Document:

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                                                                     Exhibit 4.2

                   STOCK PURCHASE AND STOCK EXCHANGE AGREEMENT

         This Stock Purchase and Stock Exchange Agreement ("Agreement") is made
as of the 19th day of March, 1996, by and between Athersys, Inc., a Delaware
corporation (the "Company"), and Michael Gallo ("Seller").

                              W I T N E S S E T H:

         WHEREAS, Seller desires to sell 29.9 shares of common stock of the
Company ("Common Stock") owned by Seller and convert 29.9 shares of Common Stock
into 29.9 Warrants (as defined in Section 2 below), and the Company desires to
purchase 29.9 shares of Common Stock owned by Seller and convert 29.9 shares of
Common Stock owned by Seller into 29.9 Warrants.

         NOW, THEREFORE, for the consideration and upon the terms and conditions
hereinafter set forth, the parties hereto agree as follows:

         1. PURCHASE AND EXCHANGE OF SHARES. Subject to the terms and provisions
of this Agreement, the Company agrees to purchase on the Closing Date (as
hereinafter defined), from Seller, and Seller agrees to sell, transfer, deliver
and convey to the Company, on the Closing Date, shares of Common Stock owned by
Seller. Subject to the terms and provisions of this Agreement, the Company
agrees to convert on the Closing Date, and Seller agrees to convert on the
Closing Date, 29.9 shares of Common Stock owned by Seller into 29.9 Warrants as
described in Section 2 below.

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         2.       EXCHANGE OF SHARES FOR WARRANTS.

         (a) Seller hereby exchanges, and the Company hereby converts, 29.9
shares of Common Stock owned by Seller for warrants to purchase up to 29.9
shares of Common Stock (the "Warrants").

         (b) The exercise price for the Warrants shall be One Dollar ($1.00) per
share.

         (c) The Warrants are exercisable, in whole or in part, at any time,
after the occurrence of: (i) the closing of an initial public offering by the
Company pursuant to an effective registration statement under the Securities Act
of 1933, as amended; or (ii) the acquisition of shares representing a majority
of the voting power of the Company by a person, entity or group other than the
holders of capital stock of the Company as of the date of this Agreement or BVF.
In addition, the Warrants are exercisable in connection with Seller's Co-Sale
Rights (as described below), but only for the number of shares to be sold
pursuant to such Co-Sale Rights.

         (d) If Seller is entitled to and wishes to exercise the Warrants,
Seller shall send written notice to the Company identifying the date for the
closing of such purchase and the number of shares to be purchased.

         (e) The Company shall have the right, at any time, in its sole
discretion, to require Seller to exercise the Warrants in whole, but not in
part. If the Company wishes to require Seller to exercise the Warrants, the
Company shall send written notice to Seller identifying the date for the closing
of such purchase.

         (f) In the event that any of Gil Van Bokkelen, John Harrington,
Huntington Willard, James Nelson, Ira Mellman or Robert Mays (the "Selling
Founders") proposes to sell shares of common stock to a third party, the Selling
Founders shall deliver written notice (the "Co-Sale Notice") with respect to
such proposed sale to Seller not later than thirty (30) days prior to the

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closing of such sale, or such shorter period as may be agreed to by the Selling
Founders and Seller. Such Co-Sale Notice shall set forth the number of shares of
common stock which the Selling Founders proposes to sell, the identity of the
transferee or transferees and the proposed closing date for such proposed sale,
and shall include a copy of any writing setting forth the terms of the proposed
sale. Upon receipt of a Co-Sale Notice, Seller shall have an option exercisable
at any time prior to the closing of the proposed sale by the Selling Founders,
to elect to participate in such sale; provided, that as a condition to the
consummation of the purchase and sale of any shares issuable upon the exercise
of the Warrants, Seller shall be obligated to exercise the Warrants for that
number of shares that he proposes to sell. Seller shall have the option to sell
his shares to the ultimate purchaser as of the proposed closing date for such
sale, and upon the same terms and conditions specified in the Co-Sale Notice,
pro rata with the Selling Founders according to the aggregate holdings of shares
of common stock by the Selling Founders and Seller as of the date of the Co-Sale
Notice, by written notice to such effect to the Selling Founders. The number of
shares to be sold by the Selling Founders shall be reduced by the number of
shares which Seller elects to so sell (within the limitation of the preceding
sentence). Failure by Seller to give such notice prior to the closing of such
sale shall be deemed a forfeiture and waiver of any right of Seller to
participate in such sale, provided that such sale is fully closed and
consummated on or before the closing date and upon the terms and conditions
specified in the Co-Sale Notice.

         (g) In addition, Seller shall have all economic rights that the Selling
Founders have under that certain Stockholders' Agreement to be entered into
among the Company and its stockholders (the "Stockholders' Agreement") in
connection with the consummation of the BVF Investment, as such Stockholders'
Agreement may be amended from time to time, and the Company's Certificate of
Incorporation and By-Laws. The Company will not take any action, the purpose of
which is to

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selectively and specifically impact the economic interest of Seller in the
Company. Upon exercise of any of the Warrants, Seller will execute and become a
party to the Stockholders' Agreement.

         3. CLOSING. The closing of the transactions contemplated by this
Agreement and all deliveries to be made at the time fixed for the closing shall
take place at the offices of Benesch, Friedlander, Coplan & Aronoff on the date
of this Agreement at 10:00 a.m. (the "Closing Date"). On the Closing Date,
Seller will deliver to the Company the certificate(s) representing all shares of
Common Stock owned by Seller, duly endorsed or with appropriate blank stock
power(s). The Company will deliver to Seller Eleven Thousand Two Hundred Dollars
($11,200) by bank or certified check as payment in full for 29.9 shares of
Common Stock owned by Seller. In addition, 29.9 shares of Common Stock owned by
Seller will be exchanged by Seller for, and converted by the Company into, the
29.9 Warrants as described in Section 6 below.

         4. REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company hereby
represents and warrants to Seller that this Agreement is the legal, valid and
binding obligation of the Company enforceable against it in accordance with its
terms, except that such enforcement may be subject to bankruptcy, insolvency,
reorganization, moratorium or similar laws now or hereafter in effect relating
to creditors' rights generally and that the remedy of specific performance and
injunctive or other equitable relief may be subject to equitable defenses and to
the discretion of the court before which any proceeding therefore may be
brought. The Company will give Seller prompt notice of any amendment to the
Stockholders' Agreement, its Certificate of Incorporation or its By-Laws. (See
attached documents).

         5. REPRESENTATIONS AND WARRANTIES OF SELLER. Seller hereby represents
and warrants to the Company that: (a) he has had supplied to him all information
concerning the Company that he has requested from the Company, he has had the
opportunity for himself and through his counsel to

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ask any questions concerning the Company, and he is not aware of any basis on
which he would have a claim against the Company; (b) he is aware that
Biotechnology Value Fund, L.P. ("BVF") intends to invest approximately $2.5
million in the Company (the "BVF Investment"); (c) he has not assigned,
transferred, encumbered or pledged to any party, or otherwise alienated, any
portion of the shares of Common Stock owned by Seller and such shares represent
all of the shares of Common Stock owned by Seller and that Seller has no other
equity interests in the Company; (d) the execution, delivery and consummation of
this Agreement by Seller does not now and will not, with the passage of time,
the giving of notice or otherwise, result in a violation or breach of, or
constitute a default under, any term or provision of any indenture, mortgage,
deed of trust, lease, instrument, order, judgment, decree, rule, regulation,
law, contract, agreement or any other restriction to which Seller is a party or
to which Seller or any of his assets is subject or bound; (e) upon delivery of
the certificate(s) representing the shares of Common Stock owned by Seller in
accordance with Paragraph 2 above, good and marketable title to all shares of
Common Stock owned by Seller will pass to the Company, free and clear of all
liens, charges, security interests, adverse claims, pledges, encumbrances and
demands whatsoever; and (f) this Agreement is the legal, valid and binding
obligation of Seller enforceable against him in accordance with its terms,
except that such enforcement may be subject to bankruptcy, insolvency,
reorganization, moratorium or similar laws now or hereafter in effect relating
to creditors' rights generally and that the remedy of specific performance and
injunctive or other equitable relief may be subject to equitable defenses and to
the discretion of the court before which any proceeding therefore may be
brought.

         6. MUTUAL AND GENERAL RELEASES. Seller, on behalf of himself, his
successors, assigns, executors, administrators, agents and professional
advisors, in exchange for good and valuable consideration, the adequacy and
receipt of which are hereby acknowledged, hereby releases and

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forever discharges the Company and its successors, assigns, officers, directors,
stockholders, employees, agents and professional advisors, of and from any and
all claims, causes of action, suits, covenants, damages and demands whatsoever,
in law or in equity, known and unknown, from the beginning of time to the
Closing Date.

         The Company on behalf of itself, its successors, assigns, officers,
directors, stockholders, employees, agents and professional advisors, in
exchange for good and valuable consideration the adequacy and receipt of which
are hereby acknowledged, hereby releases and forever discharges Seller and his
successors, assigns, executors, administrators, agents and professional
advisors, of and from any and all claims, causes of action, suits, covenants,
damages and demands whatsoever, in law or in equity, known or unknown, from the
beginning of time to the Closing Date.

         7. SEVERABILITY. In the event that any provision or term of this
Agreement is found to be void or unenforceable to any extent for any reason, it
is the agreed-upon intent of the parties hereto that all remaining provisions or
terms of this Agreement shall remain in full force and effect to the maximum
extent permitted and that this Agreement shall be enforceable as if such void or
unenforceable provision or term had never been a part hereof. To the extent that
any obligations of Seller in this Agreement shall be illegal and/or
unenforceable with respect to any jurisdiction, said covenants shall not be
affected thereby with respect to each other jurisdiction, such covenants with
respect to each such jurisdiction being construed as severable and independent.
In the event Seller shall violate any legally enforceable provision of this
Agreement as to which there is a specific time period during which the Company
is prohibited from taking certain actions or from engaging in certain
activities, as set forth in this Agreement, then, in such event, such violation
shall toll the running of such time period from the date such violation
commences until, and including, the date such violation shall cease.

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         8. BINDING EFFECT. The parties hereto agree that this Agreement shall
bind the parties hereto, their respective assigns, successors in interest, those
in contractual privity with them, and their professional representatives of any
type whatsoever, as the case may be.

         9. COMPLETE AGREEMENT. The parties hereto agree that this Agreement
represents the complete agreement of the parties hereto with respect to the
matters discussed herein and supersedes any and all prior verbal or written
agreements, including, without limitation, that certain "Memorandum of
Understanding Between the Partners of Athersys." This Agreement shall not be
modified unless so done in writing and signed by the party or parties to be
bound by any such modification.

         10. MISCELLANEOUS. This Agreement shall be governed by, and construed
in accordance with, the laws of the State of Ohio. This Agreement may be
executed in multiple counterparts, each of which when taken together shall
constitute an original.

         IN WITNESS WHEREOF, the parties hereto have executed this Stock
Purchase Agreement as of the day and year first written above.

ATHERSYS, INC.                                    "Seller"

By: /s/ Gil Van Bokkelen                          /s/ Michael Gallo
    ---------------------------                   ------------------------------
    Gil Van Bokkelen                              Michael Gallo
    President

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         The undersigned hereby agree to be bound by the terms of Sections 2(f),
2(g) and 6 of this Agreement.

/s/ Gil Van Bokkelen                        /s/ John Harrington
--------------------------------------      ------------------------------------
Gil Van Bokkelen                            John Harrington

/s/ Huntington Willard                      /s/ James Nelson
--------------------------------------      ------------------------------------
Huntington Willard                          James Nelson

/s/ Ira Mellman                             /s/ Robert Mays
--------------------------------------      ------------------------------------
Ira Mellman                                 Robert Mays

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                   SPOUSAL ACKNOWLEDGEMENT, CONSENT AND WAIVER

         The undersigned, Frances C. Gallo, hereby acknowledges that she:

       (i)        is the spouse of Michael Gallo;

      (ii)        has read the foregoing Stock Purchase Agreement (the
                  "Agreement") and understands that, among other things, it
                  relates to the sale and exchange by Michael Gallo of all
                  shares of the Common Stock of Athersys, Inc. owned by Michael
                  Gallo (the "Shares").

     (iii)        is aware that, as the spouse of Michael Gallo, she may have
                  some legal interest in the Shares;

      (iv)        ratifies, approves and consents to the terms of the Agreement
                  and to be bound thereby, insofar as it may affect any interest
                  she may have in the Shares;

       (v)        irrevocably consents to the consummation, in accordance with
                  the terms of the Agreement, of every transaction contemplated
                  therein; and

      (vi)        irrevocably waives, surrenders, or releases each and every
                  marital and other right, claim, or demand that she now or
                  hereafter may have which, if asserted, in any way might impair
                  the enforceability and/or execution of any provision of the
                  Agreement or cause the Agreement (or any provision thereof) to
                  be void or voidable.

Dated: March 10, 1996                                /s/ Frances C. Gallo
                                                     --------------------
                                                         (sign here)

                                                     /p/ Frances C. Gallo
                                                     --------------------
                                                         (print name)

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                                                                     Exhibit 4.3

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

                                WARRANT AGREEMENT

                                      AMONG

                   PRIMUS CAPITAL FUND IV LIMITED PARTNERSHIP,
                   PRIMUS EXECUTIVE FUND LIMITED PARTNERSHIP,
                 BLUE CHIP CAPITAL FUND II LIMITED PARTNERSHIP,
                         MIAMI VALLEY VENTURE FUND L.P.
             WARBURG DILLON READ LLC, OHIO INNOVATION FUND I, L.P.,
               SENTRON MEDICAL INCORPORATED, ATHERSYS INVESTOR LLC
                    HOEGH INVEST, AS, NEOMED INNOVATION, ASA,

                                       AND

                                 ATHERSYS, INC.

                          DATED AS OF OCTOBER 30, 1998

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

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                                WARRANT AGREEMENT

         THIS WARRANT AGREEMENT (this "Agreement") dated as of October 30, 1998
among ATHERSYS, INC., a Delaware corporation (the "Company"), and PRIMUS CAPITAL
FUND IV LIMITED PARTNERSHIP, PRIMUS EXECUTIVE FUND LIMITED PARTNERSHIP, BLUE
CHIP CAPITAL FUND II LIMITED PARTNERSHIP, MIAMI VALLEY VENTURE FUND L.P.,
WARBURG DILLON READ LLC, OHIO INNOVATION FUND I, L.P., ATHERSYS INVESTOR LLC,
SENTRON MEDICAL INCORPORATED, HOEGH INVEST, AS, AND NEOMED INNOVATION, ASA and
any investor listed on Exhibit A of the Share Purchase Agreement of even date
herewith (the "Investors").

                                R E C I T A L S:
                                - - - - - - - -

         This Agreement is entered into in connection with that certain Share
Purchase Agreement (the "Share Purchase Agreement"), dated concurrently herewith
among the Company and the Investors pursuant to which the Company will be
issuing and the Investors will be purchasing shares of Class C Convertible
Preferred Stock, $.01 par value per share (the "Class C Preferred"). Capitalized
terms not otherwise defined herein shall have the meanings given to them in the
Share Purchase Agreement.

         NOW, THEREFORE, for good and valuable consideration the receipt of
which is hereby acknowledged and the promises and the mutual agreements set
forth herein, the parties hereto agree as follows:

         1. ISSUANCE OF WARRANTS: FORM OF WARRANTS.

                  (a) The Company hereby agrees to issue to the Investors, on
         the Closing Date, warrants (the "Warrants") to purchase shares of the
         Company's Common Stock, $.01 par value per share (the "Common Stock")
         as set forth on EXHIBIT "A" hereto.

                  (b) The text of the Warrants and of the form of election to
         purchase Common Stock underlying the Warrants (the "Warrant Stock") to
         be set forth on the reverse thereof shall be substantially as set forth
         in the Warrant Certificate ("Warrant Certificate"), attached as EXHIBIT
         "B" to this Agreement. Each Warrant Certificate shall be executed on
         behalf of the Company by the President or Vice President of the Company
         and attested by the Secretary or an Assistant Secretary of the Company.

                  (c) Warrant Certificates shall be dated as of the date of the
         execution thereof by the Company either upon initial issuance or upon
         division, exchange, substitution or transfer as may be permitted
         hereunder.

         2. REGISTRATION. The Warrant Certificates shall be numbered and shall
be registered on the books of the Company (the "Warrant Register") as they are
issued at the Closing. The Company shall be entitled to treat the registered
holder of any Warrant Certificate on the Warrant Register (the "Holder") as the
owner in fact thereof for all purposes and shall not be bound to recognize any
equitable or other claim to or interest in such Warrant Certificate, or the
Warrants represented thereby, on the part of any other person, and shall not be
liable for any registration or transfer of
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Warrant Certificates which are registered or to be registered in the name of a
fiduciary or the nominee of a fiduciary unless made with the actual knowledge
that a fiduciary or nominee is committing a breach of trust in requesting such
registration or transfer, or with knowledge of such facts that the Company's
participation therein amounts to bad faith.

         3. TRANSFER OF WARRANT CERTIFICATE. The Warrant Certificate shall be
transferable only on the Warrant Register upon delivery of the Warrant
Certificate duly endorsed by the Holder or by its duly authorized attorney or
representative (with evidence reasonably satisfactory to the Company of such
authorization), or accompanied by evidence reasonably satisfactory to the
Company of succession, assignment or authority to transfer. Upon any
registration of transfer, the Company shall deliver a new Warrant Certificate(s)
to the person(s) entitled thereto. Notwithstanding the foregoing, the Company
shall have no obligation to cause Warrant Certificates to be transferred on the
Warrant Register to any person, unless the Holder of such Warrants shall furnish
to the Company evidence satisfactory to the Company of compliance with the
registration provisions of Section 5 of the Securities Act of 1933, as amended
(the "Act"), or the availability of an exemption from compliance with the
registration provisions of Section 5 of the Act.

         4. TERM OF WARRANTS; EXERCISE OF WARRANTS.

                  (a) Each Warrant entitles the registered owner thereof to
         purchase the number of shares of Warrant Stock as set forth on Exhibit
         A hereto, subject to adjustment pursuant to the provisions of Section 8
         of this Agreement, at any time from the issuance of the Warrant through
         and including 5:00 p.m. Cleveland, Ohio local time of the earlier to
         occur of (i) one year after the closing date of a Public Offering (an
         "IPO") (as hereinafter defined), (ii) dissolution, liquidation or
         winding up of the affairs of the Company ("Liquidation"), (iii) the
         sale, conveyance, exchange or transfer (for cash, shares of stock,
         securities, or other consideration) of all or substantially all of the
         property, assets or stock (whether by merger, consolidation or sale) of
         the Company (a "Sale"), or (iv) October 30, 2008 (the "Expiration
         Date"), at an initial purchase price per share of Warrant Stock of
         Thirteen Thousand Dollars ($13,000.00), subject to adjustment pursuant
         to the provisions of Section 8 of this Agreement (the "Warrant Price").
         For purposes of this Agreement, "Public Offering" shall mean the sale
         by the Company of Common Stock pursuant to an effective registration
         statement under the Securities Act of 1933, as amended. Notwithstanding
         anything herein to the contrary, the Holder of the Warrant must sell,
         transfer or exercise the Warrant on or before the Expiration Date or
         else it will terminate in accordance with its terms as of the close of
         business on the Expiration Date.

                  (b) The Warrant Price and the number of shares of Warrant
         Stock are subject to adjustment upon the occurrence of certain events,
         pursuant to the provisions of Section 8 of this Agreement. Subject to
         the provisions of this Agreement, each Holder shall have the right to
         purchase from the Company (and the Company shall issue and sell to such
         Holder) the number of fully paid and nonassessable shares of Warrant
         Stock specified in such Holder's Warrant Certificate(s) (as adjusted
         from time to time in accordance with the provisions of Section 8 of
         this Agreement), upon surrender of such Warrant Certificate(s) to the
         Company or its duly authorized agent, and upon payment to the Company
         of the Warrant Price, as adjusted in accordance with the provisions of
         Section 8 of this Agreement, for the number of shares of Warrant Stock
         in respect of which such Warrants are then exercised. The date of
         exercise (the "Exercise Date") of any Warrant shall be deemed to be the
         date of

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         receipt by the Company of the Warrant Certificate duly filled in and
         signed and accompanied by proper payment as hereinafter provided.
         Payment of the Warrant Price shall be made as set forth in the Warrant
         Certificate.

                  (c) Exercise Procedure: This Warrant shall be deemed to have
         been exercised when the Company has received all of the following
         items:

                           (i) a completed Exercise Notice, attached as EXHIBIT
                  "C" hereto, executed by the Holder;

                           (ii) this Warrant;

                           (iii) either (A) a check payable to the Company in an
                  amount equal to the product of the Warrant Price multiplied by
                  the number of shares of Common Stock being purchased upon such
                  exercise (the "Aggregate Warrant Price"), (B) the surrender to
                  the Company of debt or equity securities of the Company having
                  a Current Market Price equal to the Aggregate Warrant Price of
                  the Common Stock being purchased upon such exercise (provided
                  that for purposes of this subparagraph, the Current Market
                  Price of any note or other debt security shall be deemed to be
                  equal to the aggregate outstanding principal amount thereof
                  plus all accrued and unpaid interest thereon) or (C) a written
                  notice to the Company that the Holder is exercising the
                  Warrant (or a portion thereof) by authorizing the Company to
                  withhold from issuance a number of shares of Common Stock
                  issuable upon such exercise of the Warrant which when
                  multiplied by the Current Market Price of the Common Stock is
                  equal to the Aggregate Warrant Price (and such withheld shares
                  shall no longer be issuable under this Warrant).

                  (d) Subject to Section 5 of this Agreement, upon such exercise
         of Warrants, and payment of the Warrant Price as aforesaid, the Company
         shall issue and cause to be delivered with all reasonable dispatch (but
         in any event within two (2) business days) to or (subject to the
         provisions of Section 3 of this Agreement) upon the written order of
         the Holder, a certificate for the number of full shares of Warrant
         Stock so purchased upon the exercise of such Warrants, together with
         cash, as provided in Section 11 of this Agreement, in respect of any
         fraction of a share of such stock otherwise issuable upon such exercise
         prior to a Public Offering. Except under circumstances described in the
         following sentence, the shares of Warrant Stock purchased pursuant to
         the immediately preceding sentence shall be deemed to be issued to the
         Holder as the record owner of such shares as of 5:00 p.m. Cleveland,
         Ohio local time on the Exercise Date. The right of purchase represented
         by the Warrants shall be exercisable, at the election of the Holder
         thereof, either in full or from time to time in part and, in the event
         that any Warrant is exercised in respect of less than all of the shares
         of Warrant Stock purchasable on such exercise at any time prior to the
         Expiration Date, a new Warrant Certificate evidencing the remaining
         Warrants shall be issued.

         5. PAYMENT OF TAXES. The Company shall pay all documentary stamp taxes,
if any, attributable to the initial issuance of Warrant Stock upon the exercise
of Warrants; provided, however, that the Company shall not be required to pay
any tax or taxes which may be payable in respect of any permitted transfer
involved in the issue or delivery of any Warrant Certificates or Warrant Stock
in a name other than that of the registered Holder of such Warrants.

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         6. MUTILATED OR MISSING WARRANTS. Upon (i) receipt by the Company of
evidence reasonably satisfactory to it of the loss, theft, destruction or
mutilation of a Warrant Certificate, (ii) if requested by the Company, the
posting of a bond in an amount equal to the value of the lost, stolen or
destroyed Warrant Certificate, (iii) reimbursement to the Company of all
reasonable expenses incident thereto, and (iv) surrender and cancellation of
such Warrant Certificate, if mutilated, the Company will make and deliver in
lieu of such Warrant Certificate a new Warrant Certificate of like tenor and
representing an equivalent right or interest. The term "outstanding" when used
herein with reference to the Warrant Certificate as of any particular time shall
not include any Warrant Certificate in lieu of which a new Warrant Certificate
has been made and delivered by the Company in accordance with the provisions
hereof.

         7. RESERVATION OF WARRANT STOCK.

                  (a) The Company represents that there has been reserved out of
         the authorized and unissued shares of Common Stock, a number of shares
         sufficient to provide for the exercise of the right of purchase
         represented by the Warrant Certificates as initially issued, and the
         Company, which currently acts as the transfer agent for its Common
         Stock ("Transfer Agent") and every subsequent Transfer Agent for any
         shares of the Company's capital stock issuable upon the exercise of any
         of the Warrants are hereby irrevocably authorized and directed at all
         times until the Expiration Date or earlier termination of this
         Agreement to reserve such number of authorized and unissued shares of
         Common Stock as shall be required for such purpose. The Company will
         keep a copy of this Agreement on file with every subsequent Transfer
         Agent for any shares of the Company's capital stock issuable upon the
         exercise of the Warrants. The Company will supply any such subsequent
         Transfer Agent with duly executed stock certificates for issuance on
         exercise of Warrants and will itself provide or otherwise make
         available any cash which may be required by Section 11 of this
         Agreement. The Company will furnish to any such subsequent Transfer
         Agent a copy of all notices of adjustments, and certificates related
         thereto, transmitted to each Holder pursuant to Section 10 of this
         Agreement. All Warrant Certificates surrendered in the exercise of the
         rights thereby evidenced shall be canceled.

                  (b) The Company covenants that it shall comply with all
         securities laws regulating the offer and delivery of shares of Common
         Stock upon exercise of the Warrants; and that, if any shares of Common
         Stock required to be reserved for purposes of exercising the Warrants
         hereunder require registration with or approval of any governmental
         authority under any Federal or state law before such shares may be
         validly issued or delivered upon exercise of the Warrants, the Company
         shall, in good faith and as expeditiously as possible, secure such
         registration or approval, as the case may be. The Company covenants
         that all shares of Common Stock which shall be issued upon exercise of
         the Warrants shall upon issue and payment therefor be validly issued,
         fully paid and nonassessable.

         8. ADJUSTMENTS OF WARRANT PRICE AND NUMBER OF SHARES OF WARRANT STOCK.
The number and kind of securities purchasable upon the exercise of each Warrant
and the Warrant Price shall be subject to adjustment from time to time upon the
happening of certain events, as hereinafter defined, but only as to Warrants
outstanding at the time of such adjustment. Upon each adjustment of the Warrant
Price pursuant to the provisions of Section 8(c), the Holder of such Warrant
shall thereafter, prior to the Expiration Date thereof, be entitled to purchase
at the Warrant Price resulting from such adjustment, the number of shares of
Warrant Stock obtained by multiplying the Warrant Price in

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<PAGE>   6

effect immediately prior to such adjustment by the number of shares of Warrant
Stock issuable upon exercise of such Warrant immediately prior to such
adjustment and dividing the product thereof by the Warrant Price resulting from
such adjustment. The number of shares of Warrant Stock or the Warrant Price, as
the case may be, shall be subject to adjustment as follows:

                  (a) ADJUSTMENT FOR STOCK SPLITS AND COMBINATIONS. If the
         Company shall at any time after the date of the issuance of the
         Warrants effect a subdivision or combination of any outstanding Common
         Stock, the Warrant Price then in effect immediately before that
         subdivision or combination shall be proportionately adjusted by
         multiplying the then effective Warrant Price by a fraction, (i) the
         numerator of which shall be the number of Common Shares issued and
         outstanding immediately prior to such subdivision or combination, and
         (ii) the denominator of which shall be the number of Common Stock
         issued and outstanding immediately after such subdivision or
         combination. The number of Common Stock outstanding at any time shall,
         for the purposes of this Section 8(a), include the number of Common
         Shares into which any convertible securities of the Company may be
         converted, or for which any warrant, option or rights of the Company
         may be exchanged. Any adjustment under this Section 8(a) shall become
         effective at the close of business on the date the subdivision or
         combination becomes effective.

                  (b) ADJUSTMENT FOR RECLASSIFICATION, EXCHANGE OR SUBSTITUTION.
         If the Common Stock issuable upon the exercise of the Warrants 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
         provided for above, or a reorganization, merger, consolidation or sale
         of assets provided for elsewhere in this Section 8), then and in each
         such event the holder of each Warrant shall have the right thereafter
         to exercise and convert each such Warrant, after payment of the Warrant
         Price, into the kind and amounts of shares of stock and other
         securities and property receivable upon such reorganization,
         reclassification or other change, by holders of the maximum number of
         Common Stock into which such Warrants could have been converted
         immediately prior to such reorganization, reclassification or change,
         all subject to further adjustment as provided herein.

                  (c) In the event that the Company shall issue or be deemed to
         have issued any Common Stock other than Excluded Shares (as hereinafter
         defined) ("Additional Common Stock") without consideration or for a
         consideration per share less than Eleven Thousand Dollars ($11,000),
         and a Holder of Warrants shall have participated pro-rata with respect
         to its Shares of Class C Preferred in such financing (the
         "Participating Holder"), the Warrant Price in effect immediately prior
         to each such issuance for the Participating Holder's Warrant shall be
         reduced to the lowest price per share at which such Additional Common
         Shares shall have been issued.

                  (d) For the purposes of any adjustment of the Warrant Price
         pursuant to paragraph (c) above, the following provisions shall be
         applicable:

                           (x) CASH. In the case of the issuance of shares of
                  Common Stock for cash, the amount of the consideration
                  received by the Company shall be deemed to be the amount of
                  the cash proceeds received by the Company for such shares of
                  Common Stock before deducting therefrom any discounts,
                  commission, taxes or other expenses

                                        5

<PAGE>   7

                  allowed, paid or incurred by the Company for any underwriting
                  or otherwise in connection with the issuance and sale thereof;
                  and

                           (y) CONSIDERATION OTHER THAN CASH. In the case of the
                  issuance of shares of Common Stock (other than upon the
                  conversion of shares of capital stock or other securities of
                  the Company) for consideration in whole or in part other than
                  cash, including securities acquired in exchange therefor
                  (other than securities by their terms so exchangeable), the
                  consideration other than cash shall be deemed to be the fair
                  value thereof (as determined in good faith by the Board of
                  Directors of the Company, whose determination shall be
                  conclusive to the extent reasonable), irrespective of any
                  accounting treatment provided, that such fair value as
                  determined by the Board of Directors shall not exceed the
                  aggregate Current Market Price (as defined below) of the
                  Common Stock being issued as of the date the Board of
                  Directors authorizes the issuance of such Common Stock; and

                           (z) OPTIONS AND CONVERTIBLE SECURITIES. In the case
                  of the issuance of (i) options, warrants or other rights to
                  purchase or acquire shares of Common Stock (whether or not at
                  the time exercisable) other than Excluded Shares, (ii)
                  securities by their terms convertible into or exchangeable for
                  shares of Common Stock (whether or not at the time so
                  convertible or exchangeable), or (iii) options, warrants or
                  rights to purchase such convertible or exchangeable securities
                  (whether or not at the time exercisable):

                                    (1) the aggregate maximum number of shares
                           of Common Stock deliverable upon exercise of such
                           options, warrants or other rights to purchase or
                           acquire shares of Common Stock shall be deemed to
                           have been issued at the time such options, warrants
                           or other rights become exercisable for a
                           consideration equal to the consideration (determined
                           in the manner provided in clauses (x) and (y) above),
                           if any, received by the Company upon the issuance of
                           such options, warrants or other rights plus the
                           minimum purchase price provided in such options,
                           warrants or other rights for the shares of Common
                           Stock covered thereby;

                                    (2) the aggregate maximum number of shares
                           of Common Stock deliverable upon conversion of or in
                           exchange for any such convertible or exchangeable
                           securities, or upon the exercise of options, warrants
                           or other rights to purchase or acquire such
                           convertible or exchangeable securities and the
                           subsequent conversion or exchange thereof, shall be
                           deemed to have been issued at the time such
                           convertible or exchangeable securities or such
                           options, warrants or other rights are first issued
                           and for a consideration equal to the consideration,
                           if any, received by the Company for any such
                           convertible or exchangeable securities or options,
                           warrants or other rights (excluding any cash received
                           on account of accrued interest or accumulated
                           dividends), plus the additional consideration, if
                           any, to be received by the Company upon the
                           conversion or exchange of such securities and the
                           exercise of any options, warrants or other rights
                           (the consideration in each case to be determined in
                           the manner provided in clauses (x) and (y) above);

                                        6

<PAGE>   8

                                    (3) on any change in the number of shares of
                           Common Stock deliverable upon exercise of any such
                           options, warrants or other rights which have become
                           exercisable or conversion of or exchange of such
                           convertible or exchangeable securities which have
                           become convertible or exchangeable, or any change in
                           the consideration to be received by the Company upon
                           such exercise, conversion or exchange, including but
                           not limited to, a change resulting from any
                           subdivision, split-up combination or reclassification
                           thereof, the Warrant Price as then in effect shall
                           forthwith be readjusted to such Warrant Price as
                           would have been obtained had such adjustment been
                           made upon such options, warrants or other rights;
                           provided, however, no adjustment shall be made with
                           respect to such options, warrants or other rights
                           exercised prior to such change, or securities
                           converted or exchanged prior to such change;

                                    (4) on the expiration or cancellation of any
                           such options, warrants or other rights, or the
                           termination of the right to convert or exchange such
                           convertible or exchangeable securities, if the
                           Warrant Price shall have been adjusted upon such
                           securities being issued or becoming exercisable,
                           convertible or exchangeable, such Warrant Price shall
                           forthwith be readjusted to such Warrant Price as
                           would have been obtained had an adjustment been made
                           on the basis of the issuance of only the number of
                           shares of Common Stock actually issued upon the
                           exercise of such options, warrants or other rights,
                           or upon the conversion or exchange of such
                           securities; and

                                    (5) if the Warrant Price shall have been
                           adjusted when such options, warrants or other rights
                           were first issued or such convertible or exchangeable
                           securities were first issued, no further adjustment
                           of the Warrant Price shall be made for the actual
                           issuance of shares of Common Stock upon the exercise,
                           conversion or exchange thereof.

                  (e) "Excluded Shares" shall mean Common Stock issued or
         reserved for issuance by the Company: (i) as a stock dividend payable
         in Common Stock; (ii) upon any subdivision or split-up of the
         outstanding Common Stock; (iii) to employees, consultants, officers and
         directors of the Company designated from time to time by the Board of
         Directors pursuant to a stock option plan, but not exceeding Nine
         Hundred Thirty (930) Common Stock in the aggregate (adjusted for any
         stock dividend payable in Common Stock, upon any subdivision, split-up,
         combination or reclassification of Common Stock, occurring after the
         date hereof) or such higher number of Common Stock as may be designated
         by the vote or written consent of at least seventy-five percent (75%)
         of the Class C Preferred; (iv) pursuant to the terms of any acquisition
         by the Company of all or substantially all of the operating assets, or
         more than fifty percent (50%) of the voting capital stock or other
         management interest of any Person in a transaction expressly approved
         in advance by at least seventy-five percent (75%) of the Class C
         Preferred; (v) upon conversion of Class A Preferred, Class B Preferred,
         Class C Preferred, Class D Preferred or any other class of convertible
         preferred stock; (vi) Class C Preferred issued to investors for an
         aggregate purchase price not to exceed Five Million Dollars
         ($5,000,000) within 60 days of the date hereof; and (vii) 29.9 Shares
         of Common Stock issuable to Michael Gallo upon exercise of a warrant.

                                        7

<PAGE>   9

                  (f) "Current Market Price" shall mean the price per share of
         Common Stock determined by the Board of Directors as provided below.
         The Current Market Price shall be the average of the daily closing
         prices per share of Common Stock for thirty (30) consecutive business
         days immediately ending no more than fifteen (15 ) business days before
         the day in question (as adjusted for any stock dividend, split,
         combination, reclassification, reorganization or similar transaction
         that took effect during such thirty (30) business day period). The
         closing price for each day shall be the last reported sales price
         regular way, or, in case no such reported sales take place on any such
         day, the average of the last reported bid and asked prices regular way,
         in either case on the principal national securities exchange on which
         the Common Stock is listed or admitted to trading, or if not listed or
         admitted to trading on any national securities exchange, the average of
         the highest bid and the lowest asked prices quoted on the National
         Association of Securities Dealers Automated Quotation ("NASDAQ") System
         or through a similar organization if NASDAQ is no longer reporting such
         information; provided, that if the Common Stock is not traded in such a
         manner that the quotations referred to above are available for the
         period required hereunder, the Current Market Price per share of Common
         Stock shall be deemed to be the fair value as determined by the Board
         of Directors (whose determination shall be conclusive), irrespective of
         any accounting treatment; provided, that, if within fifteen (15) days
         of receiving notice of an event under paragraph 8(c) requiring the
         calculation of the Current Market Price, a Holder of at least ten
         percent (10%) of the currently outstanding Warrants requests the
         appointment of an independent appraiser, the Board of Directors shall,
         within ten (10) days of such request, appoint as an independent
         appraiser a nationally-known independent public accounting firm or
         investment bank and the Board of Directors shall direct such
         independent appraiser to conduct an appraisal and make a report on the
         Current Market Price of a Common Share within thirty (30) days of its
         appointment. The determination of Current Market Price by such
         independent appraiser shall be final and binding upon the Corporation
         and the holders of Warrants. The costs of such independent appraiser
         shall be paid by the Corporation. Any independent appraiser so utilized
         shall agree to treat all information supplied by the Corporation in a
         confidential manner.

                  (g) No adjustment in the Warrant Price shall be required
         unless such adjustment would require an increase or decrease of at
         least one percent (1%) in such price; provided, however, that any
         adjustments which by reason of this subsection (f) are not required to
         be made shall be carried forward and taken into account in any
         subsequent adjustment. All calculations under Section 8 shall be made
         to the nearest tenth of a cent or to the nearest one-hundredth of a
         share, as the case may be.

                  (h) The number of shares of Common Stock outstanding at any
         given time shall not include shares owned or held by or for the account
         of the Company, and the disposition of any such shares shall be
         considered an issuance of Common Stock for the purposes of this Section
         8.

         9. RIGHTS TO PURCHASE OTHER SECURITIES. If any of the following shall
         occur:

                  (a) any consolidation or merger to which the Company is a
         party, other than a consolidation or a merger in which the Company is
         the continuing or surviving Company and which does not result in any
         reclassification of, or change (other than as a result of a subdivision
         or combination) in, outstanding shares of the Common Stock, or

                                        8

<PAGE>   10

                  (b) any sale or transfer to another corporation or entity of
         all or substantially all of the assets of the Company;

then, and in either such case, the Holder of each Warrant then outstanding shall
have the right to purchase the kind and amount of shares of stock and/or other
securities and property receivable upon such consolidation, merger, sale or
transfer by a holder of the number of shares of Common Stock issuable upon
exercise of such Warrant immediately prior to such consolidation, merger, sale,
or transfer. The provisions of this Section 9 shall similarly apply to
successive consolidations, mergers, sales or transfers.

         10. NOTICE OF ADJUSTMENT. Whenever the number of shares of Warrant
Stock purchasable upon the exercise of each Warrant or the Warrant Price of such
Warrant Stock is adjusted or reduced, as herein provided, the Company shall mail
by first class, postage prepaid, to each Holder (a) a notice of any reduction on
or before the day the reduction takes effect, which shall state the reduced
Warrant Price and the period during which it will be in effect and/or; (b) a
certificate setting forth the number of shares of Warrant Stock purchasable upon
the exercise of each Warrant and the Warrant Price on such Warrant Stock after
an adjustment, setting forth a brief statement of the facts requiring such
adjustment and setting forth the computation by which such adjustment was made.

         11. ELIMINATION OF FRACTIONS. After a Public Offering, the Company
shall not be required to issue certificates representing fractional shares of
Common Stock upon any exercise of Warrants, but will make a payment in cash, in
lieu of issuing such fractional shares, based on the Current Market Price per
share at the time.

         12. TRANSFER OF WARRANT; STOCKHOLDERS' AGREEMENT. No holder of the
Warrants shall transfer, issue, or reissue any portion of the Warrant to any
person who does not execute a supplemental agreement, agreeing to comply with
all of the terms and conditions stated in the Stockholders' Agreement between
the Company and its stockholders dated March 19, 1996, as amended (the
"Stockholders' Agreement"), but whether or not such agreement is executed, such
person in any event shall be bound by and shall perform the obligations imposed
on all stockholders thereunder.

         13. CERTIFICATES TO BEAR LEGENDS.

                  (a) The Warrant Certificates and certificates representing
         shares of Warrant Stock shall be subject to a stop-transfer order and
         each such certificate shall bear the following legends by which each
         Holder shall be bound until such securities have been sold pursuant to
         Rule 144 or in a transaction registered under the Securities Act:

                  THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
                  ACT OF 1933 (THE "ACT"). THEY MAY NOT BE SOLD, OFFERED FOR
                  SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE
                  REGISTRATION STATEMENT AS TO THE SECURITIES UNDER THE ACT OR
                  AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY
                  THAT SUCH REGISTRATION IS NOT REQUIRED. THESE SECURITIES HAVE
                  BEEN ISSUED UNDER AND ARE

                                        9

<PAGE>   11

                  GOVERNED BY AND ARE SUBJECT TO THAT CERTAIN WARRANT AGREEMENT
                  DATED OCTOBER 30, 1998 (THE "WARRANT AGREEMENT"). A COPY OF
                  THE WARRANT AGREEMENT CAN BE OBTAINED FROM THE SECRETARY OF
                  THE COMPANY.

                  (b) The Warrant Stock shall be subject to certain restrictions
         on transfer as provided in the Stockholders' Agreement. Each
         certificate representing shares of Warrant Stock of the Company shall,
         so long as such shares are subject to such agreement, be stamped with a
         legend in substantially the following form:

                  THE TRANSFER OF THE SHARES OF STOCK REPRESENTED BY THE WITHIN
                  CERTIFICATE IS RESTRICTED UNDER THE TERMS OF AN AGREEMENT
                  DATED MARCH 19, 1996, AS AMENDED, AMONG THE CORPORATION AND
                  ITS STOCKHOLDERS, A COPY OF WHICH AGREEMENT WILL BE MAILED TO
                  THE HOLDER HEREOF WITHOUT CHARGE WITHIN FIVE (5) DAYS AFTER
                  RECEIPT BY THE CORPORATION OF WRITTEN REQUEST THEREFOR.

         14. NO RIGHTS AS STOCKHOLDERS; NOTICES TO HOLDERS. Nothing contained in
this Agreement or in any of the Warrant Certificates shall be construed as
conferring upon the Holders or their transferees the right to vote or to receive
dividends or to consent to or receive notice as stockholders in respect of any
meeting of stockholders for the election of directors of the Company or on any
other matter, or any rights whatsoever as stockholders of the Company. If,
however, at any time prior to the exercise of the Warrants any of the following
events shall occur:

                  (a) the Company shall declare any dividend or other
         distribution payable in any securities or other property upon its
         shares of Common Stock to the holders of its shares of Common Stock; or

                  (b) the Company shall offer to all of the holders of its
         shares of Common Stock any additional shares of Common Stock or
         securities convertible into or exchangeable for shares of Common Stock
         or any right to subscribe to or purchase any thereof; or

                  (c) there shall be any capital reorganization, or
         reclassification of the capital stock of the Company, or consolidation
         or merger of the Company with another corporation, or sale of all or
         substantially all of its assets to, another corporation; or

                  (d) there shall be a voluntary dissolution, liquidation,
         bankruptcy, reorganization, arrangement, assignment for the benefit of
         creditors, or winding up of the Company; or

                  (e) there shall be filed against the Company a petition for an
         involuntary dissolution, liquidation, bankruptcy or reorganization of
         the Company;

then in any one or more of said events the Company shall give notice in writing
of such event to the Holders as provided in Section 17 of this Agreement at
least twenty (20) days prior to the occurrence of such event or, if the event
requires the setting of a record date, then twenty (20) days prior to such

                                       10

<PAGE>   12

record date (except for Section 14(e) of which the Company shall give notice
within five days after the occurrence of any such event).

         15. INVESTMENT INTENT. The Warrants to be purchased pursuant to this
Agreement are being purchased for each Investors' own accounts (or on behalf of
managed accounts who are purchasing for their own accounts) and with no
intention of distributing the Warrants in violation of securities laws. Each
Holder understands that neither the Warrants nor the Common Stock have been
registered under the Act or any applicable state securities laws and that
neither the Warrants nor the Common Stock can be sold, transferred or otherwise
disposed of without registration under the Act and applicable state securities
laws, unless it has been established to the satisfaction of the Company that
they may be sold, transferred or otherwise disposed of without such
registration.

         16. VALUE OF WARRANT. The value of the Warrants in the event of a
Liquidation or Sale shall be the difference between the value of the underlying
Common Stock upon the closing of such Liquidation or Sale and the Warrant Price
of the Warrant.

         17. NOTICES. Any notice pursuant to this Agreement to be given or made
by the Holder of any Warrant Certificate to or on the Company shall be
sufficiently given or made if delivered personally or sent by telecopier or by
certified mail, addressed to the President of the Company at the Company's
principal executive offices at 11000 Cedar Avenue, Suite 210, Cleveland, OH
44106, Attn: Gil Van Bokkelen (unless notice has been given of a change of such
address), and shall be effective three (3) days after having been mailed or upon
receipt if delivered personally or sent by telecopier, with receipt confirmed by
the office of the President. Notices or demands authorized by this Agreement to
be given or made to the Holder of any Warrant Certificate shall be sufficiently
given or made if delivered personally or sent by certified mail or by
telecopier, addressed to such Holder at the address of such Holder as shown on
the Warrant Register, and shall be effective three (3) days after having been
mailed or upon receipt if delivered personally or sent by telecopier, with
receipt confirmed.

         18. GOVERNING LAW. 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.

         19. SUPPLEMENTS AMENDMENTS AND WAIVERS. Any supplement or amendment to,
or any waiver of any provision of, this Agreement shall be effective when
consented to in writing by the

                                       11

<PAGE>   13

Holders of seventy-five percent (75%) of the Warrants then outstanding
(determined as though there were one Warrant for each share of Common Stock
issuable on the exercise of the then outstanding Warrants) and by the Company.
The Company and seventy-five percent (75%) of the Holders may from time to time
supplement or amend this Agreement in order to cure any ambiguity or to correct
or supplement any provision contained herein which may be defective or
inconsistent with any other provision herein, or to make any other provisions in
regard to matters or questions arising hereunder which the Company and the
Holders may deem necessary or desirable and which shall not be inconsistent with
the provisions of the Warrant Certificates and which shall not adversely affect
the interest of the Holders.

         20. SUCCESSORS. All the covenants and provisions of this Agreement by
or for the benefit of the Company or the Holders shall bind and inure to the
benefit of their respective successors and assigns hereunder.

         21. COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which so executed shall be deemed to be an original; but
such counterparts together shall constitute but one and the same instrument.

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed on the day, month and year first above written.

                                           ATHERSYS, INC.

                                           By:      /s/ Gil Van Bokkelen
                                                    ----------------------------
                                           Title:   President and CEO

                                       12

<PAGE>   14

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

OHIO INNOVATION FUND I, L.P.

By:                /s/ Timothy G. Biro
                  ------------------------------
Title:             Managing Partner
                  ------------------------------

Name:
                  ------------------------------
Title:
                  ------------------------------
Address:          ------------------------------
                  ------------------------------
                  ------------------------------

Telephone No.:             ---------------------
Telecopier No.:            ---------------------

                                       13

<PAGE>   15

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

BLUE CHIP CAPITAL FUND II LIMITED PARTNERSHIP

By:               Blue Chip Venture Company, Ltd.

By:               /s/ John C. McIlwraith
                  ------------------------------------
                  Name:  John C. McIlwraith
                         -----------------------------
                  Title: Manager

Name:             John C. McIlwraith
                  ------------------------------------
Title:            Manager
                  ------------------------------------
Address:          2000 PNC Center
                  ------------------------------------
                  201 E. 5th Street
                  ------------------------------------
                  Cincinnati, OH 45202
                  ------------------------------------

Telephone No.:             (513) 723-2300
                           --------------------
Telecopier No.:            (513) 723-2306
                           --------------------

                                       14

<PAGE>   16

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

MIAMI VALLEY VENTURE FUND L.P.

By:               Blue Chip Venture Company of Dayton, Ltd.

By:               /s/ John C. McIlwraith
                  ------------------------------------
                  Name:  John C. McIlwraith
                  ------------------------------------
                  Title: Manager
                  ------------------------------------

Name:             John C. McIlwraith
                  ------------------------------------
Title:            Manager
                  ------------------------------------
Address:          2000 PNC Center
                  ------------------------------------
                  201 E. 5th Street
                  ------------------------------------
                  Cincinnati, OH 45202
                  ------------------------------------

Telephone No.:             (513) 723-2300
                           --------------------
Telecopier No.:            (513) 723-2306
                           --------------------

                                       15

<PAGE>   17

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

PRIMUS CAPITAL FUND IV LIMITED PARTNERSHIP

By:      Primus Venture Partners IV Limited Partnership, its general partner

By:      Primus Venture Partners IV, Inc., its general partner

By:               /s/ William Mulligan
                  ------------------------------
Title:            EVP
                  ------------------------------

Name:             ------------------------------
Title:            ------------------------------
Address:          ------------------------------
                  ------------------------------
                  ------------------------------

Telephone No.:             ------------------
Telecopier No.:            ------------------

<PAGE>   18

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

PRIMUS EXECUTIVE FUND LIMITED PARTNERSHIP

By:      Primus Venture Partners IV Limited Partnership, its general partner

By:      Primus Venture Partners IV, Inc., its general partner

By:           /s/ William Mulligan
              ------------------------------
Title:        EVP
              ------------------------------

Name:         ------------------------------
Title:        ------------------------------
Address:      ------------------------------
              ------------------------------
              ------------------------------

Telephone No.:         ---------------------
Telecopier No.:        ---------------------

<PAGE>   19

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

SENTRON MEDICAL INCORPORATED

By:           /s/ Vincent M. Paglino
              ---------------------------------
Title:        Vice President
              ---------------------------------

Name:         Vincent M. Paglino
              ---------------------------------
Title:        Vice President
              ---------------------------------
Address:      4445 Lake Forest Drive
              ---------------------------------
              Suite 600
              ---------------------------------
              Cincinnati, OH 45242
              ---------------------------------

Telephone No.:             (513) 563-3240
                           --------------------
Telecopier No.:            (513) 563-3261 (fax)
                           --------------------

<PAGE>   20

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

WARBURG DILLON READ LLC

By:           /s/ Kipp K. Schrage
              ------------------------------
Title:        Managing Director Equities
              ------------------------------

Name:         ------------------------------
Title:        ------------------------------
Address:      ------------------------------
              ------------------------------
              ------------------------------

By:           /s/ Raymond Yee
              ------------------------------
Title:        Executive Director Equities
              ------------------------------

Name:         ------------------------------
Title:        ------------------------------
Address:      ------------------------------
              ------------------------------
              ------------------------------

Telephone No.:         ---------------------
Telecopier No.:        ---------------------

<PAGE>   21

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

NEOMED INNOVATION, ASA

By:           /s/ Fredrik C. Schreuder           /s/ Carl Chr. Gilhuus-Moe, Ph.D
              -----------------------------      General Partner
Title:        General Partner
              -----------------------------

Name:         Fredrik C. Schreuder
              -----------------------------
Title:        General Partner
              -----------------------------
Address:      Parkveien 55
              -----------------------------
              N-0256 Oslo
              -----------------------------
              Norway
              -----------------------------

Telephone No.:             47-22545940
                           ----------------
Telecopier No.:            47-22545941
                           ----------------

<PAGE>   22

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

HOEGH INVEST, AS

By:           /s/ Carl Preben Hoegh
              ------------------------
Title:        Chairman
              ------------------------

Name:              Carl Preben Hoegh
              ------------------------
Title:        ------------------------
Address:      Parkveien 55
              ------------------------
              0256 Oslo
              ------------------------
              Norway
              ------------------------

Telephone No.:             47-22122800
                           -----------
Telecopier No.:            47-22552276
                           -----------
<PAGE>   23

                    WARRANT PURCHASE AGREEMENT SIGNATURE PAGE

Accepted and agreed as of
the date first above written:

ATHERSYS INVESTOR LLC

By:           /s/ Jud Martin
              -------------------------
Title:        Manager
              -------------------------

Name:         Jud Martin
              -------------------------
Title:        Manager
              -------------------------
Address:      329 W 40
              -------------------------
              Scottsfield, NE 64361
              -------------------------

Telephone No.:             308-635-3911
                           ------------
Telecopier No.:            308-635-3130
                           ------------

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