Patent ID: 8921097

Claim:
A method of purifying a non-glycosylated immunotoxin expressed in Pichia pastoris comprising a) loading a solution containing the non-glycosylated immunotoxin onto a hydrophobic interaction column; b) obtaining a first eluent comprising the non-glycosylated immunotoxin from the hydrophobic interaction column; c) loading the non-glycosylated immunotoxin containing eluent from step (b) onto a first anion exchange column; d) obtaining a second eluent comprising the non-glycosylated immunotoxin from the first anion exchange column by eluting the non-glycosylated immunotoxin from the first anion exchange column with a sodium borate solution, wherein the concentration of the sodium borate solution is between 50 mM and 200 mM; e) diluting the concentration of sodium borate in the second eluent from step (d) to 50 mM or less; f) concentrating the diluted second eluent from step (e) over a second anion exchange column; and g) obtaining the purified non-glycosylated immunotoxin from the second anion exchange column.