Background: From preventive success to understanding mechanisms of action

Vaccines combining nucleoside-modified messenger RNA (mRNA) with lipid nanoparticles (LNPs) induce protective immunity through coordinated innate and adaptive immune responses. However, whether immune response induction and post-vaccination reactions can be regulated separately remains unresolved. In a review published in Nature, Locci and Pardi summarize the known immunological mechanisms of infectious disease mRNA–LNP vaccines and the remaining challenges.

The authors explain that this vaccine platform has shown high efficacy against severe COVID-19 and has saved millions of lives since its first authorization for use in humans in 2020. They attribute these achievements to the interplay of strong innate and adaptive immune responses. Improving both immunogenicity—the ability to elicit an immune response—and tolerability—the extent to which vaccination can be tolerated—remains a challenge for next-generation vaccine development.

Key findings: Three unresolved questions about protective immunity

The review notes that recent research has advanced understanding of how these vaccines work, but key knowledge gaps remain. The first question is how the immune system detects LNPs and how LNPs exert their adjuvant effects to support immune responses. Demonstrating a vaccine’s preventive efficacy does not mean that the immunological roles of all its components have been fully established.

The second question is how to identify the signals and cellular pathways that are decisive for inducing protective immunity. The abstract emphasizes coordination between innate and adaptive immunity, but provides no experimental conditions or quantitative results showing how much protection changes when a particular receptor or pathway is modulated. The available information therefore does not support conclusions about the effects of controlling a specific immune pathway or the relative merits of different vaccine formulations.

The third question is whether immunogenicity can be separated from reactogenicity. Reactogenicity refers to the propensity to cause reactions after vaccination and is distinct from the broader concept encompassing all vaccine safety issues. The authors ask whether the immune responses needed for protection and post-vaccination reactions can be regulated separately. This should not be interpreted as a conclusion that a method for minimizing adverse reactions has already been established.

Implications and outlook: The potential and validation challenges of adjusting components

The review discusses modifying components of the mRNA–LNP platform to fine-tune immune responses against pathogens for which effective vaccines are unavailable or existing vaccines need improvement. The aim is to deepen understanding of immunological mechanisms and apply that knowledge to next-generation vaccine design. However, this is not a paper presenting new experimental evidence that a specific component change improves preventive efficacy or tolerability in humans.

The available materials are limited to bibliographic information and the abstract. They do not establish how individual components were modified, the study populations or models and comparison conditions in individual cited studies, or the effect sizes. A central question for future development is which adjustments contribute to protective immunity and how they affect post-vaccination reactions. The review distinguishes the mechanisms underlying the achievements of infectious disease mRNA–LNP vaccines from unresolved questions and outlines directions for research.

Source: Review abstract indexed in Europe PMC, DOI: 10.1038/s41586-026-10599-0.