAGE>
 
        (E) Section 4.3 of the Non-Competition and Confidentiality Agreement is
     amended and restated in its entirety to read as follows:

                 4.3. Except as otherwise agreed by Baxter in writing, including
             any Acquisition and Operating Document, Newco covenants and agrees
             that neither Newco nor any of its Affiliates shall, directly or
             indirectly, anywhere in the world, (i) engage in, or (ii) render
             consulting or advisory services to any entity that engages in, or
             (iii) be a joint venturer, partner, licensor, member, shareholder
             (other than in the case of any entity with securities that are
             publicly traded, a holder of 2% or less of the voting securities of
             such entity) or trustee of any entity for the purpose of engaging
             in the marketing, sale or distribution of any product which
             directly competes with any product of Baxter for use in On-Line
             Separation. Nothing herein or in Section 3.2 shall prevent or
             restrict Newco, or any Affiliate of Newco that is wholly-owned by
             VIMRx, from marketing, selling or distributing any product for use
             in selection as described in Section 2.1(a) above, whether or not a
             live donor or patient is connected to the selection device,
             provided that such selection does not include On-Line Separation.
             --------
             Newco's obligations under the foregoing covenant and agreement
             shall begin on the date hereof and shall expire on the date that is
             the later of (i) the date that is five (5) years after the date
             hereof or (ii) one year after the first date on which Baxter
             neither owns at least ten percent (10%) of the common stock of
             VIMRx, on a fully diluted basis, nor retains a seat on VIMRx's
             board of directors, or (iii) the date on which the Marketing, Sales
             and Distribution Agreement expires, as its term may be extended;
             provided that all of Newco's obligations under the foregoing
             --------   
             covenant and agreement shall expire not later than the date that is
             fifteen (15) years after the date hereof.

        (F) Section 7 of the Non-Competition and Confidentiality Agreement is
     amended and restated in its entirety to read as follows:

                    Recipient may utilize the Confidential Information only for
             the furtherance of the Recipient's rights and obligations under the
             Acquisition and Operating Documents. Recipient, on behalf of itself
             and its Representatives, agrees that except with respect to
             Authorized Disclosures (as that capitalized term is defined below)
             and as otherwise expressly permitted by this Agreement in
             furtherance of the Recipient's rights and obligations under the
             Acquisition and Operating Documents, Recipient will not, and will
             cause any and all of its Representatives not to, on or after the
             date hereof, in any form or manner, directly or indirectly,
             divulge, disclose or communicate to any person, or utilize for its
             commercial benefit or for the benefit of any other person, or to
             the detriment of the Owner, any Confidential Information.
             Notwithstanding anything contained in this Agreement to the
             contrary, without the express prior written consent of Baxter,

                                       22
<PAGE>
 
             neither VIMRx nor Newco may disclose or use any Confidential
             Information received by VIMRx or Newco from the Baxter Group to or
             on behalf of any of its Affiliates (other than an entity that both
             (i) is wholly-owned by VIMRx and (ii) agrees to be bound by the
             provisions of this Agreement), unless such disclosure or use
             constitutes an Authorized Disclosure. Notwithstanding anything
             contained in this Agreement to the contrary, without the express
             prior written consent of the Owner, Baxter may not disclose or use
             any Confidential Information received from the VIMRx Group or Newco
             to or on behalf of any of Baxter's Affiliates, unless such
             disclosure or use constitutes an Authorized Disclosure. In
             addition, Recipient agrees to, and will cause any and all of its
             Representatives to, protect and secure any Confidential Information
             in its possession or in the possession of its Representatives from
             unauthorized disclosure or use. The standard of care imposed on
             Recipient and its Representatives for protecting Confidential
             Information will be the care employed by Recipient and its
             Representatives to protect its confidential information but in no
             event shall the care used by Recipient and its Representatives be
             less than the exercise of reasonable and prudent care to prevent
             unauthorized disclosure or use of such Confidential Information
             (except that Recipient shall not be excused for its own negligence
             or the negligence of its Representatives). In the event of the
             destruction, loss or theft of any materials containing Confidential
             information in the possession of Recipient or its Representatives,
             Recipient shall notify Owner in writing immediately identifying the
             materials so lost or destroyed.

        (G) Section 19 of the Non-Competition and Confidentiality Agreement is
     amended and restated in its entirety to read as follows:

                 Baxter may assign its rights and obligations hereunder to any
             Affiliate of Baxter with prior notice to VIMRx and Newco. VIMRx may
             assign its rights and obligations hereunder to any Affiliate of
             VIMRx with prior notice to Baxter and Newco. Newco may assign its
             rights and obligations hereunder to any Affiliate of Newco with
             prior notice to and written consent of Baxter and VIMRx, which
             consent will not be unreasonably withheld; and Newco may assign its
             rights and obligations under this Agreement to any Affiliate of
             Newco without the prior written consent of Baxter or VIMRx,
             provided that such Affiliate is wholly-owned by VIMRx. No party may
             assign any of its rights or obligations under this Agreement,
             unless and to the extent expressly permitted herein.
             Notwithstanding anything contained in this Section 19 to the
             contrary, in the event of any permitted assignment of any party's
             rights and obligations hereunder, the assigning party shall
             continue to be bound by the obligations contained in Sections 2, 3,
             4, 5, 7, 9, 10, 11, 13, 14, 15 and 24 applicable to it as if no
             assignment had occurred. Subject to the 

                                       23
<PAGE>
 
             foregoing, this Agreement shall inure to the benefit of and be
             binding on the permitted successors and assigns of the parties
             hereto.

        12. Survival of Representations and Warranties
            ------------------------------------------

        12.1 Survival.
             -------- 

             (A) All representations and warranties contained in this Agreement
     or in any Transaction Document shall survive the Closing of the
     transactions contemplated under this Agreement. All covenants and
     agreements contained herein and in any Transaction Document shall survive
     in accordance with their respective terms; provided, however, that for the
     removal of doubt, none of the covenants set forth in Sections 6.1 hereof
     shall survive the termination of this Agreement in accordance with Section
     16 hereof.

            (B) In no event shall any party hereto be entitled to or recover
     exemplary or punitive damages in any action under this Agreement or
     relating to the subject matter hereof.
 
        13. Transactional Taxes
            -------------------

          Baxter and VIMRx shall each bear one-half of any applicable
     Transactional Taxes with respect to the sale, transfer, assignment,
     delivery or issuance of the Nexell Securities or the Acquired VIMRx
     Securities.

        14. Further Assurances and Cooperation
            ----------------------------------

          Following the date hereof, and subject to the terms and conditions
     hereof, each of Baxter, VIMRx and Nexell severally agrees to execute and
     deliver such other documents and take such other actions as shall be
     reasonably requested by another party hereto to carry out and effectuate
     the transactions contemplated by this Agreement. On and subsequent to the
     Closing Date, each party hereto severally covenants and warrants that it
     shall, whenever and as often as it shall be reasonably requested to do so
     by another party hereto to this Agreement, execute, acknowledge and deliver
     or cause to be executed, acknowledged and delivered, any and all such
     further documents and instruments as may be reasonably necessary, expedient
     or proper in order to complete any and all of the conveyances, transfers,
     sales and assignments herein provided for.

                                       24
<PAGE>
 
        15. Notices
            -------

          All notices, requests, demands and other communications permitted or
     required under this Agreement shall be in writing and shall be either
     personally delivered (including couriers such as FedEx) or sent by pre-paid
     certified mail, return receipt requested or facsimile transmission, with a
     confirmation copy personally delivered or sent by pre-paid certified mail,
     addressed or transmitted to the address or number stated below of the party
     hereto to which notice is given, or to such other address or number as such
     party may have fixed by notice given in accordance with the terms hereof:

         To Baxter:       Baxter Healthcare Corporation
                          1627 Lake Cook Road
                          Deerfield, Illinois 60015
                          Attention: President - Venture Management
                                     Associate General Counsel  Hyland Immuno
                          Facsimile: (847) 940-6289

         With a copy to:  Seyfarth, Shaw, Fairweather & Geraldson
                          55 East Monroe Street
                          Chicago, Illinois 60603-5803
                          Attention: Christopher A. Lause, Esq.
                          Facsimile: (312) 269-8869

         To VIMRx:        VIMRx Pharmaceuticals Inc.
                          2751 Centerville Road
                          Suite 210
                          Wilmington, Delaware 19808
                          Attention: Chief Executive Officer
                          Facsimile: (302) 998-3794

         With a copy to:  Epstein Becker Green, P.C.
                          250 Park Avenue
                          New York, New York 10177
                          Attention: Lowell S. Lifschultz, Esq.
                          Facsimile: (212) 661-0989

         To Nexell:       Nexell Therapeutics Inc.
                          9 Parker
                          Irvine, California  92518
                          Attention: Chief Executive Officer
                          Facsimile: (949) 470-6645

                                       25
<PAGE>
 
         With a copy to:  Epstein Becker & Green, P.C.
                          250 Park Avenue
                          New York, New York 10177
                          Attention: Lowell S. Lifschultz, Esq.
                          Facsimile: (212) 661-0989
   
   
         Any notice, sent as provided above, shall be deemed given, if sent by
     certified mail, upon delivery at the address provided for above (or, in the
     event delivery is refused, the first date on which delivery was tendered)
     or, if sent by facsimile transmission, upon receipt by the sender of
     confirmation of delivery.

        16. Expenses
            --------

            Except as set forth in Section 13 hereof, each party hereto shall
     bear its own expenses (including all fees and expenses of attorneys,
     accountants, investment bankers, brokers or other representatives or
     consultants) incurred in connection with the negotiation, preparation,
     consummation and performance of this Agreement and the Transaction
     Documents and the transactions contemplated hereby and thereby.

        17. Termination
            -----------

        17.1 Conditions. This Agreement may be terminated at any time on or
     prior to the Closing Date:

            (A)  by mutual consent of Baxter, VIMRx and Nexell;

            (B) by VIMRx, if (i) there has been a material misrepresentation or
     breach on the part of Baxter with respect to any representation or warranty
     of Baxter set forth herein, or (ii) there has been any material failure on
     the part of Baxter to comply with any of its obligations or to perform any
     of its covenants hereunder, which failure, if capable of remedy, has not
     been remedied within 15 days of receipt by Baxter of notice thereof, or
     (iii) any of the conditions set forth in Sections 7.2 and 7.3 hereof shall
     not have been fulfilled by June 30, 1999 (other than by virtue of a breach
     of this Agreement by VIMRx or Nexell) and the fulfillment thereof shall not
     have been waived by VIMRx; or

            (C) by Baxter, if (i) there has been a material misrepresentation or
     breach on the part of VIMRx or Nexell in any of its representations or
     warranties set forth herein, or (ii) there has been any material failure on
     the part of VIMRx or Nexell to comply with any of its obligations or to
     perform any of its covenants hereunder, which failure, if capable of
     remedy, has not been remedied within 15 days of receipt by VIMRx or Nexell,
     as appropriate, of notice thereof, or (iii) any of the conditions set forth
     in Sections 7.1 and 7.3 hereof shall not have been fulfilled by June 30,
     1999 (other than by virtue of a breach of the Agreement by Baxter) and the
     fulfillment thereof shall not have been waived by Baxter.

        17.2 Effective Date. A termination pursuant to Section 17.1(B) or (C)
             --------------   
     hereof shall be effective immediately upon delivery of a notice of
     termination by the 

                                       26
<PAGE>
 
     party or parties hereto having the right to terminate to
     the other party or parties hereto.

        17.3 No Liability. In the event of a termination of this Agreement as
             ------------
     provided in this Section 17, this Agreement shall forthwith terminate and
     there shall be no liability on the part of Baxter, VIMRx or Nexell, except
     for liability arising from a breach of this Agreement. Notwithstanding
     anything in this Agreement to the contrary, failure of the VIMRx
     stockholders to approve any of the matters set forth in the Proxy Statement
     relating to this Agreement or any transaction or action contemplated herein
     shall not be a breach of this Agreement.

        18. Miscellaneous
            -------------

        18.1 Entire Agreement; No Modification; Enforceability of Original
             -------------------------------------------------------------
     Transaction Agreements. This Agreement, including the Exhibits and
     ----------------------   
     Transaction Documents delivered pursuant hereto, sets forth the entire
     agreement and understanding between the parties hereto as to the specific
     subject matter hereof and thereof, and merges and supersedes all prior
     discussions, agreements and understandings of every kind and nature between
     them with respect to the specific subject matter hereof and thereof, and no
     party hereto shall be bound by any condition, definition, warranty or
     representation other than as expressly provided for in this Agreement. This
     Agreement shall not be changed or amended except by a writing signed by
     Baxter, VIMRx and Nexell. Notwithstanding anything in this Agreement to the
     contrary, except as specifically modified herein or as modified in a
     separate writing signed by Baxter, VIMRx and Nexell, as the case may be,
     all of the Original Transaction Agreements shall remain in full and effect
     in accordance with the provisions thereof.

        18.2 Waiver of Breach. The waiver by a party hereto of a breach or
             ----------------   
     violation by another party hereto of any provision of this Agreement shall
     not operate or be construed as a waiver of any subsequent breach or
     violation by any party hereto of the same or any other provision of this
     Agreement. No such waiver shall be effective unless in writing signed by
     the party hereto claimed to have made the waiver.

        18.3 Benefit of Parties; Assignment. This Agreement shall be binding
             ------------------------------           
     upon and shall inure to the benefit of the parties hereto and their
     respective heirs, executors, legal representatives, successors and
     permitted assigns. No party hereto shall have the right to assign or
     delegate any of its rights or obligations arising hereunder, except with
     the prior written consent of each other party hereto; provided, however,
                                                           -----------------
     that any party hereto may assign any or all of its rights, and delegate any
     or all of its obligations, hereunder to any person or entity who shall, by
     merger, consolidation, transfer of assets or otherwise, have acquired all
     or substantially all of the assets (not counting cash and cash equivalents)
     of such party; provided, further, that no such delegation shall relieve the
                    -----------------
     delegating party of the obligation to satisfy and discharge the
     obligation(s) so delegated. Notwithstanding the foregoing, Baxter shall
     have the right to assign this Agreement, and any rights and obligations
     arising 

                                       27
<PAGE>
 
     hereunder, to an Affiliate of Baxter without the prior written consent of
     any other party hereto; provided, that no such assignment shall relieve
     Baxter of any of its obligations hereunder. Any purported assignment or
     delegation in violation of this Section 18.3 shall be null and void ab
                                                                         --
     initio.
     ------

        18.4 Headings. The headings of the sections and paragraphs of this
             --------
     Agreement are inserted for convenience of reference only and shall not
     constitute a part hereof.

        18.5 Governing Law; Jurisdiction. This Agreement shall be governed by
             ---------------------------
     and construed in accordance with the laws of the State of Delaware without
     giving effect to principles of conflict of laws. Each party to this
     Agreement expressly and irrevocably (A) consents that any legal action or
     proceeding against it under, arising out of or in any manner relating to,
     this Agreement, or any other Document delivered in connection herewith, may
     be brought in any court of the State of Delaware located within the
     District of Delaware or in the United States District Court for the
     District of Delaware, (B) consents and submits to the personal jurisdiction
     of any of such courts in any such action or proceeding, (C) consents to the
     service of any complaint, summons, notice or other process relating to any
     such action or proceeding by delivery thereof to him, her or it by hand or
     by any other manner provided for in Section 15 hereof, (D) waives any claim
     or defense in any such action or proceeding based on any alleged lack of
     personal jurisdiction, improper venue or forum non conveniens or any
                                              --------------------  
     similar basis, and (E) waives all rights, if any, to trial by jury with
     respect to any such action or proceeding. Nothing in this Section 18.5
     shall affect or impair in any manner or to any extent the right of any
     party hereto to commence legal proceedings or otherwise proceed against any
     other party hereto in any jurisdiction or to serve process in any manner
     permitted by law.

        18.6 Multiple Counterparts; Execution by Fax. This Agreement may be
             ---------------------------------------
     signed in any number of counterparts which taken together shall constitute
     one and the same instrument. This Agreement may be executed and delivered
     by exchange of facsimile copies showing the signatures of the parties
     hereto, and those signatures need not be affixed to the same copy. The
     facsimile copies showing the signatures of the parties will constitute
     originally signed copies of the same agreement requiring no further
     execution.

        18.7 Exhibits. All Exhibits referred to in this Agreement are attached
             --------
     hereto and are incorporated herein by reference as if fully set forth
     herein.

        18.8 Construction. The language in all parts of this Agreement shall in
             ------------
    all cases be construed as a whole according to its fair meaning, strictly
    neither for nor against any party hereto, and without implying a presumption
    that the terms thereof shall be more strictly construed against one party
    hereto by reason of the rule of construction that a document is to be
    construed more strictly against the person who himself or through his agent
    prepared the same, it being agreed that representatives of all parties
    hereto have participated in the preparation hereof.

                                       28
<PAGE>
 
        18.9  Publicity.  No party to this Agreement shall issue or cause the
              ---------  
    publication of any press release or other public announcement with respect
    to this Agreement or the transactions contemplated hereby without first
    providing a draft of such press release or announcement to the other parties
    hereto and obtaining the consent of the other parties hereto; provided,
                                                                  --------
    however, that nothing herein shall prevent any party hereto from making any
    -------
    disclosure required by law.

        18.10 Number and Gender. Whenever in this Agreement the singular is
              -----------------  
    used, it shall include the plural if the context so requires, and whenever
    the masculine gender is used in this Agreement, it shall be construed as if
    the masculine, feminine or neuter gender, respectively, has been used where
    the context so dictates, with the rest of the sentence being construed as if
    the grammatical and terminological changes thereby rendered necessary have
    been made.

                                       29
<PAGE>
 
         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
     of the date first above written.

                          BAXTER HEALTH CARE CORPORATION

                          By:  /s/ Victor W. Schmitt
                               ---------------------------------
                          Name:  Victor W. Schmitt
                          Title: President, Venture Management


                          VIMRx PHARMACEUTICALS INC.


                          By:  /s/ Richard L. Dunning
                               ---------------------------------
                          Name:  Richard L. Dunning
                          Title: President and CEO


                          NEXELL THERAPEUTICS INC.


                          By:  /s/ L. William McIntosh
                               ---------------------------------
                          Name:  L. William McIntosh
                          Title: President and CEO

                                       30