mRNA-based vaccines and therapeutics: an in-depth survey of current and upcoming clinical applications

Abstract

mRNA-based drugs have tremendous potential as clinical treatments, however, a major challenge in realizing this drug class will promise to develop methods for safely delivering the bioactive agents with high efficiency and without activating the immune system. With regard to mRNA vaccines, researchers have modified the mRNA structure to enhance its stability and promote systemic tolerance of antigenic presentation in non-inflammatory contexts. Still, delivery of naked modified mRNAs is inefficient and results in low levels of antigen protein production. As such, lipid nanoparticles have been utilized to improve delivery and protect the mRNA cargo from extracellular degradation. This advance was a major milestone in the development of mRNA vaccines and dispelled skepticism about the potential of this technology to yield clinically approved medicines. Following the resounding success of mRNA vaccines for COVID-19, many other mRNA-based drugs have been proposed for the treatment of a variety of diseases. This review begins with a discussion of mRNA modifications and delivery vehicles, as well as the factors that influence administration routes. Then, we summarize the potential applications of mRNA-based drugs and discuss further key points pertaining to preclinical and clinical development of mRNA drugs targeting a wide range of diseases. Finally, we discuss the latest market trends and future applications of mRNA-based drugs.

Keywords: Administration routes; Lipid nanoparticles; Targeting mRNA delivery system; mRNA therapeutics; mRNA vaccine.

Fig. 1

Types of synthetic mRNA for therapeutic application. A. Structural elements of mRNAs include the protein-encoding open reading frame (ORF), 5′ and 3′ untranslated regions (UTRs), 5′ cap structure, and 3′ poly (A) tail. mRNA drug design may involve several modifications to these structural elements in order to improve stability and protein expression. For example, the 5′-UTR and 3′-UTR from heat shock protein 70 (Hsp70) may be utilized, uridine can be replaced with m1Ψ, and optimized codons can be included to generate desirable higher-order structure and promote stable expression. Several possible mRNA modifications are shown in red. B In addition to conventional mRNAs, different synthetic RNA types include self-amplifying RNA (saRNA), trans-amplifying RNA (taRNA) and circular RNA (circRNA). saRNAs consist of two ORFs; One is np1-np4, which forms a replication complex, and the other is the target mRNA. saRNAs may be divided into a set of two taRNAs to avoid large size and low encapsulation efficiency. A circRNA with an internal ribosome entry site (IRES) linking a target of interest can be generated by using a self-splicing intron to circularize precursor mRNA. The construct can then be purified by HPLC. A permuted intron–exon (PIE) splicing strategy can allow for the fusion of exons with half-intron sequence and external homology sequence to enhance splicing efficiency [247]. After producing the precursor mRNA with IVT, GTP, and Mg²⁺ are added as cofactors to drive group I intron splicing,circularized mRNA typically exhibits a longer half-life than its counterpart linear mRNA. C Production of mRNA-LNPs (lipid nanoparticles). mRNA and lipid solutions should be dissolved in aqueous and organic solvents, respectively. The desired solution allows mRNA stability and facilitates the easy mixing of both solutions based on polarity. These components were then mixed using a microfluidic device to obtain stable and uniform mRNA-LNP nanoparticles

Fig. 2

The potential for mRNA therapeutics and vaccines. A The process of creating novel mRNA drugs from sequence design to clinical translation. The first step is to design an mRNA sequence for a particular disease. Once mRNA is synthesized successfully, the delivery system should be established. Recently, lipid nanoparticles (LNPs) have been proven to be an efficient delivery tool. Animal models and cell-based assays may be used to evaluate the mRNA drug during preclinical testing. The mRNA drug can progress to clinical trials after successful pre-clinical tests. B The administration route is a key consideration when developing mRNA drugs for different diseases. The route might vary depending on the disorder and the type of drug. As an alternative to injections, nasal delivery is a promising method for treating infectious diseases and neurological disorders. Targeted delivery strategies for mRNA. mRNA drugs can be delivered to specific cells, tissues or organs. C–E The delivery of mRNA drugs to specific cells, tissues, or organs can be achieved using targeted mRNA delivery strategies. C Mannosylated lipopolyplexes can be delivered to splenic dendritic cells; D LNPs with different lipid components can be delivered to specific tissues or organs. For example, delivery using LNPs with shorter chains of ionizable lipids induced protein expression in liver, while LNPs with longer chains of ionizable lipids induced mRNA translation in spleen. Moreover, ionizable cationic, permanently cationic or zwitterionic helper lipids can be used for efficient mRNA expression in liver, lung or spleen. E LNPs conjugated with ligands can be used to delivered to leukocytes or tumor cells. For example, LNPs conjugated with antibody against CD5 can be delivered to T cells, while LNPs conjugated with antibody against CD117 can be delivered to hematopoietic stem cells

Fig. 3

Medical applications of RNA drugs and FDA approved RNAi drugs. A The applications of mRNA-based drugs for disease therapy include vaccines, cell therapy, therapeutic protein production, and protein replacement. mRNA-based drugs have proven to be a potent competitor in vaccine development. Along with prevention of infectious diseases, mRNA vaccines may also be used in the treatment of cancer. Regarding cell therapies, mRNAs can be applied in CAR-T cell therapy, or treatments may also be developed to target disease-relevant cell types, such as cardiac cells, blood cells, hepatocytes and neurons. For therapeutic protein production, mRNAs can be translated into patient’s own cells to produce therapeutically active proteins. These protein-encoding mRNAs can be used for antigen presentation, functional protein expression, or Cas9 protein expression for target gene modification. Furthermore, small RNAs (e.g., siRNA or miRNA) may be useful to inhibit overactive genes. For protein replacement, protein-coding mRNAs can be used as gain-of-function therapies, replacing non-functional mutant proteins to restore normal physiological function. B The table shows U.S. FDA-approved RNAi drugs currently in clinical use

Fig. 4

Development and modification strategies for mRNA-LNP cancer vaccines. A Neoantigens can be identified and validated by whole genome sequencing, RNA sequencing or protein expression from normal and tumor tissues. Validated neoantigens can be utilized for the design of mRNA therapeutics, which may be delivered using LNPs. B The different neoantigen mRNAs could be linked tandemly to be synthesized and incorporated into LNPs for delivery as a personalized cancer vaccine. Co-stimulatory molecules, such as IL-12 and IL-27, may be co-delivered to activate immune cells. Other co-stimulatory molecules could include tumor suppressor genes like PTEN and p53 to induce cancer death, adjuvants like STING^V155M and glycolipid to activate CD8⁺ cells or invariant Natural Killer T (iNKT) cells, or macrophage polarization factors like IRF5 and IKKβ to induce M1 cell polarization. Surface modifications can be made to the LNPs, such as the addition of polysaccharides to induce immune response or the inclusion of endosome escape molecules to enhance mRNA release into the cytosol for expression

Fig. 5

mRNA-based new modalities for disease treatments. A Current CAR-T technology requires the isolation of T cells from a patient and processing of the isolated cells into CAR-T cells (right panel). Next-generation CAR-T therapy is expected to be more effective, shorten the therapeutic timeframe and lower the cost. CAR-T cells may be generated in patients through intravenous injection of targeted mRNA-LNPs (left). B LNP-encapsulated mRNAs encoding genome editing enzymes and other components may be administrated through different routes. Genes of transthyretin (TTR), proprotein convertase subtilisin/kexin type 9 (PCSK9), angiopoietin-like 3 (ANGPTL3), polo-like kinase 1 (PLK1), antithrombin (AT), phenylalanine hydroxylase (PAH) or exon 45 was edited and eventually alleviated the disease progression. sgRNA: single guide RNA; LDL-C: low-density lipoprotein cholesterol; TG: triglycerides (TG). C Utilization of mRNA drugs for engineering therapeutic antibodies (Abs). LNP-based delivery can be applied to generate different types of therapeutic Abs at higher levels and with more sustainable expression than conventional antigen injections. This approach could be applied to a variety of diseases, including cancers and infectious diseases

Fig. 6

Development status and global sales forecast for mRNA-based drugs. A Composite development status of 316 mRNA-based medicines (excluding technologies that were discontinued, suspended or not updated for an extended period); analyzed with Clarivate’s Cortellis Competitive Intelligence Database on July 28, 2023. B–D Global sales forecasts to 2029 are based on analyst consensus, acquired from GlobalData’s Intelligence Center Database on June 26, 2023. B Five FDA-approved ASO (anti-sense oligo) drugs. C Five FDA-approved siRNA drugs. D Two FDA-approved mRNA vaccines are available on the market. Summary information regarding these drugs is provided in "Regulatory agency-approved drugs". Regulatory agency-approved drugs. E–G Total global sales forecasts (US$ million) for each drug up to 2029