Adjuvanticity and Toxicity of Cobalt Oxide Nanoparticles as An Alternative Vaccine Adjuvant

AIM: There are very few adjuvants licensed for use in human vaccination, and alum-based adjuvants are the most widely used. Alum adjuvants predominantly boost Th2 immune responses and there is a need for new adjuvants that also stimulate Th1 immunity. We recently reported that cobalt oxide nanoparticles (Co(3)O(4)NPs) stimulate Th1-type immune responses in vivo. Here, we exploited this property to examine whether Co(3)O(4)NP could act as an adjuvant using the model antigen ovalbumin. MATERIALS & METHODS: Female C57BL/6 mice were immunized subcutaneously twice with ovalbumin plus adjuvant (Co(3)O(4)NPs or Imject® Alum) followed by intraperitoneal stimulation with soluble ovalbumin. RESULTS: Co(3)O(4)NPs induced a more balanced Th1- and Th2-type response, triggering higher specific Th1-dependent IgG2c production in addition to Th2-dependent IgG1 and less 'allergic' IgE production, and induced less inflammation at both the subcutaneous and intraperitoneal injection sites. DISCUSSION: Co(3)O(4)NPs could be a very useful adjuvant where both Th1 and Th2 responses are needed to clear pathogens.