CRM197 carrier protein-derived peptide-MHC class II complex (CRM197-pMHCII)

The CRM197 carrier protein-derived peptide-MHC class II complex is a critical immunological assembly formed during the processing of conjugate vaccines by antigen-presenting cells (APCs). CRM197 is a genetically detoxified mutant of the diphtheria toxin (Gly52Glu) that serves as a potent carrier protein due to its ability to elicit robust T-cell help (Shinefield, 2010). Upon uptake by APCs, CRM197 is degraded into peptide fragments which are then loaded onto Major Histocompatibility Complex (MHC) class II molecules and transported to the cell surface (Bröker et al., 2011). These complexes are specifically recognized by the T-cell receptors of CD4+ T-helper cells, which is essential for the induction of high-affinity antibody responses and immunological memory against conjugated haptens or polysaccharides (Avci et al., 2011). This mechanism is the basis for several widely used vaccines targeting pathogens such as Streptococcus pneumoniae and Neisseria meningitidis. Beyond infectious diseases, this complex is being explored in cancer immunotherapy to enhance the immunogenicity of tumor-associated carbohydrate antigens (Pecetta et al., 2018).

Other names

CRM197-peptide-MHC II complexCross-reacting material 197-MHC class II complexDiphtheria toxin CRM197-derived epitope-MHC II complexCRM197-pMHCII

The complex serves as the primary ligand for CD4+ T-cell receptors (TCRs). Recognition of these CRM197-derived epitopes by T-helper cells leads to their activation and the subsequent provision of co-stimulatory signals (such as CD40 ligand and cytokines like IL-4) to B cells that have internalized the conjugate vaccine. This T-cell help is required for B-cell proliferation, immunoglobulin class switching from IgM to IgG, and the development of high-affinity memory B cells (Avci et al., 2011).