Nucleic Acid Vaccines (mRNA and DNA)

Nucleic acid vaccines deliver genetic instructions — messenger RNA (mRNA) or DNA — encoding a target antigen, so that the recipient's own cells synthesize the antigen and present it to the immune system. They carry no infectious material and no protein antigen, only the code for one. mRNA vaccines, delivered in lipid nanoparticles, came to prominence as the first widely deployed COVID-19 vaccines, demonstrating that the platform can be designed quickly from a pathogen's genetic sequence.

Definition

A nucleic acid vaccine is a preparation of mRNA or DNA encoding a target antigen, delivered so that host cells translate it into protein, thereby inducing protective immunity without using the pathogen, a live vector, or a purified protein antigen.

Scope

This topic covers how mRNA and DNA vaccines work, why endogenous antigen synthesis induces both antibody and T-cell immunity, the role of delivery systems and nucleoside modification, and the practical differences between the two nucleic-acid modalities. It is a methodological reference and does not provide schedules or eligibility advice.

Core questions

• How do mRNA and DNA vaccines instruct host cells to make antigen?
• Why does endogenous antigen production elicit both antibody and cytotoxic T-cell responses?
• What roles do lipid-nanoparticle delivery and nucleoside modification play, and how do mRNA and DNA platforms differ?

Key concepts

• Messenger RNA (mRNA) platform
• Plasmid DNA platform
• Lipid nanoparticle delivery
• Nucleoside-modified mRNA
• Endogenous antigen translation
• Sequence-driven rapid design
• Cold-chain requirements for mRNA

Mechanisms

The vaccine delivers genetic code for the antigen into host cells: mRNA is translated directly in the cytoplasm, while plasmid DNA must reach the nucleus to be transcribed before translation. The cell then produces the antigen and processes it through both major histocompatibility pathways, priming antibody responses and cytotoxic T cells. For mRNA, two advances were pivotal — encapsulation in lipid nanoparticles for stable delivery and uptake, and chemical modification of nucleosides to reduce innate immune over-activation and increase protein output, as described by Pardi and colleagues. DNA vaccines, reviewed by Kutzler and Weiner, are stable and simple to manufacture but historically less immunogenic in humans, often needing delivery aids. Because the antigen is encoded rather than supplied, a nucleic-acid vaccine can be designed directly from a pathogen's sequence, enabling rapid development, as shown by the BNT162b2 and mRNA-1273 COVID-19 vaccines.

Clinical relevance

Nucleic acid vaccines, especially mRNA, established a rapidly designable platform that induces strong humoral and cellular immunity and was validated at scale during the COVID-19 pandemic. Understanding the platform explains why such vaccines can be developed quickly from sequence data and why mRNA products have specific storage requirements. This entry describes the science of the platform and is not a source of individual vaccination advice.

Epidemiology

mRNA vaccines were authorized and administered to hundreds of millions of people during the COVID-19 pandemic, with large randomized trials (Polack and colleagues; Baden and colleagues) demonstrating high efficacy; DNA vaccines have been licensed in veterinary settings and continue in human clinical development.

History

The idea that injected nucleic acid could direct in-vivo antigen expression dates to early-1990s demonstrations of protein expression from injected mRNA and DNA. DNA vaccines advanced through the 2000s (reviewed by Kutzler and Weiner, 2008), while mRNA was long limited by instability and innate immune activation until nucleoside modification and lipid-nanoparticle delivery made it practical, a turning point summarized by Pardi and colleagues in 2018 and realized in the COVID-19 mRNA vaccines of 2020.

Key figures

• Norbert Pardi
• Drew Weissman
• David B. Weiner
• Florian Krammer

Seminal works

• pardi-2018
• kutzler-2008
• polack-2020
• baden-2021

Frequently asked questions

How do mRNA and DNA vaccines differ?

Both deliver genetic instructions for an antigen, but mRNA is translated directly in the cytoplasm and is typically delivered in lipid nanoparticles, whereas DNA must enter the cell nucleus to be transcribed first; DNA is more stable to store but has historically been less immunogenic in humans.

Why could mRNA COVID-19 vaccines be developed so quickly?

Because the vaccine only needs the genetic sequence of the target antigen, an mRNA can be designed as soon as the pathogen's sequence is known, without growing the pathogen or purifying protein — allowing very rapid development once delivery and stability problems had been solved.