Vaccine carrier protein

Vaccine carrier proteins are highly immunogenic proteins used in the construction of conjugate vaccines to enhance the immune response against poorly immunogenic antigens, such as bacterial capsular polysaccharides [NIH, 2018]. These polysaccharides are T-cell independent antigens that typically fail to induce immunological memory or high-affinity antibodies, particularly in infants and the elderly [MDPI, 2019]. By covalently linking a polysaccharide to a carrier protein, the immune system's response is shifted from a T-cell independent to a T-cell dependent pathway [ASM, 2022]. This process involves the uptake of the conjugate by B-cells, processing of the carrier protein into peptides, and presentation of these fragments to T-helper cells via MHC class II molecules [TandfOnline, 2020]. The resulting T-cell help stimulates B-cell maturation, isotype switching, and the development of long-lasting immunological memory [NIH, 2018]. Common carrier proteins include diphtheria toxoid, tetanus toxoid, and CRM197, a non-toxic mutant of diphtheria toxin [Creative Biolabs, 2023]. These proteins are essential for the efficacy of vaccines against pathogens like Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b [NIH, 2017].

Other names

Carrier proteinImmunogenic carrierConjugate vaccine carrierT-cell dependent carrierProtein carrierCRM197Tetanus toxoidDiphtheria toxoidOuter membrane protein complex (OMPC)Protein D

Vaccine carrier proteins function by providing T-cell epitopes that convert T-cell independent antigens, such as bacterial capsular polysaccharides, into T-cell dependent ones [NIH, 2018]. When a polysaccharide is conjugated to a carrier protein, the B-cell receptor (BCR) recognizes the polysaccharide, and the entire conjugate is internalized [MDPI, 2019]. Inside the B-cell, the carrier protein is proteolytically processed into peptides, which are then loaded onto MHC class II molecules and presented on the cell surface [ASM, 2022]. CD4+ T-helper cells specific for these carrier peptides recognize the MHC-peptide complex and provide essential co-stimulatory signals, such as CD40 ligand (CD40L) and cytokines like IL-4, to the B-cell [TandfOnline, 2020]. This interaction triggers B-cell proliferation, affinity maturation, isotype switching from IgM to IgG, and the generation of long-lived memory B-cells and plasma cells [NIH, 2018].