Penn Engineers Use a Century-Old Reaction to Build MRNA Vaccine Lipids With Fewer Side Effects

Most people who have rolled up a sleeve for an mRNA vaccine know the aftermath: a sore arm, some redness, a day or two of feeling off. That is inflammation, the most common side effect of shots like the COVID-19 vaccine. Researchers at the University of Pennsylvania now report that they have found a way to change the delivery vehicle behind those vaccines so it provokes less of that response while working better.

The work, published in Nature Biomedical Engineering, centers on the ionizable lipid, one of four types of lipid in the lipid nanoparticles (LNPs) that carry mRNA into cells. It is arguably the most important of the four. The team altered its structure by adding phenol groups, compounds with anti-inflammatory properties that are found in foods such as olive oil. Michael J. Mitchell, Associate Professor in Bioengineering and the paper's senior author, called the result a win-win: lipids that work better with fewer side effects.

The route to get there was unusual. Ionizable lipids have largely been made with reactions that join two components into one molecule, like two halves of a sandwich. Ninqiang Gong, a former postdoctoral fellow in the Mitchell Lab and co-first author, said those methods have been so successful that few people looked for alternatives. The team turned to chemistry's history and picked the Mannich reaction, named for the German chemist who discovered it more than a century ago. It combines three precursors rather than two, which opens up more possible products. Gong said the team created hundreds of new lipids this way.

Searching that library, the researchers found that lipids carrying a phenol group, a hydrogen and oxygen pair attached to a carbon ring, substantially cut inflammation. Earlier studies had shown that phenol-containing compounds neutralize free radicals, molecules with unpaired electrons that can disrupt the body's chemistry. When free radicals outnumber antioxidants, the result is oxidative stress, which degrades proteins, damages genetic material and can kill cells. The team checked several markers of oxidative stress to compare LNPs built from different lipids. Emily Han, a doctoral student in bioengineering and co-author, said the best performer, made with a phenol-containing lipid from the Mannich reaction, caused less inflammation.

They then tested performance. The most anti-inflammatory formulation, called C-a16, outperformed LNPs used in technologies already on the market across multiple experiments. Dongyoon Kim, a postdoctoral fellow and co-first author, said lower oxidative stress makes it easier for LNPs to do their job. The C-a16 particles produced longer-lasting effects and improved both CRISPR gene editing and the potency of cancer vaccines.

In mice, the team first delivered the gene that makes fireflies glow, a classic check of how well genetic instructions get delivered. The glow was about 15 times brighter than with the LNPs used in Onpattro, an FDA-approved treatment for hereditary transthyretin amyloidosis, a rare genetic liver disease. For CRISPR tools aimed at the faulty gene behind that disease, the new lipids more than doubled effectiveness in a mouse model compared with current delivery methods.

In a melanoma animal model, an mRNA cancer treatment delivered with C-a16 shrank tumors three times more effectively than the same treatment delivered with the LNPs used in COVID-19 vaccines. Cancer-fighting T cells also got a boost, recognizing and destroying tumor cells more efficiently with less oxidative stress. And when the lipids were used in COVID-19 mRNA vaccines, the immune response in animals was five times stronger than with standard formulations.

The research was done at Penn Engineering and the Perelman School of Medicine, with co-authors including Drew Weissman of Penn Medicine and colleagues from USTC. Funding came from the NIH, the National Science Foundation, the Burroughs Wellcome Fund and the American Cancer Society, among others. All the results so far come from animal studies, so human trials will be needed to confirm both the reduced side effects and the improved efficacy. Mitchell said he is excited to imagine what else from old chemistry remains to be rediscovered.