Specifications - *

Exhibit 10.13

WHENEVER CONFIDENTIAL INFORMATION IS OMITTED HEREIN (SUCH OMISSIONS ARE DENOTED BY AN ASTERISK *), SUCH CONFIDENTIAL INFORMATION HAS BEEN SUBMITTED SEPARATELY TO THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT.

Amendment No. 1 to Supply Agreement between Amersham Biosciences AB and Repligen Corporation dated May 26, 1999

This Amendment No. 1 to the Supply Agreement (defined below) is made, effective as of February 3, 2005 (“Amendment Date”), by and between,

RECITALS

Considering the above and in consideration of the mutual covenants contained in this Amendment No. 1, the Parties have entered into the following amendment to the Supply Agreement.

AMENDMENT

inclusive of all costs incurred by Repligen in the course of the TTP and the operation of the validation lots. In the event that the parties agree to conduct fewer than * development lots, Repligen will be paid a bonus of * for each development lot not conducted. In the event that GEHC requests fewer than * development lots and, as a result, more than * validation lots are required to achieve full validation, GEHC agrees to pay Repligen * for each additional validation lot meeting the same requirements as set forth above, which is required for full validation.

Repligen as its sole supplier for rPA during the term of the Supply Agreement, so long as Repligen is able to fulfill the following requirements:

Although the above statement constitutes the good faith intent of GEHC at the time of signing this Amendment any legally binding exclusive purchasing obligation of GEHC is subject to entering into separate written agreement being in compliance with any applicable laws and regulations.

The Parties have agreed on the price conditions for * as set forth in Appendix 3 hereto.

Repligen will assume all the costs incurred in connection with implementing best * practises according to the * and any costs for the * Plan in excess hereof relating to GEHC specific requirements shall be shared as agreed on a case by case basis. Repligen and GEHC shall agree in advance on any costs which GEHC shall assume in this respect.

GEHC shall have the right to carry out audits of the * Plan at Repligen on or in close connection to each of the milestones dates in Appendix 4 and thereafter on a regular basis. If any of the * Milestone is not timely met, and following GEHC written notice thereof, Repligen shall use its best efforts to remedy such failure as soon as possible and in each case within the remedy periods agreed in Appendix 4. If such a failure is not remedied within the agreed remedy periods then GEHC shall have the right to terminate this Amendment No. 1 with immediate effect upon a second written notice, unless the failure is of no significant importance to the overall quality of the * Plan. If this Amendment No. 1 is terminated pursuant to this Section 6.1, Amendment No. 1 to the License Agreement shall also immediately terminate and be of no further force or effect as specified in Section 2.4 of Amendment No. 1 to the License Agreement.

In order to facilitate the collaboration and planning in relation to the Articles, the Parties shall form a steering committee for the purpose of information exchange concerning, among others, the following topics:

The steering committee shall meet 1-2 times per year and consist of 2 senior officers of each Party.

In addition to its termination rights under Section 11(b) of the Supply Agreement, GEHC shall have the right to terminate the Supply Agreement with 12 months written notice if Repligen or any associated companies decides to * or if the control of Repligen’s non-therapeutic protein A business is acquired by a company which GEHC * the requirements of Section 4 a)-c) of this Amendment No. 1.

Section 11 (a) of the Supply Agreement shall be amended to read as follows:

“This Agreement will remain in effect from the date of signing up to and including December 31, 2010, and shall thereafter be automatically extended for successive periods of 2 years unless terminated with 12 months written notice prior to any such anniversary date.”

Section 4d of the Supply Agreement is amended to read in full as follows:

“On or before October 31 of each Contract Year, the parties will agree upon new, firm pricing for the subsequent Contract Year based upon: i) any change in the United States Consumer Price Index as published at the end of the third quarter of the preceding calendar year or some other index or indices as may be mutually agreed upon by the parties and ii) any other factors, *, etc. The new, firm prices will be made effective as of January 1 of the following Contract Year and will remain in effect throughout said Contract Year. In the event that the Parties cannot agree on any price changes, the prices shall remain unchanged for the following Contract Year.”

This Amendment No. 1 may be executed in counterparts each of which shall be deemed an original and all such counterparts shall constitute one and the same instrument The Parties have executed this Amendment No. 1 in two originals whereof the arties have taken one each.

Appendix 1

Specifications - *

Terms of transportation

At or below - *.

Storage conditions

*.

Shelf life

* from date of manufacturing. To be stated in the certificate of analysis. The limit is preliminary. The final shelf life is to be decided from stability studies.

Mass

*

Description

*

*

*

*

*

Requirements on properties

Appendix 2

Tentative Technology Transfer Program concerning the manufacturing process for *.

1. Scope

GEHC has developed a manufacturing process for *. GEHC has also developed analysis methods to be used for characterization of the protein as well as analyze methods to be used for in process analysis.

*

2. Technological goals

3. Specifications of *

See Appendix 1

4. Time schedule

Time schedule, including critical time and responsible persons, to be finalized

5. Milestones and Deliveries

MS1: *

-05

MS2: *

-05

MS3: *

-05

MS4: *

-05

MS5: *

-05

MS6: *

-05

MS7: *

-05

6. Deliveries

From GEHC -Repligen

*

From Repligen -GEHC

*

All documents transferred between the parties shall be in the form of Controlled copies if approved documents are transferred. In case a draft version is transferred version number, date and signature is mandatory. Acceptable ranges for all parameters, for critical parameters Proven Acceptable Ranges (PAR) is recommended for the purpose of Manufacturing Formula and Process validation, shall be included in the methods transferred to Repligen.

7. Resources

8. Contact persons

9. Progress reports

Bi-weekly short written communications on project status and performance

Appendix 3

Price conditions – *

A. Prices

The following prices will apply after delivery of the agreed development and validation lots.

First * ever sold: * per gram

After the first * ever sold the following price table shall apply:

B. Price assumptions

The above price conditions are based on (i) the process scale and optimized design as disclosed to Repligen at the meeting September 15, 2004, (ii) * overall yield level, (iii) * expression level in the fermenter, (iv) similar raw material costs compared to Biotech rPA, (v) *, (vi) *.

Upon any material deviations, i e having any impact on the price of more than *, from the assumptions set forth in this section occurring during the TTP and/or the * validation runs to follow the parties agree to adjust the prices correspondingly upon request of either party. Such request shall be made in writing not later than 30 days after completion of all of the agreed validation lots. Upon such request the parties shall conduct negotiations in, good faith with the object to restore the economical balance between the parties.

C. Price changes

The prices set forth herein shall remain fixed until December 31, *, unless adjusted by mutual agreement in accordance with Section B in this Appendix or subject to adjustment due to yield improvements resulting from major process changes according to Section 3.2 in the Amendment.

Following December 31, *, the parties shall review the price conditions on an annual basis in accordance with Section 4 d) in the Agreement as amended.

Appendix 4

Implementation Plan – *