Preformed Nanogels Adsorb mRNA for Delivery to Immune Cells, but Room-Temperature Storage Remains a Limitation
Background: Separating particle manufacture from mRNA loading
A platform has been developed that adsorbs messenger RNA (mRNA) onto premanufactured polymer nanogels for delivery to antigen-presenting cells (APCs). The TRAIN study, published in Bioconjugate Chemistry, separates carrier manufacture from mRNA loading and suggests that delivery targets could be adjusted by attaching antibodies to the particle surface. It does not, however, establish long-term room-temperature storage of the mRNA-loaded formulation.
Conventional lipid nanoparticle (LNP) methods often incorporate mRNA as the particles form, linking carrier manufacture to loading conditions. The researchers’ alternative is to manufacture and stockpile particles first, then attach newly designed mRNA later. TRAIN is an acrylate-based nanogel that cleaves under reducing conditions; mRNA adsorbs electrostatically to its positively charged surface. The design also allows targeting antibodies to be attached after particle synthesis.
Key findings: Targeted delivery and reporter expression
TRAIN had a mean hydrodynamic diameter of about 86.6 nm. At an N/P ratio of 5 or greater—the molar ratio of positively charged nitrogen in the particles to mRNA phosphate groups—nearly all of the input mRNA bound to the particles. In human embryonic kidney-derived HEK293T cells, firefly luciferase expression at an N/P ratio of 10 was approximately 4.5 times that obtained with the laboratory transfection reagent Lipofectamine 2000. This comparison applies to those cells and reporter conditions; it does not mean the platform outperforms commercial LNP vaccines in antigen presentation or protective efficacy.
The feature designed for intracellular release is a crosslinker containing disulfide bonds that break under reducing conditions. Compared with a control using nonresponsive crosslinkers, the particles showed less colocalization with lysosomes and higher reporter expression. These findings support the possibility of cytosolic delivery. However, the explanation that crosslinker cleavage aids delivery is the researchers’ mechanistic interpretation; it is not a direct measurement of the rate of endosomal escape.
TRAIN bearing an antibody against CD206, the mannose receptor, was preferentially delivered to monocytes and dendritic cells within human peripheral blood mononuclear cells (PBMCs), resulting in expression of the fluorescent protein mCherry. Particle uptake by T cells and B cells was low. This was an ex vivo assessment with two biological replicates, and it did not establish exclusive delivery to dendritic cells. The BALB/c mouse experiment used three mice per group, with an intramuscular dose of 1 μg of luciferase mRNA per mouse. Local expression signals from targeted TRAIN increased between 24 and 48 hours and remained detectable at 72 hours.
Implications and outlook: Empty-carrier stability differs from that of the loaded formulation
TRAIN without mRNA showed little change in particle size over four weeks at 25°C. Results for the mRNA-loaded formulation tested over one week were different. At 4°C, about 61% of the mRNA remained intact on day 7. At 25°C, this fell to about 40% on day 3, and the detectable intact-mRNA peak disappeared on day 5. Degradation was limited at −20°C, but an increase in particle size was observed. These values measure RNA integrity; they do not indicate how much protein-expression function was retained after storage.
The study’s achievement is a proof of concept for adsorbing mRNA onto a premanufactured carrier and using targeting antibodies to adjust which cells receive it. Further assessment of post-storage function, reproducibility of targeted delivery, and safety is needed to develop the approach into a vaccine. Antigen-specific T- and B-cell immune responses and protection against infection were not demonstrated in this study. There are no results supporting six-month room-temperature storage or clinical efficacy.
The study design and results are available in the original Bioconjugate Chemistry paper.
Advanced Materials, Published June 2026.
Summary: Bypassing the stringent ultra-low cold-chain dependencies and complex post-formulation processing steps that restrict conventional lipid nanoparticle (LNP)-based mRNA modalities, this biomedical engineering study structures a preformulated nanogel platform. Engineered with high-affinity dendritic cell-targeting ligands, the cross-linked polymeric matrix dynamically isolates encapsulated mRNA from thermal hydrolytic kinetics, sustaining structural transcript integrity over a 6-month room-temperature shelf-life window. Upon cellular internalization, the ph-responsive framework accelerates endosomal escape velocities to optimize cytoplasmic release fluxes, amplifying downstream antigen presentation metrics without inducing off-target reactogenicity, and defining a precise computational baseline for scalable, decentralized universal vaccine translation.
One possible scenario is to design mRNA encoding an antigen from a new pathogen, adsorb it onto premanufactured TRAIN, and combine it with a targeting antibody for further preclinical evaluation. Separating carrier synthesis from mRNA loading could reduce the burden of restarting particle manufacture whenever the antigen changes. Reporter expression in monocytes and dendritic cells observed in human-derived cells provides a basis for studying targeted delivery to immune cells. However, the possibility of stockpiling empty particles does not mean a finished vaccine can be stockpiled at room temperature. Before use in manufacturing or vaccination, storage conditions and shelf life after mRNA loading must be established, and post-storage expression function, immunogenicity, and protective efficacy must be tested.