Researchers at the University of Pennsylvania announced on Mar. 17 that they have developed a new type of lipid nanoparticle (LNP) that could make mRNA vaccines more effective while reducing common side effects such as soreness, mild fever, and malaise. The findings were published in Nature Materials and are based on pre-clinical tests involving human cells and mouse models.
The study is significant because it addresses the challenge of balancing vaccine efficacy with tolerability. Traditional mRNA vaccines often cause temporary side effects as a result of immune system activation, but the new LNPs aim to minimize these reactions without compromising protection.
By modifying the structure of ionizable lipids within LNPs, the researchers enhanced the metabolism of key immune cells, providing them with more energy for defense while reducing inflammatory signals that typically lead to fever and fatigue. The chemical changes also improved targeted delivery to immune organs like lymph nodes. "This is an early step, but it opens the door to a new generation of mRNA vaccines that are more potent and better tolerated," said Michael J. Mitchell, Associate Professor in Bioengineering and senior author of the study. "Instead of accepting a trade-off between efficacy and side effects, we're beginning to see that chemistry can help us improve both."
Dongyoon Kim, a postdoctoral fellow in Bioengineering and co-first author, explained how adding imidoester cross-linkers expanded the range of possible ionizable lipid structures: "We tweaked the standard lipid recipe by adding a new ingredient." The best-performing lipid, named C12-2aN, increased glycolysis—a rapid form of energy production—in dendritic cells without sacrificing vaccine effectiveness.
Amanda Murray, a doctoral student in the Mitchell Lab and co-author, noted that this approach activates immune cells in a more controlled way: "The dendritic cells are getting the energy they need to mount a protective vaccine response without triggering the same level of widespread inflammation that we normally experience after a vaccination, which causes common symptoms such as fever and muscle aches." Mice treated with C12-2aN showed lower expression of genes linked to systemic inflammation and smaller increases in body temperature compared to those given standard formulations.
The redesigned LNPs also demonstrated improved targeting by delivering over three times as much mRNA to lymph nodes relative to the liver compared with FDA-approved formulations. Kim said: "The new ingredients imparted a positive charge... That seems to have affected how the particles interact with tissues and proteins, helping steer them more often toward the right destination."
Mitchell concluded: "This study shows that rationally designing lipid chemistry allows us to do more than improve delivery... We can begin to intentionally shape immune cell metabolism, opening new avenues for immune engineering beyond vaccines."
