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 Co3O4NP 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 (R) 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. Original submitted 22 August 2011; Revised submitted 28 February 2012; Published online 20 July 2012