Nanoparticulate Carriers Used as Vaccine Adjuvant Delivery Systems

Vaccination plays a crucial role in the control of infectious diseases, but often fails to eradicate certain refractory infections for which the development of an effective vaccine is eagerly desired but elusive. In many cases, failure in developing a vaccine is attributed to the inability of the candidates, especially among subunit vaccines, to evoke appropriate immuno-responses for establishing humoral as well as cellular immunity. In past decades, nanoparticles (NPs) sizing from 10 to 500 nm, such as liposomes, inorganic or metal NPs (iNPs), viruslike particles (VLPs), emulsions, immune-stimulating complexes (ISCOMs), and polymeric NPs, have been developed a potential carrier for vaccines to stabilize and deliver the adjuvant and antigens, thus forming proper vaccine adjuvant-delivery systems (VADSs). In particular, many NPs are rationally designed according to distinct cellular features and, therefore, are specifically engineered with functional materials so that they can deliver vaccine ingredients to target antigen-presenting cells (APCs) while directing immunoresponses against antigens along a specific Th1 (T helper type 1) and/or Th2 pathway to establish robust cellular and antibody immunity. In addition, a variety of NP-based VADSs are suitable for mucosal immunization, which contributes to systemic and, particularly, topical immunity, thus forming a dual barrier to pathogen invasion. This paper describes different NP-based VADSs designed for delivering vaccines, and evaluates their potential in the preparation of new products that can be used for prophylaxis against pathogens via different immunization routes.