Needle-Free mRNA Vaccine Delivery Protects Mice From COVID-19 and Flu
A needle-free vaccination method successfully protected mice against the viruses causing COVID-19 and influenza, according to a study published in The Journal of Clinical Investigation, Newswise reported. Researchers at Rutgers and Japanese institutions tested the experimental delivery approach, which combines a high-pressure liquid jet to push mRNA into the skin with specific chemical boosters designed to strengthen immune reactions.
Traditional mRNA vaccines rely on tiny lipid-based nanoparticles to capsule fragile genetic instructions and help them enter cells. By contrast, this experimental strategy introduces unencapsulated, or naked, mRNA directly into the skin, a tissue dense with immune cells. Earlier attempts using jet injectors alone produced weak immune defenses, prompting researchers to test various chemical additives to enhance the process.
Combining aluminum phosphate with CpG improves vaccine efficacy
While individual adjuvants offered little benefit and occasionally weakened specific immune reactions, combining aluminum phosphate with short DNA molecules known as CpG significantly improved both antibody and cellular responses. The researchers traced this success to immune signals activated directly within the skin and nearby lymph nodes.
One of the most exciting discoveries in developing our carrier-free mRNA vaccines was that a combination of adjuvants could markedly improve vaccine efficacy while maintaining a favorable safety profile in our animal studies,
said senior author Satoshi Uchida of the Institute of Science Tokyo.
In subsequent challenge experiments, mice received three doses of the boosted vaccines before exposure to SARS-CoV-2 or influenza A. Infectious virus levels dropped below detection limits in lung samples across all vaccinated groups. For the COVID-19 trials, lung viral RNA measured roughly 24 times lower than in mice that received unboosted mRNA delivery. Separate tests also showed reduced local and systemic inflammation compared with conventional lipid-particle formulations.
Path to Human Clinical Trials and Safety Profiles
Although the needle-free approach demonstrated efficacy in laboratory mice, researchers emphasize that the platform requires testing in larger animals to determine appropriate human dosing standards. The delivery device and individual adjuvant components have already seen clinical use in human patients, providing a practical foundation for future development.
What encourages us is that we achieved protective immunity in mice with a delivery device and adjuvant components that have each already been clinically used in human patients,
said coauthor Wadih Arap of Rutgers New Jersey Medical School and Rutgers Cancer Institute.
The research received funding from the Japan Agency for Medical Research and Development, the Japan Science and Technology Agency, the Japan Society for the Promotion of Science, the Program for Promotion of Fundamental Studies in COVID-19 of the Tokyo Metropolitan Government, Science Tokyo’s Nanken-Kyoten and Medical Research Center Initiative for High Depth Omics, and the Levy-Longenbaugh Donor-Advised Fund. Satoshi Uchida is a founder and Chief Medical Officer of Crafton Biotechnology Co., Ltd. Renata Pasqualini and Wadih Arap are founders and equity shareholders of PhageNova Bio and MBrace Therapeutics, with Pasqualini serving as Chief Scientific Officer for PhageNova Bio.
Frequently Asked Questions About Needle-Free mRNA Delivery
Why do traditional mRNA vaccines use lipid nanoparticles?
Traditional mRNA vaccines encapsulate fragile genetic instructions in tiny fat-based particles to protect them from degradation and help them cross cell membranes.
How does the needle-free jet injection work in the skin?
A high-pressure liquid jet delivers unencapsulated mRNA directly into the skin, which naturally contains a high concentration of immune cells capable of initiating a protective response.
What specific chemical boosters were added to the naked mRNA?
Researchers combined aluminum phosphate with short DNA molecules called CpG to stimulate immune signals in the skin and nearby lymph nodes.
Are these needle-free vaccines currently available for humans?
No, the approach has only been tested in mice and requires further evaluation in larger animals and human clinical trials before regulatory review.
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