Pneumococcal polysaccharide-CRM197 conjugate (PCV-CRM197)

CRM197 carrier protein covalently conjugated to pneumococcal polysaccharides is the active immunogenic complex found in several pneumococcal conjugate vaccines (PCVs) (CDC, 2023). CRM197 is a non-toxic, genetically engineered mutant of the diphtheria toxin that functions as a carrier protein to enhance the immunogenicity of bacterial polysaccharides (Bröker et al., Vaccine, 2011). While pneumococcal capsular polysaccharides are typically T-cell independent antigens, their covalent attachment to CRM197 allows them to elicit a T-cell dependent immune response (Pollard et al., Nat Rev Immunol, 2009). This conjugation is essential for inducing protective immunity and long-term immunological memory in infants and elderly populations who respond poorly to pure polysaccharide vaccines. The complex works by facilitating B-cell uptake and subsequent presentation of carrier-derived peptides to T-helper cells via MHC class II molecules. This interaction leads to the production of high-affinity IgG antibodies and the formation of memory B-cells specific to the pneumococcal serotypes included in the vaccine. These vaccines are critical for preventing invasive pneumococcal diseases, including pneumonia, meningitis, and bacteremia caused by Streptococcus pneumoniae. Clinical efficacy is typically monitored through serotype-specific antibody titers and opsonophagocytic activity assays (CDC, 2023).

Other names

CRM197-pneumococcal polysaccharide conjugatePneumococcal conjugate vaccinePCVPrevnarVaxneuvancePreneva

The CRM197 carrier protein provides T-cell epitopes that allow the normally T-cell independent pneumococcal polysaccharides to be processed and presented by B-cells to helper T-cells (Pollard et al., Nat Rev Immunol, 2009). This interaction induces a T-cell dependent immune response, characterized by isotype switching to IgG, affinity maturation, and the development of long-term immunological memory (Bröker et al., Vaccine, 2011).