mRNA vaccination with charge-altering releasable transporters elicits human T cell responses and cures established tumors in mice

Component: Delivery Vehicle; Description: Charge-altering releasable transporters (CARTs) — cationic polymer with carbonate and aminoester groups; degrades via charge-altering mechanism (polycationic → neutral small molecules), enabling endosomal escape and mRNA release

Component: CART Composition; Description: D13:A11 (12 dodecyl carbonate monomers + 14 cationic aminoester monomers); prepared via ring-opening polymerisation using benzyl alcohol initiator

Component: Fluorescent CART; Description: BDK-CART — difluoroboron-β-diketonate fluorophore installed as initiator; ~1,000 fluorophores per mRNA molecule

Component: Payload; Description: • mRNA: Fluc (firefly luciferase), OVA, eGFP, SEAP, hCMV pp65, CD80, CD86 — capped, polyadenylated, 5-methoxyuridine-modified (Trilink)<br>• Adjuvant: CpG (TLR9 agonist; class B or C) — coformulated with mRNA into CART nanoparticles

Component: Formulation; Description: CART:mRNA at 10:1 cation:anion ratio in acidic PBS (pH 5.5); CpG premixed with mRNA; 20 s mixing; immediate injection

Component: Particle Properties; Description: Nanoparticle complexes; BDK-CART fluorescence correlates with Cy5-mRNA uptake and GFP expression

Component: Cell Types; Description: Human PBMCs (donors), HeLa cells, DC2.4 (murine DC line), A20-OVA lymphoma (BALB/c), CT26 colon carcinoma

Component: Mouse Models; Description: BALB/c; A20-OVA lymphoma (s.c. tumour model); C57BL/6-Tg(TcraTcrb)1100Mjb/J (OT-I)

Parameter: Human T Cell Activation; Details: PBMCs from HLA-A02:01+ donors (CMV+ and CMV−); treated with hCMV pp65 mRNA-CARTs, naked mRNA, irrelevant mRNA-CART, or viral peptide mix; CD8 T cell activation measured by CD69, CD137, CD70; tetramer staining (NLVPMVATV)

Parameter: In Vivo Biodistribution; Details: Fluc mRNA-CARTs via i.v. or s.c.; IVIS bioluminescence imaging at 0.5-24 h; BDK-CART flow cytometry (spleen, blood, skin, lymph nodes)

Parameter: Prophylactic Vaccination; Details: Same-day tumour inoculation + vaccination; A20-OVA cells (10⁷) + s.c. vaccine at distant site; tumour growth and survival monitored >80 d

Parameter: Established Tumour Therapy; Details: Tumours established to medium (50-100 mm³) or large (>100 mm³); 3 doses (days 7, 11, 14 or 10, 13, 17); 3 μg OVA-mRNA + 5 μg CpG in CARTs

Parameter: Vaccine Components Tested; Details: mRNA-CART + CpG, mRNA-CART (no CpG), CART alone, CART + CpG (no mRNA), naked mRNA + CpG (no CART), resiquimod (TLR7), DMXAA (STING), anti-CD40, OVA protein + LPS

Parameter: Rechallenge Experiment; Details: Mice that rejected primary tumour rechallenged with A20-OVA on day 30; T cells isolated for cytotoxicity assays

Parameter: Sample Sizes; Details: n=5-10 per group

Parameter: Statistical Tests; Details: Nonparametric Mann-Whitney U test (tumour growth); Kaplan-Meier log-rank test (survival); P < 0.05 considered significant

Analysis Category: Transfection Efficiency; Methods: Flow cytometry: GFP expression in PBMC subsets (DC, monocyte, B cell, CD4⁺, CD8⁺ T cells); HeLa cells (GFP)

Analysis Category: T Cell Activation (Human); Methods: Flow cytometry: CD69, CD137, CD70; HLA-A02:01 CMV pp65 tetramer (NLVPMVATV)

Analysis Category: In Vivo Imaging; Methods: IVIS 100 bioluminescence (D-luciferin i.p.); Living Image software

Analysis Category: Biodistribution; Methods: BDK-CART flow cytometry; Cy5-mRNA correlation; cell phenotype markers (CD11c, CD11b, B220, CD3, CD4, CD8, lineage-negative)

Analysis Category: DC Activation; Methods: HLA-DR expression by flow cytometry (human DCs)

Analysis Category: T Cell Proliferation; Methods: CellTrace Violet dye (VTD) dilution; coculture with mitomycin C-treated Ag⁺ or Ag⁻ target cells

Analysis Category: T Cell Reactivation; Methods: CD69 up-regulation after 24 h coculture with Ag⁺/Ag⁻ targets; IFNγ intracellular staining

Analysis Category: Cytotoxicity; Methods: 18 h coculture (10:1 effector:target); 7-AAD staining of target cell death

Analysis Category: Antibody Detection; Methods: ELISA: OVA-specific IgG1, IgG2a, IgG2b, IgG2c in sera

Cell Type: Dendritic cells (DCs); GFP Transfection Efficiency: ~50%

Cell Type: Monocytes; GFP Transfection Efficiency: ~75%

Cell Type: B cells; GFP Transfection Efficiency: ~25%

Cell Type: CD4⁺ T cells; GFP Transfection Efficiency: ~10%

Cell Type: CD8⁺ T cells; GFP Transfection Efficiency: ~20%

Cell Type: Lineage-negative cells; GFP Transfection Efficiency: ~20%

Cell Type: Donor; GFP Transfection Efficiency: CMV Status; Tetramer⁺ CD8 T cells; Activation with hCMV mRNA-CART

Cell Type: No. 30; GFP Transfection Efficiency: CMV⁺; Substantial; Robust (CD69⁺CD137⁺)

Cell Type: No. 34; GFP Transfection Efficiency: CMV⁺; Small; Robust

Cell Type: No. 52; GFP Transfection Efficiency: CMV⁻; None; None

Cell Type: Comparison; GFP Transfection Efficiency: -; -; mRNA-CART > viral peptide mix > naked mRNA > irrelevant CART

Route: s.c.; Peak Expression Time: 4 h; Primary Location: Localised at injection site

Route: i.v.; Peak Expression Time: 8 h; Primary Location: Spleen and lymph nodes (almost exclusively)

Route: Cellular uptake (BDK-CART); Peak Expression Time: Monocytes > DCs > B cells; Primary Location: Spleen, circulation, skin

Route: Transfected cells in draining lymph nodes; Peak Expression Time: 24 h post-s.c.; Primary Location: eGFP⁺ monocytes and DCs

Formulation: mRNA-CART + CpG; Tumour Protection: Strongest (8/8 protected); Significance: Best

Formulation: mRNA-CART (no CpG); Tumour Protection: Moderate; Significance: Inferior to +CpG

Formulation: CART + CpG (no mRNA); Tumour Protection: None; Significance: No effect

Formulation: Naked mRNA + CpG; Tumour Protection: None; Significance: No effect (CART required)

Formulation: Resiquimod (TLR7); Tumour Protection: Moderate; Significance: Inferior to CpG

Formulation: DMXAA (STING); Tumour Protection: Moderate; Significance: Inferior to CpG

Formulation: Anti-CD40; Tumour Protection: Moderate; Significance: Best alternative

Formulation: OVA protein + LPS; Tumour Protection: Moderate; Significance: Inferior to mRNA-CART

Tumour Size: Medium (50-100 mm³); Treatment: mRNA-CART + CpG; Complete Regression: 8/10 (80%); Median Survival: >75 d

Tumour Size: Medium; Treatment: CpG only; Complete Regression: 0/10; Median Survival: ~25 d

Tumour Size: Large (>100 mm³); Treatment: mRNA-CART + CpG; Complete Regression: 2/5 (40%); Median Survival: Significantly prolonged

Tumour Size: Large; Treatment: CpG only; Complete Regression: 0/5; Median Survival: No survival

Tumour Size: i.v. administration; Treatment: mRNA-CART + CpG (medium); Complete Regression: 5/5 (100%); Median Survival: >75 d

Tumour Size: i.v. administration; Treatment: mRNA-CART + CpG (large); Complete Regression: 2/5 (40%); Median Survival: Significantly prolonged

Parameter: Antigen-specific antibodies (IgG); Result: Trace amounts (vs. high titers with OVA protein + LPS)

Parameter: Antigen-specific CD4⁺ T cell proliferation; Result: Robust (Ag⁺ vs. Ag⁻ targets)

Parameter: Antigen-specific CD8⁺ T cell proliferation; Result: Robust

Parameter: CD69 up-regulation (CD4⁺/CD8⁺); Result: Ag-specific

Parameter: CD8⁺ T cell cytotoxicity (A20-OVA); Result: Strong

Parameter: CD8⁺ T cell cytotoxicity (wild-type A20); Result: Strong (shared antigens)

Parameter: CD8⁺ T cell cytotoxicity (CT26, irrelevant); Result: None

Parameter: Rechallenge protection; Result: Complete rejection (5/5)

Parameter: Naive mice (no prior treatment); Result: Tumour development (5/5)

1. Model antigen (OVA) and single tumour model: The study uses OVA as a model antigen in A20 lymphoma; efficacy against non-OVA tumour antigens or in other cancer types was not demonstrated.

2. Immunogenicity of OVA: OVA is highly immunogenic; translation to poorly immunogenic tumour-associated antigens or neoantigens may yield different results.

3. No direct comparison to other mRNA delivery platforms: While CARTs are compared to Lipofectamine and to naked mRNA, they are not directly benchmarked against leading LNP formulations in the same in vivo tumour model.

4. Preferential T cell response over antibody response: The mRNA-CART vaccine primarily induced T cell responses with "only trace amounts" of antigen-specific antibodies; this may limit efficacy against tumours that require antibody-mediated mechanisms.

5. Tumour model is lymphoma: A20 is a B cell lymphoma that may be more susceptible to immune attack than solid tumours with dense stroma or immunosuppressive microenvironments.

6. No mechanistic studies on antigen cross-presentation: The study does not definitively demonstrate whether CD8⁺ T cell responses are primed via direct transfection of DCs vs. cross-presentation.

7. CART dosing not optimised: Only one CART formulation and dose were tested; optimisation of CART composition, dose, and schedule may further improve efficacy.

8. CpG dependence: The vaccine required CpG adjuvant; patients who are poor CpG responders or who have TLR9 polymorphisms may not benefit equally.

9. No toxicity data beyond prior work: While prior publications report low toxicity, this study does not include detailed toxicity assessment of multiple dosing in tumour-bearing mice.

10. Mouse model limitations: All experiments were performed in immunocompetent BALB/c mice with an implanted tumour; the model does not recapitulate the complexity of human cancer or the patient's prior therapy history.

11. CD4⁺ T cell cytotoxicity: The study observed antigen-restricted CD4⁺ T cell cytotoxicity, but the functional relevance of this observation was not fully explored.

12. No evaluation of T cell exhaustion or persistence: The study did not assess whether cured mice develop functional memory T cells beyond the rechallenge experiment or whether T cells show signs of exhaustion.

Report prepared based on the published PNAS article. For full experimental details, supplementary figures, and complete references, please refer to the original publication.