An Endogenous Vaccine Based on Fluorophores and Multivalent Immunoadjuvants Regulates Tumor Micro-Environment for Synergistic Photothermal and Immunotherapy

Recently, near-infrared (NIR) light-based photothermal therapy (PTT) has been widely applied in cancer treatment. However, in most cases, the tissue penetration depth of NIR light is not sufficient and thus photothermal therapy is unable to completely eradicate deep, seated tumors inevitably leading to recurrence of the tumor. Due to this significant limitation of NIR, improved therapeutic strategies are urgently needed. Methods: We developed an endogenous vaccine based on a novel nanoparticle platform for combinatorial photothermal ablation and immunotherapy. The design was based on fluorophore-loaded liposomes (IR-7-lipo) coated with a multivalent immunoadjuvant (HA-CpG). In vitro PTT potency was assessed in cells by LIVE/DEAD and Annexin V-FITC/PI assays. The effect on bone marrow-derived dendritic cells (BMDC) maturation and antigen presentation was evaluated by flow cytometry (FCM) with specific antibodies. After treatment, the immune cell populations in tumor micro-environment and the cytokines in the serum were detected by FCM and Elisa assay, respectively. Finally, the therapeutic outcome was investigated in an animal model. Results: Upon irradiation with 808 nm laser, IR-7-lipo induced tumor cell necrosis and released tumor-associated antigens, while the multivalent immunoadjuvant improved the expression of co-stimulatory molecules on BMDC and promoted antigen presentation. The combination therapy of PTT and immunotherapy regulated the tumor micro-environment, decreased immunosuppression, and potentiated host antitumor immunity. Most significantly, due to an enhanced antitumor immune response, combined photothermal immunotherapy was effective in eradicating tumors in mice and inhibiting tumor metastasis. Conclusion: This endogenous vaccination strategy based on synergistic photothermal and immunotherapy may provide a potentially effective approach for treatment of cancers, especially those difficult to be surgically removed.