Materials Today Advances2022ReviewNon-viral Gene Delivery

Targeting strategies for mRNA delivery

Randall A. Meyer, Sarah Y. Neshat, Jordan J. Green, Jose Luis Santos, And Anthony D. Tuesca29 September 2026DOI 10.1016/j.mtadv.2022.100240

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Summary

mRNA gene therapy has broad therapeutic potential (protein replacement, vaccines, regenerative medicine, oncology), but clinical translation is limited by inadequate understanding of how to target specific organs or cell types for protein expression. Reports on material properties and administration routes are disparate, preventing a global understanding of how these factors contribute to organ targeting for mRNA delivery. Liver targeting: LNPs intrinsically target liver via ApoE-mediated uptake through LDLR. Optimised ionisable lipids increased liver luciferase expression 18-fold. Oxidized cholesterol variants improved protein expression.

Keywords

mRNA Lipid nanoparticle Polymeric T cells Poly(beta-amino ester)Macrophages Nanoparticles

Purpose: mRNA gene therapy has broad therapeutic potential (protein replacement, vaccines, regenerative medicine, oncology), but clinical translation is limited by inadequate understanding of how to target specific organs or cell types for protein expression. Reports on material properties and administration routes are disparate, preventing a global understanding of how these factors contribute to organ targeting for mRNA delivery.

Hypothesis: As a review/meta-analysis, this work does not test a single hypothesis. Its central thesis is:

If material properties (lipid/polymer chemistry, particle size, charge, formulation components) and routes of administration are systematically analysed and correlated with organ-specific mRNA expression, then rational design principles can be established to achieve targeted mRNA delivery to desired tissues and cell types, enabling the full therapeutic potential of mRNA medicines.

Aims: Primary Aim: To provide a thorough and robust meta-analysis of materials successfully used to target different organs for mRNA delivery.

Secondary Aims:
To summarise distinct properties of materials used for organ-targeted mRNA delivery.
To evaluate various routes of administration of mRNA therapeutics and the applications achievable.
To serve as a useful guide for the community in developing future materials for mRNA delivery.

Delivery system:

Component: Payload; Examples Discussed: mRNA (including self-amplifying mRNA, SAM), sgRNA for CRISPR-Cas9, Cas9 mRNA

Component: Lipid Nanoparticles (LNPs); Examples Discussed: Ionisable lipids (D-Lin-MC3-DMA, cKK-E12, C12-200), helper lipids (DOPE, DSPC, cholesterol), PEG-lipids, cationic lipids (DOTAP, DOTMA), lipidoids, amino-alcohol lipids, alkyne-modified MC3 analogues, oxidized cholesterol variants, zwitterionic amino phosphate lipids

Component: Polymers; Examples Discussed: Poly(beta-amino ester)s (PBAEs), charge-altering releasable transporters (CARTs), poly(ethyleneimine) (PEI), poly(glycoamidoamine) brushes, PEG-PAsp(DET), poly(N-isopropylacrylamide) (PNIPAM), PBAE-co-PCL terpolymers, poly(amine-co-ester) polymers

Component: Hybrid Systems; Examples Discussed: Lipid-polymer hybrid nanoparticles, peptide/poloxamine particles, PEGylated synthetic KL4 peptide, collagen sponge with LNPs, alginate gel

Component: Targeting Ligands; Examples Discussed: Mannose (CD206), folate, anti-CD3, anti-CD8, anti-Ly6c, tri-mannose (DC-SIGN/Langerin), aptamers

Component: Routes of Administration; Examples Discussed: Systemic IV, intramuscular, subcutaneous, intradermal, intratumoral, intrathecal, intracerebral, intracardial, inhalation, intranodal, ocular (subretinal/intravitreal), intraosseous

Component: Organ Targets; Examples Discussed: Liver, spleen, lung, tumour, skin, skeletal muscle, cardiac muscle, CNS, bone, immune cells (T cells, B cells, dendritic cells, macrophages)

Approach: This is a narrative review and meta-analysis synthesising preclinical and clinical literature. No primary experimental data are presented. The review:

Covers studies in mouse, rat, non-human primate, and human clinical trials.
Includes applications in infectious disease (COVID-19, Zika, HIV, RSV), cancer immunotherapy, protein replacement (hemophilia B, Fabry disease, HTT-I), regenerative medicine (bone, muscle, skin), and CNS disorders (Friedreich's ataxia, Alzheimer's, spinal cord injury).
Evaluates material properties (size, zeta potential, lipid tail geometry, cholesterol oxidation, polymer hydrophobicity) and routes of administration.
Summarises completed/ongoing clinical trials (Table 3).

Key methods: As a review/meta-analysis, the “methods” are literature synthesis and comparative analysis. Headline data cited from primary studies were generated using:

Biodistribution and expression imaging: Luminescence imaging, IVIS, MRI.
High-throughput screening: FIND (Fast Identification of Nanoparticle Delivery) with Cre recombinase/tdTomato reporter mice, DNA/mRNA barcoding, deep sequencing.
Flow cytometry: Immune cell transfection analysis (T cells, B cells, DCs, macrophages).
Reporter gene assays: Luciferase, GFP, tdTomato.
Clinical trial endpoints: Safety, tolerability, efficacy (e.g., COVID-19 prevention, serum TTR reduction).
Physicochemical characterisation: Size, zeta potential, pKa, cryo-TEM.

Key results: Liver targeting: LNPs intrinsically target liver via ApoE-mediated uptake through LDLR. Optimised ionisable lipids increased liver luciferase expression 18-fold. Oxidized cholesterol variants improved protein expression 4–7 fold vs. unmodified cholesterol. C12-200 LNP optimisation increased EPO production 7–8 fold. - Spleen targeting: Negatively charged nanoparticles accumulate in spleen. CART polymers targeted spleen T cells (~1.6%), B cells (~11%), dendritic cells (~60%), and macrophages (~60%) after IV injection. Poly(glycoamidoamine) brush with 10-carbon tail and tartarate backbone produced best splenic expression. - Lung targeting: Highly cationic particles accumulate in lungs. DOTMA/DOPE ratio: positive charge → lung expression; negative charge → spleen expression. PEG-lipid incorporation augments lung delivery. PBAE + PEG lipid led to exclusive lung expression. - Tumour targeting: PEGylation enhanced circulation and tumour accumulation. Cholesterol in PEG-PAsp(DET) micelles increased tumour luciferase expression ~8-fold. Intratumoral mRNA cocktail led to near-complete survival in MC38 colon carcinoma model. CD8-targeting PBAE NPs reduced tumour burden 26-fold and extended survival by 40 days. - Clinical milestones: Moderna mRNA-1273 COVID-19 vaccine efficacy 94.1%; BioNTech BNT162b2 efficacy 95%. Patisiran (siRNA LNP) approved 2018. NTLA-2001 CRISPR Cas9 LNP achieved 87% reduction in serum TTR after single dose in ATTR amyloidosis patients. - CNS targeting: Intrathecal MC3 LNP led to CNS expression; IV led to liver expression. Focused ultrasound (FUS) opens BBB for systemic gene delivery. - Immune cell targeting: Anti-CD3 LNPs transfected up to 4% of splenic T cells and 7% of circulating T cells. Mannose-functionalised NPs targeted macrophages via CD206. Anti-Ly6c LNPs targeted inflammatory leukocytes with 100-fold increase in fluc expression vs. control.

Interpretation: The authors conclude that mRNA gene therapies are at the forefront of biomedical research, but successful clinical translation requires full understanding of material properties influencing tissue localisation and cellular expression, as well as selection of the most efficient route of administration for each application. Although significant efforts have elucidated these parameters, substantial work remains before the full potential of mRNA therapeutics can be realised. The review is anticipated to guide future material development for targeted mRNA delivery across infectious disease, regenerative medicine, and other indications.

Limitations: Limitations inherent to the review:

No primary experimental data; conclusions are synthesised from existing literature.
No systematic search strategy or quantitative meta-analysis; “meta-analysis” is narrative.
Disparate nature of reports prevented critical global understanding; no central repository of findings.
Focus primarily on preclinical studies; clinical translation data limited.

Limitations of the field highlighted by the authors:

In vitro–in vivo disconnect: Weak correlation between in vitro and in vivo nucleic acid delivery efficiency.
Lack of structure-function understanding: Many individual studies evaluate only a single structure-function relationship unique to the material examined.
Nucleic acid type specificity: Materials effective for DNA or siRNA delivery are often not effective for mRNA delivery; small structural changes can switch specificity.
Screening challenges: Large number of formulation variables complicates optimisation; DOE and FIND approaches help but are not universally applied.
Route limitations: Local routes (intratumoral, intranodal, intrathecal) may not be clinically translatable for all indications; repeat dosing challenges for CNS.
Clinical translation: mRNA therapeutics have not yet achieved technological maturity of small molecules or monoclonal antibodies; regulatory and manufacturing challenges remain.
Need for better models: 3D spheroids, organ-on-a-chip, and organoids are recommended to improve prediction of in vivo outcomes.