Engineered PD-L1-targeted multifunctional proteins with self-prolonged circulation for enhanced tumor photothermal-immunotherapy

In this study, a novel Immunoglobulin G (IgG) binding, Programmed Cell Death-Ligand 1 (PD-L1) targeting affibody, IgBD-Z_PD-L1, was constructed by genetically fusing the PD-L1-specific affibody ZM1 with the IgG-binding domain (IgBD). IgBD-Z_PD-L1 could simultaneously bind to IgG, PD-L1 receptor protein, and PD-L1-positive tumor cells. Furthermore, the fusion of IgBD significantly prolonged the <i>in vivo</i> circulation half-life of IgBD-Z_PD-L1 by binding to endogenous IgG, enhancing tumor accumulation and immunotherapeutic effects. Subsequently, anti-angiogenic/immunotherapeutic and dual-targeted combination immunotherapy strategies based on IgBD-Z_PD-L1 significantly improved tumor immunotherapy efficacy. Finally, IgBD-Z_PD-L1 was conjugated with Indocyanine green (ICG) to construct a novel tumor-targeting photosensitizer, ICG-IgBD-Z_PD-L1. <i>In vivo</i>, ICG-IgBD-Z_PD-L1 enabled clear fluorescence imaging of tumors for diagnosis and displayed excellent photothermal properties for tumor thermal ablation, demonstrating potent antitumor effects. More importantly, ICG-IgBD-Z_PD-L1-mediated photothermal/immunotherapy exerted significant therapeutic effects on primary tumors and upregulated antitumor immune responses, synergistically enhancing the efficacy of immunotherapy and inhibiting tumor metastasis. As a result, this photothermal/immunotherapy strategy ultimately achieved a synergistic therapeutic effect greater than the sum of individual treatments. In conclusion, these results suggested that IgBD-Z_PD-L1 could be developed as a multifunctional IgG-delivery platform for combination tumor immunotherapy, providing a promising theoretical basis for clinical development and translation of tumor immunotherapeutic strategies.