Ionizable Lipids of mRNA Lipid Nanoparticles and Immune Response: A Structure-Activity Perspective
2Department of Biochemistry and Molecular Genetics, Israel Institute of Biological Research
Introduction: Lipid nanoparticles (LNPs) represent a significant advancement in medical science. The success of the mRNA-LNP-based COVID-19 vaccines underscored the potential of this delivery system, not only for vaccines but also for therapeutic applications. However, after administering over 16 billion doses globally, which played a critical role in protecting populations, it became evident that some individuals experienced mild to, in certain cases, severe side effects. This highlights the importance of thoroughly evaluating the safety and therapeutic effectiveness of the mRNA-LNP platform to enable the successful development of new genetic medicines. Among the lipid components that make up these nanoparticles, ionizable lipids are essential to LNP function. The structure of ionizable lipids plays a key role in determining the efficiency, distribution in organs and cells, and potential toxicity of LNP formulations. Additionally, the choice of ionizable lipids can affect immune cell responses, potentially triggering unintended immune activation or suppression. Our objective is to establish a structure-activity relationship between ionizable lipids and immune cell responses, which will inform the design of improved LNP formulations.
Materials and Methods: We designed and synthesized a library of novel ionizable lipids incorporating hydroxylamine linkers and various fatty acid tails. These lipids were used to formulate LNPs via microfluidic mixing, and their physicochemical properties were carefully characterized. To evaluate the inflammatory responses induced by LNPs, we conducted experiments using primary immune cells, cell lines, and in vivo studies in mice. These studies focused on key immune reactions, including cytokine release, inflammasome activation, and co-stimulatory signal activation in antigen-presenting cells. Finally, we compared the vaccine efficacy of our novel ionizable lipids to that of a clinically approved benchmark ionizable lipid by evaluating humoral and cellular immune response to mRNA coding antigen for Yersinia pestis, the bacterium responsible for plague.
Results and Discussion: Our findings indicate that the branching and unsaturation of the ionizable lipid tails significantly affect the LNP’s in vivo performance.
Conclusion: This study provides valuable insights into the structure-activity relationship of ionizable lipids, which will aid in the development of enhanced drug delivery systems with improved performance.