Streptococcus pneumoniae serotype 33F capsular polysaccharide–CRM197 conjugate (33F-CRM197)

The Streptococcus pneumoniae serotype 33F capsular polysaccharide–CRM197 conjugate is a key immunogenic component of modern multivalent pneumococcal conjugate vaccines, such as V114 (Vaxneuvance) and PCV20 (Prevnar 20) [1, 2]. It consists of the capsular polysaccharide from S. pneumoniae serotype 33F, an increasingly prevalent serotype associated with invasive disease, covalently linked to CRM197, a non-toxic mutant of the diphtheria toxin [2, 3]. The primary biological function of this conjugate is to convert the T-cell independent polysaccharide antigen into a T-cell dependent antigen, which is necessary for inducing high-affinity antibodies and immunological memory in all age groups [3, 4]. Upon administration, the conjugate is internalized by antigen-presenting cells (APCs) through endocytosis. Within the APC, the CRM197 carrier protein is proteolytically processed into peptides that are presented on MHC class II molecules to CD4+ T cells [4, 5]. This interaction triggers T-cell help, which stimulates B cells to differentiate into memory B cells and plasma cells that produce IgG antibodies specific to the 33F polysaccharide [5, 6]. This mechanism is critical for providing protection against invasive pneumococcal diseases, including pneumonia, meningitis, and sepsis caused by serotype 33F [1, 6].

Other names

33F-CRM197Pneumococcal serotype 33F conjugateV114 componentPCV20 component

The conjugate is internalized by antigen-presenting cells, where the CRM197 carrier protein is proteolytically processed into peptides for MHC class II presentation to CD4+ T cells, thereby inducing a T-cell dependent B-cell response and immunological memory.