Streptococcus pneumoniae serotype 22F capsular polysaccharide (Pn22F)

Streptococcus pneumoniae serotype 22F capsular polysaccharide is a complex carbohydrate structure that serves as a primary virulence factor for the 22F pneumococcal strain by inhibiting host opsonophagocytosis (CDC, 2023). In the context of immunization, this polysaccharide is chemically conjugated to the CRM197 carrier protein, a non-toxic mutant of the diphtheria toxin, to overcome the poor immunogenicity of pure polysaccharides in vulnerable populations like infants (Briles et al., 2019). The CRM197 component provides essential T-cell epitopes, transforming the immune response from T-cell independent to T-cell dependent. This process enables the activation of T-helper cells, which in turn stimulate B-cells to undergo affinity maturation and class switching, leading to the production of high-affinity IgG antibodies (Merck, 2021). These antibodies facilitate the opsonization and subsequent phagocytic killing of the bacteria by the host's immune system. The target is a critical component of next-generation polyvalent pneumococcal conjugate vaccines (PCVs) such as V114 (Vaxneuvance) and PCV20 (Prevnar 20) (Pfizer, 2021). By targeting serotype 22F, these vaccines aim to reduce the burden of invasive pneumococcal diseases, including bacteremia and meningitis, as well as non-invasive conditions like pneumonia. Clinical efficacy is typically monitored through opsonophagocytic activity (OPA) assays and serotype-specific IgG levels.

Other names

Pneumococcal polysaccharide serotype 22F22F-CRM197Serotype 22F antigenPn22FImmune system recognizing pneumococcal polysaccharide serotype 22F–CRM197 conjugate

The conjugate vaccine induces a T-cell dependent immune response where the CRM197 carrier protein provides T-helper epitopes, leading to B-cell memory and high-affinity IgG production against the 22F polysaccharide.