CRM197conjugate

CRM197 conjugate refers to a class of protein–polysaccharide vaccines in which the polysaccharide antigen is chemically linked to CRM197, a non-toxic mutant of the diphtheria toxin. CRM197 is produced by mutating the tox gene so that the enzyme activity responsible for diphtheria’s toxicity is abolished, while the carrier protein’s immunogenic epitopes remain intact. This carrier protein provides T cell help to B cells, converting a T cell–independent polysaccharide into a T cell–dependent response that generates stronger and longer-lasting immunity, including memory.

Conjugation to CRM197 enhances the immunogenicity of polysaccharide antigens, especially in infants and young children who respond poorly to unconjugated polysaccharides. The linkage preserves key epitopes on the polysaccharide while presenting peptide-derived T helper epitopes from CRM197, facilitating a more robust antibody response and better serotype coverage after vaccination. Different chemical strategies are used to couple polysaccharides to CRM197, and the choice of conjugation chemistry can influence immune response and stability.

CRM197-based conjugates are used in several licensed vaccines, including certain Haemophilus influenzae type b, pneumococcal, and meningococcal vaccines. Several products employ CRM197 as a standard carrier protein, with MenACWY-CRM and various pneumococcal conjugate vaccines representing notable examples. The platform is valued for its broad compatibility with diverse polysaccharide antigens and a generally favorable safety profile. See also conjugate vaccines, diphtheria toxin derivatives.