Brief on Recent Application of Liposomal Vaccines for Lower Respiratory Tract Viral Infections: From Influenza to COVID-19 Vaccines

Abstract

Vaccination is the most effective means of preventing infectious diseases and saving lives. Modern biotechnology largely enabled vaccine development. In the meantime, recent advances in pharmaceutical technology have resulted in the emergence of nanoparticles that are extensively investigated as promising miniaturized drug delivery systems. Scientists are particularly interested in liposomes as an important carrier for vaccine development. Wide acceptability of liposomes lies in their flexibility and versatility. Due to their unique vesicular structure with alternating aqueous and lipid compartments, liposomes can enclose both hydrophilic and lipophilic compounds, including antigens. Liposome composition can be tailored to obtain the desired immune response and adjuvant characteristics. During the current pandemic of COVID-19, many liposome-based vaccines have been developed with great success. This review covers a liposome-based vaccine designed particularly to combat viral infection of the lower respiratory tract (LRT), i.e., infection of the lung, specifically in the lower airways. Viruses such as influenza, respiratory syncytial virus (RSV), severe acute respiratory syndrome (SARS-CoV-1 and SARS-CoV-2) are common causes of LRT infections, hence this review mainly focuses on this category of viruses.

Keywords: SARS-CoV; adjuvants; liposomes; nanoparticles; vaccines.

Figure 1

Summary of the different strategies used for vaccine development. (A) Live attenuated vaccine. (B) Genetically improved live vaccine (bacterial vector). (C) Inactivated nonliving vaccine. (D) Nucleic acid-based vaccine (DNA). (E) Genetically improved protein subunit. (F) Nucleic acid-based vaccine (RNA). (G) Genetically improved live vaccine (viral vector). (H) Synthetic peptide-based vaccine.

Figure 2

Schematic representation of liposomal drug delivery systems: (A) unilamellar liposome, (B) multilamellar liposome, (C) liposome loaded with a hydrophobic drug, (D) liposome loaded with a hydrophobic drug in the bilayer membrane and a hydrophilic drug in the aqueous core, (E) pegylated liposome with surface PEG polymer chains, (F) liposome loaded with mRNA, (G) liposome with a surface-conjugated drug, targeting ligands and PEG, hydrophilic and hydrophobic drugs, (H) liposome with a surface-conjugated drug, targeting ligands, PEG polymer chains, hydrophilic drugs, hydrophobic drugs, mRNA-loaded.

Figure 3

Schematic representation of the SARS-CoV-2 virus RNA. (a) SARS-CoV-2 virus enters the airway epithelial host cells by endocytosis through the ACE2 receptor. (b) Release of virus RNA into the cytosol. (c) Replication of the RNA through ribosomes. (d) Protein translation and formation of new virions. (e) Activation of innate immunity and release of inflammasomes such as T cells, IL-1, IL-6, IL-8, IL-21, and TNF-β.