Preparation and Evaluation of Sodium Alginate Nanoparticles Containing Recombinant Diphtheria Toxoid (CRM197) and their Immunogenicity in Mice.

Introduction: Recombinant protein vaccines against infectious diseases, based on immunogenic antigen identification and employing polymeric nanoparticles as a delivery system, can provoke immune responses comparable to or better than traditional vaccines. The production of a safe and immunogenic vaccine against diphtheria was achieved by preparing sodium alginate nanoparticles containing recombinant diphtheria toxoid (CRM197).

Methods: Alginate nanoparticles loaded with CRM197 were prepared using the ionic-gelation method and thoroughly characterized. Safety and immunogenicity studies were conducted in an animal model for comparison with commercial vaccines. Antibody responses were evaluated using both qualitative and quantitative measurements, as determined by the toxin neutralization test (TNT) and indirect ELISA, respectively. IgG subclasses in the sera of immunized mice and possible pathological lesions in vital tissues of all immunized mouse groups were investigated.

Results: Nanoparticles with or without CRM197 were synthesized by the ionic gelation method. LE and LC measurements showed ˃80% and ˃20%, respectively, indicating stable and persistent release without a bursting pattern. In vivo studies showed safety and enhanced immunogenicity in mice immunized with the CRM197- loaded sodium alginate nanoparticles, with higher levels of total anti-CRM197 IgG and subclasses than those induced by conventional vaccines.

Discussion: Reducing antigen usage in vaccine production while increasing immunogenicity and safety compared with traditional vaccines are the goals of new vaccine development, which were achieved in the current study.

Conclusion: Engineered alginate nanoparticles loaded with recombinant diphtheria antigen (CRM197) demonstrated in vitro controlled and slow release, as well as safety and immunogenicity profiles against diphtheria in vivo. Nanoparticles containing CRM197 antigens equivalent to adult and children doses showed high levels of IgG1 and IgG2a, confirming the combined responses of the humoral and cellular immune systems.