Solid sorbitan esters nanoparticles are efficient and low-cost vehicles for subunit vaccines: Proof of concept with Neisseria meningitidis protein Mip

In this study we present evidence of the vaccine potential of nanoparticles based on sorbitan esters (sorbitan monooleate, Span^® 80), solid sorbitan esters nanoparticles (SSN) which are the lowest cost antigen nanovehicles proposed to date. We choose the Neisseria meningitidis macrophage infectivity potentiator (Mip) protein as a proof of concept target. The rMip-SSN nanosystems were evaluated for their physico-chemical properties, antigen loading and integrity as well as physical stability in various storage conditions. The immune response elicited by rMip-SSN was compared to that elicited by rMip-SSN with the conventional adjuvant Al(OH)₃ or with rMip in saline. SSN were able to associate, at a wide range of antigen concentrations with 100% efficiency, preserving the association and integrity of the antigen after long-term storage. Antibodies elicited by rMip-SSN mediated deposition of complement factors on the surface of meningococcal isolates and protective bactericidal titres even after rMip-SSN had been stored for nine months lyophilized at 4 °C. The association of different antigens to SSN can be easily achieved by electrostatic interactions by mixing the preformed nanosystems with the antigens of choice. Thus we can envisage the use of these nanoplatforms for the development of low-cost immunization kits ready for use for flexible vaccination strategies.