Next-Generation Vaccines: Nanoparticle-Mediated DNA and mRNA Delivery

Abstract

Nucleic acid vaccines are a method of immunization aiming to elicit immune responses akin to live attenuated vaccines. In this method, DNA or messenger RNA (mRNA) sequences are delivered to the body to generate proteins, which mimic disease antigens to stimulate the immune response. Advantages of nucleic acid vaccines include stimulation of both cell-mediated and humoral immunity, ease of design, rapid adaptability to changing pathogen strains, and customizable multiantigen vaccines. To combat the SARS-CoV-2 pandemic, and many other diseases, nucleic acid vaccines appear to be a promising method. However, aid is needed in delivering the fragile DNA/mRNA payload. Many delivery strategies have been developed to elicit effective immune stimulation, yet no nucleic acid vaccine has been FDA-approved for human use. Nanoparticles (NPs) are one of the top candidates to mediate successful DNA/mRNA vaccine delivery due to their unique properties, including unlimited possibilities for formulations, protective capacity, simultaneous loading, and delivery potential of multiple DNA/mRNA vaccines. This review will summarize the many varieties of novel NP formulations for DNA and mRNA vaccine delivery as well as give the reader a brief synopsis of NP vaccine clinical trials. Finally, the future perspectives and challenges for NP-mediated nucleic acid vaccines will be explored.

Keywords: DNA; mRNA; nanoparticles; nucleic acid; vaccine delivery; vaccines.

Figure 1

Scheme detailing the general steps of nanoparticle vaccine immunization strategy. After encapsulation of the pDNA/mRNA, the nucleic acid‐nanoparticle vaccine is administered and either taken up by local cells or APCs, where the nucleic acid payload is released and processed to create antigens which are further processed for MHCI and MHCII presentation. This leads to CD8+ cytotoxic T cells or CD4+ T helper cell activation and cell mediated immunity. Further activation of B cells mediates the humoral immunity. DC: dendritic cell, TCR: T cell receptor.

Figure 2

Challenges with nucleic acid vaccines and solution through NP‐based delivery. If injected intravenously, DNA/mRNA vaccines must be protected from many barriers to successful translation of encoded antigen/epitope. First, NPs can protect nucleic acids from degradation via endonucleases and general phagocytic elimination via the reticuloendothelial system. Second, the naked nucleic acids will face barriers entering the negatively charged cell membrane. NPs may target cells via surface ligand presentation matching a specific cell receptor and enter the cell through receptor‐mediated endocytosis. Within the cell, the NP vaccine must escape the endosome to deliver the payload. NPs have been designed to respond to the acidic pH of the endosome, triggering endosomal escape and intracellular payload release. Once in the cytosol, DNA vaccines must further translocate to the nucleus to be transcribed.

Figure 3

Lipid nanoparticle design for cellular uptake and endosomal escape. Left: Ionizable lipid complexes with the negatively charged mRNA at low pH. This facilitates endocytosis and endosomal escape. Phospholipid provides structural integrity to the bilayers while supporting endosomal escape of the mRNA to the cytosol. Cholesterol aids to stabilize the LNPs, promoting membrane fusion. Lipid‐anchored PEG prevents LNP aggregation and reduces nonspecific interactions. Right: Cryogenic transmission electron microscopy image of spherical LNPs with multilamellar structure. Reproduced with permission.^{[ 66 ]} Copyright 2017, American Chemical Society.

Figure 4

A) Schematic of the preparation procedure of PLGA‐PLL/γPGA‐EboDNA. B) Schematic of dissolving MN patch fabrication. C) Bright‐field image of MN patch with PLGA‐PLL‐SRB (red) encapsulated in the MNs. Reproduced with permission.^{[ 114 ]} Copyright 2017, Wiley‐VCH GmbH.

Figure 5

Rambutan‐like mesoporous silica nanoparticles which show superior pDNA adsorption. A) TEM images of B) Ram–MSNs and C) Ram‐MSNs‐PEI corresponding particle size distribution determined by DLS D) nitrogen sorption isotherm Reproduced with permission.^{[ 143 ]} Copyright 2019, Wiley‐VCH GmbH.

Figure 6

mRNA vectorization by PLA‐NPs with cationic peptide intermediates. A schematic representation of the vectorization strategy of mRNAs onto PLA‐NPs. The negatively charged mRNA associates with cationic peptides (RALA, LAH4 or LAH4‐L1) to form Peptide/mRNA polyplexes. Complex are adsorbed onto PLA‐NPs to form PLA‐NP/Peptide/mRNA nanocomplexes. Reproduced with permission.^{[ 154 ]} Copyright 2019, Elsevier.