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Review
. 2021 May 15:601:120586.
doi: 10.1016/j.ijpharm.2021.120586. Epub 2021 Apr 9.

mRNA-lipid nanoparticle COVID-19 vaccines: Structure and stability

Linde Schoenmaker  1 , Dominik Witzigmann  2 , Jayesh A Kulkarni  2 , Rein Verbeke  3 , Gideon Kersten  4 , Wim Jiskoot  5 , Daan J A Crommelin  6
Affiliations
Review

mRNA-lipid nanoparticle COVID-19 vaccines: Structure and stability

Linde Schoenmaker et al. Int J Pharm. .

Abstract

A drawback of the current mRNA-lipid nanoparticle (LNP) COVID-19 vaccines is that they have to be stored at (ultra)low temperatures. Understanding the root cause of the instability of these vaccines may help to rationally improve mRNA-LNP product stability and thereby ease the temperature conditions for storage. In this review we discuss proposed structures of mRNA-LNPs, factors that impact mRNA-LNP stability and strategies to optimize mRNA-LNP product stability. Analysis of mRNA-LNP structures reveals that mRNA, the ionizable cationic lipid and water are present in the LNP core. The neutral helper lipids are mainly positioned in the outer, encapsulating, wall. mRNA hydrolysis is the determining factor for mRNA-LNP instability. It is currently unclear how water in the LNP core interacts with the mRNA and to what extent the degradation prone sites of mRNA are protected through a coat of ionizable cationic lipids. To improve the stability of mRNA-LNP vaccines, optimization of the mRNA nucleotide composition should be prioritized. Secondly, a better understanding of the milieu the mRNA is exposed to in the core of LNPs may help to rationalize adjustments to the LNP structure to preserve mRNA integrity. Moreover, drying techniques, such as lyophilization, are promising options still to be explored.

Keywords: COVID-19; Lipid nanoparticle (LNP); Lyophilization; Shelf life; Storage stability; Structure; Vaccine; mRNA.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

None
Graphical abstract
Fig. 1
Fig. 1
Structural elements of in vitro transcribed (IVT) mRNA. Each of these elements can be optimized and modified in order to modulate the stability, translation capacity, and immune-stimulatory profile of mRNA. Courtesy of Verbeke et al. (2019).
Fig. 2
Fig. 2
Cryo-TEM image of mRNA-LNP showing ‘bleb’ structures with distinctly different electron density. Adapted from Brader et al. (2021) with permission.
Fig. 3
Fig. 3
Schematic representation of the proposed models for siRNA-LNP and mRNA-LNP structure. A: multilamellar vesicles; B: nanostructure core; C: homogeneous core shell as discussed by Viger-Gravel et al. (2018). Courtesy of the authors.
Fig. 4
Fig. 4
Schematic representation of the mRNA-water cylinders in the core of mRNA- LNPs (Arteta et al., 2018). Courtesy of the authors.
Fig. 5
Fig. 5
Base-catalyzed intramolecular hydrolysis of the phosphodiester bond in RNA by way of a 2′,3′-cyclic phosphate. B denotes a Brønsted base. Redrawn from Pogocki and Schöneich (2000).
Fig. 6
Fig. 6
Lipids used in the mRNA-LNP COVID-19 vaccines BNT162b2 (Comirnaty) and mRNA-1273.
Fig. 7
Fig. 7
Stability of mRNA in water analysed by luciferase expression in transfected BHK-21 cells. Courtesy of Roesler et al. (2009).
See this image and copyright information in PMC

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