Document:

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                                                                     Exhibit 4.4

                                                                  EXECUTION COPY

                                 ATHERSYS, INC.
                          REGISTRATION RIGHTS AGREEMENT
                          -----------------------------

                  THIS REGISTRATION RIGHTS AGREEMENT (the "AGREEMENT") is made
as of October 21, 1999 by and among ATHERSYS, INC., a Delaware corporation (the
"COMPANY"), and ELAN INTERNATIONAL SERVICES, LTD., a Bermuda exempt limited
liability company ("EIS").

                                R E C I T A L S:

                  A. Pursuant to a Securities Purchase Agreement dated as of the
date hereof by and between the Company and EIS (the "PURCHASE AGREEMENT"), EIS
has acquired, or will acquire in the future, certain shares of common stock of
the Company (the "COMMON STOCK"), Class E Convertible Exchangeable Preferred
Stock of the Company (the "CLASS E PREFERRED STOCK"), and a convertible
promissory note (the "NOTE"), which Class E Preferred Stock and Note are
convertible into shares of Common Stock.

                  B. The execution of the Purchase Agreement has occurred on the
date hereof and it is a condition to the closing of the transactions
contemplated thereby that the parties execute and deliver this Agreement.

                  C. The parties desire to set forth herein their agreement on
the terms and subject to the conditions set forth herein related to the granting
of certain registration rights to the Holders (as defined below) relating to the
Common Stock held by such Holders and the Common Stock underlying the Class E
Preferred Stock and the Note.

                               A G R E E M E N T:

                  The parties hereto agree as follows:

                  1. CERTAIN DEFINITIONS. As used in this Agreement, the
following terms shall have the following respective meanings:

                  "COMMISSION" shall mean the U.S. Securities and Exchange
Commission.

                  "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934,
as amended, and the rules and regulations of the Commission thereunder, all as
the same shall be in effect from time to time.

                  "HOLDERS" or "HOLDERS OF REGISTRABLE SECURITIES" shall mean
EIS and any Person who shall have acquired Registrable Securities from EIS as
permitted herein, either individually or jointly, as the case may be, in a
transaction pursuant to which registration rights are transferred pursuant to
Section 12 hereof.

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                  "PERSON" shall mean an individual, a partnership, a company,
an association, a joint stock company, a trust, a joint venture, an
unincorporated organization and a governmental or quasi-governmental entity, or
any department, agency or political subdivision thereof.

                  "REGISTRABLE SECURITIES" means (i) any shares of Common Stock
purchased pursuant to the Purchase Agreement, any shares of Common Stock issued
or issuable upon conversion of shares of Class E Preferred Stock (or issued as
dividends thereon) or the Note, and (ii) any Common Stock issued or issuable in
respect of the securities referred to in clause (i) above upon any stock split,
stock dividend, recapitalization or similar event until, in the case of any such
security, it is effectively registered under the Securities Act and disposed of
in accordance with the registration statement covering it; excluding in all
cases, however, any Registrable Securities that may be sold under Rule 144
promulgated under the Securities Act, as such rule may be amended from time to
time, or any similar rule or regulation hereafter adopted by the Commission,
without being subject to the volume limitations under Rule 144, and Registrable
Securities sold by a Person in a transaction (including a transaction pursuant
to a registration statement under this Agreement and a transaction pursuant to
Rule 144 promulgated under the Securities Act) in which registration rights are
not transferred pursuant to Section 12 hereof.

                  The terms "REGISTER," "REGISTERED" and "REGISTRATION" refer to
a registration effected by preparing and filing a registration statement in
compliance with the Securities Act.

                  "REGISTRATION EXPENSES" shall mean all expenses, other than
Selling Expenses, incurred by the Company in complying with Sections 3 or 4
hereof, including without limitation, all registration, qualification and filing
fees, exchange listing fees, printing expenses, escrow fees, fees and
disbursements of counsel for the Company, blue sky fees and expenses, and the
expense of any special audits incident to or required by any such registration.

                  "SECURITIES ACT" shall mean the Securities Act of 1933, as
amended.

                  "SELLING EXPENSES" shall mean all underwriting discounts,
selling commissions and stock transfer taxes and the costs, fees and expenses of
any accountants or other experts, including legal counsel, retained by the
Holders.

                  "UNDERWRITER(S)" means any one or more investment banking or
brokerage firms to or through whom the Company may offer and sell Common Stock
pursuant to a transaction requiring the filing of a registration statement under
the Securities Act, including one or more of such firms who manage such public
offering through such Underwriters and who are referred to herein as "MANAGING
UNDERWRITER(S)."

                  2. HOLDERS OF REGISTRABLE SECURITIES. Whenever a number or
percentage of Registrable Securities is to be determined pursuant to this
Agreement, each then-outstanding Preferred Share that is convertible into Common
Stock will be deemed to be equal to the number of shares of Common Stock for
which such Preferred Share is then so convertible.

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                  3.  DEMAND REGISTRATION.

                  (a) REQUESTS FOR REGISTRATION. In the event that (i) the
Company receives from the Holders a written request that the Company file a
registration statement on Form S-3 (or any successor form to Form S-3), or any
similar short-term registration statement, for a public offering of Registrable
Securities (a "DEMAND REGISTRATION"), the reasonably anticipated aggregate price
to the public of which, net of underwriting discounts and commissions, would be
at least U.S. $1,000,000 and (ii) the Company is a registrant eligible to use
Form S-3 to register the Registrable Securities for such an offering, within 30
days after receipt of any such request, the Company will give written notice of
such requested registration to all other Holders of Registrable Securities. The
Company shall include such other Holders' Registrable Securities in such
offering if they have responded affirmatively within 30 days after the receipt
of the Company's notice. The number of Demand Registrations pursuant to this
Section 3(a) shall not exceed one, PROVIDED, HOWEVER, that a registration will
not count as a permitted Demand Registration until it has become effective,
unless such Demand Registration has not become effective due solely to the fault
of the Holders requesting such registration, including a request by such Holders
that such registration be withdrawn.

                  (b) PRIORITY ON DEMAND REGISTRATION. If a Demand Registration
is an underwritten offering and the Managing Underwriters advise the Company
that in their opinion the number of Registrable Securities requested to be
included in such offering exceeds the number of Registrable Securities which can
be sold in such offering without adversely affecting the marketability of the
offering, the Company will include in such registration such number of
Registrable Securities allocated pro rata among the Holders thereof based upon
the number of Registrable Securities owned by each such Holder. No securities
other than Registrable Securities hereunder shall be included in such Demand
Registration without the prior written consent of Holders who collectively hold
Registrable Securities representing at least 50% of the Registrable Securities
then outstanding; PROVIDED, HOWEVER, this provision in no way limits the rights
of the Company to amend the Existing Registration Rights Agreement (as defined
in Section 4(b)(ii)) to add additional investors or stockholders as parties
thereto.

                  (c) RESTRICTIONS ON DEMAND REGISTRATION. The Company may
postpone the filing or the effectiveness of a registration statement for a
Demand Registration if the Company determines in good faith that such Demand
Registration (i) would reasonably be expected to have a material adverse effect
on (x) any proposal or plan by the Company to engage in any financing,
acquisition or disposition of assets (other than in the ordinary course of
business) or (y) any merger, consolidation, tender offer or similar transaction
or (ii) would require disclosure of any information that the board of directors
of the Company determines in good faith the disclosure of which would be
detrimental to the Company; PROVIDED, HOWEVER, that in such event, the Holders
initially requesting such Demand Registration will be entitled to withdraw such
request and, if such request is withdrawn, such Demand Registration will not
count as a permitted Demand Registration hereunder and the Company will pay any
Registration Expenses in connection with such registration.

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                  (d) OTHER REGISTRATION RIGHTS. Except as provided in this
Agreement, so long as any Holder owns any Registrable Securities, the Company
will not grant to any Persons the right to request the Company to register any
equity securities of the Company, or any securities convertible or exchangeable
into or exercisable for such securities, which conflicts with the rights granted
to the Holders hereunder, without the prior written consent of the Holders of at
least 50% of the Registrable Securities.

                  4. PIGGYBACK REGISTRATIONS. (a) RIGHT TO PIGGYBACK. If at any
time that the Company shall propose to register Common Stock under the
Securities Act (other than in a registration on Form S-3 relating to sales of
securities to participants in a Company dividend reinvestment plan, S-4 or S-8
or any successor form or in connection with an acquisition or exchange offer or
an offering of securities solely to the existing shareholders or employees of
the Company), the Company will (i) give prompt written notice to all Holders of
Registrable Securities of its intention to effect such a registration and, (ii)
subject to Section 4(b) and the other terms of this Agreement, shall include in
such registration all Registrable Securities that are permitted under applicable
securities laws to be included in the form of registration statement selected by
the Company and with respect to which the Company has received written requests
for inclusion therein by the Holders within 30 days after the receipt of the
Company's notice (each, a "PIGGYBACK REGISTRATION"). The Holders will be
permitted to withdraw all or part of the Registrable Securities from a Piggyback
Registration at any time prior to the effective date of such Piggyback
Registration.

                  (b) PRIORITY ON PIGGYBACK REGISTRATIONS. If a Piggyback
Registration is an underwritten registration on behalf of the Company, and the
Managing Underwriters advise the Company in writing that in their opinion the
number of securities requested to be included in such registration exceeds the
number which can be sold in such offering without adversely affecting the
marketability of the offering, the Company shall include in such registration,
only as may be permitted in the reasonable business judgment of the Managing
Underwriters for such registration:

                  (i) first, up to that number of securities the Company
proposes to sell;

                  (ii) second, up to that number of Registrable Securities
requested to be included in such registration by the Holders and that number of
securities requested to be included in such registration by any other Person,
pro rata among the Holders of such Registrable Securities and such other
Persons, on the basis of the number of shares owned by each of such Holders;
PROVIDED, HOWEVER, in the event of a conflict between the provisions of (i) the
Registration Rights Agreement dated March 19, 1996, as amended October 30, 1998,
by and among the Company, certain stockholders of the Company as described
therein (the "Existing Registration Rights Agreement") and the rights of any
holders of registrable securities thereunder, and (ii) this Agreement, the terms
and the rights of the holders of registrable securities contained in the
Existing Registration Rights Agreement will prevail.

                  (iii) third, up to that number of other securities requested
to be included in such registration.

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                  (c) RIGHT TO TERMINATE REGISTRATION. If, at any time after
giving written notice of its intention to register any of its securities as set
forth in Section 4(a) and prior to the effective date of the registration
statement filed in connection with such registration, the Company shall
determine for any reason not to register such securities, the Company may, at
its election, give written notice of such determination to each Holder of
Registrable Securities that requested inclusion in such registration in
accordance with Section 4(a) and thereupon be relieved of its obligation to
register any Registrable Securities in connection with such registration (but
not from its obligation to pay the Registration Expenses in connection therewith
as provided herein).

                  5. SELECTION OF UNDERWRITERS. The Company, in its sole
discretion, shall select the Underwriter(s) and Managing Underwriter(s) to
administer an offering pursuant to any Demand Registration or Piggyback
Registration subject to the consent of EIS, which shall not be unreasonably
withheld, delayed or conditioned. The Holders shall take all reasonable steps to
cooperate with the Underwriter(s) so selected to conduct the offering in a
manner customary for such underwritten offering, including without limitation,
entering into an underwriting agreement in customary form and substance with
such Underwriter(s).

                  6. EXPENSES OF REGISTRATION. All Registration Expenses
incurred in connection with the registration pursuant to Section 3 shall be
borne by the Company. All Registration Expenses relating to securities
registered on behalf of Holders of Registrable Securities incurred in connection
with all registrations pursuant to Section 4 shall be borne by such Holders. All
Selling Expenses relating to securities registered on behalf of Holders of
Registrable Securities incurred in connection with all registrations pursuant to
Section 3 or Section 4 shall be borne by such Holders.

                  7.  HOLDBACK AGREEMENTS.

                  (a) The Company will (i) not effect any public sale or
distribution of its equity securities, or any securities convertible into or
exchangeable or exercisable for such securities, for its own account during the
seven days prior to and during the 90-day period beginning on the effective date
of any underwritten Demand Registration (except (A) as part of such underwritten
registration, (B) pursuant to registration statements on Form S-4 or Form S-8 or
any successor form, (C) pursuant to a registration statement then in effect or
(D) as required under any existing contractual obligation of the Company),
unless the underwriters managing the registered public offering otherwise agree,
and (ii) use reasonable efforts to cause each holder of at least 5% (on a
fully-diluted basis) of its outstanding Common Stock, or any securities
convertible into or exchangeable or exercisable for Common Stock, purchased from
the Company at any time after the date of this Agreement (other than in a
registered public offering) to agree not to effect any public sale or
distribution (including sales pursuant to Rule 144) of any such securities
during such periods (except as part of such underwritten registration, if
otherwise permitted), unless the underwriters managing the registered public
offering otherwise agree.

                  (b) Each Holder, in the event of a public offering of Common
Stock under a registration statement on Form S-1, S-3 or S-4, will not effect
any offer, sale, distribution or

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transfer, including a sale pursuant to Rule 144 (or any similar provision then
effect) under the Securities Act (except as part of such registration),
beginning on the date of receipt of a written notice from the Company setting
forth its intention to effect such registration and ending on the earlier of (i)
180 days from the date of receipt of such written notice or (ii) 180 days from
the effective date of such Registration Statement; PROVIDED, that the directors
of the Company and holders of securities representing at least 5% of the Common
Stock consent to the 180-day period.

                  8. REGISTRATION PROCEDURES. Whenever the Company is under the
obligation to register Registrable Securities hereunder, the Company will use
all reasonable efforts to effect the registration and the sale of such
Registrable Securities, and pursuant thereto the Company will as expeditiously
as possible use its reasonable efforts to:

                  (a) subject to Sections 3(a) and 4(a) hereof, prepare and file
with the Commission a registration statement on any form for which the Company
qualifies with respect to such Registrable Securities and use all reasonable
efforts to cause such registration statement to become effective (provided that
before filing a registration statement or prospectus or any amendments or
supplements thereto, the Company will (i) furnish to the counsel selected by the
Holders copies of all such documents proposed to be filed, and will provide such
counsel a reasonable opportunity to review and comment on such documents which
documents will be subject to the review of such counsel, and (ii) notify each
Holder of Registrable Securities covered by such registration of any stop order
issued or threatened by the Commission);

                  (b) subject to Sections 3(c) and 4(c) hereof, prepare and file
with the Commission such amendments and supplements to such registration
statement and the prospectus used in connection therewith as may be reasonably
necessary to keep such registration statement effective for, in the case of a
Demand Registration, a period equal to the shorter of (i) 120 days and (ii) the
time by which all securities covered by such registration statement have been
sold, and comply with the provisions of the Securities Act with respect to the
disposition of all securities covered by such registration statement during such
period in accordance with the intended methods of disposition by the sellers
thereof set forth in such registration statement;

                  (c) furnish to each seller of Registrable Securities such
number of copies of such registration statement, each amendment and supplement
thereto, the prospectus included in such registration statement (including each
preliminary prospectus) and such other documents as such seller may reasonably
request in order to facilitate the disposition of the Registrable Securities
owned by such seller;

                  (d) use all reasonable efforts to register or qualify such
Registrable Securities under the securities or blue sky laws of such
jurisdictions as any seller reasonably requests in writing and do any and all
other acts and things which may be reasonably necessary or advisable to enable
such seller to consummate the disposition in such jurisdictions of the
Registrable Securities owned by such seller (provided that the Company will not
be required to (i) qualify generally to do business in any jurisdiction where it
would not otherwise be required to qualify

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but for this Section 8(d), (ii) subject itself to taxation in any jurisdiction,
or (iii) take any action that would subject it to general service of process in
any such jurisdiction);

                  (e) notify each seller of such Registrable Securities, at any
time when a prospectus relating thereto is required to be delivered under the
Securities Act, of the happening of any event as a result of which the
prospectus included in such registration statement contains an untrue statement
of a material fact or omits any fact necessary to make the statements therein
not misleading, and, at the request of any such seller, the Company will prepare
a supplement or amendment to such prospectus so that, as thereafter delivered to
the purchasers of such Registrable Securities, such prospectus will not contain
an untrue statement of a material fact or omit to state any fact necessary to
make the statements therein not misleading; PROVIDED, HOWEVER, that the Company
shall not be required to amend the registration statement or supplement the
Prospectus for a period of up to six months if the board of directors determines
in good faith that to do so would reasonably be expected to have a material
adverse effect on any proposal or plan by the Company to engage in any
financing, acquisition or disposition of assets (other than in the ordinary
course of business) or any merger, consolidation, tender offer or similar
transaction or would require the disclosure of any information that the board of
directors determines in good faith the disclosure of which would be detrimental
to the Company, it being understood that the period for which the Company is
obligated to keep the Registration Statement effective shall be extended for a
number of days equal to the number of days the Company delays amendments or
supplements pursuant to this provision. Upon receipt of any notice pursuant to
this Section 8(e), the Holders shall suspend all offers and sales of securities
of the Company and all use of any prospectus until advised by the Company that
offers and sales may resume, and shall keep confidential the fact and content of
any notice given by the Company pursuant to this Section 8(e);

                  (f) cause all such Registrable Securities to be listed on each
securities exchange, if any, on which similar securities issued by the Company
are then listed;

                  (g) provide a transfer agent and registrar for all such
Registrable Securities not later than the effective date of such registration
statement;

                  (h) enter into such customary agreements (including
underwriting agreements in customary form) and take all such other actions as
the Holders of a majority of the Registrable Securities being sold or the
underwriters, if any, reasonably request in order to expedite or facilitate the
disposition of such Registrable Securities;

                  (i) make available for inspection by a representative of the
Holders of Registrable Securities included in the registration statement, any
underwriter participating in any disposition pursuant to such registration
statement and any attorney, accountant or other agent retained by any such
seller or underwriter, all pertinent financial and other records, pertinent
corporate documents and properties of the Company, and cause the Company's
officers, directors, employees and independent accountants to supply all
information reasonably requested by any such seller, underwriter, attorney,
accountant or agent in connection with such registration statement;

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                  (j) otherwise use its reasonable efforts to comply with all
applicable rules and regulations of the Commission, and make available to its
security holders, as soon as reasonably practicable, an earnings statement
covering the period of at least 12 months beginning with the first day of the
Company's first full calendar quarter after the effective date of the
registration statement, which earnings statement shall satisfy the provisions of
Section 11(a) of the Securities Act and Rule 158 thereunder;

                  (k) in the event of the issuance of any stop order suspending
the effectiveness of a registration statement, or of any order suspending or
preventing the use of any related prospectus or suspending the qualification of
any Common Stock included in such registration statement for sale in any
jurisdiction, use all reasonable efforts promptly to obtain the withdrawal of
such order; and

                  (l) if the registration is an underwritten offering, use all
reasonable efforts to obtain a so-called "cold comfort" letter from the
Company's independent public accountants in customary form and covering such
matters of the type customarily covered by cold comfort letters.

                  9. OBLIGATIONS OF HOLDERS. (a) Whenever the Holders of
Registrable Securities sell any Registrable Securities pursuant to a Demand
Registration, such Holders shall be obligated to comply with the applicable
provisions of the Securities Act, including the prospectus delivery requirements
thereunder, and any applicable state securities or blue sky laws.

                  (b) The Company may require each seller of Registrable
Securities as to which any Demand Registration or Piggyback Registration is
being effected to furnish to the Company such information regarding the
distribution of such Registrable Securities as the Company may, from time to
time, reasonably request in writing and shall promptly notify the Company of any
changes in such information the Company may exclude from such registration the
Registrable Securities of any seller who unreasonably fails to furnish such
information within a reasonable time after receiving such request.

                  (c) Each holder of Registrable Securities will be deemed to
have agreed by virtue of its acquisition of such Registrable Securities that,
upon receipt of any notice described in Section 8(e), such holder will forthwith
discontinue disposition of such Registrable Securities covered by such
registration statement or prospectus until such holder's receipt of the copies
of the supplemented or amended prospectus contemplated by Section 8(e) hereof,
or until it is advised in writing by the Company that the use of the applicable
prospectus may be resumed, and has received copies of any additional or
supplemental filings that are incorporated or deemed to be incorporated by
reference in such prospectus.

                  10. INDEMNIFICATION. (a) In connection with any registration
statement for a Demand Registration in which a Holder of Registrable Securities
registered pursuant to this Agreement is participating, the Company agrees to
indemnify, to the fullest extent permitted by applicable law, each such Holder
of Registrable Securities, its officers and directors and each

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Person who controls such Holder (within the meaning of the Securities Act)
against all losses, claims, damages, liabilities, expenses or any amounts paid
in settlement of any litigation, investigation or proceeding commenced or
threatened to which each such indemnified party may become subject under the
Securities Act (collectively, "CLAIMS") insofar as such Claim arose out of (i)
any untrue or alleged untrue statement of material fact contained, on the
effective date thereof, in any such registration statement, prospectus or
preliminary prospectus or any amendment thereof or supplement thereto or (ii)
any omission or alleged omission to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading,
except insofar as the same are caused by or contained in any information
furnished in writing to the Company by such Holder expressly for use therein or
by such Holder's failure to deliver a copy of the registration statement or
prospectus or any amendments or supplements thereto after the Company has
furnished such Holder with a sufficient number of copies of the same. In
connection with an underwritten offering, the Company will indemnify the
underwriters, their officers and directors and each Person who controls the
underwriters (within the meaning of the Securities Act) to the same extent as
provided above with respect to the indemnification of the Holders of Registrable
Securities.

                  (b) In connection with any registration statements for a
Demand Registration in which a Holder of Registrable Securities is
participating, each Holder will, to the fullest extent permitted by applicable
law, indemnify the Company, its directors and officers and each Person who
controls the Company (within the meaning of the Securities Act) against any and
all Claims to which each such indemnified party may become subject under the
Securities Act insofar as such Claim arose out of (i) any untrue or alleged
untrue statement of material fact contained, on the effective date thereof, in
any such registration statement, prospectus or preliminary prospectus or any
amendment thereof or supplement thereto or (ii) any omission or alleged omission
to state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading; provided that with respect to a
Claim arising pursuant to clause (i) or (ii) above, the material misstatement or
omission is contained in the information such Seller provided to the Company
pursuant to Section 9(b).

                  (c) Any Person entitled to indemnification hereunder will (i)
give prompt written notice to the indemnifying party of any claim with respect
to which it seeks indemnification (but the failure to provide such notice shall
not release the indemnifying party of its obligation under paragraphs (a) and
(b), unless and then only to the extent that, the indemnifying party has been
prejudiced by such failure to provide such notice) and (ii) unless in such
indemnified party's reasonable judgment a conflict of interest between such
indemnified and indemnifying parties may exist with respect to such claim,
permit such indemnifying party to assume the defense of such claim with counsel
reasonably satisfactory to the indemnified party. An indemnifying party who is
not entitled to, or elects not to, assume the defense of a claim will not be
obligated to pay the fees and expenses of more than one counsel for all parties
indemnified by such indemnifying party with respect to such claim, unless in the
reasonable judgment of any indemnified party a conflict of interest may exist
between such indemnified party and any other of such indemnified parties with
respect to such claim.

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                  (d) The indemnifying party shall not be liable to indemnify an
indemnified party for any settlement, or consent to judgment of any such action
effected without the indemnifying party's consent (but such consent will not be
unreasonably withheld, delayed or conditioned). Furthermore, the indemnifying
party shall not, except with the prior written approval of each indemnified
party, consent to entry of any judgment or enter into any settlement which does
not include as an unconditional term thereof the giving by the claimant or
plaintiff to each indemnified party of a release from all liability in respect
of such claim or litigation without any payment or consideration provided by
each such indemnified party.

                  (e) If the indemnification provided for in this Section 10 is
unavailable to an indemnified party under clauses (a) and (b) above in respect
of any losses, claims, damages or liabilities referred to therein, then each
indemnifying party, in lieu of indemnifying such indemnified party, shall
contribute to the amount paid or payable by such indemnified party as a result
of such losses, claims, damages or liabilities in such proportion as is
appropriate to reflect not only the relative benefits received by the Company
(if any), the Underwriters, the sellers of Registrable Securities and any other
sellers participating in the registration statement from the sale of shares
pursuant to the registered offering of securities for which indemnity is sought
but also the relative fault of the Company, the Underwriters, the sellers of
Registrable Securities and any other sellers participating in the registration
statement in connection with the statement or omission which resulted in such
losses, claims, damages or liabilities, as well as any other relevant equitable
considerations. The relative benefits received by the Company (if any), the
Underwriters, the sellers of Registrable Securities and any other sellers
participating in the registration statement shall be deemed to be based on the
relative relationship of the total net proceeds from the offering (before
deducting expenses) to the Company (if any), the total underwriting commissions
and fees from the offering (before deducting expenses) to the Underwriters and
the total net proceeds from the offering (before deducting expenses) to the
sellers of Registrable Securities and any other sellers participating in the
registration statement. The relative fault of the Company, the Underwriters, the
sellers of Registrable Securities and any other sellers participating in the
registration statement shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by the Company or by the sellers of Registrable Securities and the
parties' relative intent, knowledge, access to information and opportunity to
correct or prevent such statement or omission.

                  (f) The indemnification provided for under this Agreement will
remain in full force and effect regardless of any investigation made by or on
behalf of the indemnified party or any officer, director or controlling person
of such indemnified party and will survive the transfer of the Registrable
Securities.

                  11. PARTICIPATION IN UNDERWRITTEN REGISTRATIONS. No Holder may
participate in any registration hereunder which is underwritten unless such
Holder (a) agrees to sell such Holder's securities on the basis provided in any
underwriting arrangements approved by the Holder or Holders entitled hereunder
to approve such arrangements, (b) as expeditiously as possible notifies the
Company of the occurrence of any event as a result of which any prospectus
contains an untrue statement of material fact or omits to state a material fact
required to be stated

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therein or necessary to make the statements therein not misleading and (c)
completes and executes all questionnaires, powers of attorney, indemnities,
underwriting agreements and other documents reasonably required under the terms
of such underwriting arrangements.

                  12. TRANSFER OF REGISTRATION RIGHTS. The rights granted to any
Holder under this Agreement may be assigned to any permitted transferee of
Registrable Securities, in connection with any transfer or assignment of
Registrable Securities by a Holder; PROVIDED, HOWEVER, that: (a) such transfer
is otherwise effected in accordance with applicable securities laws, (b) if not
already a party hereto, the assignee or transferee agrees in writing prior to
such transfer to be bound by the provisions of this Agreement applicable to the
transferor, (c) such transferee shall own Registrable Securities representing at
least 5% of the shares of Common Stock (as adjusted for any combinations,
consolidations, stock distributions, stock dividends or other recapitalizations
with respect to such shares), and (d) EIS shall act as agent and representative
for such Holder for the giving and receiving of notices hereunder.

                  13. EXCHANGE ACT COMPLIANCE. The Company shall comply with all
of the reporting requirements of the Exchange Act, if any, then applicable to it
and shall comply with all other public information reporting requirements of the
Commission which are conditions to the availability of Rule 144 for the sale of
the Registrable Securities. The Company shall cooperate with each Holder in
supplying such information as may be necessary for such Holder to complete and
file any information reporting forms presently or hereafter required by the
Commission as a condition to the availability of Rule 144.

                  14. TERMINATION OF REGISTRATION RIGHTS. All registration
rights granted under this Agreement shall terminate and be of no further force
and effect, as to any particular Holder, at such time as all Registrable
Securities held by such Holder can be sold within a four-month period without
compliance with the registration requirements of the Securities Act pursuant to
Rule 144 (including Rule 144(k)) promulgated thereunder or have been resold
pursuant to a Demand Registration.

                  15.  MISCELLANEOUS.

                  (a) REMEDIES. Any Person having rights under any provision of
this Agreement will be entitled to enforce such rights specifically to recover
damages caused by reason of any breach of any provision of this Agreement and to
exercise all other rights granted by law. The parties hereto agree and
acknowledge that money damages may not be an adequate remedy for any breach of
the provisions of this Agreement and that any party may in its sole discretion
apply to any court of law or equity of competent jurisdiction (without posting
any bond or other security) for specific performance and for other injunctive
relief in order to enforce or prevent violation of the provisions of this
Agreement; PROVIDED, HOWEVER, that in no event shall any Holder have the right
to enjoin, delay or interfere with any offering of securities by the Company.

                  (b) AMENDMENTS AND WAIVERS. This Agreement may not be modified
or amended, or any of the provisions hereof waived, except by written agreement
of the Company and Holders of at least 50% of the Registrable Securities;
PROVIDED, HOWEVER, that without the prior written

                                       11
<PAGE>   12

consent of all the Holders, no such amendment or waiver shall reduce the
foregoing percentage required to amend or waive any provision of this Agreement.

                  (c) SUCCESSORS AND ASSIGNS. This Agreement and all of the
provisions hereof shall be binding upon and inure to the benefit of the parties
hereto and their respective successors and permitted assigns. This Agreement may
be transferred by EIS to its Affiliates as well as any special purpose financing
or similar vehicle established by EIS; PROVIDED, HOWEVER, that EIS shall remain
liable for its obligations hereunder after any such assignment. Other than as
set forth above, no party shall transfer or assign this Agreement, without the
prior written consent of the other party, which will not be unreasonably
withheld, delayed or conditioned, except that Athersys may assign its rights in
this Agreement to any wholly owned subsidiary. In addition, whether or not any
express assignment has been made, the provisions of this Agreement which are for
the benefit of Holders of Registrable Securities are also for the benefit of,
and enforceable by, any permitted transferee of Registrable Securities in
accordance with Section 12 hereof.

                  (d) SEVERABILITY. In case any provision of this Agreement is
deemed to be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not be in any way affected or
impaired thereby.

                  (e) COUNTERPARTS AND FACSIMILE. This Agreement may be executed
in any number of counterparts, and each such counterpart hereof shall be deemed
to be an original instrument, but all such counterparts together shall
constitute one agreement. This Agreement may be signed and delivered to the
other party by facsimile transmission; such transmission shall be deemed a valid
signature.

                  (f) DESCRIPTIVE HEADINGS; REFERENCES. The section and
paragraph headings contained in this Agreement are for reference purposes only
and shall not affect in any way the meaning or interpretation of the Agreement.
Unless the context requires otherwise, references to "Sections" in this
Agreement are references to Sections of this Agreement.

                  (g) GOVERNING LAW. This Agreement shall be governed by and
construed in accordance with the internal laws of the State of New York, without
giving effect to principles of conflicts of laws, except that all issues
concerning the relative rights of the Company and its shareholders shall be
governed by laws of the State of Delaware, without giving effect to the
principles thereof relating to conflicts of laws.

                  (h) NOTICES. All notices, demands and requests of any kind to
be delivered to any party in connection with this Agreement shall be in writing
and shall be deemed to have been duly given if personally delivered or if sent
by nationally-recognized overnight courier or by registered or certified
first-class mail, return receipt requested and postage prepaid, or by facsimile
transmission, addressed as follows:

                                       12

<PAGE>   13

                           (i) if to the Company, to:

                           Athersys, Inc.
                           11000 Cedar Avenue
                           Cleveland, Ohio  44106
                           Facsimile:  (216) 231-0905
                           Attention:  President and CEO

                           with a copy to:

                           Jones, Day, Reavis &Pogue
                           901 Lakeside Avenue
                           Cleveland, Ohio 44114
                           Facsimile:  (216) 579-0212
                           Attention:  Christopher M. Kelly, Esq.

                           (ii) if to EIS, to:

                           Elan International Services, Ltd.
                           Flatts, Smiths Parish
                           Bermuda, FL 04
                           Facsimile:  (441) 292-2224
                           Attention:   President

                           with a copy to:

                           Brock Silverstein LLC
                           800 Third Avenue
                           New York, New York 10022
                           Facsimile:  (212) 371-5500
                           Attention:  David Robbins, Esq.

or to such other address as the party to whom notice is to be given may have
furnished to the other party hereto in writing in accordance with provisions of
this Section 15. Any such notice or communication shall be deemed to have been
received (i) in the case of personal delivery, on the date of such delivery,
(ii) in the case of facsimile transmission, on the date of telephone
confirmation of receipt, (iii) in the case of nationally-recognized overnight
courier, on the second business day after the date when sent and (iv) in the
case of mailing, on the fifth business day following that day on which the piece
of mail containing such communication is posted. Notice hereunder may be given
on behalf of the parties by their respective attorneys.

                  (i) ENTIRE AGREEMENT. This Agreement, the Confidentiality
Agreement and the other Transaction Documents (as defined in the Purchase
Agreement), contain the entire understanding of the parties with respect to the
subject matter hereof and supersede and terminate all prior agreements and
understandings among the parties with respect thereto.

                                       13
<PAGE>   14

                            [Signature page follows]

                                       14
<PAGE>   15

                  IN WITNESS WHEREOF, the parties have caused their respective
duly authorized representative to execute this Registration Rights Agreement as
of the date first written above.

                                          ATHERSYS, INC.

                                          By: /s/ Gil Van Bokkelen
                                              ----------------------------
                                                Name: Gil Van Bokkelen
                                                Title: President & CEO

                                          ELAN INTERNATIONAL SERVICES, LTD.

                                          By: /s/ Kevin Insley
                                              ----------------------------
                                                Name:
                                                Title:<PAGE>   1
                                 ATHERSYS, INC.                     Exhibit 4.6

                              AMENDED AND RESTATED
                          REGISTRATION RIGHTS AGREEMENT

                  THIS AMENDED AND RESTATED REGISTRATION RIGHTS
AGREEMENT (this "AGREEMENT"), dated as of the 28th day of April, 2000, is by and
among Athersys, Inc. (the "COMPANY"), Primus Capital Fund IV Limited
Partnership, Primus Executive Fund Limited Partnership, Blue Chip Capital Fund
II Limited Partnership, Miami Valley Venture Fund L.P., Sentron Medical
Incorporated, Warburg Dillon Read LLC, Ohio Innovation Fund I, L.P., The EBTC
Foundation, Athersys Investors II, LLC, Hoegh Invest, AS and NeoMed Innovation,
ASA (collectively, the "CLASS C INVESTORS"), and the investors listed on
SCHEDULE A attached hereto (collectively the "CLASS F INVESTORS" with the Class
C Investors and Class F Investors collectively being referred to as the
"INVESTORS"), Biotech 3 Investment L.L.C. ("BIOTECH"), and each of the
stockholders of the Company listed on SCHEDULE B attached hereto (individually,
a "STOCKHOLDER" and collectively, the "STOCKHOLDERS").

                              W I T N E S S E T H:

         WHEREAS, the Class F Investors and the Company executed that certain
Securities Purchase Agreement dated as of March 30, 2000 (the "SECURITIES
PURCHASE AGREEMENT"), pursuant to which the Class F Investors agreed to purchase
from the Company shares of the Company's Class F Convertible Preferred Stock,
par value $.01 per share, on certain terms and conditions contained in the
Securities Purchase Agreement (the "PURCHASE"); and

         WHEREAS, in connection with the Purchase the parties hereto execute
this Agreement to amend and restate the Amended and Restated Registration Rights
Agreement, dated March 30, 2000, by and among the Company, Biotech, the Class C
Investors, certain Class F Investors and the Stockholders; and

         WHEREAS, the Company desires to induce Class F Investors to consummate
the Purchase by executing this Agreement.

         NOW, THEREFORE, in consideration of the foregoing and the covenants and
agreements contained herein, the parties agree as follows:

     1.   Definitions.

         "AGREEMENT" has the meaning set forth in the Recitals.

         "AMENDED CERTIFICATE" means the Amended and Restated Certificate of
Incorporation of the Company.

         "BIOTECH" has the meaning set forth in the Preamble to this Agreement.

         "BIOTECH SHARES" means (i) any equity securities of the Company issued
or issuable upon the conversion of Preferred Shares held by Biotech or any
transferee, successor or

<PAGE>   2

assign of Biotech; (ii) any shares of equity securities of the Company held as
the date hereof or acquired hereafter by Biotech; (iii) any equity securities of
the Company issued or issuable with respect to the securities referred to in
clauses (i) and (ii) by way of a stock dividend or stock split or in connection
with a combination of shares, recapitalization, merger, consolidation or other
reorganization; and (iv) any other shares of equity securities of the Company
held by persons holding securities referred to in clauses (i), (ii) and (iii);
provided, however, that Biotech Shares shall not include any securities the sale
of which has been registered pursuant to the Securities Act or sold to the
public pursuant to Rule 144 promulgated by the Commission under the Securities
Act. For purposes of this Agreement, a Person will be deemed to be a Holder of
Biotech Shares whenever such Person holds a security exercisable for or
convertible into such Biotech Shares, whether or not such exercise or conversion
has actually been effected.

         "CLASS C INVESTORS" has the meaning set forth in the Preamble to this
Agreement.

         "CLASS C INVESTORS' SHARES" means, at any time, the following shares
held by any Class C Investors: (i) any shares of Common Stock then outstanding
that were issued upon conversion of the Class C Preferred; (ii) any shares of
Common Stock then issuable upon conversion of the Class C Preferred; (iii) any
shares of Common Stock then outstanding which were issued as, or were issued
directly or indirectly upon the conversion or exercise of other securities
issued as, a dividend or other distribution with respect to or in replacement of
other Class C Investors' Shares; (iv) any shares of Common Stock then issuable
directly or indirectly upon the conversion or exercise of other securities which
were issued as a dividend or other distribution with respect to or in
replacement of other Class C Investors' Shares; and (v) any other Shares held by
a Class C Investor; provided, however, that Class C Investors' Shares shall not
include any shares of Common Stock the sale of which has been registered
pursuant to the Securities Act or sold to the public pursuant to Rule 144
promulgated by the Commission under the Securities Act. For purposes of this
Agreement, a Person will be deemed to be a Holder of Class C Investors' Shares
whenever such Person holds a security exercisable for or convertible into such
Class C Investors' Shares, whether or not such exercise or conversion has
actually been effected.

         "CLASS C PREFERRED" means the Class C Convertible Preferred Stock, par
value $.01, of the Company.

         "CLASS F PREFERRED" means the Class F Convertible Preferred Stock, par
value $.01, of the Company.

         "CLASS F INVESTORS' SHARES" means, at any time, the following shares
held by any Class F Investors: (i) any shares of Common Stock then outstanding
that were issued upon conversion of the Class F Preferred; (ii) any shares of
Common Stock then issuable upon conversion of the Class F Preferred; (iii) any
shares of Common Stock then outstanding which were issued as, or were issued
directly or indirectly upon the conversion or exercise of other securities
issued as, a dividend or other distribution with respect to or in replacement of
other Class F Investors' Shares; (iv) any shares of Common Stock then issuable
directly or indirectly upon the conversion or exercise of other securities which
were issued as a dividend or other distribution with respect to or in
replacement of other Class F Investors' Shares; and (v) any other Shares held by
a Class F Investor; provided, however, that Class F Investors' Shares shall not
include any shares of Common Stock the sale of which has been registered
pursuant to the

                                        2

<PAGE>   3

Securities Act or sold to the public pursuant to Rule 144 promulgated by the
Commission under the Securities Act. For purposes of this Agreement, a Person
will be deemed to be a Holder of Class F Investors' Shares whenever such Person
holds a security exercisable for or convertible into such Class F Investors'
Shares, whether or not such exercise or conversion has actually been effected.

         "COMMON STOCK" means common stock, par value $.01, of the Company.

         "COMPANY" has the meaning set forth in the Preamble to this Agreement.

         "DEMAND REGISTRATIONS" means, collectively, Long-Form Demand
Registrations and Short-Form Demand Registrations.

         "DEMANDING SHAREHOLDERS" has the meaning set forth in SECTION 3(d).

         "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended,
and the rules and regulations of the SEC promulgated thereunder, all as the same
shall be in effect at that time.

         "HOLDER" means any holder of Investors' Shares or Registrable
Securities who is a party to this Agreement (or becomes a party hereto pursuant
to SECTION 12 hereof) or is a successor or assign or subsequent holder
contemplated by SECTION 13(e) hereof.

         "INVESTORS" has the meaning set forth in the Preamble to this
Agreement.

         "INVESTORS' SHARES" means, collectively, Class C Investors' Shares and
Class F Investors' Shares.

         "IPO" means the Company's first underwritten public offering of shares
of common stock consummated pursuant to a registration statement declared
effective under the Securities Act, other than a registration statement relating
solely to the sale of securities to participants in a company stock plan or a
registration relating solely to a Rule 145 transaction.

         "LONG-FORM DEMAND REGISTRATION" has the meaning set forth in SECTION
3(a)(v).

         "LONG-FORM REGISTRATION" has the meaning set forth in SECTION 3(a)(i).

         "PERSON" means any individual, sole proprietorship, partnership,
corporation, limited liability company, unincorporated society or association,
trust or other entity.

         "PIGGYBACK REGISTRATION" has the meaning set forth in SECTION 2(a).

         "PREFERRED SHARES" means the Class A Convertible Preferred Stock, $.01
par value, the Class B Convertible Preferred Stock, $.01 par value, the Class C
Convertible Preferred Stock, $.01 par value, the Class D Convertible Preferred
Stock, $.01 par value, the Class F Convertible Preferred Stock, $.01 par value,
the Class G Convertible Preferred Stock, $.01 par value, and any Blank Check
Preferred Stock, $.01 par value, now or hereafter issued.

                                        3

<PAGE>   4

         "PURCHASE" has the meaning set forth in the Preamble to this Agreement.

         "REGISTRABLE SECURITIES" means, collectively the Class C Investors'
Shares, the Class F Investors' Shares and the Biotech Shares.

         "REGISTRATION EXPENSES" has the meaning set forth in SECTION 6(a).

         "S-2 SHORT-FORM REGISTRATION" has the meaning set forth in SECTION
3(a)(iii).

         "S-3 SHORT-FORM REGISTRATION" has the meaning set forth in SECTION
3(a)(iii).

         "SEC" means the Securities and Exchange Commission or any other federal
agency at the time administering the Securities Act.

         "SHARES" means shares of capital stock of the Company.

         "SECURITIES ACT" means the Securities Act of 1933, as amended, and the
rules and regulations of the SEC promulgated thereunder, all as the same shall
be in effect at that time.

         "SECURITIES PURCHASE AGREEMENT" has the meaning set forth in the
Preamble to this Agreement.

         "SHORT-FORM DEMAND REGISTRATION" has the meaning set forth in SECTION
3(a)(v).

         "SHORT-FORM REGISTRATION" has the meaning set forth in SECTION
3(a)(iii).

         "STOCKHOLDER" and "STOCKHOLDERS" have the meanings set forth in the
Preamble to this Agreement.

     2.   Piggyback Registrations.

          (a) Right to Piggyback. Whenever the Company proposes to register any
     of its securities under the Securities Act, and the registration form to be
     used may be used for the registration of Registrable Securities, the
     Company will give prompt written notice to Biotech, the Investors and the
     Stockholders of its intention to effect such a registration (a "PIGGYBACK
     REGISTRATION"). The Company will include in such registration (i) all
     Registrable Securities with respect to which the Company has received
     written requests for inclusion therein within fifteen (15) days after the
     receipt of the Company's notice, and (ii) such other securities of the
     Company held by the Stockholders with respect to which the Company has
     received written requests for inclusion therein within fifteen (15) days
     after the receipt of the Company's notice; provided, however, that no
     registration of securities held by the Stockholders or any other
     stockholders pursuant to this SECTION 2 shall be at the exclusion of any
     Registrable Securities.

          (b) Priority on Primary Registrations. If a Piggyback Registration is
     an underwritten primary registration on behalf of the Company, and the
     managing underwriters advise the Company in writing that in their opinion
     the number of securities

                                        4

<PAGE>   5

     requested to be included in such registration exceeds the number that can
     be sold in an orderly manner in such offering within a price range
     acceptable to the Company, the Company will include in such registration
     shares in the following order until such limitation has been met: first,
     the securities the Company proposes to sell; second, the Registrable
     Securities requested to be included in such registration, pro rata among
     the holders of such Registrable Securities on the basis of the number of
     Shares owned by each such holder; third, the securities requested to be
     included in such registration by the Stockholders; and fourth, other
     securities requested to be included in such registration; provided that in
     any event, after the IPO, the Holders of the Registrable Securities shall
     be entitled to have their Shares represent at least twenty-five percent
     (25%) of the total shares included in any such registration.

          (c) Expiration of Piggyback Registration Rights. The "PIGGYBACK"
     registration rights granted to Holders of Registrable Securities under this
     SECTION 2 shall expire at the later of (i) ninety (90) days after all
     Registrable Securities are freely tradeable to the public through a broker,
     dealer or market maker in compliance with Rule 144(k) under the Securities
     Act, without limitation (or any similar rule then in force) or (ii) five
     (5) years after the closing of the IPO.

     3.   Demand Registration.

          (a)  Requests for Registration.

               (i) Subject to the terms and conditions of this Agreement, the
          Holders of a majority of the then outstanding Class C Investors'
          Shares at any time after the earlier of (i) the consummation of the
          IPO or (ii) October 31, 2000 may request registration under the
          Securities Act of all or part of their Class C Investors' Shares on
          Form S-1 or any similar long-form registration statement ("LONG-FORM
          REGISTRATION") by delivering a written request to the Company to that
          effect; provided, however, that, in the case of any such Long-Form
          Registration, the aggregate offering value of all of the shares to be
          offered must be reasonably expected to equal at least Five Million
          Dollars ($5,000,000).

               (ii) Subject to the terms and conditions of this Agreement, the
          Holders of at least twenty-five percent (25%) of the then outstanding
          Class F Investors' Shares at any time after the earlier of (i) the
          consummation of an IPO or (ii) October 31, 2000, may request a Long
          Form Registration by delivering a written request to the Company to
          that effect; provided, however, that, in the case of any such Long
          Form Registration, the aggregate offering value of all of the shares
          to be offered must be reasonably expected to equal at least Five
          Million Dollars ($5,000,000).

               (iii) Subject to the terms and conditions of this Agreement, the
          Holders of at least twenty-five percent (25%) of the then outstanding
          Class C Investors' Shares and Biotech Shares at any time may request
          registration under the Securities Act of all or part of their
          Registrable Securities on Form S-2 ("S-2 SHORT-FORM REGISTRATION") or
          S-3 ("S-3 SHORT-FORM REGISTRATION") or any similar short-form
          registration statement (collectively, a "SHORT-FORM

                                        5

<PAGE>   6

          REGISTRATION"), if available, by delivering a written request to the
          Company to that effect; provided, however, that, in the case of any
          such Short-Form Registration, the aggregate offering value of the
          Class C Investors' Shares and Biotech Shares requested to be included
          in such registration pursuant to SECTION 3(a), including, without
          limitation, SECTION 3(a)(v), must be reasonably expected to equal at
          least Five Hundred Thousand Dollars ($500,000).

               (iv) Subject to the terms and conditions of this Agreement, the
          Holders of the then outstanding Class F Investors' Shares at any time
          may request a S-3 Short-Form Registration of their Class F Investors'
          Shares, if available, by delivering a written request to the Company
          to that effect; provided, however, that, in the case of any such S-3
          Short-Form Registration, the aggregate offering value of the Class F
          Investors' Shares requested to be included in such registration
          pursuant to SECTION 3(a), including, without limitation, SECTION
          3(a)(v), must be reasonably expected to equal at least Five Hundred
          Thousand Dollars ($500,000).

               (v) If the Holders of Registrable Securities initiating a
          registration pursuant to SECTION 3(a) intend to distribute the
          Registrable Securities by means of an underwriting, they shall so
          advise the Company in their written notice. Within ten (10) days after
          receipt of any written request pursuant to (i), (ii), (iii) or (iv)
          above, the Company will give written notice of such request to all of
          the Investors and Biotech, and will include, subject to the terms of
          SECTION 3(d), in any such registration that constitutes a Demand
          Registration all securities with respect to which the Company has
          received written requests from the Investors and Biotech, for
          inclusion therein within fifteen (15) days after receipt of the
          Company's notice. Any Long-Form Registration and any Short-Form
          Registration requested pursuant to this SECTION 3(a), other than a
          registration in which the Company sells any of its securities in a
          primary offering, are referred to herein, respectively, as a
          "LONG-FORM DEMAND REGISTRATION", and a "SHORT-FORM DEMAND
          REGISTRATION". The Company may elect to include its securities in a
          primary offering in any registration requested pursuant to this
          SECTION 3(a); provided, however, that if the Company sells any of its
          securities in a primary offering, such offering shall not be deemed to
          be a Demand Registration and shall be considered a Piggyback
          Registration and will be governed by SECTION 2.

          (b) Long-Form Demand Registrations. The Holders of Class C Investors'
     Shares may request one Long-Form Demand Registration pursuant to Section
     3(a)(i), and the Holders of Class F Investors' Shares may request two (2)
     Long-Form Demand Registrations pursuant to SECTION 3(a)(ii). The Company
     will pay the Registration Expenses therefor of the Company and the Holders
     of Investors' Shares. A registration will not count as a Long-Form Demand
     Registration under this SECTION 3 until (i) it has become effective (and is
     not the subject of any stop order, injunction or other order or requirement
     of the SEC or other governmental agency or court for any reason); (ii) the
     conditions to closing specified in the purchase agreement or underwriting
     agreement entered into in connection with such registration statement are
     satisfied and (iii) the Holders are able to register and sell at least
     seventy-five percent (75%) of their desired Shares. Notwithstanding the
     terms of the preceding sentence, a registration which does not become
     effective after the Company has filed a registration statement with respect

                                        6

<PAGE>   7

     thereto solely by reason of the refusal to proceed of the Holders of
     Investors' Shares (unless such refusal is due to the disclosure of adverse
     information concerning the Company after such demand is made) shall be
     deemed to have been effected by such Holders and count as a Long-Form
     Demand Registration under this SECTION 3, unless the Holders of Investors'
     Shares making such demand shall have elected to pay the Registration
     Expenses of the Holders of Investors' Shares incurred in connection
     therewith.

          (c) Short-Form Demand Registration. The Holders of Registrable
     Securities will be entitled to request pursuant to SECTION 3(a)(iii) or
     SECTION 3(a)(iv), respectively, no more than two (2) Short-Form Demand
     Registrations in any twelve (12) month period. The Company will pay the
     Registration Expenses therefor of the Company and the Holders of
     Registrable Securities in connection with any such registration. A
     registration will not count as one of the Short-Form Demand Registrations
     under this SECTION 3(c) until it has become effective; provided that in any
     event the Company will pay the Registration Expenses of the Company and the
     Holders of Registrable Securities in connection with any such registration
     initiated as a Short-Form Demand Registration. Notwithstanding the terms of
     the preceding sentence, a registration that does not become effective after
     the Company has filed a registration statement with respect thereto solely
     by reason of the refusal to proceed of the Holders of Registrable
     Securities (unless such refusal is due to the disclosure of adverse
     information concerning the Company after such demand is made) shall be
     deemed to have been effected by such Holders and count as a Short-Form
     Demand Registration under this SECTION 3(c), unless the Holders of
     Registrable Securities making such demand shall have elected to pay the
     Registration Expenses of the Holders of Registrable Securities incurred in
     connection therewith.

          (d) Priority on Demand Registrations. If a Demand Registration is an
     underwritten public offering and the managing underwriters advise the
     Company that in their opinion the number of Registrable Securities and
     other securities requested to be included exceeds the number of Registrable
     Securities and other securities which can be sold in an orderly manner in
     such offering without materially adversely affecting the price of the
     Shares to be sold in such registrations, the Company will include in such
     registration shares in the following order until such limitation has been
     met: first, the number of securities requested to be included therein by
     the Holders of Registrable Securities pro rata among Holders of Registrable
     Securities on the basis of the number of Shares owned by such Holders (the
     "DEMANDING SHAREHOLDERS"), second, securities requested by the Company to
     be included in such registration pursuant to "piggyback" rights hereunder;
     and third, other securities requested by the Stockholders to be included in
     such registration.

          (e) Restrictions on Registrations.

               (i) The Company may postpone for a reasonable period, not to
          exceed an aggregate of one hundred twenty (120) days in any twelve
          (12) month period, the filing or the effectiveness of a registration
          statement for a Demand Registration, if the Company determines
          reasonably and in good faith that such filing would have a material
          adverse effect on any proposal or plan of the Company to engage in any
          transaction, provided that in such event the Holders of

                                        7

<PAGE>   8

          Investors' Shares initially requesting such Demand Registration will
          be entitled to withdraw such request and, if such request is
          withdrawn, such Demand Registration will not count as a permitted
          Demand Registration hereunder, and the Company will pay all
          Registration Expenses in connection with such withdrawn registration.
          In addition, the Company shall not be required to effect any
          registration in accordance with the terms of this Agreement within one
          hundred eighty (180) days after the effective date of the IPO or
          ninety (90) days after the effective date of any subsequent primary
          offering (or combined primary and secondary offering) of its
          securities (other than a registration statement on Form S-8, or any
          successor forms or a registration on Form S-4 or relating to a Rule
          145 transaction). The Company may only provide the Delay Notice only
          once in any twelve (12) month period.

               (ii) The rights granted under SECTION 3(a)(iii) and SECTION
          3(a)(iv) shall expire ninety (90) days after all Registrable
          Securities are freely tradeable to the public through a broker, dealer
          or market maker in compliance with Rule 144(k) under the Securities
          Act, without limitation (or any similar rule than in force).

               (iii) The Company shall not be required to effect a Long-Form
          Demand Registration unless it is a firmly underwritten offering by an
          underwriter of nationally recognized standing (but not limited to
          "Tier 1" or "Tier 2" underwriters). The Company shall have the sole
          right to select such underwriter; provided, that in the event the
          Company has not selected an underwriter within thirty (30) days of the
          request for Demand Registration, the Demanding Shareholders may select
          such underwriter subject to approval of the Company not to be
          unreasonably withheld.

          (f) The Company shall give prompt notice to all holders of Registrable
     Securities of the receipt of a request for registration pursuant to this
     SECTION 3.

     4.   Holdback Agreements.

          (a) Biotech, the Investors and each Stockholder agree not to effect
     any public sale or distribution (including sales pursuant to Rule 144
     promulgated pursuant to the Securities Act) of equity securities of the
     Company, or any securities convertible into or exchangeable or exercisable
     for such securities without the prior written consent of the Company or the
     managing underwriter for such period of time (not to exceed the period
     beginning seven days prior to and during the 180-day period beginning on
     the effective date of the registration statement of the IPO) (except for
     sales of (i) securities as part of such IPO, (ii) securities purchased in
     the IPO or (iii) securities purchased on the open market after the IPO and
     as otherwise permitted under Rule 144(k)), unless the underwriters managing
     the IPO otherwise agree; provided that all officers and directors of the
     Company and, the holders of at least one percent (1%) of the Company's
     capital stock enter into similar agreements; further, provided, that the
     Company and the managing underwriter shall agree not to release any of
     those other persons from the lock-up prior to the release of all of the
     Investors and Biotech.

                                        8

<PAGE>   9

          (b) The Company agrees not to effect any public sale or distribution
     of its equity securities, or any securities convertible into or
     exchangeable or exercisable for such securities, during the seven days
     prior to and during the 180-day period beginning on the effective date of
     any underwritten Piggyback Registration (except as part of such
     underwritten registration or pursuant to registrations on Form S-8 or Form
     S-4 or any successor form), unless the underwriters managing the registered
     public offering otherwise agree.

     5. Registration Procedures. Whenever the Holders of Registrable Securities
have requested that any Registrable Securities be registered pursuant to this
Agreement, the Company will use its best efforts to effect the registration and
the sale of such Registrable Securities in accordance with the intended method
of disposition thereof, and pursuant thereto the Company will expeditiously as
possible:

          (a) Prepare and file with the SEC a registration statement with
     respect to such Registrable Securities, and use its best efforts to cause
     such registration statement to become effective and remain effective until
     the earlier of (i) the date when all Registrable Securities covered by the
     registration statement have been sold, or (ii) 180 days from the effective
     date of the registration statement; provided, however, that such 180-day
     period shall be extended for a period of time equal to the period the
     holder refrains from selling any securities included in such registration
     at the request of the Company or an underwriter of any securities of the
     Company pursuant to Section 5(e); provided, further, that before filing a
     registration statement or prospectus or any amendments or supplements
     thereto, the Company will furnish to the counsel selected by the Holders of
     a majority of the Registrable Securities covered by such registration
     statement copies of all such documents proposed to be filed including
     documents that are to be incorporated by reference into such registration
     statement or supplement, which documents will be subject to the review of
     such counsel, and which proposed registration statement or amendment or
     supplement thereto shall not be filed by the Company if the Holders of a
     majority of the Registrable Securities covered by such statement, amendment
     or supplement reasonably object to such filing;

          (b) Prepare and file with the SEC such amendments and supplements to
     such registration statement and the prospectus used in connection therewith
     as may be necessary to make and to keep such registration statement
     effective for the period referred to in SECTION 5(a) and comply with the
     provisions of the Securities Act with respect to the disposition of all
     securities covered by such registration statement during such period in
     accordance with the intended methods of disposition by the sellers thereof
     set forth in such registration statement;

          (c) Furnish to each Holder of Registrable Securities such number of
     copies of such registration statement, each amendment and supplement
     thereto, the prospectus included in such registration statement (including
     each preliminary prospectus) and any other documents as such Holder may
     reasonably request in order to facilitate the disposition of the
     Registrable Securities owned by such Holder;

          (d) Use its best efforts to register or qualify such Registrable
     Securities under such other securities or blue sky laws of such
     jurisdictions as may be reasonably

                                        9

<PAGE>   10

     necessary and do any and all other acts and things that may be reasonably
     necessary or advisable to enable such Holder to consummate the disposition
     in such jurisdictions of the Registrable Securities owned by such Holder;

          (e) Promptly notify each Holder of such Registrable Securities at any
     time when a prospectus relating thereto is required to be delivered under
     the Securities Act, of the occurrence of any event as a result of which the
     prospectus included in such registration statement contains an untrue
     statement of a material fact or omits any fact necessary to make the
     statements therein not misleading, and, at the request of any such Holder,
     the Company will promptly prepare a supplement or amendment to such
     prospectus so that, as thereafter delivered to the purchasers of such
     Registrable Securities, such prospectus will not contain an untrue
     statement of a material fact or omit to state any fact necessary to make
     the statements therein not misleading; provided that, at the request of the
     Company or the underwriter, each Holder shall refrain from selling
     securities included in such registration until notified by the Company or
     the underwriter that such prospectus has been supplemented or amended and
     no longer contains an untrue statement of material fact nor omits any fact
     necessary to make the statements therein not misleading;

          (f) Promptly notify the Holders of Registrable Securities and the
     underwriters of the following events: (i) the filing of the prospectus or
     any prospectus supplement and the registration statement and any amendment
     or post-effective amendment thereto and, with respect to the registration
     statement or any post-effective amendment thereto, the declaration of the
     effectiveness of such documents; (ii) any requests by the SEC for
     amendments or supplements to the registration statement or the prospectus
     or for additional information; (iii) the issuance or threat of issuance by
     the SEC of any stop order suspending the effectiveness of the registration
     statement or the initiation of any proceedings for that purpose; and (iv)
     the receipt by the Company of any notification with respect to the
     suspension of the qualification of the Registrable Securities for sale in
     any jurisdiction or the initiation or threat of initiation of any
     proceeding for such purpose;

          (g) Cause all such Registrable Securities to be listed on each
     securities exchange on which similar securities issued by the Company are
     then listed and, if not so listed, to be listed on the NASD automated
     quotation system and, if listed on the NASD automated quotation system, use
     its best efforts to secure designation of all such Registrable Securities
     covered by such registration statement as a NASDAQ "national market system
     security" within the meaning of Rule 11Aa2-1 under the Exchange Act,
     failing that, to secure NASDAQ authorization for such Registrable
     Securities and, without limiting the generality of the foregoing, to
     arrange for at least two market makers to register as such with respect to
     such Registrable Securities with the NASD;

          (h) Provide a transfer agent and registrar for all such Registrable
     Securities not later than the effective date of such registration
     statement;

          (i) Enter into any customary agreements (including, without
     limitation, underwriting agreements in customary form), and take all other
     actions as the Holders of a majority of the Registrable Securities being
     sold or the underwriters reasonably request

                                       10

<PAGE>   11

     in order to expedite or facilitate the disposition of such Registrable
     Securities (including, without limitation, effecting a stock split or a
     combination of shares);

          (j) Make available for inspection to any Holder of Registrable
     Securities, any underwriter participating in any disposition pursuant to
     such registration statement and any attorney, accountant or other agent
     retained by any such Holder or underwriter, all financial and other
     records, pertinent corporate documents and properties of the Company, and
     cause the Company's officers, directors, employees and independent
     accountants to supply all information reasonably requested by any such
     Holder, underwriter, attorney, accountant or agent in connection with such
     registration statement, provided that, each such Holder or underwriter,
     shall, upon the reasonable request of the Company, execute and deliver to
     the Company a confidentiality and nondisclosure agreement relating to such
     information, provided that such agreement shall contain such reasonable
     terms and conditions relating to confidentiality and nondisclosure matters
     mutually agreeable to such Holder or underwriter and the Company;

          (k) Otherwise use its best efforts to comply with all applicable rules
     and regulations of the SEC, and make available to its security holders, as
     soon as reasonably practicable, an earnings statement covering the period
     of at least twelve (12) months beginning with the first day of the
     Company's first full calendar quarter after the effective date of the
     registration statement, which earnings statement shall satisfy the
     provisions of Section 11(a) of the Securities Act and Rule 158 thereunder;

          (l) Permit any Holder of Registrable Securities to participate in the
     preparation of such registration or comparable statement and to require the
     insertion therein of material, furnished to the Company in writing, which
     in the reasonable judgment of such Holder and its counsel should be
     included;

          (m) Make every reasonable effort to prevent the entry of any order
     suspending the effectiveness of the registration statement and, in the
     event of the issuance of any such stop order, or of any order suspending or
     preventing the use of any related prospectus or suspending the
     qualification of any security included in such registration statement for
     sale in any jurisdiction, the Company will use its best efforts promptly to
     obtain the withdrawal of such order;

          (n) Use its best efforts to cause such Registrable Securities covered
     by such registration statement to be registered with or approved by such
     other governmental agencies or authorities as may be necessary to enable
     the Holders thereof to consummate the disposition of such Registrable
     Securities;

          (o) Cooperate with the selling Holders of Registrable Securities and
     the underwriters to facilitate the timely preparation and delivery of
     certificates representing Registrable Securities to be sold and not bearing
     any restrictive legends, and enable such Registrable Securities to be in
     such lots and registered in such names as the underwriters may request at
     least two business days prior to any delivery of Registrable Securities to
     the underwriters;

                                       11

<PAGE>   12

          (p) Provide a CUSIP number for all Registrable Securities not later
     than the effective date of the registration statement;

          (q) Prior to the effectiveness of the registration statement and any
     post-effective amendment thereto and at each closing of an underwritten
     offering, obtain "cold comfort" letters and updates thereof from the
     Company's independent certified public accountants addressed to the selling
     Holders of Registrable Securities and the underwriters, such letters to be
     in customary form and covering matters of the type customarily covered in
     "cold comfort" letters by underwriters in connection with primary
     underwritten offerings; and

          (r) Take all such other actions either necessary or appropriate to
     permit the Registrable Securities of a Holder to be registered and disposed
     of in accordance with the method of disposition described herein.

     6.   Registration Expenses.

          (a) All expenses incident to the Company's performance of or
     compliance with this Agreement including, without limitation, all
     registration and filing fees, fees and expenses of compliance with
     securities or blue sky laws, printing expenses, messenger and delivery
     expenses, fees and disbursements of counsel for the Company, fees and
     disbursements of one counsel selected by the participating Holders of
     Investors' Shares in an amount not to exceed Twenty Thousand Dollars
     ($20,000) for a Long-Form Demand Registration and Fifteen Thousand Dollars
     ($15,000) for each Short-Form Demand Registration and Piggyback
     Registration, and all independent certified public accountants,
     underwriters (excluding discounts and commissions) and other persons
     retained by the Company (all such expenses being herein called
     "REGISTRATION EXPENSES"), will be borne by the Company and the Company will
     pay its internal expenses (including, without limitation, all salaries and
     expenses of its officers and employees performing legal or accounting
     duties), the expense of any annual audit or quarterly review, the expense
     of any liability insurance and the expenses and fees for listing the
     securities to be registered on each securities exchange on which similar
     securities issued by the Company are then listed or on the NASD automated
     quotation system.

          (b) To the extent Registration Expenses are not required to be paid by
     the Company, each Holder of securities included in any registration
     hereunder will pay those expenses (including discounts and commissions)
     allocable to the registration of such Holder's securities so included, and
     any expenses (including discounts and commissions) not so allocable will be
     borne by all sellers of securities included in such registration in
     proportion to the aggregate selling price of the securities to be so
     registered.

     7.   Indemnification.

          (a) The Company agrees to indemnify to the extent permitted by law,
     each Holder of Registrable Securities, its officers, directors and
     partners, as the case may be, and each person who controls such Holder
     (within the meaning of the Securities Act) against all losses, claims,
     damages, liabilities and expenses caused by any untrue or

                                       12

<PAGE>   13

     allegedly untrue statement of material fact contained in any registration
     statement, prospectus or preliminary prospectus or any amendment thereof or
     supplement thereto, or any omission or alleged omission of a material fact
     required to be stated therein or necessary to make the statements therein
     not misleading, except insofar as the same are caused by or contained in
     any information furnished in writing to the Company by such Holder
     expressly for use therein or by such Holder's failure to deliver a copy of
     the registration statement or prospectus or any amendments or supplements
     thereto after the Company has furnished such Holder with a sufficient
     number of copies of the same. In connection with an underwritten offering,
     the Company will indemnify such underwriters, their officers, directors and
     partners, as the case may be, and each person who controls such
     underwriters (within the meaning of the Securities Act) to the same extent
     as provided above with respect to the indemnification of the Holders of
     Registrable Securities.

          (b) In connection with any registration statement in which a Holder of
     Registrable Securities is participating, each such Holder will furnish to
     the Company in writing such information and affidavits as the Company
     reasonably requests for use in connection with any such registration
     statement or prospectus and, to the extent permitted by law, will,
     severally and not jointly, if Registrable Securities held by such Holder
     are included in the securities as to which such registration, qualification
     or compliance is being effected, indemnify the Company, its directors and
     officers and each person who controls the Company (within the meaning of
     the Securities Act) against any losses, claims, damages, liabilities and
     expenses resulting from any untrue or allegedly untrue statement of
     material fact contained in the registration statement, prospectus or
     preliminary prospectus or any amendment thereof or supplement thereto, or
     any omission or alleged omission of a material fact required to be stated
     therein or necessary to make the statements therein not misleading, but
     only to the extent that such untrue statement or omission is contained in
     any information so furnished in writing by such Holder; provided, that the
     obligation to indemnify will be individual to each Holder and will be
     limited to the net amount of proceeds received by such Holder from the sale
     of Registrable Securities pursuant to such registration statement.

          (c) Any person entitled to indemnification hereunder will (i) give
     prompt written notice to the indemnifying party of any claim with respect
     to which it seeks indemnification and (ii) unless in such indemnified
     party's reasonable judgment a conflict of interest between such indemnified
     party and the indemnifying party may exist with respect to such claim,
     permit such indemnifying party to assume the defense of such claim with
     counsel reasonably satisfactory to the indemnified party. If such defense
     is assumed by the indemnifying party, the indemnified party will not be
     subject to any liability for any settlement made by the indemnifying party
     without its consent (but such consent will not be unreasonably withheld);
     provided, however, that any consent to entry of any judgment or entry into
     any settlement must include as an unconditional term thereof the giving by
     the claimant or plaintiff to such indemnified party of a full release from
     all liability in respect to such claim or litigation. An indemnifying party
     who is not entitled to, or elects not to, assume the defense of a claim
     will not be obligated to pay the fees and expenses of more than one counsel
     for all parties indemnified by such indemnifying party with respect to such
     claim, unless in the reasonable judgment of any indemnified party a
     conflict of interest may exist between such indemnified party and any

                                       13

<PAGE>   14

     other of such indemnified parties with respect to such claim. The failure
     of any indemnified party to give notice as provided herein shall not
     relieve the indemnifying party of its obligations under this Section 7
     unless the failure to give such notice is materially prejudicial to an
     indemnifying party's ability to defend such action, and then in such case,
     it shall be relieved only to the extent of such material prejudice.

          (d) The indemnification provided for under this Agreement will remain
     in full force and effect regardless of any investigation made by or on
     behalf of the indemnified party or any officer, director or controlling
     person of such indemnified party and will survive the transfer of
     securities, the completion of any offering of Registrable Securities in a
     registration statement and the termination of this Agreement. The Company
     also agrees to make such provisions, as are reasonably requested by an
     indemnified party, for contribution to such party in the event the
     Company's indemnification is unavailable for any reason.

     8. Participation in Underwritten Registrations. No person may participate
in any registration hereunder that is underwritten unless such person (a) agrees
to sell such person's securities on the basis provided in any underwriting
arrangements approved by the person or persons entitled hereunder to approve
such arrangements, and (b) completes and executes all questionnaires, powers of
attorney, indemnities, underwriting agreements and other documents required
under the terms of such underwriting arrangements.

     9. Reports Under the Securities Laws. With a view to making available to
the Holders of Registrable Securities the benefits of Rule 144 promulgated under
the Securities Act and any other rule or regulation of the SEC that may at any
time permit such Holder to sell securities of the Company to the public without
registration, the Company agrees to use its best efforts to:

          (a) Make and keep public information available, as those terms are
     understood and defined in Rule 144 under the Securities Act, at all times
     subsequent to ninety (90) days after the effective date of any registration
     statement covering an underwritten public offering filed under the
     Securities Act by the Company;

          (b) File with the SEC in a timely manner all reports and other
     documents required of the Company under the Securities Act and the Exchange
     Act, at any time after it is subject to such registration requirements; and

          (c) Furnish to any such Holder so long as such Holder owns any of the
     Registrable Securities forthwith upon request a written statement by the
     Company that it has complied with the reporting requirements of Rule 144
     (at any time after ninety (90) days after the effective date of the first
     registration statement filed by the Company for an offering of its
     securities to the general public), and of the Securities Act and the
     Exchange Act any time after it has become subject to such reporting
     requirements), a copy of the most recent annual or quarterly report of the
     Company, and such other reports and documents so filed by the Company as
     may be reasonably requested by any such Holder in availing any such Holder
     of any rule or regulation of the SEC permitting the selling of any such
     securities without registration.

                                       14

<PAGE>   15

     10. Certain Limitations in Connection with Future Grants of Registration
Rights. From and after the date of this Agreement, the Company shall not enter
into any agreement with any holder or prospective holder of any securities of
the Company providing for the granting to such holder of registration rights
unless such agreement is approved by the Holders of seventy-five percent (75%)
of the Registrable Securities then outstanding. Notwithstanding the foregoing,
any amendments or agreements that affect the rights of the Class C Preferred or
grant rights which are senior to or pari passu to the rights of the Class C
Preferred must be approved by Holders of at least seventy-five percent (75%) of
the Class C Preferred, and any amendments or agreements that affect the rights
of the Class F Preferred or grant rights which are senior to or pari passu to
the rights of the Class F Preferred must be approved by Holders of at least
seventy-five percent (75%) of the Class F Preferred.

     11. Financial Statements; Inspection.

          (a) Delivery of Financial Statements. The Company shall deliver to
     each Holder of at least 100,000 Class F Investors' Shares (subject to
     adjustments for stock splits and the like) (a "Major Class F Holder"):

               (i) Monthly Reports. As soon as available and in any event within
          thirty (30) days after the end of each of the first eleven (11) months
          of each fiscal year of the Company, consolidated balance sheets of the
          Company and its subsidiaries as of the end of such months and
          consolidated statements of income and cash flows of the Company and
          its subsidiaries for such month and for the period commencing at the
          beginning of the fiscal year, and ending with the end of such month
          setting forth in each case in comparative form the corresponding
          figures for the corresponding period of the preceding fiscal year, and
          including comparisons to monthly budgets, all in reasonable detail;
          and

               (ii) Annual Reports. As soon as available and in any event within
          ninety (90) days after the end of each fiscal year of the Company, a
          copy of the annual audit report for such year for the Company and its
          subsidiaries, including therein consolidated balance sheets of the
          Company and its subsidiaries as of the end of such fiscal year and
          consolidated statements of income and cash flows of the Company and
          its subsidiaries for such fiscal year, setting forth in each case in
          comparative form the corresponding figures for the preceding fiscal
          year; and

               (iii) Budgets. As soon as available after approval by the Board
          of Directors, but in any event at least thirty (30) days prior to the
          beginning of each fiscal year, a business plan and operating budgets
          (prepared on a monthly basis) for the forthcoming fiscal year.

          (b) Inspection. The Company shall permit each Major Class F Holder,
     with such Holder to pay its own expenses, to visit and inspect the
     Company's properties during normal working hours, to examine its books of
     account and records and make copies thereof and to discuss the Company's
     affairs, finances and accounts with its officers, all at such reasonable
     times, and upon reasonable notice, as may be requested by such Holder and
     all such queries to be reasonably related to the Holder's investment in the
     Company; provided, however, that the Company shall not be obligated
     pursuant to

                                       15

<PAGE>   16

     this Section 11(b) to provide access to any information which it deems in
     good faith to be a trade secret or other confidential or proprietary
     information.

          (c) Termination of Information and Inspection Rights. The rights set
     forth in Section 11(a) and (b) shall terminate as to each Holder and be of
     no further force or effect when the Company is required to file reports
     (and does so) pursuant to Section 13 or 15(d) of the Exchange Act.

     12. Transfer of Registration Rights. Provided that the Company is given
written notice by the Holder of Registrable Securities prior to, at the time of
or reasonably soon after such transfer stating the name and address of the
transferee and identifying the securities with respect to which the rights under
this Agreement are being assigned, and provided that to the Company's reasonable
satisfaction, such proposed transferee is not a competitor or potential
competitor of the Company, the rights granted to Holders hereunder may be
transferred to any transferee acquiring, in the aggregate, shares representing
at least 100,000 Shares (subject to adjustments for stock splits and the like).

     13.  Miscellaneous.

          (a) No Inconsistent Agreements. The Company will not hereafter enter
     into any agreement with respect to its securities which is inconsistent
     with or violates the rights granted to the Holders of Registrable
     Securities in this Agreement.

          (b) Adjustments Affecting Registrable Securities. The Company will not
     take any action, or permit any change to occur, with respect to its
     securities which would materially and adversely affect the ability of the
     Holders of Registrable Securities to include such Registrable Securities in
     a registration undertaken pursuant to this Agreement or which would
     materially and adversely affect the marketability of such Registrable
     Securities in any such registration (including, without limitation,
     effecting a stock split or a combination of shares).

          (c) Remedies. Any person having rights under any provision of this
     Agreement will be entitled to enforce such rights specifically to recover
     damages caused by reason of any breach of any provision of this Agreement
     and to exercise all other rights granted by law. The parties hereto agree
     and acknowledge that money damages may not be an adequate remedy for any
     breach of the provisions of this Agreement and that any party may in its
     sole discretion apply to any court of law or equity of competent
     jurisdiction (without posting any bond or other security) for specific
     performance and for other injunctive relief in order to enforce or prevent
     violation of the provisions of this Agreement.

          (d) Amendments and Waivers. Except as otherwise provided herein, the
     provisions of this Agreement may be amended or waived only upon the prior
     written consent of the Company and Holders of at least seventy-five percent
     (75%) of the Registrable Securities (excluding all Registrable Securities
     held by the Company). Notwithstanding the foregoing, any amendments or
     agreements that affect the rights of the Class C Preferred or grant rights
     which are senior to or pari passu to the rights of the Class C Preferred
     must be approved by Holders of at least seventy-five percent (75%) of

                                       16

<PAGE>   17

     the Class C Preferred, and any amendments or agreements that affect the
     rights of the Class F Preferred or grant rights which are senior to or pari
     passu to the rights of the Class F Preferred must be approved by Holders of
     at least seventy-five percent (75%) of the Class F Preferred.

          (e) Successors and Assigns. All covenants and agreements in this
     Agreement by or on behalf of any of the parties hereto will bind and inure
     to the benefit of the respective successors and assigns of the parties
     hereto whether so expressed or not. In addition, whether or not any express
     assignment has been made, the provisions of this Agreement which are for
     the benefit of purchasers or Holders of Registrable Securities are also for
     the benefit of, and enforceable by, any subsequent Holder of Registrable
     Securities.

          (f) Severability. Whenever possible, each provision of this Agreement
     shall be interpreted in such manner as to be effective and valid under
     applicable law, but if any provision of this Agreement is held to be
     prohibited by or invalid under applicable law, such provision shall be
     ineffective only to the extent of such prohibition or invalidity, without
     invalidating the remainder of this Agreement.

          (g) Counterparts. This Agreement may be executed in two or more
     counterparts, each of which constitutes an original and all of which
     counterparts taken together shall constitute one and the same Agreement.

          (h) Descriptive Headings; Interpretation. The descriptive headings of
     this Agreement are inserted for convenience only and do not constitute a
     part of this Agreement. The use of the word "including" in this Agreement
     shall be by way of example rather than limitation.

          (i) Governing Law. This Agreement shall be governed and construed in
     accordance with the laws of the State of Delaware.

          (j) Notices. All notices, requests, demands, claims, and other
     communications hereunder shall be in writing and shall be deemed to have
     been duly given if delivered personally, telecopied, sent by nationally
     recognized overnight courier (charges prepaid) or mailed by registered or
     certified mail (return receipt requested), postage prepaid, to the parties
     at the addresses specified in the Class F Stock Purchase Agreement (or at
     such other address for a party as shall be specified by like notice).

          (k) Delays or Omissions. No delay or omission to exercise any right,
     power or remedy accruing to any party to this Agreement, whether or not
     upon any breach or default of the other party, shall impair any such right,
     power or remedy of such party nor shall it be construed to be a waiver of
     any such breach or default, or an acquiescence therein, or of any similar
     breach or default thereafter occurring; nor shall any waiver of any single
     breach or default be deemed a waiver of any other breach or default
     theretofore or thereafter occurring. Any waiver, permit, consent or
     approval of any kind or character on the part of any party of any breach or
     default under this Agreement, or any waiver on the part of any party of any
     provisions or conditions of this Agreement, must be made in writing, shall
     be effective only to the extent specifically set forth in such writing and

                                       17

<PAGE>   18

     comply with Section 13(d) above. All remedies, either under this Agreement,
     or by law or otherwise afforded to any Holder, shall be cumulative and not
     alternative.

          (l) Entire Agreement. This Agreement and the documents referred to
     herein constitute the entire agreement between the parties hereto
     pertaining to the subject matter hereof and any other written or oral
     agreements between the parties hereto are expressly canceled.

                   [BALANCE OF PAGE LEFT BLANK INTENTIONALLY]

                                       18

<PAGE>   19

         IN WITNESS WHEREOF, the parties have executed this Amended and Restated
Registration Rights Agreement as of the date first above written.

                                         ATHERSYS, INC.

                                         By:    /s/Gil Van Bokkelen, Ph.D.
                                            ----------------------------------
                                         Name:  Gil Van Bokkelen, Ph.D.
                                         Title: President and Chief Executive
                                                Officer

                [STOCKHOLDER SIGNATURES BEGIN ON FOLLOWING PAGE]

                                       19
<PAGE>   20
PRESIDENT LIFE SCIENCES CO., LTD.                ELWIN W. ANDERSON AND BETTY
                                                 LOU ANDERSON JTWROS

By: /s/ Por-Hsiung Lai                           /s/ Elwin W. Anderson
   ------------------------------                   ----------------------------
   Por-Hsiung Lai                                Elwin W. Anderson
   President

                                                 /s/ Betty Lou Anderson
                                                    ----------------------------
                                                 Betty Lou Anderson

ALGODON 453, INC.                                ATHERSYS INVESTORS LLC

By: /s/ Bill Ring                                By: /s/ Jud Martin
   ------------------------------                   ----------------------------
   Bill Ring                                        Dr. Jud Martin
   President                                        Manager

ATHERSYS INVESTORS II, L.L.C.                    ATHERSYS INVESTORS III, L.L.C.

By: /s/ Jud Martin                               By: /s/ Jud Martin
   ------------------------------                   ----------------------------
   Dr. Jud Martin                                   Dr. Jud Martin
   Manager                                          Manager

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

                                       8
<PAGE>   21

B&N INVESTMENTS                              BAIE FINE, L.L.C.

By:/s/ Robert Betcher                        By: /s/ Robert S. Jackson
   ------------------------------                ----------------------------
   Robert Betcher                                Robert S. Jackson
   Partner                                       Title:Manager

By:/s/ Nancy Betcher
   ------------------------------
     Nancy Betcher
     Partner

BEN NICKMAN ATHERSYS                         BIOTECH 3 INVESTMENT L.L.C.
PARTNERS, L.P.                               By: BVF Partners L.P., its Manager
                                             By: BVF Inc., its general partner

By: /s/ Jennifer Sabelhaus                   By: /s/ Mark N. Lampert
   ------------------------------                ----------------------------
   Jennifer Sabelhaus                            Mark N. Lampert
   General Partner                               President

BLUE CHIP CAPITAL FUND II                    BRIDGEWOOD CAPITAL PARTNERS
LIMITED PARTNERSHIP
By: Blue Chip Venture Company, Ltd.

By: /s/ John C. McIlwraith                   By: /s/ Michael Weisberg
   ------------------------------                ----------------------------
   John C. McIlwraith                            Michael Weisberg
   Manager                                       General Partner

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

<PAGE>   22

RICHARD J. BRYSACZ TTEE                      BRIAN AND SUSAN CARLSON
SHARING PLAN                                 JT/WROS
U/A DTD 01-02-92

By: /s/ Richard J. Brysacz                   By: /s/ Brian Carlson
   ------------------------------                ----------------------------
   Richard J. Brysacz                            Brian Carlson
   Title:                                        Title:

                                             By: /s/ Susan M. Carlson
                                                 ----------------------------
                                                 Susan Carlson
                                                 Title:

CASE WESTERN RESERVE                         WARBURG DILLON READ LLC
UNIVERSITY

By: /s/ William M. Rose                      By: /s/ Kipp K. Schrage
   ------------------------------                ----------------------------
   William M. Rose                               Kipp Schrage
   Treasurer                                     Managing Director, Equities

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

CHELSEY CAPITAL                              CRESTWOOD CAPITAL
                                             INTERNATIONAL LTD.

By: /s/ Stuart Feldman                       By: /s/ Michael Weisberg
   ------------------------------                ----------------------------
   Mr. Stuart Feldman                            Michael Weisberg
   President                                     General Partner

<PAGE>   23

CRESTWOOD CAPITAL PARTNERS                       CRESTWOOD CAPITAL PARTNERS II
L.P.                                             L.P.

By: /s/ Michael Weisberg                         By: /s/ Michael Weisberg
   ------------------------------                   -------------------------
   Michael Weisberg                                 Michael Weisberg
   General Partner                                  General Partner

CURRAN PARTNERS, L.P.                            DKM REVOCABLE TRUST, UID
                                                 OCTOBER 25, 1993

By: /s/ John P. Curran                           By: /s/ Daniel A. Madison
   ------------------------------                   -------------------------
   John P. Curran                                   Daniel A. Madison
   General Partner                                  Trustee

DRW VENTURE PARTNERS L.P.                        THE EBTC FOUNDATION

By: Dain Rauscher Corporation, its general
partner

By: /s/ Mary Zimmer                              By: /s/ Frank E. Samuel, Jr.
   ------------------------------                   -------------------------
   Mary Zimmer                                      Frank E. Samuel, Jr.
   Director, DRW Finance & Administration           President

EGM MEDICAL TECHNOLOGY FUND,                     EGM MEDICAL TECHNOLOGY
L.P.                                             OFFSHORE FUND, L.P.
By: Emerging Growth Management Co., its          By: Emerging Growth Management
general partner                                  Co., its
                                                 general partner

By: /s/ Michael T. Jackson                       By: /s/ Michael T. Jackson
   ------------------------------                   -------------------------
   Michael T. Jackson                               Michael T. Jackson
   General Partner                                  General Partner

<PAGE>   24

GALLADIO HOLDING B.V.                            GERALDINE HEIBEL TRUST

By:/s/ Mark Rosman                               By: /s/ Richard Heibel
   ------------------------------                   -------------------------
   Mark Rosman                                      Richard Heibel
   Title:                                           Title:

GENE FUND L.P.                                   GRANT-JESTADT-GRANT, L.L.C.

By:                                              By: /s/ Tim Grant
   ------------------------------                   -------------------------
   Wei-Wu He                                        Timothy L. Grant
   Title:                                           Member

HARPEL VENTURE PARTNERS                          EDWARD L. HENDERSHOT CHARLES
                                                 SCHWAB & CO., INC. CUST. IRA
                                                 ROLLOVER

By: /s/ James W. Harpel
    -----------------------------
    James W. Harpel
    General Partner                              By: /s/ Edward Hendershot
                                                    -------------------------
                                                 Edward L. Hendershot
                                                 Title:

RUTH M. HENDERSHOT TTEE,                         HOEGH INVEST, AS
THE RUTH M. HENDERSHOT
TRUST U/A DTD APRIL 22, 1993

                                                 By: /s/ Carl Preben Hoegh
                                                    -------------------------
                                                    Carl Preben Hoegh
By: /s/ Ruth M. Hendershot                          Chairman
   ------------------------------
     Ruth M. Hendershot
     Trustee

<PAGE>   25

ING BARINGS, LLC                                 INVESCO GLOBAL HEALTH
                                                 SCIENCES FUND

By: /s/ H. Gill Sawhney
   -------------------------------
   H. Gill Sawhney                               By: /s/ Glen A. Payne
   Managing Director                                -------------------------
                                                 Name:  Glen A. Payne
                                                 Title:     Secretary

KBC EQUITY FUNDS                                 KOONS OF ALEXANDRIA, LLC
BIOTECHNOLOGY

By: /s/ Youri Amerijckx
   -------------------------------
    /s/ Ignace Van Oortegem                    By: /s/ Michael L. Field
   --------------------------------                --------------------------
   Youri Amerijckx                                 Michael L. Field
   Equity Fund Manager                             President

MANSCHOT OPPORTUNITY FUND,                     MEDICAL VENTURE MANAGEMENT
L.P.

By:  Manschot Investor Group LLC, its
     General Partner                           By: /s/ Fredrik C. Schreuder
                                                   --------------------------
                                                   Name: Fredrik C. Schreuder
                                                   Title:   President

By: /s/ Tom P. Chapman III
   -------------------------------
   Tom P. Chapman III
   Title: Authorized Representative

MCP GLOBAL CORPORATION, LTD.                   MGT CORPORATION

By: /s/ Mia N. Pogue                           By: /s/ Thomas M. Ehlers
   --------------------------------                --------------------------
   Mai N. Pogue                                    Thomas M. Ehlers
   Director                                        Title: President

<PAGE>   26

MIAMI VALLEY VENTURE FUND L.P.                 MICHAEL LEE FIELD CHARLES
By:  Blue Chip Venture Company of Dayton,      SCHWAB & CO., INC. CUST. IRA
Ltd.                                           ROLLOVER

By: /s/ John C. McIlwraith                     By: /s/ Michael L. Field
   --------------------------------                --------------------------
   John C. McIlwraith                              Michael L. Field
   Manager                                         Title:

MICHAEL T. JACKSON TRUST                       NEOMED INNOVATION, ASA

By: /s/ Michael T. Jackson                     By:/s/ Carl Christian Gilhuus-Moe
   --------------------------------               ---------------------------
   Michael T. Jackson                              Carl Christian Gilhuus-Moe
   Trustee                                         General Partner

                                               By:/s/ Erik Amble
                                                  ---------------------------
                                                  Erik Amble
                                                  General Partner

ODIN PARTNERS, L.P.                            OHIO INNOVATION FUND I, L.P.

By: /s/ John A. Gibbons                        By: /s/ Timothy G. Biro
   --------------------------------                --------------------------
   John Gibbons                                    Timothy G. Biro
   Managing Partner                                Managing Partner

<PAGE>   27

<TABLE>
<CAPTION>

<S>                                            <C>
PALMETTO PARTNERS, LTD.                        DONALD L. AND CAROL A. POE
By:  Palmetto Capital Corporation, its         JNT TEN
managing general partner

By: /s/ James M. Kendrigan                     /s/ Donald L. Poe
   --------------------------------            --------------------------
   James M. Kendrigan                          Donald L. Poe
   Vice President and Managing Director

                                               /s/ Carol A. Poe
                                               --------------------------
                                               Carol A. Poe

PRIMUS CAPITAL FUND IV LIMITED                 PRIMUS EXECUTIVE FUND LIMITED
PARTNERSHIP                                    PARTNERSHIP
By:  Primus Venture Partners IV Limited        By:  Primus Venture Partners IV Limited
Partnership, its general partner               Partnership, its general partner

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

By: /s/ William C. Mulligan                    By: /s/ William C. Mulligan
   --------------------------------                --------------------------
   William C. Mulligan                             William C. Mulligan
   Executive Vice President                        Executive Vice President

R&P FAMILY LIMITED                             RICHARD B.  SANDERS AND MARY L.
PARTNERSHIP                                    SANDERS JT TEN

By: /s/ Ronald J. Shimek                           /s/ Richard B. Sanders
   --------------------------------                --------------------------
   Ron Shimek                                      Richard B. Sanders
   Title:

                                                   /s/ Mary L. Sanders
                                                   --------------------
                                                   Mary L. Sanders
</TABLE>

<PAGE>   28

<TABLE>
<CAPTION>
<S>                                            <C>

SENTRON MEDICAL INC.                           SUSAN NOONAN AND ANTHONY J.
                                               RUSSO,  TENANTS-IN-COMMON

By: /s/ Clint Dederick                             /s/ Susan Noonan
   --------------------------------                --------------------------
   Clint Dederick                                  Susan Noonan
   Group Director, Venture Projects

                                                   /s/ Anthony J. Russo
                                                   --------------------------
                                                   Anthony J. Russo

TALMOR CAPITAL MANAGEMENT,                     TRIVENTURES
L.L.C.

By: /s/ Edmund H. Melhado                      By: /s/ Jim Lustig
   --------------------------------                --------------------------
   Edmund H. Melhado                               Jim Lustig
   Portfolio Manager                               Partner

VAN WAGONER FUNDS                              VAN WAGONER CAPITAL PARTNERS,
By:  Van Wagoner Capital Management, its       L.P.
general partner                                By:  Van Wagoner Capital Management, its
                                               general partner

By: /s/ Audrey Lam                             By: /s/ Audrey Lam
   --------------------------------                --------------------------
   Audrey Lam                                      Audrey Lam
   Managing Director                               Managing Director
</TABLE>

<PAGE>   29

VAN WAGONER CROSSOVER FUND,                    WILLIAM H. ROLFERT
L.P.                                           CHARLES SCHWAB & CO., INC.
By:  Van Wagoner Capital Management, its       CUST. IRA CONTRIBUTION
general partner

By: /s/ Audrey Lam                             By: /s/ William H. Rolfert
   --------------------------------                --------------------------
   Audrey Lam                                      William H. Rolfert
   Managing Director                               Title:

MICHAEL ARBAUGH AND KAREN                      INVESCO HEALTH SCIENCES FUND
LOPRESTO, AS JOINT TENANTS

                                               By:/s/ Glen A. Payne
                                                  ---------------------------
By: /s/ Michael Arbaugh  /s/ Karen LoPresto       Name: Glen A. Payne
   ----------------------------------------       Title:
   Name:
   Title:

/s/ John W. Allison                            /s/ Jonas Alsenas
-------------------------------                ------------------------------
John W. Allison                                Jonas Alsenas

/s/ Linda Kiss Baker                           /s/ Emily H. Brasfield
-------------------------------                ------------------------------
Linda Kiss Baker                               Emily H. Brasfield

/s/ Brian P. Clifford                          /s/ Ron Cohen
-------------------------------                ------------------------------
Brian P. Clifford                              Ron Cohen

/s/ Robert N. Comstock                         /s/ Timothy E. Davis, Jr.
-------------------------------                ------------------------------
Robert N. Comstock                             Timothy Edward Davis, Jr.

<PAGE>   30

/s/ Michel Desbard                             /s/ Daniel V. Drake
-------------------------------                ------------------------------
Michel Desbard                                 Daniel V. Drake

/s/ John Harrington                            /s/ Paul Kelly
-------------------------------                ------------------------------
John J. Harrington                             Paul Kelly

/s/ Tinka Kurth                                /s/ Robert W. Mays
-------------------------------                ------------------------------
Tinka Kurth                                    Robert Mays

/s/ Edward F. McManus                          /s/ Ira Mellman
-------------------------------                ------------------------------
Edward F. McManus                              Dr. Ira Mellman

/s/ Richard K. Nason                           /s/ Samuel E. Navarro
-------------------------------                ------------------------------
Richard Nason                                  Samuel E. Navarro

/s/ James Nelson                               /s/ Kevin O'Connell
-------------------------------                ------------------------------
Dr. James Nelson                               Kevin O'Connell

/s/ Brian O'Connor                             /s/ Marc A. Pentopoulos
-------------------------------                ------------------------------
Brian O'Connor                                 Marc A. Pentopoulos

/s/ Robert Perry                               /s/ Barclay Phillips
-------------------------------                ------------------------------
Robert Perry                                   Barclay A. Phillips

/s/ H. Gill Sawhney                            /s/ Dr. Leon Smith
-------------------------------                ------------------------------
H. Gill Sawhney                                Dr. Leon Smith

<PAGE>   31

/s/ Lloyd E. Smith                             /s/ Gil Van Bokkelen
-------------------------------                ------------------------------
Lloyd E. Smith                                 Gil Van Bokkelen

/s/ John R. Van Bokkelen                       /s/ William Van Bokkelen
-------------------------------                ------------------------------
John R. Van Bokkelen                           William Van Bokkelen

/s/ Arthur C.A. van der Goes                   /s/ Joe Vona
-------------------------------                ------------------------------
Arthur C.A. van der Goes                       Joe Vona

/s/ Laurie M. Wade                             /s/ David Wendel
-------------------------------                ------------------------------
Laurie M. Wade                                 David I. Wendel

/s/ Huntington Willard                         /s/ Raymond Yee
-------------------------------                ------------------------------
Dr. Huntington Willard                         Raymond Yee

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