Purpose: Dendritic cell (DC)-based vaccines require efficient antigen delivery, but free ovalbumin (OVA) is poorly taken up by DCs and is often degraded, sequestered, or exocytosed. Existing OVA delivery systems often suffer from low loading capacity (<10%), lack of imaging ability, or chemical modification that can impair antigen function. A water-soluble conjugated polymer brush with high antigen-loading capacity and intrinsic fluorescence for tracking is needed.
Hypothesis: A water-soluble conjugated polymer brush (WSCPB) composed of a poly(p-phenyleneethynylene) (PPE) backbone and poly(L-lysine) (PLL) side chains—PPE-PLL—can efficiently bind OVA via electrostatic interaction, enhance OVA uptake by DCs, enable fluorescence tracking, induce DC maturation and cytokine release, and elicit strong antitumor immune responses in vivo when used as an OVA-pulsed DC vaccine.
Aims: Synthesize and characterize PPE-PLL as an OVA delivery system. - Evaluate OVA loading capacity, binding, and pH-dependent release. - Assess cellular uptake, cytotoxicity, DC maturation, and cytokine release in vitro. - Evaluate in vivo immune responses and antitumor efficacy of PPE-PLL@OVA-pulsed DCs in a B16F10 melanoma mouse model.
Delivery system:
Component: Polymer architecture; Details: Water-soluble conjugated polymer brush (WSCPB): PPE-PLL
Component: Backbone; Details: Poly(p-phenyleneethynylene) (PPE), conjugated polymer
Component: Side chains; Details: Poly(L-lysine) (PLL); degree of polymerization ~20
Component: Payload; Details: Ovalbumin (OVA), model antigen
Component: Complexation; Details: Electrostatic binding; PPE-PLL@OVA complexes
Component: Targeting ligand; Details: None
Component: Imaging / tracking; Details: PPE intrinsic fluorescence; FRET between PPE-PLL and FITC-OVA
Component: Water solubility; Details: Up to 8.75 mg/mL
Component: Particle size; Details: PPE-PLL ~130 nm; PPE-PLL@OVA ~195 nm (hydrodynamic)
Component: Zeta potential; Details: PPE-PLL +54 mV; decreases with OVA loading
Component: Optimal mass ratio; Details: PPE-PLL:OVA = 1:2 for further experiments
Approach: In vitro: DCs cultured in RPMI 1640; B16F10 melanoma cells. - In vivo: C57BL/6 mice; B16F10 tumor model. - DC vaccine preparation: DCs pulsed with PPE-PLL, free OVA, or PPE-PLL@OVA (5.0 µg/mL OVA) for 2 h, then cultured 24 h. - Vaccination: Mice vaccinated subcutaneously twice at weekly intervals with 2 × 10⁶ DCs per group; for antitumor study, three vaccinations every 7 days before tumor inoculation. - Groups (n = 6/group): Blank/NS, DCs, PPE-PLL-pulsed DCs, OVA-pulsed DCs, PPE-PLL@OVA-pulsed DCs. - Tumor model: B16F10 cells injected subcutaneously after vaccination; tumor volume monitored every 2 days from day 2 to 60; mice euthanized when tumor >2,000 mm³.
Key methods: Polymer characterization: ¹H NMR, GPC, UV-vis, photoluminescence (PL), zeta potential, DLS, TEM. - OVA binding/loading: Ultrafiltration and fluorescence quantification; agarose gel electrophoresis with Coomassie blue staining. - OVA release: UV absorption at 280 nm, FRET (PPE-PLL to FITC-OVA), and DLS at pH 6.0 vs 7.4. - Cytotoxicity: MTT assay in DCs. - Cellular uptake: Flow cytometry and confocal laser scanning microscopy (CLSM) with FITC-OVA. - DC maturation: Flow cytometry for CD80⁺ and CD86⁺. - Cytokine detection: ELISA for TNF-α, IL-12p70, IFN-γ, IL-1β. - Antitumor efficacy: Tumor volume and survival analysis.
Key results: OVA loading capacity: PPE-PLL = 88.69%, much higher than linear PPE-propanamine (8.99%) and linear PLL (16.37%). - Zeta potential: PPE-PLL +54 mV; decreased to +6 mV at PPE-PLL:OVA 1:4; negative (−16 mV) at 1:5. Mass ratio 1:2 chosen for further studies. - OVA release: Faster at pH 6.0 than pH 7.4; at 24 h, ~80% vs ~65% by UV; FRET ratio ~1.84 vs ~1.69. DLS confirmed faster OVA peak increase at pH 6.0. - Cytotoxicity: PPE-PLL and PPE-PLL@OVA showed low toxicity; >90% DC viability up to 50 µg/mL. - Cellular uptake: PPE-PLL@OVA enhanced FITC-OVA uptake in DCs compared with free OVA by flow cytometry and CLSM. - DC maturation: CD80⁺/CD86⁺ increased from 14.9% (DCs) to 64.9% (PPE-PLL@OVA), vs 52.5% (OVA) and 22.1% (PPE-PLL). - Cytokine release: TNF-α and IL-12p70 levels were significantly increased after PPE-PLL@OVA treatment. - In vivo immune response: Serum TNF-α and IFN-γ were significantly increased in PPE-PLL@OVA-pulsed DC group. - Antitumor efficacy: PPE-PLL@OVA-pulsed DC vaccine greatly inhibited B16F10 tumor growth; 100% survival at 60 days after tumor inoculation, compared with other groups. Body weight showed no significant changes.
Interpretation: The authors claim that PPE-PLL is a WSCPB with good photostability, strong antigen-loading capacity, and excellent water solubility. PPE-PLL@OVA enhances DC uptake, maturation, and cytokine release, and the resulting DC vaccine induces strong immune responses and high antitumor activity in a B16F10 melanoma model. They conclude that this system has potential for DC-based cancer immunotherapy, though it cannot yet be directly applied to human patients.
Limitations: In vivo model only: Murine B16F10 melanoma model; no human DC or human tumor data. - Model antigen: OVA is a model antigen; translation to clinically relevant tumor antigens is not demonstrated. - No targeting ligand: Delivery relies on nonspecific electrostatic interactions. - Small sample size: n = 6 mice per group. - No long-term toxicity or safety data. - Mechanistic details of endosomal escape and antigen cross-presentation are not fully resolved. - Just Accepted manuscript: The final peer-reviewed version may differ in minor details. - No direct clinical translation yet, as acknowledged by the authors.
