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 disrupts 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. Rational lipid design enables independent control of delivery efficiency, tissue targeting, immune activation, and stability: the C24 formulation reduces off-target liver expression 6-fold while maintaining potency, adjuvant lipidoids provide TLR7/8 activation, and specific formulations remain stable at 4°C for at least 19 days. These mechanisms collectively explain the exceptional clinical efficacy of LNP-mRNA SARS-CoV-2 vaccines.

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
n = 10

Screening

We screened in sources based on their abstracts that met the following 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)?

We considered all screening questions together and made a holistic judgement about whether to screen in each paper.

Data extraction

We asked a large language model to extract data across multiple domains, including:

• LNP Composition:

Extract lipid nanoparticle composition and design details for SARS-CoV-2 mRNA delivery.

• mRNA Specifications:

Extract detailed characteristics of the nucleoside-modified mRNA.

• Cellular Uptake Mechanism:

Extract mechanistic details of how LNPs deliver mRNA into target cells.

• Delivery Efficiency:

Extract quantitative measures of mRNA delivery effectiveness.

• Structural Properties:

Extract physical and structural characteristics that enable mRNA delivery.

• Biodistribution Pattern:

Extract biodistribution data showing where LNPs deliver mRNA after administration.

• Inflammatory Effects:

Extract data on how LNPs contribute to immune activation beyond mRNA delivery.

• Stability Factors:

Extract factors affecting LNP-mRNA stability and delivery performance over time.

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 consist of four core lipid components: ionizable lipids, helper lipids, cholesterol, and PEG-lipids. The ionizable lipid component is critical for mRNA complexing and pH-dependent release.

mRNA Cargo Characteristics

The nucleoside-modified mRNA cargo encoded the SARS-CoV-2 spike protein with specific structural modifications.

Cellular Uptake and Delivery Mechanisms

LNPs deliver mRNA through a multi-step process involving cellular uptake, endosomal escape, and cytoplasmic release. The ionizable lipids play a central role in this process.

Uptake pathways and cell types:
Muscle-resident myeloid and lymphoid cells were directly transduced, with >10% of these cells successfully receiving mRNA.

Endosomal escape mechanism:
The cellular uptake occurred via endocytosis, and ionizable lipids became protonated in the acidic endosomal environment. This protonation triggered ion pairing with endosomal phospholipids to open the endosomal membrane.

Structural interactions:
The Comirnaty formulation revealed unique mRNA-lipid interaction patterns. Atomic force microscopy demonstrated that molecular strands corresponding to mRNA could be pulled from nanoparticles with stepwise rupture of mRNA-lipid bonds.

Delivery Efficiency and Protein Expression

Quantitative delivery efficiency varied across formulations, with several showing superior performance compared to standard formulations.

Biodistribution Patterns

Immune Activation and Adjuvant Properties

LNPs demonstrated intrinsic adjuvant activity contributing to robust immune responses.
The ionizable lipid component induced IL-6 cytokine production, critical for T follicular helper cell differentiation.

Stability and Storage Considerations

LNP-mRNA stability depended critically on storage temperature and formulation design.
The C24 LNP was entirely stable in bioactivity and mRNA integrity when stored 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. The delivery cascade initiates with formulation design, where ionizable lipids complex with negatively charged mRNA through electrostatic and hydrogen bonding interactions. Following intramuscular administration, LNPs interact with muscle cells and immune cells through endocytic uptake, with >10% of muscle-resident myeloid and lymphoid cells successfully transduced.

The critical endosomal escape step relies on pH-dependent protonation of ionizable lipids in acidic endosomes. Upon cytoplasmic release, the nucleoside-modified mRNA is translated by cellular ribosomes to produce spike protein antigen.

Beyond simple mRNA delivery, LNPs function as adjuvants by triggering innate immune responses. These advances demonstrate how rational lipid design can independently modulate delivery efficiency, tissue targeting, immune activation, and stability—the four key parameters determining LNP-mRNA vaccine performance.

References

1. Xuexiang Han et al. (2023). Adjuvant lipidoid-substituted lipid nanoparticles augment the immunogenicity of SARS-CoV-2 mRNA vaccines. Nature Nanotechnology
2. J. Szebeni et al. (2023). Insights into the Structure of Comirnaty Covid-19 Vaccine. ACS Nano
3. Suman Alishetty et al. (2021). Novel lipid nanoparticle provides potent SARS-CoV-2 mRNA vaccine.
4. S. Kent et al. (2024). Blood Distribution of SARS-CoV-2 Lipid Nanoparticle mRNA Vaccine in Humans. medRxiv
5. Afshana Quadiri et al. (2024). Spike mRNA Vaccine Encapsulated in Lipid Nanoparticle Induced Potent Responses. bioRxiv
6. Afshana Quadiri et al. (2025). A Spike-Based mRNA Vaccine Encapsulated in Phospholipid 1,2-Dioleoyl-sn-Glycero-3-PhosphoEthanolamine. Vaccines
7. M. Alameh et al. (2021). Lipid nanoparticles enhance the efficacy of mRNA and protein subunit vaccines. Immunity
8. Dorottya Laczkó et al. (2020). A Single Immunization with Nucleoside-Modified mRNA Vaccines. Immunity
9. Devdoot Majumdar et al. (2023). Understanding Mechanisms of Adjuvancy in Muscle by mRNA/Lipid Nanoparticles. Journal of Immunology
10. Natalia Martinez et al. (2025). Structure–Function Correlation of Lipid Nanoparticles for Lung and Spleen Targeted mRNA Delivery. Advanced Healthcare Materials