Lipid Nanoparticles in mRNA Vaccine Delivery

How do lipid nanoparticles deliver nucleoside-modified mRNA for SARS-CoV-2 vaccine antigens?

Lipid nanoparticles deliver nucleoside-modified mRNA for SARS-CoV-2 vaccines by encapsulating the mRNA through electrostatic and hydrogen bonding interactions, facilitating cellular uptake via endocytosis, and releasing the mRNA into the cytoplasm when ionizable lipids protonate in acidic endosomes and disrupt the endosomal membrane to enable translation.

Abstract

Lipid nanoparticles deliver nucleoside-modified mRNA for SARS-CoV-2 vaccines through a coordinated physicochemical and biological process. LNPs composed of ionizable lipids, helper lipids, cholesterol, and PEG-lipids form 50-85 nm particles that encapsulate mRNA via electrostatic interactions and hydrogen bonding. Following intramuscular administration, LNPs are taken up by muscle-resident immune cells through endocytosis, with >10% of myeloid and lymphoid cells successfully transduced. The critical delivery step occurs when ionizable lipids protonate in acidic endosomes (pH ~5-6), triggering ion pairing with endosomal phospholipids that disrupt membranes and releases mRNA into the cytoplasm. Nucleoside modifications such as m1ψ reduce innate immune recognition of the mRNA cargo, while optimized formulations achieve 93-95% encapsulation efficiency and mRNA detectability for 14-28 days post-vaccination in humans.

Beyond mRNA delivery, LNPs function as intrinsic adjuvants by triggering rapid neutrophil and dendritic cell recruitment within 24 hours and inducing IL-6 production critical for germinal center responses. This dual functionality produces potent immunogenicity, with optimized formulations achieving 10-fold higher neutralizing titers than standard LNPs and protective immunity at doses as low as 0.25 µg.

Methods

We analyzed 10 sources from an initial pool of 200, using 6 screening criteria. Each paper was reviewed for 8 key aspects that mattered most to the research question.

Records from Elicit search

• n = 200
• Papers screened using: Lipid Nanoparticle Delivery System, Nucleoside-Modified mRNA, SARS-CoV-2 Antigen Target, Delivery Mechanism Data, Study Type, Delivery System Scope
• n = 200 Papers screened out
• n = 190 Papers included for extraction

Screening

We screened in sources based on their abstracts that met these criteria:

• Lipid Nanoparticle Delivery System: Does this study investigate lipid nanoparticles (LNPs) as delivery vehicles for mRNA?
• Nucleoside-Modified mRNA: Does this study involve nucleoside-modified mRNA (such as pseudouridine-modified or other nucleoside modifications) rather than unmodified mRNA?
• SARS-CoV-2 Antigen Target: Does the mRNA in this study encode SARS-CoV-2 antigens (such as spike protein, nucleocapsid, or other viral proteins) rather than non-SARS-CoV-2 antigens?
• Delivery Mechanism Data: Does this study report on delivery mechanisms, cellular uptake, biodistribution, or pharmacokinetics of LNP-mRNA systems?
• Study Type: Is this a preclinical study (in vitro, ex vivo, animal models) or clinical study rather than an opinion piece, editorial, commentary, or conference abstract without peer review?
• Delivery System Scope: Does this study focus on lipid-based delivery systems rather than non-lipid delivery systems (such as polymeric nanoparticles, viral vectors, or protein subunit vaccines)?

Results

Characteristics of Included Studies

All 10 studies investigated lipid nanoparticle delivery systems for nucleoside-modified mRNA encoding SARS-CoV-2 spike protein antigens. Seven studies had full text available, while three were abstract-only. The studies employed diverse approaches including novel lipid development, structural characterization, immunogenicity testing in animal models, and clinical pharmacokinetic analysis in humans.

LNP Composition and Formulation Design

LNP formulations for SARS-CoV-2 mRNA delivery consist of four core lipid components: ionizable lipids, helper lipids, cholesterol, and PEG-lipids.

• Ionizable lipid: Examples include C24, ALC-0315, C12-TLRa.
• Helper lipid: Examples include DSPC, DOPC, DOPE, Monoolein.
• Cholesterol: Standard component for structural support.
• PEG-lipid: Examples include DMG-PEG2000 for immune evasion and circulation.

mRNA Cargo Characteristics

The nucleoside-modified mRNA cargo encoded the SARS-CoV-2 spike protein with specific structural modifications, including m1ψ modifications and various structural features such as a trinucleotide cap structure and poly-A tail.

Cellular Uptake and Delivery Mechanisms

LNPs deliver mRNA through a multi-step process involving cellular uptake, endosomal escape, and cytoplasmic release.

Delivery Efficiency and Protein Expression

Quantitative delivery efficiency varied across formulations, with several showing superior performance compared to standard formulations. The C24 LNP showed enhanced protein expression levels and neutralizing antibody responses compared to other formulations.

Biodistribution Patterns

Following intramuscular administration, LNPs demonstrated specific biodistribution kinetics with primary target tissues being skeletal muscle at the injection site and draining lymph nodes.

Immune Activation and Adjuvant Properties

LNPs triggered strong innate immune responses, enhancing immune activation through cytokine production and dendritic cell maturation.

Stability and Storage Considerations

LNP-mRNA stability depended critically on storage temperature and formulation design, with noted stability at 4°C for at least 19 days.

Synthesis

The mechanisms by which lipid nanoparticles deliver nucleoside-modified mRNA for SARS-CoV-2 vaccines involve an integrated series of physicochemical and biological processes—highlighting the significance of formulation design, cellular interactions, endosomal escape, and immune activation in the efficacy of LNP-mRNA vaccines.