Introduction: The advent of lipid nanoparticles (LNPs) as a delivery platform for mRNA therapeutics has revolutionized the biomedical field, particularly in treating infectious diseases, cancer, genetic disorders, and metabolic diseases. Recent Advances in Therapeutic LNPs: LNPs, composed of ionizable lipids, phospholipids, cholesterol, and polyethylene glycol (PEG) lipids, facilitate efficient cellular uptake and cytosolic release of mRNA while mitigating degradation by nucleases. However, as synthetic entities, LNPs face challenges that alter their therapeutic efficacy and safety concerns. Toxicity/Reactogenicity/Immunogenicity: This review provides a comprehensive overview of the latest advancements in LNP research, focusing on preclinical safety assessments encompassing toxicity, reactogenicity, and immunogenicity. Summary and Outlook: Additionally, it outlines potential strategies for addressing these challenges and offers insights into future research directions for enhancing the application of LNPs in mRNA therapeutics.

The spleen is emerging as a key vaccination target. However, existing lipid nanoparticles (LNPs) primarily accumulate in the liver, limiting their efficacy in vaccine therapy. The cholesterol in current LNP formulations promotes their uptake by hepatocytes, while the polyethylene glycol-modified (PEGylated) lipids induce PEG immunogenicity, further reducing the efficacy in the setting of repeated administrations. We develop a three-component (ThrCo) LNP by replacing cholesterol and PEGylated lipids in Pfizer-BioNTech LNPs with zwitterionic pyridine carboxybetaine (PyCB) ionizable lipids (ILs), achieving ~70% lower liver accumulation and a 4.5-fold increase in spleen-specific mRNA translation. PyCB ILs enhance LNP hydrophilicity, stabilizing the outer membrane to compensate for cholesterol removal. PyCB groups also exhibit strong protonation at endosomal pH, facilitating mRNA translation. The zwitterionic surface of ThrCo LNP reduces protein adsorption, thereby preventing the accelerated blood clearance effect caused by PEGylated lipids following repeated administrations. Thus, ThrCo LNP–based vaccines efficiently deliver mRNA to splenic antigen-presenting cells, boosting immune responses and improving therapeutic outcomes.

Recent advancements in vaccine delivery systems have seen the utilization of various materials, including lipids, polymers, peptides, metals, and inorganic substances, for constructing non-viral vectors. Among these, lipid-based nanoparticles, composed of natural, synthetic, or physiological lipid/phospholipid materials, offer significant advantages such as biocompatibility, biodegradability, and safety, making them ideal for vaccine delivery. These lipid-based vectors can protect encapsulated antigens and/or mRNA from degradation, precisely tune chemical and physical properties to mimic viruses, facilitate targeted delivery to specific immune cells, and enable efficient endosomal escape for robust immune activation. Notably, lipid-based vaccines, exemplified by those developed by BioNTech/Pfizer and Moderna against COVID-19, have gained approval for human use. This review highlights rational design strategies for vaccine delivery, emphasizing lymphoid organ targeting and effective endosomal escape. It also discusses the importance of rational formulation design and structure–activity relationships, along with reviewing components and potential applications of lipid-based vectors. Additionally, it addresses current challenges and future prospects in translating lipid-based vaccine therapies for cancer and infectious diseases into clinical practice.