Process for production diphtheria toxin

The present invention relates to a process for producing mutant forms of diphtheria toxin, and in particular to a process for producing a non-toxic mutant of diphtherialtoxin, for example the mutant known as CRM107, and a toxic conjugate thereof, which can be used for therapeutic purposes. The present invention provides a method of purifying diphtheria toxin comprising (1) fermenting a microorganism strain capable of producing diphtheria toxin using glucose as a carbon source, the method comprising adding glucose to a growing culture whereby the addition of glucose maintains microorganism growth effective to support diphtheria toxin production; and (2) purifying the diphtheria toxin from the culture by contacting a toxin containing preparation derived therefrom with an ion exchange matrix, eluting a fraction containing the toxin, applying the eluate to a hydrophobic matrix, and eluting a fraction containing the toxin.