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                                                                     EXHIBIT 4.5

                                                                  EXECUTION COPY

                           FIFTH AMENDED AND RESTATED
                          REGISTRATION RIGHTS AGREEMENT

                                                         December 23, 2003

To each of the several holders of Restricted Stock named in Exhibit A attached
hereto.

Ladies and Gentlemen:

         Pursuant to the Registration Rights Agreement dated as of November 26,
1997 by and among t. Breeders, Inc., now known as Viacell, Inc., a Delaware
corporation (the "Company"), and the purchasers listed in the signature pages
thereto (as amended and restated by that certain Amended and Restated
Registration Rights Agreement, dated April 11, 2000, and as further amended by
the Second Amended and Restated Registration Rights Agreement, dated November
10, 2000, the Third Amended and Restated Registration Rights Agreement, dated
October 25, 2001, and the Fourth Amended and Restated Registration Rights
Agreement, dated September 30, 2003, the "Old Registration Rights Agreement"),
the Company granted certain registration rights to the holders of the Company's
(i) Series A Convertible Preferred Stock, $.01 par value (the "Series A
Preferred"), (ii) Series B Convertible Preferred Stock, $.01 par value (the
"Series B Preferred"), (iii) Series C Convertible Preferred Stock, $.01 par
value (the "Series C Preferred"), (iv) Series D Convertible Preferred Stock,
$.01 par value (the "Series D Preferred"), (v) Series E Convertible Preferred
Stock, $.01 par value (the "Series E Preferred"), (vi) Series F Convertible
Preferred Stock, $.01 par value (the "Series F Preferred"), (vii) Series G
Convertible Preferred Stock, $.01 par value (the "Series G Preferred"), (viii)
Series H Convertible Preferred Stock, $.01 par value (the "Series H Preferred"),
(ix) Series I Convertible Preferred Stock, $.01 par value (the "Series I
Preferred"), (x) Series J Convertible Preferred Stock, $.01 par value (the
"Series J Preferred"), and (xi) the Warrant Agreements exercisable for Common
Stock (as defined herein) issuable pursuant to the Series D Unit/Series E
Preferred Stock Purchase Agreement, dated as of November 26, 1997, the Warrant
Agreements exercisable for Common Stock issuable to ARE-One, dated February 24,
2000, the Warrant Agreements exercisable for Common Stock issuable to Amgen
Inc., dated as of April 9, 2002, the Warrant Agreements exercisable for
Preferred Stock issuable to General Electric Capital Corporation, in connection
with the debt facility, dated October 16, 2003, and the Warrant Agreements
exercisable for Common Stock issuable pursuant to the Series J Purchase
Agreement, dated September 30, 2003 (collectively, the "Warrants"). Pursuant to
this Fifth Amended and Restated Registration Rights Agreement (this
"Agreement"), the Company is granting certain registration rights to the holder
of shares of Series K Preferred Stock, $.01 par value (the "Series K Preferred,"
and together with the Series A Preferred, Series B Preferred, Series C
Preferred, Series D Preferred, Series E Preferred, Series F Preferred, Series G
Preferred, Series H Preferred, Series I Preferred and Series J Preferred, the
"Preferred Securities"), who purchases such shares pursuant to a Securities
Purchase Agreement of even date herewith (the "Series K Purchase Agreement"). In
addition, the parties to the Old Registration Rights Agreement intend that, upon
execution of this Agreement, the provisions of the Old Registration Rights
Agreement shall be terminated and superseded in their entirety by this
Agreement. The Company covenants and agrees with each of you as follows:

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         1.       Termination of Old Registration Rights Provisions. The Old
Registration Rights Agreement is hereby terminated in its entirety and is of no
further force or effect.

         2.       Certain Definitions. As used in this Agreement, the following
terms shall have the following respective meanings:

                  (a)      "Commission" shall mean the Securities and Exchange
Commission, or any other federal agency at the time administering the Securities
Act.

                  (b)      "Common Stock" shall mean the Common Stock, $.01 par
value, of the Company, as constituted as of the date of this Agreement.

                  (c)      "Conversion Shares" shall mean shares of Common Stock
issued or issuable upon conversion or exercise of the Preferred Securities.

                  (d)      "Exchange Act" shall mean the Securities Exchange Act
of 1934, as amended, or any similar federal statute, and the rules and
regulations of the Commission thereunder, all as the same shall be in effect at
the time.

                  (e)      "Registration Expenses" shall mean the expenses so
described in Section 8.

                  (f)      "Restricted Stock" shall mean the Conversion Shares
and the shares of Common Stock issued or issuable upon exercise or conversion of
the Warrants (or upon conversion of any Preferred Securities issuable pursuant
to the Warrants), excluding any such shares which have been (a) registered under
the Securities Act pursuant to an effective registration statement filed
thereunder and disposed of in accordance with the registration statement
covering them or (b) publicly sold pursuant to Rule 144 under the Securities
Act; provided, that for the purposes of this definition, the holder of any such
Preferred Securities or Warrants shall be deemed to be the holder of the shares
of Common Stock issuable upon the conversion or exercise of such Preferred
Securities or Warrants.

                  (g)      "Securities Act" shall mean the Securities Act of
1933, as amended, or any similar federal statute, and the rules and regulations
of the Commission thereunder, all as the same shall be in effect at the time.

                  (h)      "Selling Expenses" shall mean the expenses so
described in Section 8.

                  (i)      "Senior Securities" shall mean the (i) Series C
Preferred, Series D Preferred, Series E Preferred, Series F Preferred, Series G
Preferred, Series H Preferred, Series I Preferred, Series J Preferred and Series
K Preferred and (ii) the Warrants.

         3.       Certain Transfers

                  (a)      Notice of Proposed Transfer. Prior to any proposed
transfer of any Preferred Securities or Restricted Stock (other than under the
circumstances described in Sections 4, 5 or 6), the holder thereof shall give
written notice to the Company of its intention to effect such transfer. Each
such notice shall describe the manner of the proposed transfer and, if requested
by the Company, shall be accompanied by an opinion of counsel satisfactory to
the Company (it being agreed that Ropes & Gray LLP or Goodwin Procter LLP shall
be satisfactory) to the effect that the proposed transfer may be effected
without registration under the Securities Act, whereupon the holder of such
stock shall be entitled to transfer such

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stock in accordance with the terms of its notice; provided, however, that no
such opinion of counsel shall be required for a transfer to (i) any affiliate of
such holder as defined under Rule 144 of the Securities Act, (ii) its partners,
shareholders, members or other equity holders, (iii) any Immediate Family member
(as defined below), (iv) any heir, executor or legal representative, (v) to any
charitable organization qualified under Section 501(c)(3) of the Internal
Revenue Code of 1986, as amended, for no consideration, or (vi) any trustee of
an inter-vivos trust or testamentary trust for the benefit of Immediate Family
members. Each certificate for Preferred Securities or Conversion Shares
transferred as above provided shall bear the legend set forth in Section 3(b),
except that such certificate shall not bear such legend if (i) such transfer is
in accordance with the provisions of Rule 144 or Rule 144A (or any other rule
permitting public sale without registration under the Securities Act) or (ii)
the opinion of counsel referred to above is to the further effect that the
transferee and any subsequent transferee (other than an affiliate of the
Company) would be entitled to transfer such securities in a public sale without
registration under the Securities Act. The restrictions provided for in this
Section 3(a) shall not apply to securities which are not required to bear the
legend prescribed by Section 3(b) in accordance with the provisions of that
Section. As used herein, "Immediate Family" shall mean any lineal ancestors or
descendants, spouse, sibling, in-laws, aunts, uncles, nieces and nephews.

                  (b)      Restrictive Legend. Each certificate representing
Preferred Securities or Restricted Stock shall, except as otherwise provided in
Section 3(a) or this Section 3(b), be stamped or otherwise imprinted with a
legend substantially in the following form:

                  "THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES
                  ACT OF 1933 AND MAY NOT BE TRANSFERRED OR OTHERWISE DISPOSED
                  OF UNLESS IT HAS BEEN REGISTERED UNDER THAT ACT OR AN
                  EXEMPTION FROM REGISTRATION IS AVAILABLE."

A certificate shall not bear such legend if in the opinion of counsel
satisfactory to the Company (it being agreed that Ropes & Gray LLP or Goodwin
Procter LLP shall be satisfactory) the securities represented thereby may be
publicly sold without registration under the Securities Act.

         4.       Required Registration.

                  (a)      At any time after 180 days after any registration
statement covering the initial public offering of securities of the Company
under the Securities Act shall have become effective, the holders of Senior
Securities constituting at least 50% of the total outstanding shares of
Restricted Stock then held by the holders of Senior Securities may request the
Company to register under the Securities Act all or any portion of the shares of
Restricted Stock held by such requesting holder or holders for sale in the
manner specified in such notice. For purposes of this Section 4 and Sections 5
and 6, the only securities which the Company shall be required to register
pursuant hereto shall be shares of Common Stock, provided, however, that, in any
underwritten public offering contemplated by this Section 4 or Sections 5 and 6,
the holders of Preferred Securities shall be entitled to sell such Preferred
Securities to the underwriters for conversion or exercise and sale of the shares
of Common Stock issued upon conversion or exercise thereof. Notwithstanding
anything to the contrary contained herein, no request may be made under this
Section 4 within 180 days after the effective date of a registration statement
filed by the Company covering a firm commitment underwritten public offering in
which the holders of Restricted Stock shall have been entitled to join pursuant
to Sections 5 or 6 and in which there shall have been effectively registered all

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shares of Restricted Stock as to which registration shall have been requested.
If any registration made pursuant to this Section 4 is an underwritten offering,
then the holders of the Senior Securities holding at least 50% of the total
shares of Restricted Stock being included in the underwritten offering shall
select the underwriter, subject to the consent of the Company (which consent
shall not be unreasonably withheld).

                  (b)      Following receipt of any notice under this Section 4,
the Company shall immediately notify all holders of Restricted Stock from whom
notice has not been received and shall use its best efforts to register within
60 days of the initial request under the Securities Act, for public sale in
accordance with the method of disposition specified in such notice from
requesting holders, the number of shares of Restricted Stock specified in such
notice (and in all notices received by the Company from other holders within 30
days after the giving of such notice by the Company). If such method of
disposition shall be an underwritten public offering, the holders of a majority
of the shares of Restricted Stock to be sold in such offering may designate the
managing underwriter of such offering, subject to the approval of the Company,
which approval shall not be unreasonably withheld or delayed. The Company shall
be obligated to register Restricted Stock pursuant to this Section 4 on two (2)
occasions only, provided, however, that such obligation shall be deemed
satisfied only when a registration statement covering all shares of Restricted
Stock specified in notices received as aforesaid for sale in accordance with the
method of disposition specified by the requesting holders shall have become
effective and, if such method of disposition is a firm commitment underwritten
public offering, all such shares shall have been sold pursuant thereto.

                  (c)      The Company shall be entitled to include in the
registration statement referred to in this Section 4, for sale in accordance
with the method of disposition specified by the requesting holders, shares of
Common Stock to be sold by the Company for its own account, except as and to the
extent that, in the opinion of the managing underwriter (if such method of
disposition shall be an underwritten public offering), such inclusion would
adversely affect the marketing of the Restricted Stock to be sold. Except for
registration statements on Form S-4, S-8 or any successor thereto, the Company
will not file with the Commission any other registration statement with respect
to its Common Stock, whether for its own account or that of other stockholders,
from the date of receipt of a notice from requesting holders pursuant to this
Section 4 until the completion of the period of distribution of the registration
contemplated thereby.

         E.       Incidental Registration. If the Company at any time (other
than pursuant to Section 4 or Section 6) proposes to register any of its
securities under the Securities Act for sale to the public, whether for its own
account or for the account of other security holders or both (except with
respect to registration statements on Forms S-4, S-8 or another form not
available for registering the Restricted Stock for sale to the public), each
such time it will give written notice to all holders of outstanding Restricted
Stock of its intention so to do. Upon the written request of any such holder,
received by the Company within 30 days after the giving of any such notice by
the Company, to register any of its Restricted Stock (which request shall state
the intended method of disposition thereof), the Company will use its best
efforts to cause the Restricted Stock as to which registration shall have been
so requested to be included in the securities to be covered by the registration
statement proposed to be filed by the Company, all to the extent requisite to
permit the sale or other disposition by the holder (in accordance with its
written request) of such Restricted Stock so registered. In the event that any
registration pursuant to this Section 5 shall be, in whole or in part, an

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underwritten public offering of Common Stock, the number of shares of Restricted
Stock to be included in such an underwriting may be reduced (first by excluding
Series A Preferred and Series B Preferred holders on a pro rata basis and
second, if necessary by excluding the holders of the Senior Securities on a pro
rata basis) if and to the extent that the managing underwriter shall be of the
opinion that such inclusion would adversely affect the marketing of the
securities to be sold by the Company therein, provided, however, that such
number of shares of Restricted Stock shall not be reduced if any shares are to
be included in such underwriting for the account of any person other than the
Company or requesting holders of Restricted Stock, and provided, further,
however, that in no event may less than one-third of the total number of shares
of Common Stock to be included in such underwriting be made available for shares
of Restricted Stock. Notwithstanding the foregoing provisions, the Company may
withdraw any registration statement referred to in this Section 5 without
thereby incurring any liability to the holders of Restricted Stock.

         6.       Registration on Form S-3. In addition to the rights set forth
in Section 4, if at any time (i) a holder or holders of Preferred Securities or
Restricted Stock request that the Company file a registration statement on Form
S-3 or any successor thereto for a public offering of all or any portion of the
shares of Restricted Stock held by such requesting holder or holders, the
reasonably anticipated aggregate price to the public of which would exceed
$1,000,000, which registration statement may be a shelf registration statement,
and (ii) the Company is a registrant entitled to use Form S-3 or any successor
thereto to register such shares, then the Company shall use its best efforts to
register within 30 days of such request under the Securities Act on Form S-3 or
any successor thereto, for public sale in accordance with the method of
disposition specified in such notice, the number of shares of Restricted Stock
specified in such notice. Whenever the Company is required by this Section 6 to
use its best efforts to effect the registration of Restricted Stock, each of the
procedures and requirements of Section 4 (including but not limited to the
requirement that the Company notify all holders of Restricted Stock from whom
notice has not been received and provide them with the opportunity to
participate in the offering) shall apply to such registration, provided,
however, that there shall be no limitation on the number of registrations on
Form S-3 which may be requested and obtained under this Section 6, and provided,
further, however, that the requirements contained in the first sentence of
Section 4(a) shall not apply to any registration on Form S-3 which may be
requested and obtained under this Section 6.

         7.       Registration Procedures. If and whenever the Company is
required by the provisions of Sections 4, 5 or 6 to use its best efforts to
effect the registration of any shares of Restricted Stock under the Securities
Act, the Company will, as expeditiously as possible:

                  (a)      prepare and file with the Commission a registration
statement (which, in the case of an underwritten public offering pursuant to
Section 4, shall be on Form S-1 or other form of general applicability
satisfactory to the managing underwriter selected as herein provided) with
respect to such securities and use its best efforts to cause such registration
statement to become and remain effective for the period of the distribution
contemplated thereby (determined as hereinafter provided). Notwithstanding the
provisions of this Section 7(a), the Company's obligation to file a registration
statement, or cause such registration statement to become and remain effective,
shall be suspended for a period not to exceed 90 days in any 12-month period if
there exists at the time material non-public information relating to the Company
which, in the reasonable opinion of the Company, should not be disclosed and the
Company has provided the holders of Preferred Securities and Restricted Stock
with prior notice in writing of such suspension;

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                  (b)      prepare and file with the Commission such amendments
and supplements to such registration statement and the prospectus used in
connection therewith as may be necessary to keep such registration statement
effective for the period specified in paragraph (a) above and comply with the
provisions of the Securities Act with respect to the disposition of all
Restricted Stock covered by such registration statement in accordance with the
sellers' intended method of disposition set forth in such registration statement
for such period;

                  (c)      furnish to each seller of Restricted Stock and to
each underwriter such number of copies of the registration statement and the
prospectus included therein (including each preliminary prospectus) as such
persons reasonably may request in order to facilitate the public sale or other
disposition of the Restricted Stock covered by such registration statement;

                  (d)      use its best efforts to register or qualify the
Restricted Stock covered by such registration statement under the securities or
"blue sky" laws of such jurisdictions as the sellers of Restricted Stock or, in
the case of an underwritten public offering, the managing underwriter reasonably
shall request, provided, however, that the Company shall not for any such
purpose be required to qualify generally to transact business as a foreign
corporation in any jurisdiction where it is not so qualified or to consent to
general service of process in any such jurisdiction;

                  (e)      use its best efforts to list the Restricted Stock
covered by such registration statement with any securities exchange on which the
Common Stock of the Company is then listed;

                  (f)      immediately notify each seller of Restricted Stock
and each underwriter under such registration statement, at any time when a
prospectus relating thereto is required to be delivered under the Securities
Act, of the happening of any event of which the Company has knowledge as a
result of which the prospectus contained in such registration statement, as then
in effect, includes an untrue statement of a material fact or omits to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading in light of the circumstances then existing;

                  (g)      if the offering is underwritten and at the request of
any seller of Restricted Stock, use its best efforts to furnish on the date that
Restricted Stock is delivered to the underwriters for sale pursuant to such
registration: (i) an opinion dated such date of counsel representing the Company
for the purposes of such registration, addressed to the underwriters and to such
seller, stating that such registration statement has become effective under the
Securities Act and that (A) to the best knowledge of such counsel, no stop order
suspending the effectiveness thereof has been issued and no proceedings for that
purpose have been instituted or are pending or contemplated under the Securities
Act, (B) the registration statement, the related prospectus and each amendment
or supplement thereof comply as to form in all material respects with the
requirements of the Securities Act (except that such counsel need not express
any opinion as to financial statements contained therein) and (C) to such other
effects as reasonably may be requested by counsel for the underwriters or by
such seller or its counsel and (ii) a letter dated such date from the
independent public accountants retained by the Company, addressed to the
underwriters and to such seller, stating that they are independent public
accountants within the meaning of the Securities Act and that, in the opinion of
such accountants, the financial statements of the Company included in the
registration statement or the prospectus, or any amendment or supplement

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thereof, comply as to form in all material respects with the applicable
accounting requirements of the Securities Act, and such letter shall
additionally cover such other financial matters (including information as to the
period ending no more than five business days prior to the date of such letter)
with respect to such registration as such underwriters reasonably may request;
and

                  (h)      make available for inspection by each seller of
Restricted Stock, any underwriter participating in any distribution pursuant to
such registration statement, and any attorney, accountant or other agent
retained by such seller or underwriter, all financial and other records,
pertinent corporate documents and properties of the Company, and cause the
Company's officers, directors and employees to supply all information reasonably
requested by any such seller, underwriter, attorney, accountant or agent in
connection with such registration statement.

         For purposes of Section 7(a) and 7(b) and of Section 4(c), the period
of distribution of Restricted Stock in a firm commitment underwritten public
offering shall be deemed to extend until each underwriter has completed the
distribution of all securities purchased by it, and the period of distribution
of Restricted Stock in any other registration shall be deemed to extend until
the earlier of the sale of all Restricted Stock covered thereby and 180 days
after the effective date thereof.

         In connection with each registration hereunder, the sellers of
Restricted Stock will furnish to the Company in writing such information with
respect to themselves and the proposed distribution by them as reasonably shall
be necessary in order to assure compliance with federal and applicable state
securities laws.

         In connection with each registration pursuant to Sections 4, 5 or 6
covering an underwritten public offering, the Company and each seller agree to
enter into a written agreement with the managing underwriter selected in the
manner herein provided in such form and containing such provisions as are
customary in the securities business for such an arrangement between such
underwriter and companies of the Company's size and investment stature.

         8.       Expenses. All expenses incurred by the Company in complying
with Sections 4, 5 and 6, including, without limitation, all registration and
filing fees, printing expenses, fees and disbursements of counsel and
independent public accountants for the Company, fees and expenses (including
counsel fees) incurred in connection with complying with state securities or
"blue sky" laws, fees of the National Association of Securities Dealers, Inc.,
transfer taxes, fees of transfer agents and registrars, costs of insurance and
fees and disbursements of one counsel for the sellers of Restricted Stock, but
excluding any Selling Expenses, are called "Registration Expenses". All
underwriting discounts and selling commissions applicable to the sale of
Restricted Stock are called "Selling Expenses".

         The Company will pay all Registration Expenses in connection with each
registration statement under Sections 4, 5 or 6. All Selling Expenses in
connection with each registration statement under Sections 4, 5 or 6 shall be
borne by the participating sellers in proportion to the number of shares sold by
each, or by such participating sellers other than the Company (except to the
extent the Company shall be a seller) as they may agree.

         9.       Indemnification and Contribution.

                  (a)      By the Company. In the event of a registration of any
of the Restricted Stock under the Securities Act pursuant to Sections 4, 5 or 6,
the Company will indemnify

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and hold harmless each seller of such Restricted Stock thereunder, each
underwriter of such Restricted Stock thereunder and each other person, if any,
who controls such seller or underwriter within the meaning of the Securities
Act, against any losses, claims, damages or liabilities, joint or several, to
which such seller, underwriter or controlling person may become subject under
the Securities Act or otherwise, insofar as such losses, claims, damages or
liabilities (or actions in respect thereof) arise out of or are based upon any
untrue statement or alleged untrue statement of any material fact contained in
any registration statement under which such Restricted Stock was registered
under the Securities Act pursuant to Sections 4, 5 or 6, any preliminary
prospectus or final prospectus contained therein, or any amendment or supplement
thereof, or arise out of or are based upon the omission or alleged omission to
state therein a material fact required to be stated therein or necessary to make
the statements therein not misleading, and will reimburse each such seller, each
such underwriter and each such controlling person for any legal or other
expenses reasonably incurred by them in connection with investigating or
defending any such loss, claim, damage, liability or action, provided, however,
that the Company will not be liable in any such case if and to the extent that
any such loss, claim, damage or liability arises out of or is based upon an
untrue statement or alleged untrue statement or omission or alleged omission so
made in conformity with information furnished by any such seller, any such
underwriter or any such controlling person in writing specifically for use in
such registration statement or prospectus.

                  (b)      By each Preferred Holder. In the event of a
registration of any of the Restricted Stock under the Securities Act pursuant to
Sections 4, 5 or 6, each seller of such Restricted Stock thereunder, severally
and not jointly, will indemnify and hold harmless the Company, each person, if
any, who controls the Company within the meaning of the Securities Act, each
officer of the Company who signs the registration statement, each director of
the Company, each underwriter and each person who controls any underwriter
within the meaning of the Securities Act, against all losses, claims, damages or
liabilities, joint or several, to which the Company or such officer, director,
underwriter or controlling person may become subject under the Securities Act or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of any material fact contained in the registration statement
under which such Restricted Stock was registered under the Securities Act
pursuant to Sections 4, 5 or 6, any preliminary prospectus or final prospectus
contained therein, or any amendment or supplement thereof, or arise out of or
are based upon the omission or alleged omission to state, therein a material
fact required to be stated therein or necessary to make the statements therein
not misleading, and will reimburse the Company and each such officer, director,
underwriter and controlling person for any legal or other expenses reasonably
incurred by them in connection with investigating or defending any such loss,
claim, damage, liability or action, provided, however, that such seller will be
liable hereunder in any such case if and only to the extent that any such loss,
claim, damage or liability arises out of or is based upon an untrue statement or
alleged untrue statement or omission or alleged omission made in reliance upon
and in conformity with information pertaining to such seller, as such, furnished
in writing to the Company by such seller specifically for use in such
registration statement or prospectus, and provided, further, however, that the
liability of each seller hereunder shall be limited to the proportion of any
such loss, claim, damage, liability or expense which is equal to the proportion
that the public offering price of the shares sold by such seller under such
registration statement bears to the total public offering price of all
securities sold thereunder, but not in any event to exceed the proceeds received
by such seller from the sale of Restricted Stock covered by such registration
statement.

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                  (c)      Notice. Promptly after receipt by an indemnified
party hereunder of notice of the commencement of any action, such indemnified
party shall, if a claim in respect thereof is to be made against the
indemnifying party hereunder, notify the indemnifying party in writing thereof,
but the omission so to notify the indemnifying party shall not relieve it from
any liability which it may have to such indemnified party other than under this
Section 9 and shall only relieve it from any liability which it may have to such
indemnified party under this Section 9 if and to the extent the indemnifying
party is prejudiced by such omission. In case any such action shall be brought
against any indemnified party and it shall notify the indemnifying party of the
commencement thereof, the indemnifying party shall be entitled to participate in
and, to the extent it shall wish, to assume and undertake the defense thereof
with counsel satisfactory to such indemnified party, and, after notice from the
indemnifying party to such indemnified party of its election so to assume and
undertake the defense thereof, the indemnifying party shall not be liable to
such indemnified party under this Section 9 for any legal expenses subsequently
incurred by such indemnified party in connection with the defense thereof other
than reasonable costs of investigation and of liaison with counsel so selected,
provided, however, that, if the defendants in any such action include both the
indemnified party and the indemnifying party and the indemnified party shall
have reasonably concluded that there may be reasonable defenses available to it
which are different from or additional to those available to the indemnifying
party or if the interests of the indemnified party reasonably may be deemed to
conflict with the interests of the indemnifying party, the indemnified party
shall have the right to select a separate counsel and to assume such legal
defenses and otherwise to participate in the defense of such action, with the
expenses and fees of such separate counsel and other expenses related to such
participation to be reimbursed by the indemnifying party as incurred.

                  (d)      Contribution. In order to provide for just and
equitable contribution to joint liability under the Securities Act in any case
in which either (i) any holder of Restricted Stock exercising rights under this
Agreement, or any controlling person of any such holder, makes a claim for
indemnification pursuant to this Section 9 but it is judicially determined (by
the entry of a final judgment or decree by a court of competent jurisdiction and
the expiration of time to appeal or the denial of the last right of appeal) that
such indemnification may not be enforced in such case notwithstanding the fact
that this Section 9 provides for indemnification in such case, or, (ii)
contribution under the Securities Act may be required on the part of any such
selling holder or any such controlling person in circumstances for which
indemnification is provided under this Section 9; then, and in each such case,
the Company and such holder will contribute to the aggregate losses, claims,
damages or liabilities to which they may be subject (after contribution from
others) (i) in such proportion as is appropriate to reflect the relative fault
of the Company on the one hand and of such holder on the other in connection
with the statements or omissions which resulted in such losses, claims, damages
or liabilities, as well as any other relevant equitable considerations or (ii)
if the allocation provided by clause (i) above is not permitted by applicable
law, in such proportion so that such holder is responsible for the portion
represented by the percentage that the public offering price of its Restricted
Stock offered by the registration statement bears to the public offering price
of all securities offered by such registration statement, and the Company is
responsible for the remaining portion; provided, however, that, in any such
case, (A) no such holder will be required to contribute any amount in excess of
the public offering price of all such Restricted Stock offered by it pursuant to
such registration statement; and (B) no person or entity guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
will be entitled to contribution from any person or entity who was not guilty of
such fraudulent misrepresentation. The relative fault of the Company on the one
hand and

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of such holder on the other shall be determined by reference to, among other
things, whether the untrue statement or alleged untrue statement of a material
fact or omission or alleged omission relates to information supplied by the
Company or such holder and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission.

         10.      Changes in Common Stock or Preferred Stock. If, and as often
as, there is any change in the Common Stock or the Preferred Stock by way of a
stock split, stock dividend, combination or reclassification, or through a
merger, consolidation, reorganization or recapitalization, or by any other
means, appropriate adjustment shall be made in the provisions hereof so that the
rights and privileges granted hereby shall continue with respect to the Common
Stock or the Preferred Stock as so changed.

         11.      Rule 144 Reporting. With a view to making available the
benefits of certain rules and regulations of the Commission which may at any
time permit the sale of the Restricted Stock to the public without registration,
at all times after 90 days after any registration statement covering a public
offering of securities of the Company under the Securities Act shall have become
effective, the Company agrees to:

                  (a)      make and keep public information available, as those
terms are understood and defined in Rule 144 under the Securities Act;

                  (b)      use its best efforts to file with the Commission in a
timely manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act; and

                  (c)      furnish to each holder of Restricted Stock forthwith
upon request a written statement by the Company as to its compliance with the
reporting requirements of such Rule 144 and of the Securities Act and the
Exchange Act, 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 such
holder may reasonably request in availing itself of any rule or regulation of
the Commission allowing such holder to sell any Restricted Stock without
registration.

         12.      Representations and Warranties of the Company. The Company
represents and warrants to you as follows:

                  (a)      The execution, delivery and performance of this
Agreement by the Company have been duly authorized by all requisite corporate
action and will not violate any provision of law, any order of any court or
other agency of government, the Certificate of Incorporation, as amended to
date, or By-laws of the Company or any provision of any indenture, agreement or
other instrument to which it or any or its properties or assets is bound,
conflict with, result in a breach of or constitute (with due notice or lapse of
time or both) a default under any such indenture, agreement or other instrument
or result in the creation or imposition of any lien, charge or encumbrance of
any nature whatsoever upon any of the properties or assets of the Company.

                  (b)      This Agreement has been duly executed and delivered
by the Company and constitutes the legal, valid and binding obligation of the
Company, enforceable in accordance with its terms.

                                       10
<PAGE>

         13.      Miscellaneous.

                  (a)      Successors and Assigns. All covenants and agreements
contained in this Agreement by or on behalf of any of the parties hereto shall
bind and inure to the benefit of the respective successors and assigns of the
parties hereto (including without limitation transferees of any Preferred
Securities or Restricted Stock), whether so expressed or not, provided, however,
that registration rights conferred herein on the holders of Preferred Securities
or Restricted Stock shall only inure to the benefit of a transferee of Preferred
Securities or Restricted Stock if (i) there is transferred to such transferee at
least 20% of the total shares of Restricted Stock originally issued pursuant to
the respective purchase agreement under which such shares of Restricted Stock
were originally purchased, to the direct or indirect transferor of such
transferee or (ii) such transferee is a partner, shareholder or affiliate of a
party hereto; provided further that such transferee agrees in writing to be
bound by all terms and conditions of this Agreement.

                  (b)      Notices. All notices, requests, consents and other
communications hereunder shall be in writing and shall be deemed effectively
given upon being delivered in person, mailed by the next business day service of
a nationally recognized courier, mailed by certified or registered mail, return
receipt requested, or sent by telecopier (and promptly confirmed by any of the
foregoing methods of delivery), addressed as follows:

                           If to the Company:

                           131 Clarendon Street
                           Boston, Massachusetts 02116
                           Attention:  Marc D. Beer
                           Tel:  (617) 266-4373
                           Fax: (617) 266-9391

                           with a copy to:

                           Laura C. Hodges Taylor, Esq.
                           Goodwin Procter LLP
                           Exchange Place
                           Boston, MA  02109
                           Tel:  (617) 570-1000
                           Fax: (617) 523-1231

                           If to a Purchaser:

at such Purchaser's respective address set forth on Exhibit A, with a copy (i)
in the case of communications to Nomura International plc, to:

                           Doug Warner
                           Weil, Gotshal & Manges
                           One South Place
                           London EC2M 2WG
                           Tel: 44 20 7903 1036
                           Fax: 44 20 7903 0990

                                       11
<PAGE>

(ii) in the case of communications to BB BioVentures L.P., MPM BioVentures
Parallel Fund, L.P., or MPM Asset Management Investors 2000A LLC, to:

                           Laura C. Hodges Taylor, Esq.
                           Goodwin, Procter LLP
                           Exchange Place
                           Boston, MA 02109
                           Tel: (617) 570-1000
                           Fax: (617) 523-1231

(iii) in the case of communications to TD Javelin Capital Fund II, L.P., TD
Lighthouse Capital Fund, L.P., Zero Stage Capital V Limited Partnership, or Zero
Stage Capital VI, L.P., to:

                           Law Offices of Gloria M. Skigen
                           Two Greenwich Plaza, Third Floor
                           Greenwich, CT 06830
                           Tel: (203) 861-1717
                           Fax: (203) 861-2498

(iv) in the case of communications to Cynthia A. Fisher, Cynthia A. Fisher 1999
Family Trust, Fisher (WD) Family LP or Aurora Assets LLC, to:

                                    John J. Concannon III
                                    Bingham Dana LLP
                                    150 Federal Street
                                    Boston, Massachusetts 02110
                                    Tel: (617) 951-8874
                                    Fax: (617) 951-8736

(v) in the case of Genzyme Corporation to:

                                    Genzyme Corporation
                                    One Kendall Square
                                    Cambridge, Massachusetts 07139
                                    Attention: Chief Legal Officer
                                    Tel.: (617)252-7500
                                    Fax: (617-252-7553

and (vi) in the case of Compagnie Financiere Montchoisi S.A., Luxembourg to:

                                    Beatrice Casarin
                                    R. Zurcher Consulenze SA
                                    Corso Pestalozzi 4a
                                    6900 Lugano
                                    Switzerland
                                    Tel: (41) 91 923-7174
                                    Fax: (41) 91 922-6216

or, in any such case, at such other address or addresses as may have been
furnished in writing to the Company by such Purchaser.

                                       12
<PAGE>

         If to any subsequent holder of Preferred Securities or Restricted
Stock:

at such address as may have been furnished to the Company in writing by such
holder; or, in any such case, at such other address or addresses as shall have
been furnished in writing to the Company (in the case of a holder of Preferred
Securities or Restricted Stock) or to the holders of Preferred Securities or
Restricted Stock (in the case of the Company) in accordance with the provisions
of this paragraph.

                  (c)      Governing Law. This Agreement shall be governed by
and construed in accordance with the laws of the Commonwealth of Massachusetts
without reference to conflicts or choice of law provisions thereof.

                  (d)      Amendment; Waiver. This Agreement may not be amended
or modified, and no provision hereof may be waived, without the written consent
of the Company and the holders of at least 75% of the outstanding shares of
Restricted Stock, acting together as a single class.

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

                  (f)      Termination of Registration Rights. The obligations
of the Company to register shares of Restricted Stock under Sections 4, 5 or 6
shall terminate on the eleventh anniversary of the date of this Agreement.

                  (g)      "Lock-Up" Agreement. If requested in writing by the
underwriters for the initial underwritten public offering of securities of the
Company, each holder of Restricted Stock who is a party to this Agreement shall
agree not to sell publicly any shares of Restricted Stock or any other shares of
Common Stock (other than shares of Restricted Stock or other shares of Common
Stock being registered in such offering), without the consent of such
underwriters, for a period of not more than 180 days following the effective
date of the registration statement relating to such offering; provided, however,
that all persons entitled to registration rights with respect to shares of
Common Stock who are not parties to this Agreement, all other persons selling
shares of Common Stock in such offering, all persons holding in excess of 1% of
the capital stock of the Company on a fully diluted basis and all executive
officers and directors of the Company shall also have agreed not to sell
publicly their Common Stock under the circumstances and pursuant to the terms
set forth in this Section 13(g).

                  (h)      Subsequent Registration Rights. The Company shall not
grant to any third party any registration rights, except in connection with a
new equity financing, and in such case, such registration rights shall not be
more favorable than any of those contained herein, so long as any of the
registration rights under this Agreement remain in effect.

                  (i)      Severability. If any provision of this Agreement
shall be held to be illegal, invalid or unenforceable, such illegality,
invalidity or unenforceability shall attach only to such provision and shall not
in any manner affect or render illegal, invalid or unenforceable any other
provision of this Agreement, and this Agreement shall be carried out as if any
such illegal, invalid or unenforceable provision were not contained herein.

                  (j)      Injunctive Relief. Each of the parties acknowledge
that any breach of this Agreement by any one of them will cause irreparable harm
to the other parties thereto

                                       13
<PAGE>

and that in the event of such breach, the parties hereto shall be entitled, in
addition to monetary damages and to any other remedies available under this
Agreement and at law, to equitable relief, including injunctive relief.

                  (k)      Entire Agreement. This Agreement, together with the
other Related Agreements (as defined in the Series K Purchase Agreement),
embodies the entire agreement and understanding between the parties hereto with
respect to the subject matter hereof and supersedes all prior oral or written
agreements and understanding relating to the subject matter hereof, including,
without limitation, the Old Registration Rights Agreement. No statement,
representation, warranty, covenant or agreement of any kind not expressly set
forth in this Agreement shall affect, or be used to interpret, change or
restrict, the express terms and provisions of this Agreement.

                  (l)      Captions. The captions of the sections, subsections
and paragraphs of this Agreement have been added for convenience only and shall
not be deemed to be a part of this Agreement.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       14
<PAGE>

         Please indicate your acceptance of the foregoing by signing and
returning the enclosed counterpart of this letter, whereupon this Fifth Amended
and Restated Registration Rights Agreement shall be a binding agreement between
the Company and you.

                                  VIACELL, INC.

                                  By:  /s/ Marc D. Beer
                                       --------------------------------------
                                       Marc D. Beer
                                       Chief Executive Officer

AGREED TO AND ACCEPTED as of the date first above written.

                      [PURCHASER SIGNATURE PAGE TO FOLLOW]

                                       15
<PAGE>

                                  VIACELL, INC.

                     SIGNATURE PAGE FOR HOLDERS OF WARRANTS,
               SERIES A PREFERRED STOCK, SERIES B PREFERRED STOCK,
               SERIES C PREFERRED STOCK, SERIES D PREFERRED STOCK,
               SERIES E PREFERRED STOCK, SERIES F PREFERRED STOCK,
               SERIES G PREFERRED STOCK, SERIES H PREFERRED STOCK,
               SERIES I PREFERRED STOCK, SERIES J PREFERRED STOCK
                          AND SERIES K PREFERRED STOCK,

By his, her or its execution and delivery of this signature page, the
undersigned hereby joins in and agrees to be bound by the terms and conditions
of each of the following agreements, subject to, and as of the date of, the
execution and delivery of such agreements by ViaCell, Inc. (the "Corporation"):
(i) the Fourth Amended and Restated Investor's Rights Agreement to which this
signature page is attached, by and among the Corporation and the Investors named
therein (the "Investors' Rights Agreement"), as a "Series A Investor," "Series B
Investor," "Series C Investor," "Series D Investor," "Series E Investor,"
"Series F Holder," "Series G Investor," "Series H Investor," "Series I
Investor," "Series J Investor" and/or "Series K Investor" thereunder, (ii) the
Fifth Amended and Restated Registration Rights Agreement to which this signature
page is attached, by and among the Corporation and the Purchasers named therein
(the "Registration Rights Agreement"), as a holder of "Warrants" and/or a
"Series A Purchaser," "Series B Purchaser," "Series C Purchaser," "Series D
Purchaser," "Series E Purchaser," "Series F Holder," "Series G Purchaser,"
"Series H Purchaser," "Series I Purchaser," "Series J Purchaser," and/or "Series
K Purchaser" thereunder, and (iii) Fifth Amended and Restated Stockholders
Agreement to which this signature page is attached, by and among the Corporation
and the Stockholders named therein (the "Stockholders Agreement"), as a "Series
A Purchaser," "Series B Purchaser," "Series C Purchaser," "Series D Purchaser,"
"Series E Purchaser," "Series F Holder," "Series G Purchaser," "Series H
Purchaser," "Series I Purchaser," "Series J Purchaser," and/or "Series K
Purchaser" thereunder, and authorizes this signature page to be attached to the
Investors' Rights Agreement, the Registration Rights Agreement and the
Stockholders Agreement, or counterparts thereof.

         EXECUTED this ____ day of _________, 2003.

                                             ________________________________
                                             Print Name of Investor

                                             By:_____________________________
                                             Name:___________________________
                                             Title:__________________________

                                             Record Address:_________________
                                             ________________________________
                                             ________________________________

                                             Facsimile No.:__________________

<PAGE>

                                    EXHIBIT A

WARRANT HOLDERS:

BB BioVentures L.P.
111 Huntington Avenue.
Boston, MA 02199

TD Javelin Capital Fund, L.P.
2850 Cahaba Road
Suite 240
Birmingham, AL 35223

Zero Stage Capital V Limited Partnership
101 Main Street, 17th Floor
Cambridge, MA 02142

Seaflower Health and Technology Fund, L.L.C.
1000 Winter Street
Suite 1000
Waltham, MA 02154

Amgen Inc.
One Amgen Center Drive
Thousand Oaks, CA  91320-1789
Attention:  Treasurer

ARE-One Innovation Drive
135 N. Los Robles Avenue, Suite 250
Pasadena, CA 91101

General Electric Capital Corporation
GE Capital Funding
Life Science & Technology Finance
Attn: Portfolio Manager
401 Merritt Seven, Suite 23
Norwalk, CT 06851

SERIES A PURCHASERS:

Charles J. Kraus and Elaine Kraus
Kraus as Joint Tenants
with Rights of Survivorship
6570 Altura Place
Boca Raton, FL 33433

Charles Greenberg
6150 N. Highway 1
Little River, CA 95456

Claire S. Ellis a/k/a
Claire S. Ellis (Greenberg)
6150 N. Highway 1
Little River, CA 95456

SERIES B PURCHASERS:

James A. Funt
8625 Evergreen Place
Philadelphia, PA 19118

Jessica Wallraff
2200 Colorado Ave., #304
Santa Monica, CA 90404

Noah Greenberg
180 W. Houston Street, Apt. 3H
New York, NY 10014

Altoona Partners, L.P.
332 Fifth Avenue
Pittsburgh, PA 15222

Robert Kraus
5312 Lyoncrest Court
Dallas, TX 75287

Ina Kraus
5312 Lyoncrest Court
Dallas, TX 75287

Cheryl Messik
1040 W. Ingomar Road
Pittsburgh, PA 15237
Michael Kraus
1040 W. Ingomar Road
Pittsburgh, PA 15237

Irwin Leav
21 Codger Lane
Sudbury, MA 01776

Leslie Clark
82 Arnold Road
Wellesley, MA 02181

                                      A-1
<PAGE>

SERIES C PURCHASERS:

Zero Stage Capital V Limited Partnership
101 Main Street, 17th Floor
Cambridge, MA 02142

Seaflower Health and Technology Fund,
L.L.C.
1000 Winter Street, Suite 1000
Waltham, MA 02154

Massachusetts BioMedical Initiatives, Inc.
One Innovation Drive
Worcester, MA  01605

SERIES D PURCHASERS:

Zero Stage Capital V Limited Partnership
101 Main Street, 17th Floor
Cambridge, MA 02142

Seaflower Health and Technology Fund,
L.L.C.
1000 Winter Street
Suite 1000
Waltham, MA 02154

BB BioVentures L.P.
111 Huntington Avenue.
Boston, MA 02199

TD Javelin Capital Fund, L.P.
2850 Cahaba Road
Suite 240
Birmingham, AL 35223

SERIES E PURCHASERS:

Zero Stage Capital V Limited Partnership
101 Main Street, 17th Floor
Cambridge, MA 02142

Seaflower Health and Technology Fund,
L.L.C.
1000 Winter Street
Suite 1000
Waltham, MA 02154

BB BioVentures L.P.
111 Huntington Avenue.
Boston, MA 02199

TD Javelin Capital Fund, L.P.
2850 Cahaba Road
Suite 240
Birmingham, AL 35223

SERIES F PURCHASERS:

Cynthia A. Fisher
186 Park Street
Newton, MA 02458

Cynthia A. Fisher 1999 Family Trust
c/o Kirstin Lynde, Trustee
23 Massasoit Ave.
Sudbury, MA  01776-2364
AND
c/o Jonathan Goldstein, Trustee
TA Associates, Inc.
125 High Street, Suite, 2500
Boston, MA 02110

Fisher (WD) Family LP
c/o W. Donald Fisher
Box 120 RR4
Mill Road
Selinsgrove, PA 17870
AND
7683 Fairway Woods Drive
Sarasota, FL 34238

SERIES G PURCHASERS:

BB BioVentures L.P.
111 Huntington Avenue.
Boston, MA 02199

MPM BioVentures Parallel Fund, L.P.
111 Huntington Avenue.
Boston, MA 02199

MPM Asset Management Investors
2000A LLC
111 Huntington Avenue.
Boston, MA 02199

                                      A-2
<PAGE>

TD Javelin Capital Fund, L.P.
2850 Cahaba Road
Suite 240
Birmingham, AL 35223

TD Javelin Capital Fund II, L.P.
2850 Cahaba Road
Suite 240
Birmingham, AL 35223

TD Lighthouse Capital Fund, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

Zero Stage Capital VI L.P.
101 Main Street, 17th Floor
Cambridge, MA 02142

SERIES H PURCHASERS:

DWS Investment GMBH
Gruneburgweg 113-115
60612 Frankfurt am Main
Germany

Nomura International plc
One St. Martin's le Grand
London, EC1A 4NP
United Kingdom
Attn: Denise Pollard-Knight

Stephens-Viacell LLC
111 Center Street
Suite 2400
Little Rock, AK 72201
Attn: Skip Clemmons

Pharmbio Growth Fund Pte Ltd.
250 North Bridge Rd.
#27-04 Raffles City Tower
Singapore 179101

Zero Stage Capital VII, L.P.
101 Main Street, 17th Floor
Cambridge, MA 02142
Attn: Brian Johnson

Zero Stage Capital (Cayman) VII, L.P.
101 Main Street, 17th Floor
Cambridge, MA 02142
Attn: Brian Johnson

BB Bioventures, L.P.
111 Huntington Avenue.
Boston, MA 02199

MPM Bioventures Parallel Fund, L.P.
111 Huntington Avenue.
Boston, MA 02199

MPM Asset Management Investors
2000A LLC
111 Huntington Avenue.
Boston, MA 02199

Capital Technologies CDPQ Inc.
1981 McGill College Ave., Suite 1300
Montreal H3A 2N4
Quebec, Canada

UOB Venture Technology Investment Ltd.
80 Raffles Place #30-20
UOB Plaza 2
Singapore 048624
Attn: Jean Thoh

UOB Venture Investments II Limited
80 Raffles Place #30-20
UOB Plaza 2
Singapore 048624
Attn: Jean Thoh

TD Javelin Capital Fund II, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

TD Lighthouse Capital Fund, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

                                      A-3
<PAGE>

Fisher (WD) Family LP
c/o W. Donald Fisher
Box 120 RR4
Mill Road
Selinsgrove, PA 17870
AND
7683 Fairway Woods Drive
Sarasota, FL  34238

Fund Isabella Limited Partnership
312 Walnut Street, Suite 3540
Cincinnati, OH 45202
Attn: Margaret Wyant

Sharon Whitely
21 Union Wharf
Boston, MA 02109

Pedro Huertas
283 Simon Willard Road
Concord, MA 01742

Thomas Duckworth
77 Stonegate Lane
Lake Forest, IL 60045

Patricia Hanratty
Pamet Ventures
225 Bay Point Road
Swansea, MA 02777

Kathleen M. Elliott
197 8th Street, #410
Charlestown, MA 02129

Karen Shaeffer
1574 Peregrine Point Drive
Sarasota, FL 34321

Donna Tamaroff
766 Spring Valley Road
Doylestown, PA 18901

Ann Sprague
3445 W. Foxes Den Drive
Tucson, AZ 85745

Susan Whitehead
263 Washington Street
Suite 100
Wellesley Hills, MA 02481

Elaine Hyman,
Custodian for Charles B. Hyman
Custodian for Julia B. Hyman
Custodian for Emily B. Hyman
281 Barr Avenue
Teaneck, NJ 07666

SERIES I PURCHASERS:

Biomedical Sciences Investment Fund
PTE LTD
250 North Bridge Road
#27-04 Raffles City Tower
Singapore 179101
Attn: Sze Kuan SIM

Genzyme Corporation
One Kendall Square
Cambridge, MA 02139
Attn: Executive Vice President,
Therapeutics and Genetics

UOB Capital Investments Pte Ltd.
80 Raffles Place #30-20
UOB Plaza 2
Singapore 048624
Attn: Jean Thoh

Stephens-ViaCell LLC
111 Center Street
Suite 2400
Little Rock, AK 72201
Attn: Skip Clemmons

Zero Stage Capital VII, L.P.
101 Main Street, 17th Floor
Cambridge, MA 02142
Attn: Brian Johnson

Zero Stage Capital (Cayman) VII, L.P.
101 Main Street, 17th Floor
Cambridge, MA 02142
Attn: Brian Johnson

Zero Stage Capital SBIC VII, L.P.
101 Main Street, 17th Floor
Cambridge, MA 02142

                                      A-4
<PAGE>

Attn: Brian Johnson

Nomura International plc
One St. Martin's le Grand
London, EC1A 4NP
United Kingdom
Attn: Denise Pollard-Knight

Tullis-Dickerson Capital Focus II, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

TD Origen Capital Fund, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

TD Lighthouse Capital Fund, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

TD Javelin Capital Fund II, L.P.
One Greenwich Plaza, 3rd Floor
Greenwich, CT 06830
Attn: James L.L. Tullis

SmithKline Beecham Corporation
d/b/a GlaxoSmithKline, Inc.
5 Moore Dr.
Research Triangle Park, NC 27709
Attn:  General Counsel

Glaxo Group Limited
GSK House
980 Great West Rd.
Brentford, Middlesex
UK TW 8 9GS
Attn: General Counsel

SERIES I HOLDERS:

MPM Bio Ventures II QP L.P.
111 Huntington Ave. - 31st floor
Boston, MA 02199

MPM Bio Ventures GmbH & Co. Parallel
Bet. KG
Prannerstr. 15
80333 Munchen, Germany

MPM Bio Ventures II L.P.
111 Huntington Ave. - 31st floor
Boston, MA 02199

MPM Asset Management Inv. 2001L.L.C.
111 Huntington Ave. - 31st floor
Boston, MA 02199

Kourion RM (Regenerative Medizin)
GmbH
Helenenstr. 19
40764 Langenfeld, Germany
MPM Founders LLC
111 Huntington Ave. - 31st floor
Boston, MA 02199

Philip H. Coelho
3146 Gold Camp Drive
Rancho Cordova, CA 95670-6022

Dr. Johannes Fischer
Schopenhauerstr. 3
41470 Neuss, Germany
IRK-Vermogensverwaltungs GmbH
Am Rindergraben 2
41470 Neuss, Germany

TTHU Technologietransfer Heinrich-
Heine-Universitat GmbH
Konigsallee 20
40212 Dusseldorf, Germany

Gesellschaft von Freunden und Forderern
an der Heinrich-Heine-Universitat
Dusseldorf e.V.
Ernst-Schneider-Platz 1
40212 Dusseldorf, Germany

Dr. Andreas Knipper
Am Kaulacker 13
41470 Neuss, Germany

Dr. Hans-Dieter Royer
Am Botanischen Garten 31,
40225 Dusseldorf, Germany

                                      A-5
<PAGE>

SERIES J PURCHASERS:

Genzyme Corporation
One Kendall Square
Cambridge, MA 02139
Attn: Stephen Potter

Permal Investment Holdings N.V.
900 Third Avenue
New York, NY 10022
Attn: Judy Tchou

Stephens Group
111 Center Street
Suite 2400
Little Rock AK 72201-4330
Attn: Skip Clemmons

Compagnie Financiere Montchoisi S.A.,
Luxembourg
Societe Anonyme Holding
15, Boulevard Roosevelt - 2450
Luxembourg
R.C.S. Luxembourg: B-24.944
Attn: Mr. Didier Kirsch

Deutsche Bank Int'l Trust Co. (Jersey)
Ltd.
P.O. Box 634, St. Paul's Gate
New Street, St. Helier
Jersey JE4 8YP
Channel Islands
Attn: John Bertram

BB BioVentures L.P.
111 Huntington Avenue.
Boston, MA 02199

MPM BioVentures Parallel Fund, L.P.
111 Huntington Avenue.
Boston, MA 02199

MPM Asset Management Investors
2000A LLC
111 Huntington Avenue
Boston, MA 02199

SWAN Private Equity Verwaltungs GmbH
Hochstrasse 12
47877
Willich-Schiefbahn, Germany
Attn: Markus Voelkel

Fund Isabella Limited Partnership
312 Walnut Street, Suite 3540
Cincinatti, OH 45202
Attn: Susan Schieman

General Electric Capital Corporation
GE Capital Funding
Life Science & Technology Finance
Attn: Portfolio Manager
401 Merritt Seven, Suite 23
Norwalk, CT 06851

Cheyne Value Fund LP
13 Park Place
London SW1A 1LP
Attn: Gary Ibbott, CFO

Timo Kipp
Tschuggen Grand House - 7050 Arosa,
Switzerland

SIF Investment Company
Lowenstrausse 19 - 8001 Zurich,
Switzerland
Attn: N. Peter Ruys, President
      Matthias Jenzer, Vice President

Sven Ley
Herrenwiesstrasse 26 - 82031 Grunwald -
Germany

David Pitblado
9 The Vale
London SW3 6AG
ENGLAND

UOB Venture Technology Investments
Ltd
80 Raffles Place, #30-20
UOB Plaza 2
Singapore 048624
Attn: Jean Thoh

                                      A-6
<PAGE>

UOB Venture Investments II Limited
80 Raffles Place, #30-20
UOB Plaza 2
Singapore 048624
Attn: Jean Thoh

3V SourceOne Ventures Fund Limited
321 Orchard Road, #08-06
Singapore (238866)
Attn: Eugene Hsu

High Tor Limited
P.O. Box N-4857
2 Cable Beach Court
Nassau, Bahamas
Attn: Paul R. Sandford

Kendall Family Investments, LLC
1251 Avenue of the Americas
New York, NY 10020
Attn: General Counsel

Moore Macro Fund, L.P.
c/o Moore Capital Management, LLC
1251 Avenue of the Americas
New York, NY 10020
Attn: General Counsel
AND
Citco Fund Administrator
One Montague Place
Nassau, Bahamas

SERIES K PURCHASER:

Amgen Inc.
One Amgen Center Drive
Thousand Oaks, CA  91320-1789
Attention:  Treasurer

                                      A-7