Generation of a Human Monoclonal Antibody to Cross-Reactive Material 197 (CRM₁₉₇) and Development of a Sandwich ELISA for CRM₁₉₇ Conjugate Vaccines

Cross-reactive material 197 (CRM₁₉₇) is a non-toxic mutant of diphtheria toxin containing a single amino acid substitution of glycine 52 with glutamic acid. CRM₁₉₇ has been used as a carrier protein for poorly immunogenic polysaccharide antigens to improve immune responses. In this study, to develop a sandwich ELISA that can detect CRM₁₉₇ and CRM₁₉₇ conjugate vaccines, we generated a human anti-CRM₁₉₇ monoclonal antibody (mAb) 3F9 using a phage-displayed human synthetic Fab library and produced mouse anti-CRM₁₉₇ polyclonal antibody. The affinity (K_D) of 3F9 for CRM₁₉₇ was 3.55 nM, based on Bio-Layer interferometry, and it bound specifically to the B fragment of CRM₁₉₇. The sandwich ELISA was carried out using 3F9 as a capture antibody and the mouse polyclonal antibody as a detection antibody. The detection limit of the sandwich ELISA was ＜1 ng/ml CRM₁₉₇. In addition, the 3F9 antibody bound to the CRM₁₉₇-polysaccharide conjugates tested in a dose-dependent manner. This ELISA system will be useful for the quantification and characterization of CRM₁₉₇ and CRM₁₉₇ conjugate vaccines. To our knowledge, this study is the first to generate a human monoclonal antibody against CRM₁₉₇ and to develop a sandwich ELISA for CRM₁₉₇ conjugate vaccines.