An Overview on the Development of mRNA-Based Vaccines and Their Formulation Strategies for Improved Antigen Expression In Vivo

Abstract

The mRNA-based vaccine approach is a promising alternative to traditional vaccines due to its ability for prompt development, high potency, and potential for secure administration and low-cost production. Nonetheless, the application has still been limited by the instability as well as the ineffective delivery of mRNA in vivo. Current technological improvements have now mostly overcome these concerns, and manifold mRNA vaccine plans against various forms of malignancies and infectious ailments have reported inspiring outcomes in both humans and animal models. This article summarizes recent mRNA-based vaccine developments, advances of in vivo mRNA deliveries, reflects challenges and safety concerns, and future perspectives, in developing the mRNA vaccine platform for extensive therapeutic use.

Keywords: IVT mRNA; LNPs; electroporation; mRNA vaccine; protamine.

Figure 1

mRNA structure for optimal protein expression in vivo. An improved mRNA candidate contains 5’-cap, poly(A), 5’- and 3’-UTRs, and the coding sequence.

Figure 2

Nucleoside bases usually modified in the vaccination process. Uridine (U) is generally modified to pseudouridine (ψ), 2-thiouridine (s2U) and 5-methyluridine, cytidine (C) to 5-methylcytidine, and adenosine (A) to 5-methyladenosine (m5A).

Figure 3

Formulations of mRNA with nanobiomaterial for in vivo drug delivery. (A) Protamine-complexed mRNA for drug delivery. (B) Synthetic components and electron microscopy images of various LNPs. LNPs have been reported to synthesize by mixing anionic mRNA with lipophilic compounds in ethanol using a microfluidic device. At lower pH, the lipid-mRNA complex can accelerate both endocytosis as well as endosomal escape. Phospholipid used during the formulation process gives structural integrity to the lipid bilayers and can contribute to the endosomal release of the mRNA to the cytoplasm. Cholesterol assists to stabilize lipid nanoparticles and stimulates membrane fusion. The lipid-coated PEG (poly-ethylene-glycol) prevents the aggregation of LNP and decreases nonspecific interactions (up). Cryogenic transmission electron microscopy image indicates that the lipid nanoparticles have a spherical shape consisting of a multilamellar structure (bottom) (Adapted with permission with little modification from [57]).

Figure 4

mRNA electroporation into the dendritic cell for vaccination process. mRNA transfection induces DC to present antigens, which then transfuse into the patient to establish immune defense.