Delivery Strategies for mRNA Vaccines

Abstract

The therapeutic potential for messenger RNA (mRNA) in infectious diseases and cancer was first realized almost three decades ago, but only in 2018 did the first lipid nanoparticle-based small interfering RNA (siRNA) therapy reach the market with the United States Food and Drug Administration (FDA) approval of patisiran (Onpattro™) for hereditary ATTR amyloidosis. This was largely made possible by major advances in the formulation technology for stabilized lipid-based nanoparticles (LNPs). Design of the cationic ionizable lipids, which are a key component of the LNP formulations, with an acid dissociation constant (pKa) close to the early endosomal pH, would not only ensure effective encapsulation of mRNA into the stabilized lipoplexes within the LNPs, but also its subsequent endosomal release into the cytoplasm after endocytosis. Unlike other gene therapy modalities, which require nuclear delivery, the site of action for exogenous mRNA vaccines is the cytosol where they get translated into antigenic proteins and thereby elicit an immune response. LNPs also protect the mRNA against enzymatic degradation by the omnipresent ribonucleases (RNases). Cationic nano emulsion (CNE) is also explored as an alternative and relatively thermostable mRNA vaccine delivery vehicle. In this review, we have summarized the various delivery strategies explored for mRNA vaccines, including naked mRNA injection; ex vivo loading of dendritic cells; CNE; cationic peptides; cationic polymers and finally the clinically successful COVID-19 LNP vaccines (Pfizer/BioNTech and Moderna vaccines)—their components, design principles, formulation parameter optimization and stabilization challenges. Despite the clinical success of LNP-mRNA vaccine formulations, there is a specific need to enhance their storage stability above 0 °C for these lifesaving vaccines to reach the developing world.

The Impact of Metal Nanoparticles on Female Reproductive System: Risks and Opportunities

“…With the COVID-19 outbreak and the licensing of mRNA-based vaccines, nanostructural technologies have been used to transport mRNA. These correspond to liposomes, nanostructures characterized by an inhomogeneous mixture of lipid components: neutral or charged lipids that promote the entry of nucleic material by electrostatic interaction, cholesterol that decreases permeability and increases stability, PEG-lipids that hinder binding to nonspecific proteins and helper lipids that facilitate their fusion with target membranes [ 118 , 119 , 120 ]. Thus, distinguishing the applications of nanomedicine from nanotoxicology becomes critical, and understanding the cut-off point between biomedical application and adverse effects will allow us to improve possible therapeutic applications: only by combining diagnostic testing and prevention will it be possible to improve both sides of this coin.…”

How far are the new wave of mRNA drugs from us? mRNA product current perspective and future development

“…The development of mRNA delivery systems has gone through the stage of fisetin, a naturally occurring cationic protein that can complex negatively charged mRNA molecules into nano-sized nucleic acid particles to protect mRNA from degradation by RNA enzymes in serum, which was discovered in 1961 ( 32 ). Cationic polymers neutralize the negative charge of the nucleic acid drug to increase the efficiency of entry into the cell ( 76 ). Polyethyleneimine (PEI) was a common polymer used for gene delivery, but the high molecular weight of PEI resulted in high cytotoxicity, making its successful use for vaccines in a limited number of animal studies, and chemical modifications of PEI were continually being explored ( 77 ).…”

“…mRNA-LNP complexes delivered by LNPs systems were primarily targeted at the liver, however, the mechanism of mRNA escaping into the cytoplasm was not fully understood. New directions for the continued development of LNPs systems were focused on ionizable lipids and formulations, all of which combinations of optimization areas are almost limitless, and success in any of these parameters could beneficial effects and provide new approaches to successful vaccine disease prevention ( 76 ).…”

Stability Study of mRNA-Lipid Nanoparticles Exposed to Various Conditions Based on the Evaluation between Physicochemical Properties and Their Relation with Protein Expression Ability

“…However, it is difficult to express sufficient amounts of protein to achieve a therapeutic effect with the administration of naked mRNA. This is because mRNA is a large molecule of approximately 10 5-10 6 Da and has a high density of negative charge, making it difficult for mRNA to pass through the cell membrane [11]. Furthermore, mRNA is an unstable molecule that is easily degraded; therefore, its formulation is essential for the development of mRNA therapeutics.…”