Effects of rotavirus NSP4 protein on the immune response and protection of the SR69A-VP8* nanoparticle rotavirus vaccine.

Rotavirus causes severe diarrhea and dehydration in young children. Even with the implementation of the current live vaccines, rotavirus infections still cause significant mortality and morbidity, indicating a need for new rotavirus vaccines with improved efficacy. To this end, we have developed an SR69A-VP8*/S60-VP8* nanoparticle rotavirus vaccine candidate that will be delivered parenterally with Alum adjuvant. In this study, as parts of our further development of this nanoparticle vaccine, we evaluated 1) roles of rotavirus nonstructural protein 4 (NSP4) that is the rotavirus enterotoxin, a possible vaccine target, and an immune stimulator, and 2) effects of CpG adjuvant that is a toll-like receptor 9 (TLR9) ligand and agonist on the immune response and protection of our SR69A-VP8*/S60-VP8* nanoparticle vaccine. The resulted vaccine candidates were examined for their IgG responses in mice. In addition, the resulted mouse sera were assessed for i) blocking titers against interactions of rotavirus VP8* proteins with their glycan ligands, ii) neutralization titers against rotavirus replication in cell culture, and iii) passive protection against rotavirus challenge with diarrhea in suckling mice. Our data showed that the Alum adjuvant appeared to work better with the SR69A-VP8*/S60-VP8* nanoparticles than the CpG adjuvant, while an addition of the NSP4 antigen to the SR69A-VP8*/S60-VP8* vaccine may not help to further increase the immune response and protection of the resulted vaccine.