Patent ID: 8624003

Claim:
A process for preparing a purified conjugate in a solution, wherein the conjugate comprises a maytansinoid molecule linked to an antibody, the process comprising the steps of: (a) contacting a maytansinoid molecule comprising a thiol group with a bifunctional linker reagent to covalently attach the linker to the maytansinoid molecule, wherein an excess of maytansinoid molecule relative to the bifunctional linker reagent is used, and thereby prepare an unpurified first mixture comprising the maytansinoid molecule having linkers hound thereto, (b) conjugating an antibody to the maytansinoid molecule having linkers bound thereto by reacting the unpurified first mixture with the antibody in a solution having a pH from about 4 to about 9 to prepare a second mixture, and (c) subjecting the second mixture to tangential flow filtration, dialysis, gel filtration, adsorptive chromatography, selective precipitation or a combination thereof to thereby prepare the purified conjugate.