<PAGE>

                                                                   Exhibit 10.18

                                 FIRST AMENDMENT

      THIS FIRST AMENDMENT (the "AMENDMENT") is made and entered into as of
February 14, 2006, by and between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A
DELAWARE LIMITED LIABILITY COMPANY ("LANDLORD") and VIACELL, INC., A DELAWARE
CORPORATION ("TENANT").

                                    RECITALS

A.    Landlord and Tenant are parties to that certain lease dated December 22,
      2003, which lease has been previously amended by a commencement letter
      dated January 22, 2004 (collectively, the "LEASE"). Pursuant to the Lease,
      Landlord has leased to Tenant space currently containing approximately
      42,944 rentable square feet (the "ORIGINAL PREMISES") consisting of
      approximately (i) 24,909 rentable square feet of lab space (the "LAB
      SPACE") on the 1st and 2nd floors of the science building (the "SCIENCE
      BUILDING") in the building commonly known as the Cambridge Science Center;
      and (ii) 18,035 rentable square feet of office space (the "OFFICE SPACE")
      on the 15th floor of the office building (the "OFFICE BUILDING") in the
      building commonly known as the Cambridge Science Center. The Cambridge
      Science Center is comprised of the Office Building and the Science
      Building and is located at 245 First Street, Cambridge, Massachusetts.

B.    Tenant has requested that additional office space containing approximately
      7,648 rentable square feet described as Suite No. 1100 on the 11th floor
      of the Office Building shown on EXHIBIT A hereto (the "OFFICE EXPANSION
      SPACE") be added to the Original Premises and that the Lease be
      appropriately amended and Landlord is willing to do the same on the
      following terms and conditions.

      NOW, THEREFORE, in consideration of the above recitals which by this
reference are incorporated herein, the mutual covenants and conditions contained
herein and other valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, Landlord and Tenant agree as follows:

1.    EXPANSION AND EFFECTIVE DATE. Effective as of the Office Expansion
      Effective Date (defined below), the Premises, as defined in the Lease, is
      increased from 42,944 rentable square feet, comprised of 24,909 rentable
      square feet of Lab Space in the Science Building and 18,305 rentable
      square feet of Office Space in the Office Building, to 50,592 rentable
      square feet, comprised of 24,909 rentable square feet of Lab Space in the
      Science Building and 25,683 rentable square feet of Office Space in the
      Office Building by the addition of the Office Expansion Space, and from
      and after the Office Expansion Effective Date, the Original Premises and
      the Office Expansion Space, collectively, shall be deemed the Premises, as
      defined in the Lease. The Term for the Office Expansion Space shall
      commence on the Office Expansion Effective Date and end on the Termination
      Date (i.e., September 30, 2014). The Office Expansion Space is subject to
      all the terms and conditions of the Lease except as expressly modified
      herein and except that Tenant shall not be entitled to receive any
      allowances, abatements or other financial concessions granted with respect
      to the Original Premises unless such concessions are expressly provided
      for herein with respect to the Office Expansion Space.

                                       1
<PAGE>

      1.01. The "OFFICE EXPANSION EFFECTIVE DATE" shall be the later to occur of
            (i) February 1, 2006 ("TARGET OFFICE EXPANSION EFFECTIVE DATE"), and
            (ii) the date upon which the Landlord Work (as defined in the Work
            Letter attached as EXHIBIT B hereto) in the Office Expansion Space
            has been substantially completed; provided, however, that if
            Landlord shall be delayed in substantially completing the Landlord
            Work in the Office Expansion Space as a result of the occurrence of
            a Tenant Delay (defined below), then, for purposes of determining
            the Office Expansion Effective Date, the date of substantial
            completion shall be deemed to be the day that said Landlord Work
            would have been substantially completed absent any such Tenant
            Delay(s). A "TENANT DELAY" means any act or omission of Tenant or
            its agents, employees, vendors or contractors that actually delays
            substantial completion of the Landlord Work, including, without
            limitation, the following:

            a.    Tenant's failure to furnish information or approvals within
                  any time period specified in the Lease or this Amendment,
                  including the failure to prepare or approve preliminary or
                  final plans by any applicable due date;

            b.    Tenant's selection of equipment or materials that have long
                  lead times after first being informed by Landlord that the
                  selection may result in a delay;

            c,    Changes requested or made by Tenant to previously approved
                  plans and specifications;

            d.    The performance of work in the Office Expansion Space by
                  Tenant or Tenant's contractor(s) during the performance of the
                  Landlord Work; or

            e.    If the performance of any portion of the Landlord Work depends
                  on the prior or simultaneous performance of work by Tenant, a
                  delay by Tenant or Tenant's contractor(s) in the completion of
                  such work.

            The Office Expansion Space shall be deemed to be substantially
            completed on the date that Landlord reasonably determines that all
            Landlord Work has been performed (or would have been performed
            absent any Tenant Delays), other than any details of construction,
            mechanical adjustment or any other matter, the noncompletion of
            which does not materially interfere with Tenant's use of the Office
            Expansion Space. Notwithstanding the foregoing, if Tenant disputes
            Landlord's determination that the Landlord Work in the Office
            Expansion Space is substantially complete, then the question of
            whether the Landlord Work for the Office Expansion Space is
            substantially complete shall be submitted to Landlord's architect
            for determination and such determination by Landlord's architect
            shall be final and binding on the parties hereto. The adjustment of
            the Office Expansion Effective Date and, accordingly, the
            postponement of Tenant's obligation to pay Rent on the Office
            Expansion Space shall be Tenant's sole remedy and shall constitute
            full settlement of all claims that Tenant might otherwise have
            against Landlord by reason of the Office Expansion Space not being
            ready for occupancy by Tenant on the Target Office Expansion
            Effective Date.

                                       2
<PAGE>

      1.02. In addition to the postponement, if any, of the Office Expansion
            Effective Date as a result of the applicability of Section 1.01. of
            this Amendment, the Office Expansion Effective Date shall be delayed
            to the extent that Landlord fails to deliver possession of the
            Office Expansion Space for any other reason (other than Tenant
            Delays by Tenant), including but not limited to, holding over by
            prior occupants. Any such delay in the Office Expansion Effective
            Date shall not subject Landlord to any liability for any loss or
            damage resulting therefrom. If the Office Expansion Effective Date
            is delayed, the Termination Date under the Lease shall not be
            similarly extended.

2.    BASE RENT. In addition to Tenant's obligation to pay Base Rent for the
      Original Premises, Tenant shall pay Landlord Base Rent for the Office
      Expansion Space as follows:

<TABLE>
<CAPTION>
                     ANNUAL RATE PER SQUARE
      PERIOD                  FOOT             MONTHLY BASE RENT
      ------         ----------------------    -----------------
<S>                  <C>                       <C>
2/15/06 - 12/31/10            $27.00               $17,208.00
1/1/11 - 9/30/14              $31.00               $19,757.33
</TABLE>

      All such Base Rent shall be payable by Tenant in accordance with the terms
      of the Lease.

      Landlord and Tenant acknowledge that the foregoing schedule is based on
      the assumption that the Office Expansion Effective Date is the Target
      Office Expansion Effective Date. If the Office Expansion Effective Date is
      other than the Target Office Expansion Effective Date, the schedule set
      forth above with respect to the payment of any installment(s) of Base Rent
      for the Office Expansion Space shall be appropriately adjusted on a per
      diem basis to reflect the actual Office Expansion Effective Date, and the
      actual Office Expansion Effective Date shall be set forth in a
      confirmation letter to be prepared by Landlord. However, the effective
      date of any increases or decreases in the Base Rent rate shall not be
      postponed as a result of an adjustment of the Office Expansion Effective
      Date as provided above.

3.    ADDITIONAL SECURITY DEPOSIT. No additional security deposit shall be
      required in connection with this Amendment.

4.    TENANT'S PRO RATA SHARE. For the period commencing with the Office
      Expansion Effective Date and ending on the Termination Date, Tenant's Pro
      Rata Share for the Office Expansion Space is 5.1484%.

5.    OFFICE EXPENSES AND OFFICE TAXES. For the period commencing with the
      Office Expansion Effective Date and ending on the Termination Date, Tenant
      shall pay for Tenant's Pro Rata Share of Office Expenses and Office Taxes
      applicable to the Office Expansion Space in accordance with the terms of
      the Lease, provided, however, during such period, the Base Year for the
      computation of Tenant's Pro Rata Share of Office Expenses applicable to
      the Office Expansion Space is calendar year 2006, and the Base Year for
      the computation of Tenant's Pro Rata Share of Office Taxes applicable to
      the Office Expansion Space is Fiscal Year 2006 (i.e., July 1, 2005 to June
      30, 2006).

                                       3
<PAGE>

6.    IMPROVEMENTS TO OFFICE EXPANSION SPACE.

      6.01. CONDITION OF OFFICE EXPANSION SPACE. Tenant has inspected the Office
            Expansion Space and agrees to accept the same "as is" without any
            agreements, representations, understandings or obligations on the
            part of Landlord to perform any alterations, repairs or
            improvements, except as may be expressly provided otherwise in this
            Amendment.

      6.02. RESPONSIBILITY FOR IMPROVEMENTS TO OFFICE EXPANSION SPACE. Landlord
            shall perform improvements to the Office Expansion Space in
            accordance with the Work Letter attached hereto as EXHIBIT B.

7.    EARLY ACCESS TO OFFICE EXPANSION SPACE. If Tenant is permitted to take
      possession of the Office Expansion Space before the Office Expansion
      Effective Date, such possession shall be subject to the terms and
      conditions of the Lease and this Amendment and Tenant shall pay Base Rent
      and Additional Rent applicable to the Office Expansion Space to Landlord
      for each day of possession prior to the Office Expansion Effective Date.
      However, except for the cost of services requested by Tenant (e.g. freight
      elevator usage), Tenant shall not be required to pay Rent for the Office
      Expansion Space for any days of possession before the Office Expansion
      Effective Date during which Tenant, with the approval of Landlord, is in
      possession of the Office Expansion Space for the sole purpose of
      performing improvements or installing furniture, equipment or other
      personal property.

8.    OTHER PERTINENT PROVISIONS. Landlord and Tenant agree that, effective as
      of the date of this Amendment (unless different effective dates are
      specifically referenced in this Section), the Lease shall be amended in
      the following additional respects:

      8.01. LANDLORD'S NOTICE ADDRESSES. Effective as of the date hereof,
            Landlord's Notice Addresses as set forth in Article I.M. of the
            Lease are hereby deleted and replaced with the following:

            "Landlord:                                With a copy to:

            MA-Riverview/245 First Street, L.L.C.     Equity Office
            c/o Equity Office                         Two North Riverside Plaza
            100 Summer Street                         Suite 2100
            Boston, Massachusetts  02110              Chicago, Illinois  60606
            Attn:  Property Manager                   Attn:  Managing Counsel -
                                                             Boston Region"

      8.02. OFFICE EXPANSION SPACE ACCELERATION OPTION.

            A.    If Landlord and Tenant enter into a written lease agreement or
                  amendment (the "NEW AGREEMENT") to lease an entire floor of
                  office space in the Office Building (the "FULL FLOOR SPACE")
                  at the prevailing market rate for such Full Floor Space,
                  Tenant shall have the right to accelerate the Termination Date
                  with respect to the Office Expansion Space only (the "OFFICE
                  EXPANSION SPACE ACCELERATION OPTION") from the Termination
                  Date to the day immediately preceding the

                                       4
<PAGE>

                  commencement date of the Full Floor Space (the "ACCELERATED
                  OFFICE EXPANSION SPACE TERMINATION DATE"), if:

                  1.    Tenant is not in default under the Lease at the date
                        Tenant provides Landlord with an Office Expansion Space
                        Acceleration Notice (hereinafter defined); and

                  2.    no part of the Office Expansion Space is sublet (other
                        than pursuant to a Permitted Transfer, as defined in
                        Article XII of the Lease) for a term extending past the
                        Accelerated Office Expansion Space Termination Date; and

                  3.    the Lease has not been assigned (other than pursuant to
                        a Permitted Transfer, as defined in Article XII of the
                        Lease); and

                  4.    Landlord receives written notice of acceleration
                        ("OFFICE EXPANSION SPACE ACCELERATION NOTICE") not less
                        than 30 days prior to the Accelerated Office Space
                        Expansion Termination Date.

            B.    If Tenant exercises its Office Expansion Space Acceleration
                  Option, Tenant shall remain liable for all Base Rent,
                  Additional Rent and other sums due under the Lease up to and
                  including the Accelerated Office Expansion Space Termination
                  Date even though billings for such may occur subsequent to the
                  Accelerated Office Expansion Space Termination Date.

      8.03  PARKING. Effective as of the Office Expansion Effective Date,
            Section I of EXHIBIT E of the Lease shall be amended by increasing
            the number of unreserved parking spaces to sixty one (61).
            Accordingly, effective as of the Office Expansion Effective Date,
            all references in the Lease to "52 Spaces" shall be deleted and
            replaced with "61 Spaces".

9.    MISCELLANEOUS.

      9.01. This Amendment and the attached exhibits, which are hereby
            incorporated into and made a part of this Amendment, set forth the
            entire agreement between the parties with respect to the matters set
            forth herein. There have been no additional oral or written
            representations or agreements. Under no circumstances shall Tenant
            be entitled to any Rent abatement, improvement allowance, leasehold
            improvements, or other work to the Premises, or any similar economic
            incentives that may have been provided Tenant in connection with
            entering into the Lease, unless specifically set forth in this
            Amendment. Tenant agrees that neither Tenant nor its agents or any
            other parties acting on behalf of Tenant shall disclose any matters
            set forth in this Amendment or disseminate or distribute any
            information concerning the terms, details or conditions hereof to
            any person, firm or entity without obtaining the express written
            consent of Landlord.

      9.02. Except as herein modified or amended, the provisions, conditions and
            terms of the Lease shall remain unchanged and in full force and
            effect.

                                       5
<PAGE>

      9.03. In the case of any inconsistency between the provisions of the Lease
            and this Amendment, the provisions of this Amendment shall govern
            and control.

      9.04. Submission of this Amendment by Landlord is not an offer to enter
            into this Amendment but rather is a solicitation for such an offer
            by Tenant. Landlord shall not be bound by this Amendment until
            Landlord has executed and delivered the same to Tenant.

      9.05. The capitalized terms used in this Amendment shall have the same
            definitions as set forth in the Lease to the extent that such
            capitalized terms are defined therein and not redefined in this
            Amendment.

      9.06. Tenant hereby represents to Landlord that Tenant has dealt with no
            broker other than Trammell Crow Company in connection with this
            Amendment. Tenant agrees to indemnify and hold Landlord, its
            trustees, members, principals, beneficiaries, partners, officers,
            directors, employees, mortgagee(s) and agents, and the respective
            principals and members of any such agents (collectively, the
            "LANDLORD RELATED PARTIES") harmless from all claims of any brokers
            other than Trammell Crow Company claiming to have represented Tenant
            in connection with this Amendment. Landlord hereby represents to
            Tenant that Landlord has dealt with no broker in connection with
            this Amendment. Landlord agrees to indemnify and hold Tenant, its
            trustees, members, principals, beneficiaries, partners, officers,
            directors, employees, and agents, and the respective principals and
            members of any such agents (collectively, the "TENANT RELATED
            PARTIES") harmless from all claims of any brokers claiming to have
            represented Landlord in connection with this Amendment.

      9.07. Each signatory of this Amendment represents hereby that he or she
            has the authority to execute and deliver the same on behalf of the
            party hereto for which such signatory is acting.

                       [SIGNATURES ARE ON FOLLOWING PAGE]

                                       6
<PAGE>

      IN WITNESS WHEREOF, Landlord and Tenant have duly executed this Amendment
as of the day and year first above written.

WITNESS/ATTEST:                       LANDLORD:

                                      MA-RIVERVIEW/245 FIRST STREET, L.L.C., A
                                      DELAWARE LIMITED LIABILITY COMPANY

                                      By:  Equity Office Management, L.L.C.,
                                           a Delaware limited liability company,
                                           its non-member manager

                                           By: /s/ Glenn Verrette
                                               ----------------------
__________________________________
                                           Name: Glenn Verette
Name (print): ____________________

__________________________________         Title: VP Leasing - Boston region

Name (print): ____________________

WITNESS/ATTEST:                       TENANT:

                                      VIACELL, INC., A DELAWARE CORPORATION

                                      By: /s/ Stephen G. Dance
                                          -----------------------

__________________________________    Name: Stephen G. Dance

Name (print): ____________________

__________________________________    Title: Chief Financial Officer

Name (print): ____________________

                                       7
<PAGE>

                                    EXHIBIT A

                 OUTLINE AND LOCATION OF OFFICE EXPANSION SPACE

      This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and VIACELL, INC., A DELAWARE CORPORATION ("TENANT") for
Office Space in the Office Building located at 245 First Street, Cambridge,
Massachusetts.

                                       8
<PAGE>

                                    EXHIBIT B

                                   WORK LETTER

      This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and VIACELL, INC., A DELAWARE CORPORATION ("TENANT") for
Office Space in the Office Building located at 245 First Street, Cambridge,
Massachusetts.

As used in this Work Letter, the "PREMISES" shall be deemed to mean the Office
Expansion Space, as defined in the attached Amendment.

1.    Landlord, at its sole cost and expense (subject to the terms and
      provisions of Section 2 below) shall perform improvements to the Premises
      in accordance with the following work list (the "WORK LIST") using
      building standard methods, materials and finishes. The improvements to be
      performed in accordance with the Work List are hereinafter referred to as
      the "LANDLORD WORK". Landlord shall enter into a direct contract for the
      Landlord Work with a general contractor selected by Landlord. In addition,
      Landlord shall have the right to select and/or approve of any
      subcontractors used in connection with the Landlord Work.

                                    WORK LIST

      a.    Landlord shall re-paint the existing painted areas within the
            Premises using building standard paint. Tenant shall have the right
            to choose which of the building standard paint colors Landlord will
            use in the Premises.

      b.    Landlord shall install new building standard carpet on all existing
            carpeted areas within the Premises. Tenant shall have the right to
            choose which of the building standard carpet colors and styles
            Landlord will install in the Premises.

      c.    Landlord shall build a kitchen with a sink and cabinets in the
            Premises at the location indicated on attached EXHIBIT A in a
            building standard manner with building standard materials.

      d.    Landlord shall install a door in the server room in a location to be
            determined by Tenant (subject to Landlord's reasonable approval
            thereof).

            Tenant shall notify Landlord of its paint and carpet selections, as
            well as Tenant's desired location of the server room door (the
            "PLANS") on or before January 6, 2006 (the "PLANS DUE DATE"). Tenant
            covenants and agrees to cause said final, approved Plans to be
            delivered to Landlord on or before said Plans Due Date and to devote
            such time as may be necessary in consultation with Landlord in order
            to submit the Plans within the required time limit. Time is of the
            essence in respect of preparation and submission of Plans by Tenant.
            If the Plans are not fully completed and approved by the Plans Due
            Date, Tenant shall be responsible for one day of Tenant Delay (as
            defined in the Amendment to which this Exhibit is attached) for each
            day during the period beginning on the day following the Plans Due
            Date and ending on the date completed Plans are approved.

                                       9
<PAGE>

2.    All other work and upgrades, subject to Landlord's approval, shall be at
      Tenant's sole cost and expense, plus any applicable state sales or use tax
      thereon, payable upon demand as Additional Rent. Tenant shall be
      responsible for any Tenant Delay in completion of the Premises resulting
      from any such other work and upgrades requested or performed by Tenant.

3.    Landlord's supervision or performance of any work for or on behalf of
      Tenant shall not be deemed to be a representation by Landlord that such
      work complies with applicable insurance requirements, building codes,
      ordinances, laws or regulations or that the improvements constructed will
      be adequate for Tenant's use.

4.    Allowance Available to Tenant.

      a.    Provided Tenant is not in default under the Lease, Tenant shall be
            entitled to request an allowance (the "ALLOWANCE REQUEST") of up to
            $38,240.00 (i.e. $5.00 per rentable square foot of the Premises)
            (the "MAXIMUM ADDITIONAL ALLOWANCE") from Landlord in order to
            finance certain additional improvements to the Premises. The amount
            of the Maximum Additional Allowance requested by Tenant is referred
            to as the "ADDITIONAL ALLOWANCE". The Additional Allowance may only
            be used for (i) the cost of preparing design and construction
            documents and mechanical and electrical plans for work to be
            performed in the Premises, (ii) telecommunications and computer
            wiring and cabling in connection with work to be performed in the
            Premises, (iii) hard costs in connection with work to be performed
            in the Premises, (iv) furniture for the Premises (the cost of which
            shall not exceed 15% of the total Additional Allowance), (v)
            Tenant's actual moving expenses in connection with moving to the
            Premises, and (vi) management of the construction of the
            improvements to the Premises. In order to request the Additional
            Allowance, Tenant must complete, execute and deliver to Landlord, no
            later than 60 days prior to the Final Additional Allowance
            Disbursement Date (defined below), the "REQUEST FOR ADDITIONAL
            ALLOWANCE" in the form attached hereto as EXHIBIT C.

      b.    Provided Tenant is not in default under this Lease, Landlord
            (subject to subsection (c) below), shall disburse the Additional
            Allowance to Tenant subject to and in accordance with the provisions
            applicable to the disbursement of the Office Allowance described in
            Section A of EXHIBIT D to the Lease. In no event shall Tenant be
            entitled to any disbursement of the Additional Allowance after
            December 31, 2006 (the "FINAL ADDITIONAL ALLOWANCE DISBURSEMENT
            DATE"). Any Additional Allowance paid to or on behalf of Tenant
            hereunder shall be repaid to Landlord as Additional Rent in equal
            monthly installments throughout the remainder of the initial Term,
            commencing on the first day of the first full calendar month
            following the date the Additional Allowance is disbursed to Tenant,
            at an interest rate equal to 9% per annum. If Tenant is in default
            under this Lease after the expiration of applicable cure periods,
            the entire unpaid balance of the Additional Allowance paid to or on
            behalf of Tenant shall become immediately due and payable and,
            except to the extent required by applicable law, shall not be
            subject to mitigation or reduction in connection with a reletting of
            the Premises by Landlord.

      c.    Landlord's obligation to disburse the Additional Allowance and the
            right to

                                       10
<PAGE>

            receive repayment of same from Tenant, as described above, is
            referred to herein as the "LOAN". Notwithstanding anything to the
            contrary contained in this Amendment, Landlord may transfer or
            assign all or part of the Loan, without the prior consent of Tenant,
            as follows: (a) if Landlord or any subsequent permitted assignee of
            the Loan is a partnership or limited liability company, in a
            distribution without consideration, to a partner (including a
            limited partner) of such partnership or a member of such limited
            liability company; (b) to any parent or majority-owned subsidiary of
            Landlord (or, with respect to a permitted assignee holding the Loan,
            to the parent or majority-owned subsidiary of such permitted
            assignee); (c) to (x) any taxable REIT subsidiary of Equity Office
            Properties Trust (EOPT), or (y) Equity Office Properties Management
            Corp., a Delaware corporation, or any one of its subsidiaries; (d)
            to the Amended and Restated Equity Office Properties Management
            Corp. Trust dated as of September 30, 2002, of which Equity Office
            Properties Management Corp. is the sole beneficiary; or (e) to any
            "affiliate" (as defined in Rule 12b-2 of the Exchange Act) of
            Landlord (or, with respect to a permitted assignee holding the Loan,
            to any affiliate of such permitted assignee) (for convenience, each
            and all of the foregoing entities described above is referred to as
            a "LANDLORD AFFILIATE"). In the event of any such assignment of the
            Loan, Tenant, upon request of Landlord, shall execute and deliver to
            Landlord, or the Landlord Affiliate, a commercially reasonable
            promissory note, prepared by Landlord or the Landlord Affiliate,
            which will evidence the Tenant's obligation to repay the Additional
            Allowance to the Landlord or the Landlord Affiliate, as applicable,
            generally in accordance with the repayment provisions described in
            subsection (b) above.

      d.    If at any time prior to disbursement of the Additional Allowance it
            is determined that Landlord and/or any Landlord Affiliate (as
            described above) owns more than 10% of an Ownership Interest in
            Tenant (as such term is described in the Request Form For Additional
            Allowance attached as EXHIBIT C), then, rather than Landlord
            disbursing the Additional Allowance, Landlord may cause a Landlord
            Affiliate to disburse the Additional Allowance to Tenant and, as a
            condition to the Landlord Affiliate making such disbursement, Tenant
            shall execute and deliver to the Landlord Affiliate a commercially
            reasonable promissory note, prepared by Landlord or the Landlord
            Affiliate, which will evidence the Tenant's obligation to repay the
            Additional Allowance to the Landlord Affiliate or its assigns
            generally in accordance with the repayment provisions described in
            subsection (b) above.

5.    This Exhibit shall not be deemed applicable to any additional space added
      to the Premises at any time or from time to time, whether by any options
      under the Lease or otherwise, or to any portion of the Original Premises
      or any additions to the Premises in the event of a renewal or extension of
      the original Term of the Lease, whether by any options under the Lease or
      otherwise, unless expressly so provided in the Lease or any amendment or
      supplement to the Lease.

                                       11
<PAGE>

                                    EXHIBIT C

                      REQUEST FORM FOR ADDITIONAL ALLOWANCE

      This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and VIACELL, INC., A DELAWARE CORPORATION ("TENANT") for
Office Space in the Office Building located at 245 First Street, Cambridge,
Massachusetts.

                        REQUEST FOR ADDITIONAL ALLOWANCE

TO: Landlord

DATE: _______________________

REGARDING: Lease Agreement dated as of December 22, 2003, by and between
MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY COMPANY, as
"Landlord", and VIACELL, INC., A DELAWARE CORPORATION, as "Tenant", as same may
have been amended from time to time, including, without limitation, pursuant to
that certain First Amendment between Landlord and Tenant dated ______, 20_ (the
"AMENDMENT") (collectively, the "LEASE"), relating to which Landlord has leased
to Tenant certain premises in the building commonly known as 245 First Street
located at 245 First Street, Cambridge, Massachusetts (the "Building").

REQUEST FOR ADDITIONAL ALLOWANCE: Pursuant to Section 4 (the "ADDITIONAL
ALLOWANCE PROVISION") of the Work Letter attached as EXHIBIT B in the Amendment,
Tenant hereby requests that Landlord disburse $___________________ (the
"ADDITIONAL ALLOWANCE") [not to exceed $38,240.00, being the Maximum Additional
Allowance (as defined in the Additional Allowance Provision)] to Tenant for the
purposes allowed therein. It is understood that the Additional Allowance
requested by Tenant shall be disbursed as described in the Additional Allowance
Provision, and Tenant shall repay such sum as described in the Additional
Allowance Provision.

REPRESENTATION BY TENANT: Tenant recognizes and acknowledges that Equity Office
Properties Trust, a Maryland real estate investment trust ("EOPT") and an
affiliate of Landlord, intends to qualify as a "real estate investment trust"
for purposes of the Internal Revenue Code and that maintaining such status is of
material concern to EOPT and Landlord. Accordingly, Tenant represents and
warrants to Landlord that as of the date hereof [INSTRUCTION TO TENANT: CHECK
(A) OR (B) BELOW, BUT NOT BOTH. IF (A) IS CHECKED, THEN (B) IS NOT APPLICABLE;
AND IF (B) IS CHECKED, THEN (A) IS NOT APPLICABLE.]:

______(a)   the disbursement of the Additional Allowance to Tenant and to be
            repaid to Landlord (the "LOAN"), plus all other securities of Tenant
            held by Landlord or, to the knowledge of Tenant, any affiliate of
            Landlord (such other securities, collectively, the "OTHER
            SECURITIES"), do not constitute 10% or more of either (a) the total
            voting power of all outstanding securities of Tenant on an aggregate
            basis or (b) the total dollar value of all outstanding securities of
            Tenant on an

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<PAGE>

            aggregate basis (each of the foregoing items (a) and (b) are
            referred to as an "OWNERSHIP INTEREST IN TENANT"). Tenant shall
            notify Landlord of any redemption, repurchase or other actions taken
            by Tenant or any other person, which would cause the Loan plus all
            Other Securities to constitute ten percent (10%) or more of either
            (i) the total voting power of all outstanding securities of Tenant
            on an aggregate basis or (ii) the total dollar value of all
            outstanding securities of Tenant on an aggregate basis. For purposes
            of this provision, the term "securities" (or, in the singular,
            "security") shall have the meaning used for such term in the
            Investment Company Act of 1940, as amended.

            OR

______(b)   Tenant is unable to make the representation in subsection (a) above
            because Landlord and/or the affiliate(s) of Landlord do hold 10% or
            more of an Ownership Interest in Tenant (as described above), as
            described more fully --- below:

       _________________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            ____________________________________________________________________

            _____________________________________________

THE UNDERSIGNED REPRESENTS HEREBY THAT HE OR SHE HAS THE AUTHORITY TO EXECUTE
AND DELIVER THIS REQUEST FORM ON BEHALF OF THE TENANT, AND THE TENANT SHALL BE
FULLY BOUND HEREBY.

TENANT:

VIACELL, INC., A DELAWARE CORPORATION

By:     ______________________________

Name:   ______________________________

Title:  ______________________________


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