An Overview of Nanocarrier-Based Adjuvants for Vaccine Delivery

Abstract

The development of vaccines is one of the most significant medical accomplishments which has helped to eradicate a large number of diseases. It has undergone an evolutionary process from live attenuated pathogen vaccine to killed whole organisms or inactivated toxins (toxoids), each of them having its own advantages and disadvantages. The crucial parameters in vaccination are the generation of memory response and protection against infection, while an important aspect is the effective delivery of antigen in an intelligent manner to evoke a robust immune response. In this regard, nanotechnology is greatly contributing to developing efficient vaccine adjuvants and delivery systems. These can protect the encapsulated antigen from the host's in-vivo environment and releasing it in a sustained manner to induce a long-lasting immunostimulatory effect. In view of this, the present review article summarizes nanoscale-based adjuvants and delivery vehicles such as viral vectors, virus-like particles and virosomes; non-viral vectors namely nanoemulsions, lipid nanocarriers, biodegradable and non-degradable nanoparticles, calcium phosphate nanoparticles, colloidally stable nanoparticles, proteosomes; and pattern recognition receptors covering c-type lectin receptors and toll-like receptors.

Keywords: adjuvants; nanocarriers; nanotechnology; non-viral vectors; vaccine delivery systems; vaccines; viral vectors.

Figure 1

Representative mechanism of action of adjuvants. (a) After vaccination, depot formation (in some cases), release of particles and soluble antigen; (b) Secretion of cytokines and chemokines, which are involved in the recruitment of various immune cells at the injection site thereby formation of immunocompetent environment; (c) Antigen uptake through various pattern recognition receptors (PRRs), e.g., Toll-like receptor (TLR) which are expressed on surface as well as intracellularly. These PRRs are recognized and activated by the antigens and adjuvants; (d) Antigen uptake by antigen-presenting cells (APCs) leads to maturation and activation of immune cells and further processing for presentation to major histocompatibility complex (MHC) by upregulating the expression of MHC; (e) Activated APCs then migrate to draining lymph node to interact with lymphocyte; (f) this leads to immunomodulation by triggering humoral and cellular immunity [19,20].