key: cord-0690932-8dj9caqp
authors: Szabó, Gábor Tamás; Mahiny, Azita Josefine; Vlatkovic, Irena
title: COVID-19 mRNA vaccines: platforms and current developments
date: 2022-02-19
journal: Mol Ther
DOI: 10.1016/j.ymthe.2022.02.016
sha: 1a47d27c0b74ae09c650f3b5415fdf1f8e4f6646
doc_id: 690932
cord_uid: 8dj9caqp

Since the first successful application of messenger ribonucleic acid (mRNA) as a vaccine agent in a preclinical study nearly 30 years ago, numerous advances have been made in the field of mRNA therapeutic technologies. This research uncovered the unique favorable characteristics of mRNA vaccines, including their ability to give rise to non-toxic, potent immune responses and the potential to design and upscale them rapidly, making them an excellent vaccine candidate during the coronavirus disease 2019 (COVID-19) pandemic. Indeed, the first two vaccines against COVID-19 to receive accelerated regulatory authorization were nucleoside-modified mRNA vaccines, which showed more than 90% protective efficacy against symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection alongside tolerable safety profiles in the pivotal phase III clinical trials. Real-world evidence following the deployment of global vaccination campaigns utilizing mRNA vaccines has bolstered clinical trial evidence and further illustrated that this technology can be used safely and effectively to combat COVID-19. This unprecedented success also emphasized the broader potential of this new drug class not only for other infectious diseases, but for other indications such as cancer and inherited diseases. This review presents a brief history and the current status of developments of four mRNA vaccine platforms: nucleoside-modified and unmodified mRNA, circular RNA, and self-amplifying RNA as well as an overview of the recent progress and status of COVID-19 mRNA vaccines. We also discuss the current and anticipated challenges of these technologies which may be important for future research endeavors and clinical applications.

Since the first successful application of messenger ribonucleic acid (mRNA) as a vaccine agent 27 in a preclinical study nearly 30 years ago, numerous advances have been made in the field of 28 mRNA therapeutic technologies. This research uncovered the unique favorable characteristics 29 of mRNA vaccines, including their ability to give rise to non-toxic, potent immune responses 30 and the potential to design and upscale them rapidly, making them an excellent vaccine 31 candidate during the coronavirus disease 2019 (COVID-19) pandemic. Indeed, the first 32 two vaccines against COVID-19 to receive accelerated regulatory authorization 33 were nucleoside-modified mRNA vaccines, which showed more than 90% protective efficacy 34 against symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection 35 alongside tolerable safety profiles in the pivotal phase III clinical trials. Real-world evidence 36 following the deployment of global vaccination campaigns utilizing mRNA vaccines has 37 bolstered clinical trial evidence and further illustrated that this technology can be used safely 38 and effectively to combat COVID-19. This unprecedented success also emphasized the broader 39 potential of this new drug class not only for other infectious diseases, but for other indications 40 such as cancer and inherited diseases. This review presents a brief history and the current 41 status of developments of four mRNA vaccine platforms: nucleoside-modified and unmodified Introduction 47 Vaccines are important tools to prevent, control, and/or eradicate infectious diseases 48 and are fundamental components of public health programs worldwide. 1 In this review, we summarize the preclinical and clinical data of the vaccine candidates 68 which fall under four mRNA vaccine platforms: non-replicating linear nucleoside-modified and 69 J o u r n a l P r e -p r o o f unmodified mRNA, circular RNA (circRNA), and self-amplifying RNA (saRNA). In addition, we 70 discuss potential challenges which may hinder future vaccine development programs. 71 The path to COVID-19 mRNA vaccine development 72 When compared to traditional vaccines, which are relatively slow and laborious to 73 develop 11,1,12 , mRNA-based vaccines have features which allow them to be rapidly designed 74 and upscaled while still being highly potent and low cost. 6 Although mRNA vaccines were 75 already being investigated in clinical trials for other diseases, e.g., cancer, their far-reaching 76 potential was not realized until the COVID-19 pandemic, where mRNA vaccine candidates 77 were one of the first to enter clinical trials and obtain accelerated regulatory approvals. 13 Another approach to reduce dose levels is the use of an mRNA platform which is able to self- cleaved by the host cell protease furin into subunits (S1 and S2), which support cellular entry. 64 173 Interestingly, the C terminal motif of the cleaved S1 subunit can bind to neuropillin-1 (NRP- however, its potential usage in mRNA-1273 vaccine production is currently not publicly 229 disclosed and can only be speculated. 230 The dosing of nucleoside-modified LNP-mRNAs against COVID-19 applied in clinical 231 trials ranged between 10 µg and 250 µg RNA (Table 1) (Table   270 2). (Table 3) . 

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1159 1160 degraded by proteasomes (pink circles) and presented on MHC class I (pink circles) leading to specific CD8 + 1173 cytotoxic T-cell response against SARS-CoV-2. Antigens can also be anchored to the membrane of the APC and 1174 directly recognized by BCRs leading to B cell responses; however, such a path and its contribution to antibody 1175 production is currently under debate. Finally, the antigen protein can be exported from the cell and endocytosed 1176 back to the same or another APC, degraded by endosomal proteases, and presented on MHC II structures 1177 resulting in CD4 + helper T-cell response. Immunization progresses with CD4 + helper T cells further helping in 1) 1178 activation of B cells that produce SARS-CoV-2 neutralizing antibodies and 2) activate CD8 + cytotoxic T cells that 1179 may specifically recognize and eliminate virus

BCR: B-cell receptor; circRNA: circular ribonucleic acid; IRES: 1181 internal ribosome entry site; IVT: in vitro translation; LNP: lipid nanoparticle; MHC: major histocompatibility 1182 complex; mRNA: messenger ribonucleic acid; saRNA: self-amplifying ribonucleic acid; SARS-CoV-2: severe acute 1183 respiratory syndrome coronavirus 2; S protein: spike protein; TCR: T-cell receptor

Figure 2. Widely used mRNA-based COVID-19 vaccines: Comparison of ingredients

BioNTech/Pfizer) and mRNA-1273 (Moderna) are composed from 1-methylpseudouridine modified 1188 full-length spike with proline substitutions mRNA that is GC-rich, codon optimized and composed from standard 1189 mRNA components: cap, 5'UTR, coding sequence, 3'UTR, and a polyA tail. BNT162b2 is co-transcriptionally 1190 capped with ((m2 7,3′-O )Gppp(m 2′-O )ApG) cap1, has human α-globin 5'-UTR, AES and mtRNR1 3′-UTR motifs, two 1191 stop codons and polyA tail consisting of A30LA70. 84,82 mRNA-1273 is enzymatically capped, has undisclosed 5'UTR 1192 and on human β-globin gene-based 3'UTR, three stop codons and undisclosed length of the polyA tail

Lipids are integrated into LNPs under specific molar ratios. 81,79,190,191 In 1197 addition to the mRNA and LNP component, the only ingredients are salts (PBS and Tris buffers for BNT162b2 and 1198 mRNA-1273, respectively) and 10% sucrose that is used as a cryoprotectant for both mRNA-vaccines

AES: Amino-terminal enhancer of split; mtRNR1: mitochondrially encoded 12S rRNA

SM-102: 9-Heptadecanyl 8-{

Figure 3: Manufacturing and scale-up of nucleoside-modified mRNA-vaccines

The first step in nucleoside-modified mRNA vaccine production consists of an IVT reaction. This reaction, which 1208 is conducted under specific conditions, is based on mixing linearized plasmid template, phage RNA polymerase, 1209 nucleoside-triphosphates (including 1-methylpseudouridine (m1Ψ)) and Cap1 structure