E. Bayon, J. Morlieras, T. Courant, A. Gonon, P. Marche, F. Navarro
Keywords: lipid nanoparticle, antigen delivery, immune responses
Summary:The development of vaccines was one of the major health advances of the last century. However, new vaccine formulations are still highly anticipated in the near future for facing some health challenges, such as the arrival of new infectious agents or resistant strains, the increase of chronic inflammatory and childhood diseases... “Historical” vaccines, based on attenuated or killed strains, were highly immunogenic but carried a significant risk to alter immune functions. Instead, subunit vaccines, made of synthetic antigens, are generally safer but much less immunogenic. Therefore, they require the co-administration with an adjuvant. The use of Alum, the first approved adjuvant for human vaccines, enhances the humoral immune response but fails to induce cell-mediated immunity and its toxicity is more and more controversial. Novel immunostimulant molecules and adjuvant delivery systems are currently under development, aiming at promoting the immune responses with a better control of their safety. For this purpose, we have designed a novel biocompatible lipid-based nanocarrier for the delivery of antigens and the induction of potent immune responses. These particles are nanostructured lipid carriers with a diameter less than a hundred microns, made of a lipid core surrounded by a shell of pegylated surfactants. Besides being biocompatible, biodegradable and highly stable over time, these nanoparticles also display the ability to readily circulate in the organism until they reach the lymph nodes where they can interact with immune cells. Thus they can be used as an antigen delivery system, by chemically grafting the antigen onto their shell, which prevents its degradation while being transported to the antigen presenting cells (APCs). The model antigen ovalbumin has successfully been grafted onto the particle shell as a proof of concept. Then, we focused on the delivery of P24, a protein antigen from the capsid of HIV, by developing different grafting strategies. The ability of these nanoformulations to induce immune responses in mice has been evaluated by using different formulations of nanoparticles, combined or not with immunostimulatory molecules, according to a schedule of two intra-peritoneal injections at a 3-weeks interval. On one hand, we dosed the antigen-specific antibodies in the mice sera and on the other hand, we collected the spleen cells in order to re-expose them in vitro to the given antigen (OVA or p24). A panel of secreted cytokines has been dosed in the supernatants, especially the IFNγ, which gives us clues on the induction of the cell-mediated immune response. Our results highlight the great benefit from the use of such nanostructured lipid carriers for delivering protein antigens, by inducing both higher humoral and cell-mediated immune responses. In perspectives, we are considering to further explore the possibilities offered by these engineered nanoparticles for developing vaccine formulations of a great interest, by incorporating additional functions such as the active targeting of dendritic cells, or by developing other dosage forms enabling oral delivery or nasal administration. This work paves the way for the future development of lipid nanoemulsions as potent and safe adjuvant delivery systems.