Identification of a novel vaccine adjuvant that stimulates and maintains diphtheria toxoid immunity.

Immunomodulation by plant-derived medicines is well-documented with effects on both innate and adaptive immunity. This study reports potent and long-lasting diphtheria toxoid-specific immunity by the botanical medicinal, Rehmannia Six Formula, using an in vivo mouse model of vaccine immunity. A significant vaccine adjuvant effect was observed with an increase in serum anti-diphtheria toxoid total and IgG antibodies following oral administration of Rehmannia Six Formula to mice. This response was antigen-specific and was still detectable six months following botanical medicinal treatment, suggesting that Rehmannia Six Formula could help maintain protective antibody levels in populations where vaccine coverage is low. Rehmannia Six Formula was well-tolerated with no adverse effects on mouse weight or survival observed in this study and suggests a potential role as a novel vaccine adjuvant preparation.