Rutgers University and Japanese institutions tested a needle-free mRNA vaccine in mice and found that a high-pressure liquid jet into the skin worked better with aluminum phosphate and short CpG DNA molecules. The combination produced stronger immune responses and drove lung viral RNA down after SARS-CoV-2 infection.
Rutgers and Japanese institutions
The study used naked mRNA, which means the message was delivered without lipid particles, and it paired that delivery with two adjuvants. For readers tracking future vaccine delivery, the practical shift is not the mRNA itself but the route and the immune boost built around it.
After three vaccine doses, mice were challenged with SARS-CoV-2 or influenza A virus. Infectious virus in lung samples fell below the detection limit in both challenge groups.
In the COVID experiment, lung viral RNA was about 24 times lower than in mice vaccinated without adjuvants. That is the clearest sign that the adjuvant mix changed what reached the lungs after infection, not just what happened at the injection site.
Aluminum phosphate and CpG DNA
Using aluminum phosphate and short CpG DNA molecules separately did not give much improvement, and some adjuvants weakened part of the immune response. The combination, by contrast, improved both antibody production and the cellular immune response, which the researchers linked to immune signals in the skin and nearby lymph nodes.
One part of the result is stronger than the survival data alone: all mice in the influenza groups survived, but the study did not establish any extra survival benefit from the adjuvant combination. That leaves the more useful signal in the immune measurements and the lower lung RNA, not in a better survival rate.
Larger animals, then doses
The authors say the method still needs testing in larger animals, and appropriate doses must be determined before possible clinical trials involving people. A reader should treat this as a preclinical delivery study, not a human-ready vaccine platform, even though the less inflammatory profile compared with lipid-particle mRNA vaccines is an important step.
For now, the unresolved question is which larger animals will be used next and what doses will be tested.
