X0306 4/A 2019-05-23 2019-05-28 0 0000730272 REPLIGEN CORP RGEN 0001046351 COOPER GLENN L MD C/O REPLIGEN CORPORATION 41 SEYON ST., BLDG 1, STE 100 WALTHAM MA 02453 1 0 0 0 Common Stock 2019-05-23 4 M 0 24000 5.00 A 64709 D Common Stock 2019-05-23 4 S 0 4734 66.91 D 59975 D Common Stock 2019-05-23 4 S 0 266 67.53 D 59709 D Stock Option (Right to Buy) 5.00 2019-05-23 4 M 0 24000 0.00 D 2019-08-24 Common Stock 24000 0 D Sale of common stock to cover the exercise price and a portion of the tax liability resulting from the exercise of Mr. Cooper's stock options was allowed pursuant to an exception to a lock-up agreement, signed by Mr. Cooper on April 26, 2019 in connection with the public offering of the Company's common stock. $66.91 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $66.42 to $67.36, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range. $67.53 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $67.52 to $67.57, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range. This option is currently exercisable. This Form 4/A is being filed to add transaction lines in Table I and Table II to reflect the exercise of stock options prior to the same-day sales of shares previously reported in the original Form 4, filed on May 28, 2019 (the "Original Form 4"). Each of the same-day transactions reported in this Form 4/A were also previously reported in the Original Form 4. /s/ Jeffrey P. Leduc (Attorney in Fact) 2019-06-19