Cationic nanoparticles enhance T cell tumor infiltration and antitumor immune responses to a melanoma vaccine

Component: Polymer Core; Description: Poly(D,L-lactic-co-glycolic acid) (PLGA), 50:50, Resomer RG 502

Component: Cationic Component; Description: Polyamidoamine (PAMAM) dendrimers, ethylenediamine core, generations 3, 4, or 5

Component: Formulation (PMG5); Description: PLGA + PAMAM G5; synthesized via modified nanoprecipitation (acetone + PVA aqueous solution); lyophilized with 10% sucrose cryoprotectant

Component: Particle Properties (PMG5); Description: • Hydrodynamic diameter: ~170 nm<br>• PDI: ~0.1<br>• Zeta potential: +39 mV<br>• Stable at 37°C for ≥10 days (size, PDI, surface charge)

Component: PMG3 Properties; Description: • Hydrodynamic diameter: 231.7 ± 2.4 nm<br>• Zeta potential: +39.2 ± 0.6 mV

Component: PMG4 Properties; Description: • Hydrodynamic diameter: 172.4 ± 3.0 nm<br>• Zeta potential: +42.6 ± 0.6 mV

Component: Cancer Vaccine; Description: Replication-deficient adenovirus serotype 5 (Ad5) encoding human tyrosinase-related protein 2 (TRP2) — a melanoma-associated tumor antigen; Ad5-TRP2

Component: Immune Checkpoint Modulation (ICM); Description: Anti-PD-1 (100 μg/mouse) + anti-4-1BB (100 μg/mouse); administered intraperitoneally on days 8, 11, 13, 16, 18 post-tumor challenge

Component: Dosing (PM formulations); Description: 1.6 mg per administration (peritumoral, days 8, 11, 13 post-tumor challenge)

Component: Tumor Model; Description: B16.F10 murine melanoma (subcutaneous, 2×10⁵ cells/mouse); C57BL/6J female mice

Component: Vaccine Dose; Description: 1 × 10⁸ PFUs Ad5-TRP2 (subcutaneous, contralateral flank, day 1 post-tumor challenge)

Parameter: Cell Model; Details: BMDCs (bone marrow-derived dendritic cells) from C57BL/6J mice; cultured with GM-CSF (20 ng/mL) for 10 days

Parameter: In Vitro Uptake Studies; Details: BMDCs incubated with PM formulations (0.06-0.24 mg) for 48 h; flow cytometry (PAMAM intrinsic fluorescence); endocytosis inhibitors: sucrose (clathrin), MBCD (caveolae), amiloride (macropinocytosis)

Parameter: DC Activation; Details: BMDCs treated with PMG5 (1.6 mg), Ad5-TRP2, CpG, or soluble PAMAM G5 for 2 days; flow cytometry for CD40, CD80, CD86, MHC I; Luminex for cytokine secretion

Parameter: TLR Screening; Details: HEK-Blue TLR reporter cell lines (TLR2, 3, 4, 5, 7, 8, 9, 13); NF-κB-induced SEAP expression

Parameter: Prophylactic Study; Details: Mice vaccinated with Ad5-TRP2 (5×10⁷, 1×10⁸, or 5×10⁸ PFUs); day 14: TRP2-specific CD8⁺ T cell quantification, then B16.F10 challenge; survival monitored to day 55

Parameter: Therapeutic Studies; Details: Mice challenged with B16.F10 (day 0); Ad5-TRP2 vaccination (day 1); PM treatments (days 8, 11, 13); tumor volume and survival monitored; rechallenge at day 60 for tumor-free survivors

Parameter: Depletion Studies; Details: Anti-NK (PK136), anti-CD4 (GK1.5), anti-CD8 (2.43) antibodies (150 μg/mouse) administered on days 6, 7, 8, then every 3 days to day 30

Parameter: Histology; Details: Tumor and skin tissues harvested day 14; H&E and anti-CD8 IHC; CD8⁺ T cells quantified in 0.92 mm² total area per sample

Parameter: Sample Sizes; Details: Prophylactic: n=5/group; Therapeutic: n=9-10/group; Depletion: n=5/group

Parameter: Statistical Tests; Details: One-way/two-way ANOVA with Tukey posttest; log-rank (Mantel-Cox) with Dunnett's adjustment for survival; GraphPad Prism

Analysis Category: Nanoparticle Characterization; Methods: TEM (JEOL JEM-1230), SEM (Hitachi), DLS (Zetasizer Nano ZS), DSC (TA Instruments Q20), zeta potential

Analysis Category: Cellular Uptake; Methods: Flow cytometry (BD FACScan; PAMAM intrinsic fluorescence); endocytosis inhibitor studies

Analysis Category: DC Activation/Maturation; Methods: Flow cytometry: CD11c-FITC, CD40-APC, CD80-APC, CD86-APC, MHC I-PE (anti-mouse antibodies)

Analysis Category: Cytokine Secretion; Methods: Luminex multiplex assay (supernatants)

Analysis Category: TLR Agonist Screening; Methods: HEK-Blue reporter cell lines; SEAP activity (OD₆₅₀)

Analysis Category: TRP2-Specific CD8⁺ T Cells; Methods: Flow cytometry: H-2Kᵇ/TRP2 tetramer (MBL), anti-CD8a-FITC, anti-CD3-PECy5; PBL collected day 14 post-vaccination/challenge

Analysis Category: Tumor Measurements; Methods: Calipers; volume = (length × width × height) × π/6

Analysis Category: Survival Analysis; Methods: Kaplan-Meier curves; log-rank test; endpoint: tumor ≥20 mm length/width or ≥10 mm height

Analysis Category: Immunohistochemistry; Methods: Anti-CD8 antibody (IHC); PANNORAMIC 1000 digital slide scanner; SlideViewer 2.5 software

Analysis Category: Cell Depletion; Methods: Anti-NK (PK136), anti-CD4 (GK1.5), anti-CD8 (2.43); 150 μg/mouse i.p.

Parameter: Hydrodynamic diameter; PMG3: 231.7 ± 2.4 nm; PMG4: 172.4 ± 3.0 nm; PMG5: ~170 nm

Parameter: Zeta potential; PMG3: +39.2 ± 0.6 mV; PMG4: +42.6 ± 0.6 mV; PMG5: +39 mV

Parameter: BMDC uptake (MFI); PMG3: 5.46 ± 0.67; PMG4: 8.93 ± 0.63; PMG5: 8.13 ± 0.30

Parameter: Stability (37°C, 10 days); PMG3: Stable; PMG4: Stable; PMG5: Stable

Parameter: PMG5 uptake mechanism; PMG3: Energy-dependent; clathrin- and caveolae-mediated (sucrose and MBCD inhibited); PMG4: -; PMG5: -

Marker: CD40; PMG5 (1.6 mg): Significant increase; Soluble PAMAM G5: No significant increase; CpG (positive control): Significant increase

Marker: CD80; PMG5 (1.6 mg): No significant increase; Soluble PAMAM G5: Significant increase; CpG (positive control): Significant increase

Marker: CD86; PMG5 (1.6 mg): No significant increase; Soluble PAMAM G5: No significant increase; CpG (positive control): Significant increase

Marker: MHC I; PMG5 (1.6 mg): No significant increase; Soluble PAMAM G5: No significant increase; CpG (positive control): Significant increase

Marker: IL-6; PMG5 (1.6 mg): No significant increase; Soluble PAMAM G5: -; CpG (positive control): Significant increase

Marker: IP-10; PMG5 (1.6 mg): No significant increase; Soluble PAMAM G5: -; CpG (positive control): Significant increase

Marker: TLR agonism; PMG5 (1.6 mg): None detected (TLR2-9,13); Soluble PAMAM G5: None detected; CpG (positive control): N/A

Vaccine Dose (PFUs): Naïve (unvaccinated); TRP2-Specific CD8⁺ T cells (%): Baseline; Survival at Day 55: 0%

Vaccine Dose (PFUs): 5 × 10⁷; TRP2-Specific CD8⁺ T cells (%): Increased; Survival at Day 55: 60%

Vaccine Dose (PFUs): 1 × 10⁸; TRP2-Specific CD8⁺ T cells (%): Increased; Survival at Day 55: 60%

Vaccine Dose (PFUs): 5 × 10⁸; TRP2-Specific CD8⁺ T cells (%): Highest (trend); Survival at Day 55: 80%

Treatment: Naïve; TRP2-Specific CD8⁺ T cells (%): 0.39 ± 0.21; Median Survival (days): 35; Tumor-Free at Day 90: 0/9

Treatment: PMG5 only; TRP2-Specific CD8⁺ T cells (%): Not different from naïve; Median Survival (days): -; Tumor-Free at Day 90: -

Treatment: CpG (soluble); TRP2-Specific CD8⁺ T cells (%): 0.96 ± 0.31; Median Survival (days): -; Tumor-Free at Day 90: -

Treatment: Ad5-TRP2 alone; TRP2-Specific CD8⁺ T cells (%): 1.21 ± 0.28; Median Survival (days): ~35; Tumor-Free at Day 90: -

Treatment: Ad5-TRP2/CpG; TRP2-Specific CD8⁺ T cells (%): 0.96 ± 0.31; Median Survival (days): -; Tumor-Free at Day 90: 2/9

Treatment: Ad5-TRP2/PMG5; TRP2-Specific CD8⁺ T cells (%): 2.08 ± 0.73; Median Survival (days): 103; Tumor-Free at Day 90: 5/9 (rechallenge protected)

Treatment: Ad5-TRP2/PMG3; Median Survival (days): ~32; Survival at Day 100: 0% (10/10 succumbed)

Treatment: Ad5-TRP2/PMG4; Median Survival (days): ~40; Survival at Day 100: 20%

Treatment: Ad5-TRP2/PMG5; Median Survival (days): 103; Survival at Day 100: 55%

Treatment: Ad5-TRP2/ICM; Median Survival (days): -; Survival at Day 100: -

Treatment: Ad5-TRP2/PMG3/ICM; Median Survival (days): Increased vs. PMG3 alone; Survival at Day 100: 70%

Treatment: Ad5-TRP2/PMG4/ICM; Median Survival (days): Increased vs. PMG4 alone; Survival at Day 100: 60%

Treatment: Ad5-TRP2/PMG5/ICM; Median Survival (days): Similar to PMG5 alone; Survival at Day 100: 50%

Treatment: TRP2-specific CD8⁺ T cells (ICM groups); Median Survival (days): ~6.5-7.9% (not significantly different); Survival at Day 100: -

Treatment: Ad5-TRP2/PMG5; Intratumoral CD8⁺ T cells: Significantly enhanced; Peritumoral CD8⁺ T cells: Significantly enhanced

Treatment: Ad5-TRP2/PMG3; Intratumoral CD8⁺ T cells: Lower than PMG5; Peritumoral CD8⁺ T cells: Lower than PMG5

Treatment: Ad5-TRP2/PMG4; Intratumoral CD8⁺ T cells: Lower than PMG5; Peritumoral CD8⁺ T cells: Lower than PMG5

Treatment: PMG5 (no vaccine); Intratumoral CD8⁺ T cells: No significant change (no tumor); Peritumoral CD8⁺ T cells: -

Depletion: No depletion; Ad5-TRP2/PMG5: 80%; Ad5-TRP2/PMG5/ICM: 60%

Depletion: NK depletion; Ad5-TRP2/PMG5: 40% (trend, NS); Ad5-TRP2/PMG5/ICM: 80% (not required)

Depletion: CD4 depletion; Ad5-TRP2/PMG5: 20% (trend, NS); Ad5-TRP2/PMG5/ICM: 80% (not required)

Depletion: CD8 depletion; Ad5-TRP2/PMG5: 0% (complete abrogation); Ad5-TRP2/PMG5/ICM: 0% (complete abrogation)

Depletion: CD4+CD8 depletion; Ad5-TRP2/PMG5: -; Ad5-TRP2/PMG5/ICM: 0% (by day 26)

Depletion: Primary effector; Ad5-TRP2/PMG5: CD8⁺ T cells (and contribution from CD4⁺/NK); Ad5-TRP2/PMG5/ICM: CD8⁺ T cells only

Parameter: Body weight; Result: No significant decrease; no signs of distress

Parameter: No observed toxicity; Result: All treatments well-tolerated

1. Mechanism not fully defined: The authors acknowledge "the molecular mechanism by which PMG5 promotes its adjuvant effect is not definitively understood." PMG5 did not activate TLRs or significantly upregulate DC maturation markers (CD80/CD86/MHC I), suggesting "there are likely yet to be determined innate immune molecular pathways" at play.

2. TAA-based antigen: TRP2 is a tumor-associated antigen, not a tumor-specific antigen. The authors note that "TSAs admittedly may be better at generating an immune response" but lack scalability. The use of a "poorly immunogenic TAA" is justified as a rigorous test, but translation to patient-specific TSAs is uncertain.

3. Peritumoral administration required: PMG5 was administered peritumorally, which requires accessible tumors; applicability to metastatic or deep-seated tumors was not demonstrated.

4. Immunosuppressive TME still incompletely overcome: While PMG5 improved outcomes, 5/9 mice in the PMG5 group still succumbed to tumors, and the addition of ICM to PMG5 did not further enhance survival beyond PMG5 alone.

5. Limited mechanistic insight into PMG3/PMG4 differences: PMG5 outperformed PMG3 and PMG4, but the exact reasons (size, surface properties, uptake, or other factors) were not conclusively determined. The authors note "further studies will be required."

6. No comparison to other cationic nanoparticle adjuvants: The study does not benchmark PMG5 against other well-established nanoparticle adjuvants (e.g., poly(I:C)-loaded particles, CpG-loaded particles) in the same model.

7. In vivo imaging missing: While T cell infiltration was quantified histologically, the study did not include imaging of T cell trafficking, biodistribution of PMG5, or real-time monitoring of immune responses.

8. In vitro DC activation modest: PMG5 only significantly upregulated CD40 (and marginally at that) without affecting other maturation markers, suggesting the in vivo adjuvant effects may involve cell types beyond DCs or indirect mechanisms.

9. Exclusion of late-stage tumor model: Treatment began on day 1 post-tumor challenge (therapeutic but still early); efficacy against larger, more established tumors was not tested.

10. B16.F10 model limitations: B16.F10 is a poorly immunogenic melanoma model that is notoriously difficult to treat, but it may not fully recapitulate the complexity of human melanoma or the human TME.

11. Female mice only: All studies used female C57BL/6J mice; sex-specific differences in immune responses were not investigated.

12. No toxicity studies beyond weight: While no weight loss or signs of distress were observed, comprehensive immunotoxicity or off-target organ toxicity studies were not performed.

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