The new era of vaccines: the "nanovaccinology".

Vaccinations are the most effective preventive methods against infectious diseases and represent one of the most relevant successes of medicine. Vaccine development is constantly evolving; therefore, the number of vaccine candidates is progressively increasing. However, most of new potential vaccines are characterized by a lower immunogenicity, with the inability to stimulate powerful and long-lasting immune responses. Hence, to get modern and effective vaccines, we need adjuvants and innovative delivery systems that increase their immunogenicity. The use of nanotechnology in vaccinology is providing the opportunity to contrast these difficulties and develop effective vaccines. Particularly, nanoparticles used as vehicles of vaccine components, are able to increase the host's immune responses and, due to their size, to reach specific cellular districts. To date, a certain number of nanovaccines has been approved for human health and many are studied in clinical or pre-clinical trials. There are several types of nanoparticles considered as possible delivers of vaccine antigens. These nanoparticles-based synthetic delivery systems, in the size range of 20-200 nm, protect antigen from degradation, enhance its presentation and facilitate its uptake by professional antigen-presenting cells. Virus-like particles, self-assembled proteins, micelles, liposomes, inorganic nanoparticles, and polymers are the most studied of these systems. In this review, we provide a general overview of different types, methods of synthesis, characterizations, properties and applications of nanoparticles in vaccine production.