Description
Large inactivated toxins such as tetanus toxoid, diphtheria toxoid and diphtheria CRM197 are used as carriers in vaccines to develop strong immune responses. Conjugate vaccines rely on these immunogenic molecules to stimulate long-lasting immunity to attached polysaccharides or peptides.
CRM197, is a natural genetically inactive diphtheria toxin (mutant) produced in the native host, Corynebacterium diphtheriae. Mutant forms of diphtheria toxin (DT), cross-reactive material 197 (CRM197) is a non-toxic DT mutant containing a lesion in the A chain blocking ADP-ribosylation. CRM results from a single base change in the structural gene resulting in the substitution of glutamic acid for glycine. While CRM shows no enzymatic activity, it is immunologically indistinguishable from diphtheria toxin. In its applications, CRM 197 is similar to diphtheria toxoid. CRM has the advantage of being a well defined protein in contrast to formaldehyde treated toxin (toxoid) which is non-specifically cross linked and subject to rearrangement. CRM functions as a carrier for polysaccharides and haptens making them immunogenic.
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