A d-peptide-based oral nanotherapeutic modulates the PD-1/PD-L1 interaction for tumor immunotherapy

BACKGROUND: PD-1/PD-L1 immune checkpoint inhibitors are currently the most commonly utilized agents in clinical practice, which elicit an immunostimulatory response to combat malignancies. However, all these inhibitors are currently administered via injection using antibody-based therapies, while there is a growing need for oral alternatives. METHODS: This study has developed and synthesized exosome-wrapped gold–peptide nanocomplexes with low immunogenicity, which can target PD-L1 and activate antitumor immunity in vivo through oral absorption. The (Super)PDL1(exo) was characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and gel silver staining. The transmembrane ability of (Super)PDL1(exo) was evaluated by flow cytometry and immunofluorescence. Cell viability was determined using the Cell Counting Kit-8 (CCK-8) assay. ELISA experiments were conducted to detect serum and tissue inflammatory factors, as well as serum biochemical indicators. Tissue sections were stained with H&E for the evaluation of the safety of (Super)PDL1(exo). An MC38 colon cancer model was established in immunocompetent C56BL/6 mice to evaluate the effects of (Super)PDL1(exo) on tumor growth in vivo. Immunohistochemistry (IHC) staining was performed to detect cytotoxicity factors such as perforin and granzymes. RESULTS: First, (Super)PDL1 was successfully synthesized, and milk exosome membranes were encapsulated through ultrasound, repeated freeze–thaw cycles, and extrusion, resulting in the synthesis of (Super)PDL1(exo). Multiple characterization results confirmed the successful synthesis of (Super)PDL1(exo) nanoparticles. Furthermore, our data demonstrated that (Super)PDL1(exo) exhibited excellent colloidal stability and superior cell transmembrane ability. In vitro and in vivo experiments revealed that (Super)PDL1(exo) did not cause damage to multiple systemic organs, demonstrating its good biocompatibility. Finally, in the MC38 colon cancer mouse model, it was discovered that (Super)PDL1(exo) could inhibit the progression of colon cancer, and this tumor-suppressive effect was mediated through the activation of tumor-specific cytotoxic T lymphocyte (CTL)-related immune responses. CONCLUSION: This study has successfully designed and synthesized an oral nanotherapeutic, (Super)PDL1(exo), which demonstrates small particle size, excellent colloidal stability, transmembrane ability in tumor cells, and biocompatibility. In vivo experiments have shown that it effectively activates T-cell immunity and exerts antitumor effects.