Synthesis and characterization of modified nanodiamonds for use as a potential vaccine adjuvant delivery platform for a candidate ricin toxin vaccine.

Adjuvants are a necessary excipient in most vaccine formulations to promote efficient antigen uptake and sampling by professional antigen presenting cells (APCs) in local tissues and regional lymph nodes. Nanoparticles have the unique capacity to serve as both antigen carriers and adjuvants by virtue of their size, shape, and modifiable surface properties. Nanodiamonds represent a novel type of diamond-based nanoparticle because they have easily modified surface chemistry and high binding capacity for surface display of protein antigens. Nanodiamonds are also non-toxic but still capable of stimulating a limited inflammatory response. In this study, we modified nanodiamonds with different surface chemistries and investigated in a murine model their ability to act as an adjuvant delivery platform for a ricin subunit vaccine, RiVax. The nanodiamonds were compared to RiVax adjuvanted with aluminum salts, liposomes, and gold nanoparticles. Vaccine efficacy was assessed based on an immunity to lethal challenge model. Our studies found that although the nanodiamonds could be coated with RiVax, the resulting formulation did not improve the protective capabilities of RiVax in a murine model. However, modified nanodiamonds were also investigated and characterized and may be investigated in the future as an improvement over their unmodified counterparts.