X0306 4 2018-01-22 0 0000730272 REPLIGEN CORP RGEN 0001606030 Hunt Anthony C/O REPLIGEN CORPORATION 41 SEYON ST, BLDG 1, STE 100 WALTHAM MA 02453 1 1 0 0 Chief Executive Officer Common Stock 2018-01-22 4 S 0 8970 35.947 D 83613 D Sale of common stock was effected pursuant to a 10(b)5-1 trading plan adopted on November 17, 2017. $35.947 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $35.58 to $36.28, 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. /s/ Jeffrey P. Leduc (Attorney in Fact) 2018-01-24