RNA vaccines: The dawn of a new age for tuberculosis?

Abstract

Since 2019, there has been a growing focus on mRNA vaccines for infectious disease prevention, particularly following the emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). mRNA vaccines offer advantages such as rapid production and the ability to induce robust cellular and antibody responses, which are essential for combating infections that require cell-mediated immunity, including Tuberculosis (TB). This review explores recent progress in TB mRNA vaccines and addresses several key areas: (1) the urgent need for new TB vaccines; (2) current advancements in TB vaccine development, and the advantages and challenges of mRNA technology; (3) the design and characteristics of TB mRNA vaccines; (4) the immunological mechanisms of TB mRNA vaccines; (5) manufacturing processes for TB mRNA vaccines; and (6) safety and regulatory considerations. This interdisciplinary review aims to provide insights for researchers working to address critical questions in TB mRNA vaccine development.

Keywords: Mycobacterium tuberculosis; Tuberculosis; immunological mechanisms; mRNA vaccines; manufacture and quality control.

Figure 1.

Overview of current TB vaccine candidates in clinical trials. The pipeline provides data on TB vaccine candidates in clinical development, but does not include information on candidates that have been withdrawn, terminated, or are in preclinical development.

Figure 2.

A comparison of TB linear mRNA vectors. Both conventional non-amplified and self-amplifying mRNAs share fundamental components, including a cap, 5′ UTR, 3’ UTR, and poly(a) tail of varying lengths. In addition to these components, self-amplifying RNA (saRNA) also encodes four non-structural proteins (nsP1–4) and a subgenomic promoter derived from the genome of the alphavirus genome.

Figure 3.

A comparison of TB circular RNA. Pre-circRNA was synthesized by IVT, and then TB circRNA was generated by two cyclization strategies: enzyme synthesis and intron self-splicing.

Figure 4.

Mechanisms underlying the adaptive immune responses elicited by TB mRNA vaccines. The TB mRNA vaccines are enclosed in nanoparticles and internalized by myocytes or antigen-presenting cells. The mRNA is released into the cytoplasm upon escaping from endosomes, where it is then translated into antigenic proteins by ribosomes. Subsequently, endogenous antigens are degraded into polypeptides by the proteasome and presented to CD8⁺ T cells via MHC I (①). Additionally, secreted antigens can be internalized by cells, degraded within lysosomes, and presented on the cell surface to helper T cells via MHC class II for CD4⁺ T cell recognition (②). Simultaneously, the secreted exogenous target protein can also directly stimulate B cells to generate anti-tuberculosis antibodies targeting Mtb (③).

Figure 5.

A schematic diagram of the TB mRNA vaccine preparation process. The production of TB mRNA involves a two-step process that includes both synthesis and purification. The mRNA sequence can be generated via either a single-step or a two-step enzymatic approach. In the latter case, the two-step enzymatic reaction consists of in vitro transcription of the DNA template to produce an RNA polymerase transcript, which can subsequently be capped using vaccinia capping enzyme along with a methyl donor. This procedure concludes with purification to eliminate the DNA template, followed by TFF for buffer exchange and concentration, and finally sterile filtration through a 0.2 µm filter.

Figure 6.

Characterization and release testing criteria for plasmid DNA, mRNA drug substances and mRNA drug products.